PROSTHODONTICS-George A. Zarb, Charles L. Bolender et al.-Prosthodontic Treatment for Edentulous Patients_ Complete Dentures and Implant-Supported Prostheses-Mosby (2003)

194 Part Two Preparing the Patient for Complete Denture Treatment

The pour technique involves pouring the fluid is converted into a polymer. Careful control of the
mix into a sprued mold made of a reversible hydro- time and wattage of the oven is essential to yield
colloid material (agar agar). The flask is placed porous-free resins and still ensure complete poly-
under pressure at room temperature or at a slightly merization. The technique is more time efficient
higher temperature (45˚C). Polymerization is com- and cleaner than the conventional technique.
pleted in about 30 to 45 minutes. The technique is However, its limitations are related due to its cost-
obviously simpler and cleaner with regard to flask- effectiveness for a wide production base, particu-
ing and deflasking but is prone to problems, such larly because of high equipment expenses and
as shifting of denture teeth during pouring of the fragility of the plastic flasks, which are easily prone
acrylic into the mold. The use of a hydroflask to damage. Microwave-activated resins have com-
increases atmospheric pressure around the mold, parable physical and mechanical properties to con-
minimizing air inclusions in the mix, thus yielding ventionally heat-activated resins, with claims of
a denser resin base. even greater dimensional stability. This could be
attributed to the excellent temperature control in
In comparison with heat-activated resins, the resin and equal distribution of temperature
chemically activated resins do, in general, have a throughout the resin and gypsum mold, respec-
higher residual monomer content of 3% to 5%. tively.
Polymerization in those resins is never as complete
as in heat-activated resins. This results in inferior Light-Activated Resin Bases
mechanical properties and dramatically compro-
mises biocompatibility of the denture bases. Light-activated resins, also termed VLC resins, are
The materials exhibit higher solubility; they have copolymers of urethane dimethacrylate and an
inferior color stability, due to oxidation of the acrylic resin copolymer along with microfine silica
amine accelerator; and creep rates are usually high, fillers. The polymerization process is activated by
especially under increased stresses. However, placing the premixed, moldable resin on the master
chemically activated resins, particularly when com- cast on a rotating table, in a light chamber and
pression molded, display less shrinkage on poly- exposing it to high intensity visible light of 400 to
merization than their heat-activated counterparts, 500 nm, for an appropriate period of about 10
leading to greater dimensional accuracy. This could minutes. In this technique, after an initial cure of
be attributed to a reduction in the residual stresses the resin base, the teeth are repositioned on the
induced during the processing cycle. base using a light-cured template, and contouring is
carried out, followed by a final cure in the light
Microwave-Activated Resins chamber. The resin is coated with a nonreactive
barrier compound to prevent oxygen inhibition of
Microwaves are electromagnetic waves in the the polymerization process. Light-activated resins
megahertz frequency range that have been recently contain no methacrylate monomer and could be
advocated to activate the polymerization process of readily used in monomer-sensitive patients. The
acrylic resin base. The procedure was greatly sim- produced resin contains high molecular weight
plified in 1983, with the introduction of a special oligomers, which results in smaller polymerization
glass fiber–reinforced plastic flask, suitable for use shrinkage, reportedly half that of conventional
in a microwave oven. The acrylic resin is mixed in resins. The physical and mechanical properties of
the proper powder/liquid ratios, and the composi- the resins compare well with conventional heat-
tion of the liquid monomer is usually modified to activated resins, particularly in regard to impact
control the boiling of monomer, in a very short strength and hardness. Some studies, however, have
curing cycle of about 3 minutes. In this technique reported lower elastic moduli and slightly lower
heat is rapidly generated within the monomer as a flexural strength for VLC resins, which could
result of numerous rapid intermolecular collisions. increase deformation of the dentures during func-
As the degree of polymerization increases, tion. The inferior bond strength of VLC resins to
monomer content decreases proportionally, and as resin denture teeth has been a main concern;
energy is further absorbed, the remaining monomer

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 195

however, significant improvement of this bond has future. Attempts to improve radiopacity of the
been achieved with the use of bonding agents. denture bases have been carried out to facilitate
the detection of fragments of resin bases that may
Modified Acrylic Resin Bases be accidentally ingested or, more seriously, inhaled
by the patient. These attempts included the use of
For the prevention of shortcomings in the mechan- metal inserts, radiopaque salts and fillers, and
ical properties of conventional heat-activated organometallic compounds. Examples are barium
acrylic resins, modifications have been introduced sulphate (8% wt), bismuth (10% to 15% concentra-
into the structure of the polymers to improve tions), halogen-containing copolymers, or addi-
mechanical properties, such as flexural, tensile, tives such as 2,3-dibromopropyl methacrylate.
and impact strengths, as well as fatigue resistance. Unfortunately, many of those attempts have been
Chemical modifications to produce graft copoly- accompanied by adverse effects on the esthetics
mer resins, through the incorporation of a rubber and strength of the denture base resins or, more
phase, have been attempted. The resulting resin seriously, cytotoxic effects that may endanger the
consists of a matrix of PMMA in which is dis- patient. Table 12-1 provides a summary of com-
persed an interpenetrating network (IPN) of rubber monly used denture base resins, their processing
and PMMA. The resins absorb more energy at techniques, and properties.
higher strain rates before fracture occurs, resulting
in a significant increase in impact strength. MATERIALS USED IN THE
However, this modification has been shown to be FABRICATION OF PROSTHETIC
accompanied by a reduction in the stiffness or DENTURE TEETH
rigidity of the resins.
Prosthetic or denture teeth are produced in a variety
Rubber reinforcement of PMMA is a success- of molds and shades and are available as vacuum-
ful alternative to conventional resins. However, the fired porcelain, acrylic resins, modified acrylic,
high cost of the material restricts its routine use for and composite resins. In general, teeth used in the
denture fabrication. Mechanical reinforcement of fabrication of dentures should demonstrate
acrylics has also been attempted through the inclu- optimum physical and mechanical properties to
sion of fibers such as glass, carbon, aramid withstand rigorous demands of masticatory func-
(Kevlar) fibers, nylon and ultra high modulus poly- tions, such as chewing, biting, shearing, or crush-
ethylene (UHMPE) polymers, as well as metal ing of food, and simultaneously exhibit superior
inserts (wires, plates, fillers). The resulting resins esthetics, particularly in the anterior region of the
have demonstrated an increase in impact and flex- mouth (Box 12-4).
ural strength, as well as a significant improvement
in fatigue resistance, effectively minimizing Acrylic Resin Teeth
denture fractures.
Acrylic resin (PMMA) denture teeth are manufac-
Various problems have been associated with tured either by the compression-molded dough
this route of reinforcement of PMMA resins. This technique or by injection molding. Some teeth
includes tissue irritation from protruding glass contain an IPN. Such resins exhibit low creep and
fibers, poor esthetics associated with dark carbon flow rates, and minimum dissolution in solvents,
fibers (black), or straw-colored Kevlar fibers. which is an important requirement for resin teeth.
Other limitations relate to an increase in production Most resin teeth are highly cross-linked in the
time, difficulties in handling, precise orientation, coronal portion to provide resistance to crazing, but
placement, or bonding of the fibers within the with little or slight cross-linking in the gingival or
resin. In the case of metal inserts, failure due to body portion to improve bond to the denture base.
stress concentration around the embedded inserts A significant advantage of acrylic resin teeth is that
has been reported. they bond chemically to the denture base, provided

The availability and quality of fibers for
denture reinforcement are improving very quickly
with great promises for better results in the near

Table 12-1
Processing Techniques and Properties of Denture Base Resins

Denture Base Resin Processing Technique/ Advantages Disadvantages
Method of Activation
Conventional heat- Low thermal conductivity Low
activated PMMA Compression-molded/dough Good biocompatibility Low impact and flexural
technique density strengths
Flask and gypsum mold
Water bath short or Good esthetics, color Short fatigue life
long cycles stability, surface finish Low abrasion

Insoluble in oral fluids resistance
Chemical bond with resin Radiolucent

teeth
Acceptable dimensional

stability
Easily repaired/modified
Easy to fabricate/low cost

Heat-activated rubber Compression molded High impact strength Reduced stiffness/rigidity
reinforced PMMA Water bath short or long More expensive than
cycles
conventional PMMA

Heat-activated fiber Compression molded High impact and flexural Unesthetic color of Carbon
reinforced PMMA Water bath short or long strengths and Kevlar fibers

cycles Good fatigue resistance Inferior surface finish
High stiffness Increased production time
Difficulty in handling and

placement of fibers

Chemically activated Compression-molded/dough Dimensionally accurate High residual monomer
PMMA or pour/fluid resin Pour resins easy to deflask content
Processing is less time-
Agar mold High creep rates
Chemically activated consuming Reduced stiffness
Lower impact/fatigue strength
Color instability High solubility
Tooth movement/tooth bond

failures in pour resins

Microwave-activated Compression molded Short processing time High capital cost
PMMA Fiber reinforced plastic flask Processing technique Flasks easily fractures/
Microwave energy in an
easy/clean limited serviceability
oven at 500-600 W Dimensional accuracy Porosity if time/temperature
Curing time as short as Comparable physical/
of oven not controlled
3 minutes mechanical properties
to conventionally
processed resins

Light-activated PMMA No flask required Simple processing technique High capital cost
High intensity visible light Short processing time Inferior bond to resin
No methacrylate monomer
(wavelength 400-500 nm) Low polymerization denture
In special light chamber Decreased elastic
Curing time 10 minutes shrinkage
Improved fit teeth modulus Slightly
Comparable impact strength lower flexural strength

and hardness to conven-
tionally processed resins

PMMA, Polymethylmethacrylate.

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 197

Box 12-4 dimension of occlusion, particularly in long-time
denture wearers. However, newer, chemically
Requirements of Prosthetic modified acrylic resin teeth are more wear resist-
Denture Teeth ant and stain much less than earlier-used resin
teeth.
1. Durable bond with the denture base material
2. Resistance to oral fluids/solvents Composite resin teeth have also been intro-
3. High impact strength to withstand forces duced as a suitable material for fabrication of
denture teeth. They contain microfine filler parti-
during mastication cles of silica and have demonstrated wear proper-
4. High abrasion resistance with little or no ties that are clinically acceptable. Continued
improvements in the polymer structure may facili-
wear to maintain the predetermined vertical tate its widespread use by most clinicians in the
dimension of occlusion and withstand future.
parafunctional movements
5. Esthetically pleasing, inconspicuous, ade- Porcelain is another material that has been quite
quate translucency, color stability, good popular for fabrication of denture teeth for many
surface texture, and ease of characterization years. Porcelain teeth, in general, exhibit superior
to produce a natural appearance esthetic qualities, excellent color stability, and high
6. Easily adjusted and refined by grinding and abrasion resistance. They are mechanically
easily polished attached to resin bases by means of pins or diatoric
holes, and this attachment precludes their ability to
that the tooth surface was thoroughly dewaxed. be ground, or reshaped, to fit limited interarch
This in turn facilitates grinding of the teeth to spaces. Bonding of porcelain teeth to acrylic bases
accommodate the available interocclusal spaces has been recently enhanced by a combination of
and allows reshaping of the teeth to fit small spaces micromechanical retention and chemical bonding.
for esthetic purposes, without fear of destroying the This is carried out by treating the ridge lap area of
bond to the base. The use of adhesive promoters the tooth with an etchant such as hydrofluoric acid
such as (4-methacryloxyethyl trimellitic anhydride gel, followed by a silane-coupling agent.
[4-META]) has been recently advocated to facili-
tate bonding of highly cross-linked acrylic teeth to Another limitation of porcelain teeth includes
resin bases. Adhesive resin cements containing this their ability to cause significant wear of opposing
compound have also been used to facilitate enamel and metallic occlusal surfaces. The teeth
bonding of resin bases to base metal alloys. are quite brittle, can easily crack or chip on impact,
and are difficult to grind for occlusal adjustments
The esthetic qualities of acrylic resin teeth because they lose their surface glaze and repolish-
have improved significantly over the years, and ing is quite difficult. Porcelain teeth produce noisy
clinically they are quite acceptable. The teeth are clicking sounds on contact with each other.
prepared in layers of different shades with lighter However, the teeth are not without merits. They are
shades towards the incisal or occlusal portions, dimensionally stable; are hard, in comparison with
thus increasing their translucency. Both acrylic the softer acrylic resins; exhibit no permanent
and porcelain teeth can also be characterized with deformation under occlusal loading; and are insol-
surface stains to enhance their natural appearance. uble in oral fluids and in most organic solvents.
A specifically great advantage of acrylic resin
teeth is the ease of their occlusal reshaping to In the selection of denture teeth for complete
achieve the desired articulation needed for various dentures, and considering the recently mentioned
occlusal schemes. Resin teeth have high resiliency properties of the various materials, the dentist
and are tougher than porcelain teeth, making them should avoid combining posterior resin teeth with
less liable to fracture or chipping on impact. porcelain anterior teeth. The significant differences
Unfortunately, they exhibit inferior abrasion resist- in abrasion resistances in both materials, with
ance, which could lead to alteration in the vertical acrylic resin wearing more rapidly than porcelain,
would potentially create destructive occlusal forces
in the anterior region of the mouth. Table 12-2

198 Part Two Preparing the Patient for Complete Denture Treatment

compares the properties of acrylic and porcelain treatment purposes in the management of edentu-

teeth. lous patients.

DENTURE-LINING MATERIALS Short-Term Soft Liners (Tissue Conditioners)

Denture-lining materials are used to refit the sur- These materials are soft, resilient materials com-
faces of complete dentures and to help condition monly used as temporary liners and have been
traumatized tissues, providing an interim or perma- widely used in dentistry to manage a multitude of
nent cushionlike effect. These materials are gener- patient problems and for various clinical applica-
ally classified into the following types: tions (Box 12-5).

1. Short-term soft liners (tissue conditioners) Tissue conditioners are provided mostly as a
2. Long-term soft liners powder/liquid system, but preformed sheets of
acrylic gels are also available. The powder contains
Soft denture liners are polymers with a glass tran- a polymer, a polyethylmethacrylate (PEMA), or its
sition temperature (Tg) that is below that of mouth copolymers, and the liquid contains a mixture of
temperature. The Tg is the temperature at which a ethyl alcohol (solvent) and an aromatic ester
polymer ceases to be glossy and brittle and changes (dibutyl phthalate), which acts as a plasticizer that
to a rubberlike form. The soft resilient nature of lowers the Tg of the polymer rendering it a soft gel.
these materials inside the mouth provides them The gelation of tissue conditioners is a physical
with a whole range of diagnostic, adjunctive, and process, which is devoid of any chemical reaction
or any monomeric substances that could cause
tissue irritation. Upon mixing the powder and

Table 12-2
Advantages and Disadvantages of Acrylic Resin and Porcelain Teeth

Property Acrylic Resin Teeth Porcelain Teeth

Bond with resin base Chemical bond Mechanical via pins or diatoric holes
Mechanical properties Less brittle than porcelain Very brittle/chipping occurs on impact
High resilience and toughness
Solubility in oral fluids and Insoluble; some dimensional Insoluble; inert in oral fluids; no
dimensional changes dimensional changes
changes
Maintenance of vertical Poor abrasion resistance; wear is Excellent abrasion resistance; hard,
dimension (VDO) wear is insignificant; VDO tends to
significant, wear can result in be maintained
Effect on opposing occlusion reduced VDO
Can oppose natural teeth or Abrades opposing tooth enamel/
Tooth contouring/occlusal metallic occlusal surfaces metallic surfaces
adjustment/repolishing Relatively easy
Difficult, may result in loss of surface
Grinding of ridge lap areas Easy to grind without compromising glaze
tooth-resin bond
Esthetic properties Difficult to grind; compromises
Excellent, can be characterized as tooth-resin bond; difficult to
Clicking sounds required position or retain in limited
interarch spaces
None on contact with opposing teeth
Excellent, can be characterized as
required

Noisy, clicking occurs with opposing
porcelain teeth

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 199

Box 12-5 formulated to remain soft and resilient for longer
periods. The mechanism of action of tissue condi-
Indications for Short-Term Soft tioners is related to their specific viscoelastic prop-
Liners/Tissue Conditioners erties, which is a combination of both viscous fluid
and elastic solid behavior. Viscous behavior allows
1. Treatment and conditioning of abused/irri- adaptation of the gel to the inflamed/irritated
tated denture supporting tissues lining ill- mucosa underlying the denture, which greatly
fitting dentures allows the tissues to rest and improves the fit of the denture. After an initial easy
regain their health prior to impression flow, the gel becomes highly viscous, and its flow
making for new dentures thereafter is affected by the magnitude of the load
applied on the denture as well as its duration. This
2. For provisional adjunctive/diagnostic pur- consequently affects stress distribution in the
poses such as recovery of the vertical dimen- mucosa. Concurrently, under cyclic/intermittent
sion of occlusion and correcting occlusion of loading such as during chewing, the material
old prosthesis; also to assess the necessity of demonstrates a time-dependent elastic behavior
using a permanent soft liner for patients that allows it to recover initial deformation, absorb-
with chronic pain or soreness associated ing impact forces and cushioning the underlying
with denture wearing tissues. Thus viscoelastic and elastic properties of
tissue conditioners result in an even distribution
3. Temporary relining of immediate den- of load on the underlying mucosa and a cushioning
tures/immediate surgical splints of cyclic forces of mastication. This in turn allows
the traumatized mucosa to recover, particularly
4. Relining cleft palate speech aids under an ill-fitting denture.
5. Tissue-conditioning during implant healing
6. Functional impression materials Short-term soft liners can also be used as func-
tional impression materials. Requirements for this
liquid, the alcohol/plasticizer mix diffuses into the clinical application differ slightly from those
swellable acrylic beads. Gelation involves the required for tissue conditioning.
entanglement of outer polymer chains of swollen
beads, resulting in a tacky set gel with high cohe- For traumatized tissues to be effectively condi-
sive properties, which enhances its retention to the tioned, a tissue conditioner should demonstrate
fitting surface of the denture. The set gel has vis- adequate flow and elastic properties. Maintenance
coelastic and elastic properties that allow it to act of this viscoelastic behavior is the key to its clini-
as a shock absorber. The temporary nature of tissue cal success. A functional impression material, on
conditioners stems from the fact that both the the other hand, should display good flow but with
alcohol and the plasticizer leach out and are par- minimal elastic recovery. The material should flow
tially replaced by water. The material thus hardens readily under functional stresses, ensuring contin-
within a considerably short time, which varies from ual adaptation to the underlying soft tissues as they
a few days to a week or two, and gradually loses its are altered under stresses. However, for guaranteed
proclaimed cushioning effect. In addition, the mate- accuracy of the impression, the material must
rial becomes increasingly vulnerable to surface undergo minimum elastic recovery and should
deterioration, contamination, and fouling by exhibit adequate dimensional stability in terms of
microorganisms, which in turn can lead to further weight change, water sorption, and solubility. Casts
irritation to the already abused mucosal tissues. should be poured immediately after removal of the
impression from the patient’s mouth. Functional
Ideally, for adequate cushioning, a tissue condi- impressions are routinely removed from the
tioner should be replaced with a fresh mix every 2 patient’s mouth after a few days. Results of recent
to 3 days. This procedure should continue until full studies recommend even shorter periods of 24
recovery of the tissues has occurred. The gelation hours to obtain optimum results.
characteristics and viscoelastic properties of tissue
conditioners vary due to differences in their com- Materials that are available as short-term soft
position and structures, such as powder particle liners vary considerably in their compositions and
size and ethyl alcohol content. Some materials are

200 Part Two Preparing the Patient for Complete Denture Treatment

properties; some fulfill the requirements of an polymers, polyphosphazine fluoropolymers, fluo-
optimum functional impression material more effi- roethylene, and polyvinyl siloxane addition sili-
ciently than others. The choice of materials should cones. Currently, the most commonly used
be based on a thorough understanding of their materials are plasticized acrylics and silicone
properties in conjunction with their effective clini- rubber, which are either chemically or heat acti-
cal applications. vated. Requirements of an ideal permanent soft
liner are presented in Box 12-6.
Self-Administered Home Relines
Plasticized Acrylics
Numerous over-the-counter temporary reline mate-
rials are available for patients’ use and are mar- Heat-activated plasticized acrylic liners are sup-
keted as “home relines.” The materials allow the plied as preformed sheets or in a powder/liquid
patient to adjust the fit of their dentures. They are form. The powder consists of a higher methacrylate
supplied as preformed thermoplastic pads or in a polymer (PEMA) and benzoyl peroxide as an ini-
powder/liquid form and have a similar composition tiator. The liquid consists of a higher methacrylate
and manipulation as treatment liners. The main monomer (such as ethyl, n-butyl or 2-ethoxyethyl
limitation and danger of these materials are the methacrylate) together with a plasticizer, commonly
high potential for their misuse. Improper adherence a phthalate ester. The plasticizer lowers the Tg of
to manufacturer’s instructions on the proper mixing the resin and acts as a lubricant between
of the components or long-term use of these liners the polymer chains, enabling them to deform more
can lead to trauma, can cause irritation to the easily. The liner is processed in the laboratory,
underlying tissues, may adversely affect the usually at the time of processing a new denture.
denture base materials, and may cause occlusal
errors. There is a unanimous consensus that Chemically activated acrylic resins are also
patients should be strongly discouraged from using available as soft liners. Their chemical composition
these materials as a substitute for seeking proper is similar to that of heat-activated resins, but they
professional help. are polymerized by a peroxide-tertiary amine
system. These materials are applied as chairside

Long-Term Soft Liners Box 12-6

Long-term/permanent soft liners are mostly used as Requirements of an Ideal
a therapeutic measure for patients who cannot tol- Long-Term Soft Liner
erate the stresses induced by dentures. There is
strong theoretical evidence to justify the use of 1. Biocompatibility
these materials in the management of edentulous 2. Good dimensional stability
patients who suffer from chronic pain, soreness, or 3. Low water sorption and water solubility
discomfort due to prolonged contact between the 4. Good wettability by saliva
rigid denture base materials and the underlying 5. Permanent softness/compliance/viscoelas-
tissues. Such as the case in patients with sharp,
thin, or heavily resorbed ridges or those with severe ticity
bony undercuts. In these situations a viscoelastic soft 6. Adequate abrasion resistance and tear
liner would be a welcome adjunct to compensate for
the dramatically depleted mucoperiosteal support. resistance
The liner permits wider dispersion of forces and 7. Good bond to the denture base
absorption of impact forces that are involved in func- 8. Unaffected by aqueous environment and
tional and parafunctional movements.
cleansers, easy to clean
Materials available as permanent soft liners 9. Simple to manipulate
include plasticized acrylics, silicone rubber, plasti- 10. Color stable and exhibits good esthetics
cized vinyl polymers and copolymers, hydrophilic 11. Inhibits colonization of fungi and other

microorganisms

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 201

relines, and polymerization usually takes a few However, biodegradation of plasticized acrylics
minutes. However, as with other mouth-cured in the oral environment is their main weakness. The
liners, they can only be used on a temporary basis plasticizer and other soluble materials in the liner
because of their tendency to foul and debond from leach out in saliva resulting in a progressive loss of
the denture within a few weeks, a major drawback resiliency, diminishing their cushioning effect. The
that limits their clinical application. The presence resulting hard, rough surface of the liner then pro-
of free monomer also results in inferior mechanical motes calculus and food accumulation and under-
properties and reduced biocompatibility. goes fouling with microorganisms, as well as color
changes and staining.
Silicone Soft Liners
The major drawback of silicones as soft liners
Another commonly used long-term soft liner is sil- is their intrinsic inability to bond with the denture
icone rubber. Silicone liners are provided with heat base resin, which is more evident around the borders
activation or room temperature vulcanization of the denture. High water sorption by the liner
(RTV). accentuates this problem further, detrimentally
affecting the adhesion between the liner and resin
Heat-activated silicone is supplied as a single base. This is a particular problem in RTV silicones,
paste that consists of poly(dimethyl siloxane), a which tend to swell, split, or peel off the denture
viscous liquid to which silica is added as a filler, base. Attempts to enhance the bond with resin
and benzoyl peroxide as an initiator. The liner sets bases include adding bonding agents; using special
by a cross-linking reaction that is catalyzed by heat primers applied to the acrylic base, as in the case of
and the peroxide initiator. It is processed against RTV silicones; or confining the borders of the liner
the acrylic dough of the new denture. The addition to end within the denture border, rather than
of an adhesive usually enhances the bond between extending it to the periphery of the denture base.
the liner and the acrylic resin base. However, such a design may be accompanied
with the risk of decreasing the shock absorbability
RTV silicones, on the other hand, use a con- of the liner.
densation cross-linking process catalyzed by an
organo-tin compound. The materials are supplied Despite their shortcomings, silicone rubbers,
as paste and liquid and are also laboratory particularly those that are heat activated, have a
processed to the fitting surface of the denture base. myriad of properties that enhances their clinical
The fact that these materials achieve a lower degree preeminence over plasticized acrylics, mostly their
of cross-linking than their heat-activated counter- high resilience and prolonged elasticity over time,
parts certainly compromises many of their attrib- which in turn, enables them to maintain their cush-
utes as long-term liners. ioning effect longer than other soft liners.

Advantages and Disadvantages of Most challenging in the use of long- and short-
Permanent Soft Liners term soft liners is their tendency to support growth
of C. albicans and other microorganisms on and
Despite the vast clinical benefits that have been within the liners. The porous nature, particularly of
recognized for plasticized acrylics and silicones as silicones, reportedly facilitates water absorption
soft liners, both materials exhibit properties that and diffusion of nutrient materials. This is further
are by far short of fulfilling requirements of an complicated by the difficulty of cleaning most of
ideal permanent liner. This fact has limited their these liners with routine mechanical or chemical
efficacy and life expectancy, reportedly to a methods, such as brushing, or hypochlorite and
maximum of 1 year of serviceability. peroxide denture cleansers (Figure 12-1).

Plasticized acrylic soft liners exhibit good, Excellent oral and denture hygiene and the use
durable bond strength to the acrylic base, have been of antimicrobial agents can effectively minimize
shown to exhibit higher tear and abrasion resist- fungal/microbial colonization of liners. Cleaning
ance, and can achieve a much better polish than sil- of soft liners can be carried out with a soft brush in
icones. conjunction with a very mild detergent or nonabra-
sive dentifrice. Alternatively, the external surface

202 Part Two Preparing the Patient for Complete Denture Treatment

AB

C

Figure 12-1 A, Recently completed resilient liner on a mandibular denture.
B, A 6-month-old resilient liner with foci of yeast colonies already apparent. C, A neglected
12-month-old resilient liner with almost total coverage by yeast colonies.

of the denture can be cleaned as described, but the used, may be the most appropriate of the various
liner itself can be wiped with cotton under cold types available, but they too are only temporary
water. Box 12-7 provides a comparison of proper- expedients and must be inspected regularly by the
ties of plasticized acrylics versus silicone rubber. dentist and replaced when unsatisfactory. As
pointed out earlier, the application of proper
Clinical experience indicates almost universal cleansers and home care habits has contributed to
tissue tolerance of soft liners and acceptable patient the use of these materials with significantly bene-
reactions. However, currently, the materials have to ficial results. It must be emphasized, however, that
be considered as temporary expedients because using these materials does not preclude adherence
none of the advocated permanent soft liners has a to the fundamental principles of complete denture
life expectancy comparable to that of the resin construction. Nevertheless, when used intelli-
denture base. Improved strength, permanent gently, soft liners are an excellent adjunct in remov-
resiliency, improved adhesion to the denture bases, able prosthodontics.
the ability to inhibit growth of microorganisms,
and chemical stability continue to be the main DENTURE CLEANSERS
focus of ongoing research. These attempts include
surface coatings of liners with sealants such as flu- Education of patients is crucial to enhance their
orinated copolymers and integration with antifun- awareness of both limitations and inherent weak-
gal components. Silicone rubbers, when properly

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 203

Box 12-7 carbonate. Maintenance of adequate denture
hygiene, through mechanical or chemical methods,
A Comparison of the Properties or both, is essential to minimize and preferably
of Plasticized Acrylics versus eliminate adverse tissue reactions. It must be an
Silicone Rubber integral component of postinsertion patient care.

Plasticized Acrylics Denture cleansing materials and techniques
Less resilient include mechanical brushing, the use of chemical
Hardens by time/loss of plasticizer cleansers, or both. Commonly available denture clean-
Good durable bond with denture base sing materials include (1) oxygenating cleansers, (2)
More resistant to growth of Candida albicans alkaline hypochlorite solutions, (3) dilute mineral
Acceptable tear strength acids, (4) abrasive powders and pastes, and (5)
Better abrasion resistance enzyme-containing materials (proteases) (Box 12-8).
Reasonable resistance to damage by denture
Mechanical Techniques
cleanser
Patients are routinely instructed to clean their den-
Silicone Rubber tures by light brushing with a soft denture brush or
Highly resilient a multifluted soft nylon brush with rounded ends
Retains softness and elasticity and soap and water. The mechanical cleaning
Low bond strength to acrylic base, particularly action of the brush is usually sufficient to remove
loosely attached soft food debris, without abrading
RTV silicones the denture base and teeth. However, it is ineffec-
More susceptible to growth of C. albicans/ other tive for denture disinfection. The removal of hard
calculus deposits, plaque, and stains require more
microorganisms vigorous measures such as the daily use of immer-
Low tear strength sion chemical denture cleansers or brush-on diluted
Low abrasion resistance acid cleansers.
Less resistant to damage by cleansers particu-
The use of hard bristle brushes, forceful brush-
larly RTV silicones ing, or abrasive dentifrices, such as calcium car-
bonate or hydrated silica, may cause abrasion of
RTV, Room temperature vulcanization. polymeric materials or result in scratches on their
surface. The rough, irregular surfaces promote
nesses in the physical and mechanical properties of
the inserted prosthesis. Furthermore, it must be Box 12-8
emphasized that improper care of dentures can
have serious detrimental effects on the health of the Requirements of an Ideal
denture-supporting tissues. Most patients are Denture Cleanser
unaware of the risks of microbial plaque accumula-
tions around and under the denture-tissue inter- 1. Nontoxic
faces and the potential for promoting adverse 2. Easy to remove and harmless to the patient
pathological mucosal reactions such as denture
stomatitis and angular cheilitis. (eyes-skin-clothes) if accidentally spilled or
splashed
The presence of denture deposits and their rate 3. Harmless to the denture base materials and
of accumulation are directly related to the pres- denture teeth as well as soft liners
ence of a protein-rich saliva and the microporous 4. Able to dissolve all the denture deposits such
nature of the polymeric base, which facilitates as calculus
microbial plaque formation and ensuing calculus 5. Exhibits a bacteriocidal and fungicidal effect
deposition. The organic portion of calculus consists 6. Long shelf life and inexpensive
of microproteins that bond the deposits to the
denture surface, whereas the inorganic portion
mostly contains calcium phosphate and calcium

204 Part Two Preparing the Patient for Complete Denture Treatment

accumulation of denture deposits, increase staining 1 teaspoon of hypochlorite (Clorox) and 2 teaspoons
and fouling with oral microorganisms, and they of a glassy phosphate (Calgon) in half a glass of
dramatically compromise denture esthetics. Pastes water, to help control calculus and heavy stains.
with some gentle abrasives (sodium bicarbonate or
acrylic resin) may be used. Similarly, patients Alkaline hypochlorites are not recommended
should be strongly advised against using abrasive for dentures fabricated from cast base metal alloys.
household kitchen or bathroom cleansers, such as The chlorine ions can result in corrosion and dark-
scouring powder, to clean their dentures. ening of these metals. Concentrated hypochlorite
solutions should also not be used because pro-
Chemical Denture Cleansers longed use may alter the color of the denture base
resins. Bleaches may eventually discolor soft
The most commonly used commercial chemical denture liners, particularly silicones. The impor-
denture cleansers use immersion techniques; these tance of avoiding soaking dentures in hot water
include alkaline peroxides and hypochlorites. should be stressed to the patient to avoid distortion
Advantages of immersion cleansers include full of the denture bases.
accessibility of the solutions to all areas of the
denture, minimum damage from mishandling den- Other Techniques/Materials
tures, minimum abrasion of denture bases and
teeth, and use simplicity of the technique. ● Ultrasonic units provide vibrations that can
be used to clean dentures. When this tech-
Oxygenating Cleansers Alkaline peroxides are nique is used, the denture is placed into a
provided in powder and tablet forms. The material cleaning unit, which is filled with a soaking
contains alkaline compounds, detergents, sodium chemical agent supplied by the manufac-
perborate, and flavoring agents. When mixed with turer. The cleansing action of the soaking
water, sodium perborate decomposes releasing per- agent is supplemented by the mechanical
oxides, which in turn decomposes releasing oxygen. debriding action of the ultrasonic vibrations.
Cleansing is a result of the oxidizing ability of the This in turn creates areas of vacuum next to
peroxide decomposition and from the effervescent the denture surface and thus dislodges and
action of the evolved oxygen. This effectively dispenses debris. Despite its effectiveness,
breaks down, dissolves, and floats away organic this technique may not adequately remove
deposits and kills microorganisms. Peroxides are plaque on the denture surface. It is mostly
not as effective, though, in removing heavy calcu- available for use in institutions such as
lus deposits. Some are not compatible with soft nursing homes and hospitals.
denture liners. Overnight immersion of dentures in
an alkaline peroxide solution is a safe, effective ● Dilute acids (citric acid, isopropyl alcohol,
method of denture cleaning and sterilization, par- hydrochloric acid, or plain household
ticularly among geriatric or disabled patients, vinegar) are available to remove obstinate
whose limited manual dexterity may deter them deposits. The brush-on cleanser is swabbed
from using mechanical brushing techniques. onto the denture surfaces with a brush. The
materials attack the inorganic phosphate
Hypochlorite Solutions Diluted household portion of denture deposits, thus reducing
bleaches (sodium hypochlorites) are commonly calculus accumulations. Vinegar can also kill
used as denture cleansers, for removing plaque and microorganisms but less effectively than
light stains, and are capable of killing denture bleaching solutions. Brush-on materials
adherent organisms. One technique involves the must be used cautiously, and the denture
immersion of the dentures in a solution of one part must be rinsed thoroughly to avoid contact
of 5% sodium hypochlorite in three parts of water of the material with the skin and mucosa.
(1:3 water) followed by light brushing. Alternatively, Diluted acids may also cause corrosion of
the denture is immersed in a solution containing some alloys.

● Denture cleansers containing enzymes
(mutanese and protease) have been shown to

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 205

reduce denture plaque significantly, with a natural mandibular teeth. An unfavorable/irregular
daily 15-minute soak, particularly when occlusal plane, heavy anterior occlusal contacts,
combined with mechanical brushing of the and heavy masticatory forces directed onto a virtu-
dentures. ally thin palatal resin plate may collectively con-
● Other materials and techniques include the tribute to denture fracture. In such a situation, the
use of silicone polymers. These cleansers choice of a cast metal base has been recommended
provide a protective coating, which inter- as an effective alternative to resin bases.
feres with bacterial adherence to the denture
surface until their next application. A variety of metals and metal alloys have been
Overnight air-drying and microwave radia- used as complete denture bases. Currently, the mate-
tion have been also used to disinfect and rials of choice include cast base metal alloys: cobalt-
clean resin bases, mostly in conjunction with chromium, nickel-chromium, cobalt chromium
mechanical brushing. nickel, and more recently titanium alloys.

Table 12-3 describes disadvantages of the various In this technique a relatively thin metal base is
types of denture cleansers. cast to contact the denture-bearing mucosa surface,
covering the whole palate, providing superior fit
CAST METAL ALLOYS AS DENTURES, and comfort to the patient. Acrylic resin is used to
BASES retain the denture teeth and provide buccal/labial
flanges that enhance the esthetic quality of the
Despite the popularity of PMMA as a denture base denture. The processed acrylic resin is attached to
material, its inherent weaknesses in mechanical the cast metal base by a retentive meshwork. The
properties increases its susceptibility to impact and acrylic resin and metal meet at a definite finish line
fatigue failure. Both are considered to be the two to ensure a strong butt junction. Care must be taken
main causes of denture fractures. The reinforcement to avoid inadequate shaping of the palatal contours
of conventional PMMA resins through the incorpo- at the finish line or placing the acrylic resin–metal
ration of rubber inclusions and fibers has signifi- junction too far laterally or medially, which could
cantly enhanced the impact and flexural strengths of result in crowding or inadequate contact with the
the material as well as its fatigue resistance. lateral border of the tongue, causing discomfort or
However, there are various clinical situations where altering the patient’s phonetics (Figure 12-2).
a dentist may select an alternative material. One
such situation is where a single maxillary complete Cobalt-chromium alloys, often referred to as
denture opposes a full or partial complement of stellite alloys, consist of about 60% cobalt and 25%
to 30% chromium, together with minor alloying
elements such as manganese and silicone to
enhance its fluidity for casting. Other components

Table 12-3
Disadvantages of the Various Types of Denture Cleansers

Cleanser Main Constituent Disadvantages
Oxygenating cleansers Alkaline perborate
Ineffective for removal of heavy calculus
Hypochlorite solutions Dilute sodium hypochlorite deposits; harmful to soft liners

Dilute acids Hydrochloric acid May bleach denture base resins
Denture cleansing powder/paste Citric acid/isopropyl alcohol May discolor soft liners
Abrasive agents Corrosion of base-metal alloys
Unpleasant odor
Corrosion of some alloys
Unpleasant odor
Abrasion of denture polymeric bases

and teeth

206 Part Two Preparing the Patient for Complete Denture Treatment

Nickel-chromium alloys contain about 70%
nickel and a lower content of chromium (16%). The
inclusion of beryllium (0.5%) in minor quantities
lowers the melting range and enhances fluidity of
the alloy. The inclusion of aluminum (2%) leads to
the formation of an intermediate (Ni3-Al) com-
pound that increases the strength and hardness of
the alloy. Box 12-9 lists the advantages and disad-
vantages of base metal alloys, as compared to all
resin complete denture bases as listed in Table 12-1.

The controversy surrounding the biocompati-
bility of cobalt- and nickel-containing alloys as
A potential allergenics and the biological risks of
metal ions released in the mouth during corrosion
(such as beryllium, a carcinogenic hazard) suggests
the merits of another cast base metal, titanium, as
an alternative. Superiority of titanium stems from
its remarkable biocompatibility and high corrosion
resistance. In addition, it exhibits high dimensional
stability, low density, and mechanical properties
that are comparable to those of cobalt-chromium
alloys. The main drawback of titanium as a denture

B Box 12-9

Figure 12-2 Metal bases for complete dentures. Advantages and Disadvantages
A, Gold, stellite (cobalt/chromium), or titanium alloy of Base Metal Alloys
covers the palate and residual ridges with the borders
formed in acrylic resin. It should be noted that many Advantages
dentists prefer to not cover the residual ridges with
metal so as to facilitate relieving and relining High thermal conductivity
procedures for acrylic resin covered sites in the future. Increased tissue tolerance
B, Also note that the posterior palatal seal area need Reduced bulk across the palate creates more
not be made of metal. Many dentists prefer a “mesh”
area here to provide excellent retention for an acrylic tongue space/increased comfort to patient
posterior palatal seal. The tuberosity regions may need Dimensional stability/increased accuracy of fit
to be entirely covered in metal or a mesh plus acrylic
as dictated by the interarch space. of the denture base
Superior biocompatibility of titanium bases
included are aluminum, gallium, copper, iron, and Stronger bases that withstand high masticatory
platinum. Molybdenum, tungsten, and carbon are
also added as hardening and strengthening ele- stresses
ments. The resulting alloys display high strength, Increased weight, enhances stability of a
hardness, high modulus of elasticity (stiffness),
low density, and high corrosion resistance, and mandibular denture
they have a substantially lower cost than gold
alloys. Disadvantages

Greater technical costs
Difficulty of rebasing and relining metal/cur-

rently facilitated with adhesives
Less margin of error permissible in the poste-

rior palate seal area
Increased weight for a maxillary denture

Chapter 12 Materials Prescribed in the Management of Edentulous Patients 207

base alloy relates to difficulties in its casting tech- Cunningham JL, Benington IC: An investigation of the variables
nique. Casting problems of titanium are a result of which may affect the bond between plastic teeth and denture
its relatively low density, high melting point (about base resins, J Dent 27:129-135, 1999.
1700˚ C), high chemical affinity to gases (oxygen,
hydrogen, nitrogen), and its reactivity with compo- Da Silva L, Martinez A, Rilo B et al: Titanium for removable
nents of most investment materials. This has led to denture bases, J Oral Rehabil 27:131-135, 2000.
a variety of problems such as low casting effi-
ciency, casting porosities, difficulty in finishing, Jagger DC, Harrison A, Jandt KD: The reinforcement of den-
soldering, and welding of the metal. Casting tita- tures, J Oral Rehabil 26:185-194, 1999.
nium is a relatively expensive laboratory technique
that requires high-cost equipment. John J, Gangadhar SA, Shah I: Flexural strength of heat-poly-
merized polymethylmethacrylate denture resin reinforced
Recent advances in casting technology and with glass, aramid or nylon fibres, J Prosthet Dent 86:
melting techniques, such as electric arc melting and 424-427, 2001.
laser welding; in investment materials; and in
alloying titanium with other metals to attain lower Kawano F, Ohguri T, Koran A III et al: Influence of lining design
melting and casting temperatures have greatly of three processed soft denture liners on cushioning effect, J
facilitated the casting of titanium-based metals and Oral Rehabil 26:962-968, 1999.
its use in dental laboratories.
Koran A III: Prosthetic applications of Polymers. In Craig RG,
SUMMARY Powers JM, editors: Restorative dental materials, ed 11, St
Louis, 2002, Mosby Inc.
The premise in preparing this review chapter is that
dentists should possess sufficient knowledge of the Malmström HS, Mehta N, Sanchez R et al: The effect of two dif-
properties of the different prosthodontic materials ferent coatings on the surface integrity and softness of a
they deal with so that they can exercise prudent tissue conditioner, J Prosthet Dent 87:153-157, 2002.
judgment in their selection. This knowledge should
be preferably based on evidence-based information McCabe JF, Carrick TE, Kamohara H: Adhesive bond strength
plus large scale, long-term clinical trials to ensure and compliance for denture soft lining materials,
treatment efficacy and effectiveness. Biomaterials 23:1347-1352, 2002.

Bibliography Murata H, Kawamura M, Hamada T et al: Dimensional stability
and weight changes of tissue conditioners, J Oral Rehabil
Au AR, Lechner SK, Thomas CJ et al: Titanium for removable 28:918-923, 2001.
partial dentures (III): 2-year clinical follow-up in an under-
graduate program, J Oral Rehabil 27:979-985, 2000. O’Brien WJ: Dental materials and their selection, ed 3,
Chicago, 2002, Quintessence Publishing Co, Inc.
Blagojevic V, Murphy VM: Microwave polymerization of
denture base materials: a comparative study, J Oral Rehabil Ödman PA: The effectiveness of an enzyme-containing denture
26:804-808, 1999. cleanser, Quintessence Int 23:187-190, 1992.

Clarke RL: Glassy polymers. In Braden M, Clarke RL, Parker S: Soft prosthesis materials. In Braden M, Clarke RL,
Nicholson J, Parker S, editors: Polymeric dental materials, Nicholson J, Parker S, editors: Polymeric dental materials,
Verlag Berlin, 1997, Springer. Verlag Berlin, 1997, Springer.

Combe EC, Burke FJT, Douglas WH: Dental biomaterials, Phoenix RD: Denture base resins, technical considerations and
Boston, 1999, Kluwer Academic. processing technique. In Anusavice KJ, editor: Phillips’
science of dental materials, ed 10, Philadelphia, 1996,
Cunningham JL: Shear bond strength of resin teeth to heat- WB Saunders.
cured and light-cured denture base resins, J Oral Rehabil
27:312-316, 2000. Qudah S, Harrison A, Huggett R: Soft lining materials in pros-
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Shay K: Denture hygiene: a review and update, J Contemp Dent
Pract 1:28-41, 2000.

Taguchi N, Murata H, Hamada T et al: Effect of viscoelastic
properties of resilient denture liners on pressures under den-
tures, J Oral Rehabil 28:1003-1008, 2001.

Takahashi Y, Chai T, Takahashi T et al: The bond strength of
denture teeth to denture base resins, Int J Prosthodont
13:59-65, 2000.

Takamata T, Setcos JC: Resin denture bases: review of accuracy
and methods of polymerization, Int J Prosthodont 2:
555-560, 1989.

Tan HK, Woo A, Kim S et al: Effect of denture cleansers, surface
finish and temperature on Molloplast B resilient liner, color,
hardness and texture, J Prosthodont 9:148-155, 2000.

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13C H A P T E R

Developing an Analogue/Substitute for
the Maxillary Denture-Bearing Area

David M. Davis

If dentures and their supporting tissues are to coex- The mucosa is formed by stratified squamous
ist for a reasonable length of time, the dentist must epithelium, which often is keratinized, and a subja-
fully understand the anatomy of the supporting and cent narrow layer of connective tissue known as the
limiting structures involved, for these are the foun- lamina propria. In the edentulous person, the
dation of the denture-bearing area. The denture mucosa covering the hard palate and the crest of
base must extend as far as possible without inter- the residual ridge, including the residual attached
fering in the health or function of the tissues. It is gingiva, is classified as masticatory mucosa. It is
convenient to regard the impression surface of a characterized by a well-defined keratinized layer on
denture as comprising two areas: a stress-bearing its outermost surface that is subject to changes in
or supporting area and a peripheral or limiting area. thickness depending on whether dentures are worn
Each of these is discussed separately, but like the and on the clinical acceptability of the dentures.
sides of a coin they are inseparable.
Although the importance of the mucosa from a
ANATOMY OF SUPPORTING health standpoint cannot be neglected, the thick-
STRUCTURES ness and consistency of the submucosa are largely
responsible for the support that the mucous mem-
The foundation for dentures is made up of bone of brane affords a denture because in most instances,
the hard palate and residual ridge, covered by the submucosa makes up the bulk of the mucous
mucous membrane. The denture base rests on the membrane. In a healthy mouth, the submucosa is
mucous membrane, which serves as a cushion firmly attached to the periosteum of the underlying
between the base and the supporting bone. supporting bone and will usually withstand suc-
cessfully the pressures of the dentures. When
Mucous Membrane the submucosal layer is thin, the soft tissues will
be nonresilient, and the mucous membrane will be
The mucous membrane is composed of mucosa easily traumatized. When the submucosal layer is
and submucosa. The submucosa is formed by con- loosely attached to the periosteum or it is inflamed
nective tissue that varies in character from dense to or edematous, the tissue is easily displaceable, and
loose areolar tissue and also varies considerably in the stability and support of the dentures are
thickness. The submucosa may contain glandular, adversely affected.
fat, or muscle cells and transmits the blood and
nerve supply to the mucosa. Where the mucous Hard Palate
membrane is attached to bone, the attachment
occurs between the submucosa and the periosteal The ultimate support for a maxillary denture is the
covering of the bone. bone of the two maxillae and the palatine bone. The
palatine processes of the maxillae are joined
together at the medial suture (Figure 13-1). The

211

212 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures
C
B

A
D

Figure 13-1 Both the maxillae and the palatine bone provide support for an upper den-
ture. Individual differences in form determine how forces should be directed to these bones
during function. A, Spiny projections that would irritate tissues under a denture. B, Rough
and irregular bone of the maxillary ridges. C, Incisive foramen, which comes to lie closer to
the crest of the ridge as resorption takes place. Thus the location of the incisive papilla,
which covers the incisive foramen, in relation to the crest of the ridge is a guide to the
amount of resorption that has occurred. D, Greater palatine foramen, which often has a spiny
overhanging edge to it.

palatine processes of the maxillae and the palatine and although it contributes to the support of the
bone form the foundation for the hard palate and denture, the horizontal portion of the hard palate
provide considerable support for the denture. More lateral to the midline provides the primary support
important, they support soft tissues that increase area for the denture. In the area of the rugae, the
the surface areas of the basal seat. palate is set at an angle to the residual ridge and is
rather thinly covered by soft tissue. This area con-
A cross section of the hard palate shows that the tributes to the stress-bearing role, though in a sec-
palate is covered by soft tissue of varying thickness, ondary capacity. The submucosa covering the
even though the epithelium is keratinized through- incisive papilla and the nasopalatine canal contains
out. In the region of the medial palatal suture, the the nasopalatine vessels and nerves.
submucosa is extremely thin, with the result that
the mucosal layer is practically in contact with the Residual Ridge
underlying bone. For this reason, the soft tissue
covering the medial palatal suture is nonresilient The shape and size of the alveolar ridges change
and may need to be relieved to avoid trauma from when the natural teeth are removed. The resorption
the denture base. Anterolaterally, the submucosa following extraction of the teeth is rapid at first, but
contains adipose tissue, and posterolaterally it con- it continues at a reduced rate throughout life. If the
tains glandular tissue. This tissue is displaceable,

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 213

teeth have been out for many years, the residual although the peripheral tissues should be contacted
ridge may become small, and the crest of the ridge to provide a border seal.
may lack a smooth, cortical bony surface under the
mucosa. There may be large, nutrient canals and As the mucous membrane extends from
sharp bony spicules (see Figure 13-1). the crest along the slope of the residual ridge to
the reflection, it loses its firm attachment to the
The mucous membrane covering the crest of underlying bone (Figure 13-2). The more loosely
the ridge in a healthy mouth is firmly attached to attached mucous membrane in this region has a
the periosteum of the bone by the connective tissue nonkeratinized or slightly keratinized epithelium,
of the submucosa. The stratified squamous epithe- and the submucosa contains loose connective tissue
lium is thickly keratinized. The submucosa is and elastic fibers. This loosely attached tissue will
devoid of fat or glandular cells and is characterized not withstand the forces of mastication transmitted
by dense collagenous fibers that are contiguous through the denture base as well as the mucous
with the lamina propria. The submucosal layer, membrane covering the crest of the ridge and the
though relatively thin in comparison with other palate.
parts of the mouth, is still sufficiently thick to pro-
vide adequate resiliency to support the denture. Histological studies of the effect of wearing
dentures on the keratinization of the mucosa of the
The crest of the edentulous ridge is an impor- crest of the residual ridges and the palate have pro-
tant area of support. However, the bone is subject to duced conflicting results. However, most studies
resorption, which limits its potential for support, indicate that wearing dentures does not seem to
unlike the palate, which is resistant to resorption. be harmful to the epithelium, even though in den-
Because of this, the ridge crest should be looked on ture wearers the keratinization is of reduced thick-
as a secondary supporting area, rather than a pri- ness. Cytological studies indicate that increased
mary supporting area. The inclined facial surface amounts of keratinized material are present in
of the maxillary ridge provides little support, edentulous ridges when the clinical quality of the

Figure 13-2 Arrows denote the line of demarcation between the attached and unat-
tached mucous membrane. Attached mucous membrane is desirable for support. However, it
is the peripheral area that contributes to the border seal. Notice the prominent incisive
papilla lying anteriorly on the center of the residual ridge.

214 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

dentures is good, an indication that well-fitting den-
tures may be important in maintaining the normal
histological condition of the mouth. Stimulation of
the mucosa of the residual ridge through tooth-
brush physiotherapy also increases the presence of
keratinized material. Histologically, removing the
dentures from the mouth for 6 to 8 hours a day,
preferably during periods of sleep, allows kera-
tinization to increase and the signs of inflamma-
tion, often found in the submucosa when dentures
are worn, to be dramatically reduced.

Shape of the Supporting Structure Figure 13-3 The enlarged tuberosities limit the
space available and will compromise the occlusal plane
The configuration of the bone that provides the and distal extension of the mandibular denture.
support for the maxillary denture varies consider-
ably with each patient. Factors that influence the the occlusal plane and may interfere with the lower
form and size of the supporting bone include (1) its denture, if it is not surgically removed.
original size and consistency; (2) the person’s gen-
eral health; (3) forces developed by the surround- Sharp, Spiny Processes Frequently, there are
ing musculature; (4) the severity and location of sharp, spiny processes on the maxillary and pala-
periodontal disease (a frequent cause of tooth loss); tine bones (see Figure 13-1). These usually cause
(5) forces accruing from the wearing of dental no problems because they are covered deeply by
prostheses; (6) surgery at the time of removal of the soft tissue. However, in individuals with consider-
teeth; and (7) the relative length of time different able resorption of the residual ridge, these sharp
parts of the jaws have been edentulous. In addition, spines can irritate the soft tissue left between them
a number of anatomical features influence the and the denture base. The posterior palatine foram-
shape of the hard palate and residual ridge. These ina often have a sharp, spiny overhanging edge that
are described in the following material. may irritate the covering soft tissues as a result of
pressure from the denture.
Incisive Foramen This is located beneath the
incisive papilla, which is situated on a line imme- Torus Palatinus The torus palatinus is a hard
diately behind and between the central incisors. It bony enlargement that occurs in the midline of the
lies nearer to the crest of the ridge as resorption roof of the mouth and is found in about 20% of the
progresses (see Figure 13-2). Thus the location of population (Figure 13-4). It is covered by a thin
the incisive papilla gives an indication as to the layer of mucous membrane that is easily trauma-
amount of resorption that has taken place. The tized by the denture base unless a relief is provided.
nasopalatine nerves and blood vessels pass through This relief should conform accurately to the shape
the foramen, and care should be taken that the den- of the torus because an extensive arbitrary relief
ture base does not impinge on them. robs the denture of part of its support area.

Maxillary Tuberosity The tuberosity region can ANATOMY OF PERIPHERAL
hang down abnormally low because when the max- OR LIMITING STRUCTURES
illary posterior teeth are retained after the
mandibular molars have been extracted and not The limiting structures of the upper denture can be
replaced, the maxillary teeth overerupt, bringing divided into three areas: (1) the labial vestibule,
the process with them (Figure 13-3). These
enlargements often are fibrous but can be bony.
This excess tissue can prevent proper location of

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 215

Figure 13-4 A torus palatinus is covered by a thin Labial Vestibule
layer of mucous membrane, which is easily trauma-
tized by the denture base unless a relief is provided. The labial vestibule is divided into a left and right
labial vestibule by the labial frenum, which is a
which runs from one buccal frenum to the other on fold of mucous membrane at the median line. It
the labial side of the ridge; (2) the right and left contains no muscle and has no action of its own.
buccal vestibule, which extends from the buccal It starts superiorly in a fan shape and converges as
frenum to the hamular notch; and (3) the vibrating it descends to its terminal attachment on the labial
line, which extends from one hamular notch to the side of the ridge. The labial notch in the
other across the palate (Figure 13-5). labial flange of the denture must be just wide
enough and just deep enough to allow the frenum
to pass through it without manipulation of the lip
(Figure 13-6).

The mucous membrane lining the labial
vestibule has a relatively thin mucosa. The submu-
cosal layer is thick and contains large amounts of
loose areolar tissue and elastic fibers. The mucosa
of the vestibular spaces is classified as lining
mucosa. It is normally devoid of a keratinized layer
and is freely movable with the tissues to which it is
attached because of the elastic nature of the lamina
propria. Lining mucosa also forms the covering of
the lips and cheeks, the alveololingual sulcus, the

1
2 12 2

13 13

33
66

11
44

5 10 5
7 7
9 98
8

AB

Figure 13-5 Correlation of anatomical landmarks. A, Intraoral drawing of the maxillary
arch; 1, labial frenum; 2, labial vestibule; 3, buccal frenum; 4, buccal vestibule; 5, coronoid
bulge; 6, residual alveolar ridge; 7, maxillary tuberosity; 8, hamular notch; 9, posterior
palatal seal region; 10, foveae palatinae; 11, median palatine raphe; 12, incisive papilla; 13,
rugae. B, Maxillary final impression shows the corresponding denture landmarks: 1, labial
notch; 2, labial flange; 3, buccal notch; 4, buccal flange; 5, coronoid contour; 6, alveolar
groove; 7, area of tuberosity; 8, pterygomaxillary seal in area of hamular notch; 9, area of
posterior palatal seal; 10, foveae palatinae; 11, median palatine groove; 12, incisive fossa;
13, rugae.

216 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures
A

B

Figure 13-6 A, A broad maxillary labial frenum. B, The labial flange must fit snugly
around the frenum.

soft palate, the ventral surface of the tongue, and the extent of an impression and hence on the
the unattached gingiva found on the slopes of the denture base.
residual ridges.
The buccal frenum forms the dividing line
The main muscle of the lip, which forms the between the labial and buccal vestibules. It is
outer surface of the labial vestibule, is the orbic- sometimes a single fold of mucous membrane,
ularis oris. Its tone depends on the support it sometimes double, and, in some mouths, broad and
receives from the labial flange and the position fan shaped. The levator anguli oris muscle attaches
of the teeth. The fibers of the orbicularis oris beneath the frenum and consequently affects the
pass horizontally through the lips and anasto- position of the frenum. The orbicularis oris pulls
mose with the fibers of the buccinator muscle. the frenum forward, and the buccinator pulls it
Because the fibers run in a horizontal direction, backward. Thus it requires more clearance for its
the orbicularis oris has only an indirect effect on action than the labial frenum does (Figure 13-7).

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 217

tuberosity and the hamulus of the medial pterygoid
plate (see Figure 13-8). The mucous membrane
of the hamular notch consists of a thick submu-
cosa made up of loose areolar tissue. This tissue, in
the center of the deep part of the hamular notch,
can be safely displaced by the posterior palatal
border of the denture to help achieve a posterior
palatal seal.

Figure 13-7 An upper denture with a properly Vibrating Line
formed notch for the buccal frenum. The buccal
frenum requires more clearance than the labial frenum The vibrating line is an imaginary line drawn
because it will move posteriorly as a result of the across the palate that marks the beginning of
action of the buccinator muscle and anteriorly as a motion in the soft palate when an individual says
result of the action of the orbicularis oris. “ah.” It extends from one hamular notch to the
other (Figure 13-9). At the midline, it usually
Buccal Vestibule passes about 2 mm in front of the fovea palatinae.
These are indentations near the midline of the
The buccal vestibule lies opposite the tuberosity palate formed by a coalescence of several mucous
and extends from the buccal frenum to the hamular gland ducts. They are always in soft tissue, which
notch. The size of the buccal vestibule varies with makes them an ideal guide for the location of the
the contraction of the buccinator muscle, the posi- posterior border of the denture.
tion of the mandible, and the amount of bone lost
from the maxilla. The size and shape of the distal The vibrating line is not to be confused with
end of the buccal flange of the denture must be the junction of the hard and soft palate because the
adjusted to the ramus and the coronoid process of vibrating line is always on the soft palate. It is not
the mandible and to the masseter muscle. When the a well-defined line and should be described as an
mandible opens or moves to the opposite side, the area rather than a line. The distal end of the den-
width of the buccal vestibule is reduced. When ture should extend at least to the vibrating line. In
the masseter muscle contracts under heavy closing most instances it should end 1 to 2 mm posterior to
pressures, it reduces the size of the space the vibrating line. The submucosa in the region of
available for the distal end of the buccal flange. The the vibrating line contains glandular tissue similar
extent of the buccal vestibule can be deceiving to that in the submucosa in the posterolateral part
because the coronoid process obscures it when the of the hard palate. However, because the soft palate
mouth is opened wide. Therefore it should be does not rest directly on bone, the tissue for a few
examined with the mouth as nearly closed as possi- millimeters on either side of the vibrating line can
ble. This space usually is higher than any other part be repositioned in the impression to improve the
of the border. The mucous membrane lining the posterior palatal seal.
buccal vestibule is similar to that lining the labial
vestibule. In addition, the distal end of the denture must
cover the tuberosities and extend into the hamular
Distal to the buccal frenum lies the root of the notches. Overextension at the hamular notches will
zygoma, which is located opposite the first molar not be tolerated because of pressure on the pterygoid
region (Figure 13-8). With increasing resorption of hamulus and interference with the pterygo-
the ridge, it becomes more noticeable, and a den- mandibular raphe, which extends from the hamulus
ture may require relief over this area to prevent to the top inside back corner of the retromolar pad
soreness of the underlying tissue. in the mandible. When the mouth is opened wide,
the pterygomandibular raphe is pulled forward
The hamular notch, which forms the distal limit (Figure 13-10). If the denture extends too far into
of the buccal vestibule, is situated between the the hamular notch, the mucous membrane covering
the raphe will be traumatized.

218 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

A A
C B

Figure 13-8 A, The root of the zygoma is close to the crest of the residual alveolar ridge
because of the amount of resorption of the alveolar ridge. The bone is thinly covered by
mucous membrane and may require relief of the denture border to prevent soreness. B,
Hamular notch. C, Hamular process of the medial pterygoid plate.

PRINCIPLES AND OBJECTIVES and materials vary, they should be selected on the
OF IMPRESSION MAKING basis of biological factors. Too often techniques
follow shortcuts without a consideration of the
The objectives of an impression are to provide sup- future damage that such procedures may induce.
port, retention, and stability for the denture. An
impression also will act as a foundation for For a successful impression to be achieved, the
improved appearance of the lips and, at the same following concepts should be adhered to, irrespec-
time, should maintain the health of the oral tissues. tive of the selected technique:
The impression should record all the potential den-
ture-bearing surfaces available. To a large extent, 1. The tissues of the mouth must be healthy.
this surface is readily identified if the biological 2. The impression should extend to include all of
considerations of impression making are under-
stood correctly. However, the denture’s retention is the basal seat within the limits of the functions
enhanced considerably if the denture extends of the supporting and limiting tissues.
peripherally to harness the resiliency of most of the 3. The border must be in harmony with the
surrounding limiting structures. An impression that anatomical and physiological limitations of
records the depth of the sulcus, but not its width, the oral structures.
will result in a denture that lacks adequate reten- 4. A physiological type of border-molding
tion. Although impression techniques, methods, procedure should be performed by the den-
tist or by the patient under the guidance of
the dentist.

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 219

X

Figure 13-9 The vibrating line marked by an indelible pencil. Notice the two fovea
palatinae (X) in the middle of the soft palate.

5. Proper space for the selected impression or inflammation of the denture foundation tissues.
material should be provided within the These must be eliminated before the impressions are
impression tray. made; otherwise, the new dentures will not fit the tis-
sues once they are no longer distorted by the
6. The impression must be removed from the swelling. The patient will then complain that the den-
mouth without damage to the mucous mem- tures, although fitting well initially, became loose
brane of the residual ridges. after a few days. The most effective way of resolving
the inflammation is to ensure that patients leave their
7. A guiding mechanism should be provided dentures out of the mouth for at least 24 hours before
for correct positioning of the impression the impressions are made, although a longer period
tray in the mouth. often is required to resolve the problem completely.
Many patients understandably object to leaving their
8. The tray and the impression material should dentures out because it is extremely disfiguring. The
be made of dimensionally stable materials. use of tissue conditioners is a very effective alterna-
tive, although patients should still be encouraged to
9. The external shape of the impression must leave their old dentures out as much as possi-
be similar to the external form of the com- ble before the impressions are made. Preparation of
plete denture. the mouth before construction of the new dentures is
discussed in detail in Chapters 7 and 8.
All of these factors will contribute to a successful
impression, but probably the two most important MAXILLARY IMPRESSION PROCEDURES
factors in making satisfactory impressions are a
properly formed and accurately fitting impression Impressions are made with a variety of materials
tray and proper positioning of the tray within the and techniques. Some materials are more fluid than
mouth. others before they harden or set. The softer materi-
als displace soft tissue to a lesser extent and require
PREPARATION OF THE MOUTH

It is essential that the oral tissues be healthy before
impressions are made. There should be no distortion

220 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

A
B

C

Figure 13-10 A, The maxillary tuberosity. B, The pterygomandibular raphe, which is
pulled forward when the mouth is opened wide. C, The retromolar pad of the mandible. The
cheek lies to the right in this picture and the palate to the left.

less force in their molding than do more viscous impression-making procedure. If the tray is too
materials. These variations in the working proper- large, it will distort the tissues around the borders
ties of materials make it possible to devise different of the impression and will pull the soft tissues
techniques for controlling the position and shape under the impression away from the bone, distort-
of the oral tissues. Some techniques are intended to ing the dimensions of the sulcus in the process. If it
record the shape of the tissues with a minimum of is too small, the border tissue will collapse inward
displacement; others are intended to displace the onto the residual ridge. This too will distort the
border tissues to a predetermined extent. Still oth- accurate recording of the border extension of the
ers are devised to obtain controlled displacement of denture and prevent the proper support of the lips
the tissues under the denture. Impressions that by the denture flange. A properly formed tray
record the tissues with minimum displacement are enables the dentist to carry the impression material
described as mucostatic, whereas those that dis- to the mouth and control it without distorting the
place the tissues are classified as mucodisplacing. soft tissues that surround it.
There is, however, no evidence to indicate that one
technique produces better long-term results than Individual or custom trays have borders that
another. The choice is made by the dentist on the can be adjusted so they control the movable soft tis-
basis of the oral conditions, concept of the function sues around the impression but do not distort them.
of the tissues surrounding the denture, and ability At the same time, space is provided inside the tray
to handle the available impression materials. so that the shape of the tissues covering the den-
ture-bearing area may be recorded with minimal or
Regardless of the type of impression being selective displacement. Because each mouth is dif-
made, the tray is the most important part of the ferent, these requirements cannot be achieved suc-

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 221

cessfully with stock trays. Therefore most impres- Impression compound is a thermoplastic
sion procedures involve making a preliminary material with a high viscosity. Like silicone putty,
impression only in a stock tray. This is then poured the material will flow beyond the tray to compen-
in artificial stone and the resulting cast used to con- sate for underextension and will support itself in
struct a custom tray. The final impression is then this position once it is chilled. Therefore it is not
made with the custom tray. necessary to correct any underextension of the
stock tray before using this material. Also, addi-
PRELIMINARY IMPRESSIONS tions can be made to it if part of the impression
is deficient. Its high viscosity means that it records
Stock trays are constructed in either metal or plastic surface detail poorly. In addition, it is nonelastic
and may be perforated or unperforated. Although and so will not record undercuts accurately. In pre-
they are available in a range of shapes and sizes, vious editions of this text, a technique is described
they cannot fit the upper jaw of each individual whereby a preliminary compound impression is
without distorting the soft tissues. It is, however, carefully and diligently “converted” into a superb
important that the preliminary impression is as custom tray. The technique has, however, been
accurate as possible. An unsatisfactory preliminary eclipsed by the one described in this chapter and in
impression will result in an unsatisfactory custom the next one on mandibular impression making.
tray. This will in turn require considerable effort and The current technique reflects a synthesis of three
time-consuming modifications before it can be used considerations: developments in biomaterials,
to make the final impression. Even a correctly a better understanding of the macroscopic and
selected stock tray will not fit the denture-bearing microscopic anatomy plus physiology of the eden-
area perfectly. Therefore when the impression is tulous milieu, and compelling clinical experiences
made, it is advisable to select an impression mate- underscoring its applied merits. The material of
rial that has a relatively high viscosity, thereby choice for most dentists is now a high-viscosity
allowing the material to compensate more easily for alginate impression material.
the deficiencies of the tray. The most suitable mate-
rials are alginate (irreversible hydrocolloid), Tray Selection
silicone putty, or impression compound.
The space available in the mouth for the upper
Silicone putty impression material has a high impression is studied carefully by observation of
viscosity. It will flow beyond the tray to compen- the width and height of the vestibular spaces with
sate for underextension of the stock tray, and once the mouth partway open and the upper lip held
set, it will support itself in this position. It exhibits slightly outward and downward. An edentulous
some degree of elasticity and so will record under- stock tray that is approximately 5 mm larger than
cuts with reasonable accuracy. Its high viscosity the outside surface of the residual ridge is selected.
means that it records surface detail poorly, and The dentist places the tray in the mouth and ini-
in addition, it cannot be added to if part of the tially positions it by centering the labial notch of
impression is deficient. the tray over the labial frenum. The posterior extent
of the tray relative to the posterior palatal seal
The irreversible hydrocolloids record detail area is maintained, and then the handle is
accurately if they are properly controlled. Because dropped downward to permit visual inspection
they do not absorb the mucous secretions from the (Figure 13-11). Posteriorly, the tray must include
palate, they can exhibit defects in the palatal part of both the hamular notches and vibrating line.
the impression. Furthermore, the irreversible
hydrocolloids lose moisture rapidly and can conse- Alginate impression material will not support
quently change their size. The casts must therefore itself away from the confines of the tray, so any
be poured soon after the impressions are removed areas of underextension need to be corrected with
from the mouth. The weight of the artificial stone soft boxing wax before the impression is made.
of the cast may be sufficient to distort the bor- A common site for a stock tray to be underextended
ders of the impression, particularly if they are not is around the tuberosities and into the buccal
supported by the borders of the tray.

222 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

AB

C

Figure 13-11 The stock tray must be of proper size and must be correctly positioned in
the mouth. A, The patient is asked to open the mouth halfway, and the tray is rotated into
the mouth in the horizontal plane using the handle. B, The tray is centered by positioning
the labial notch over the labial frenum. C, The handle of the tray is dropped downward to
permit visual inspection of the posterior extension across the palate and hamular notches.

vestibules. In addition, soft boxing wax can be used Impression Making
to line the entire border of the stock tray to create
a rim that helps adapt the borders of the tray to the Before making the preliminary impression, it is
limiting tissues. Such a wax periphery also pro- advisable to practice placing the tray in position.
tects fragile border tissues from the risk of the The patient is asked to open the mouth halfway, and
impinging tray’s hard material (e.g., metal). Across the tray is first centered below the upper residual
the posterior border of the tray, wax is adapted to ridge. The upper lip is elevated, and the tray is car-
the tissue of the posterior palatal seal area by care- ried upward anteriorly into position, with the labial
ful elevation of the tray in this region, with the frenum used as a centering guide. When the tray is
anterior part of the tray in the proper position. located properly anteriorly, the index fingers are
Again, the borders of the tray are observed visually placed in the first molar region on each side of the
relative to the limiting anatomical structure (Figure tray, and with alternating pressure they seat the tray
13-12). The objective is to obtain a preliminary upward until the wax across the posterior part of
impression that is slightly overextended around the the tray comes into contact with the tissue in the
borders. posterior palatal seal area. The fingers of one hand

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 223

Figure 13-12 The modified stock tray is ready for technique is the same except that the borders of the
making the preliminary impression. stock tray are not modified with wax. There is no
need to use a tray adhesive for impression com-
are shifted into the middle of the tray, and border pound, although one is necessary for silicone putty.
molding is carried out. Preloading of the palate and around the tuberosities
is not undertaken. The tray is loaded with the
The labial and buccal vestibules can be molded impression material and seated in the mouth in
by asking the patient to “suck down” onto the tray. exactly the same manner as for alginate impression
In addition, the patient should be asked to move the material.
mandible from side to side and then open wide.
These movements will record the influence of the The borders of the custom tray should now be
coronoid processes on the shape of the buccal determined. Two choices are available. Either
vestibules. the periphery is outlined with a disposable indeli-
ble marker on the impression at the chairside (the
The tissue surface and borders of the tray, preferred option), or the outline is somewhat arbi-
including the rim of wax, are painted with an adhe- trarily marked on the poured cast in the laboratory.
sive material to ensure that the alginate impression The completed impression should be observed next
material adheres to the tray. The irreversible hydro- to the patient’s mouth and the junction of the
colloid is mixed according to the manufacturer’s attached and unattached mucosal tissue visually
instruction and is placed in the tray and evenly dis- identified on the border of the impression (Figure
tributed to fill the tray to the level of its borders. 13-14). The impression is poured in artificial stone,
A small amount of impression material is placed in and the custom tray outline should now be evident
the anterior part of the palate and in the sulci oppo- on the cast. If the outline has not been marked on
site the tuberosities to help prevent air from being the impression, it can be drawn directly on the cast.
trapped in these parts of the preliminary impres- However, with the patient not present for a correla-
sion (Figure 13-13, A). The loaded tray is then posi- tion between anatomical features and the cast, this
tioned in the mouth in a manner similar to that becomes an educated guess.
during the practice sessions (Figure 13-13, B, C, and
D). Once the material has set, the cheeks and upper Clinical experience has shown that a large
lip are lifted away from the borders of the impres- number of edentulous patients seeking treatment
sion to introduce air between the soft tissue at the for new complete dentures are already wearing
reflection and the border of the impression. While complete dentures. If these have been worn suc-
the lip is elevated, the tray is removed from the cessfully for a number of years and if the extension
mouth in one motion and inspected to ensure that all of the base is satisfactory, then logic suggests that
the basal seat has been recorded (Figure 13-13, E). these dentures can be used as a starting point for
developing an accurate impression of the denture-
If impression compound or silicone putty is bearing surface.
used for making the preliminary impression, the
As part of the protocol for restoring the health
of the supporting tissue, the denture will have been
relined with a tissue conditioner. The result can be
regarded as the preliminary impression and used to
produce the preliminary cast by pouring artificial
stone into the fitting surface of the denture. If
undercuts exist on the fitting surface of the denture
(e.g., around the tuberosities), then artificial stone
should not be used. It would be impossible to
remove the denture from the cast without damaging
either the cast or, even worse, the denture.
The undercuts can, of course, be removed
before adding the tissue conditioner, but this means
that the fitting surface of the denture has been

224 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

AB

CD

E
Figure 13-13 A, A small amount of irreversible hydrocolloid is placed into the palate
and around the tuberosities. B, The upper lip is elevated and the tray carried upward anteri-
orly. The labial notch is lined up with the labial frenum. C, The tray is seated posteriorly by
the index fingers in the region of the first molars. D, The tray is held in place with a finger
placed into the center of the palate. E, The completed impression.

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 225

The elastomeric impression materials and irre-
versible hydrocolloids are all used in spaced cus-
tom trays. To avoid displacing the border tissues, a
less viscous irreversible hydrocolloid is used for
making the final impression compared with that
used for the preliminary impression. Irrespective of
which material is selected, the optimum result will
be achieved only if the custom tray has been con-
structed and refined correctly.

Figure 13-14 The clinically determined proposed Construction of the Custom Tray
denture base outline is drawn on with a disposable
indelible marker. Baseplate wax, approximately 1 mm thick, is
placed on the cast within the outlined border to
irretrievably altered. This is of no consequence if provide space in the tray for the final impression
the replacement denture is successful. However, if material. The posterior palatal seal area on the cast
the new denture does not meet the patient’s is not covered with the wax spacer. Therefore the
approval, then a very awkward situation can completed custom tray will contact the mucous
develop. If undercuts exist, the cast should be pro- membrane across the posterior palatal border, and
duced preferably in silicone putty, which exhibits additional stress placed here during the making of
sufficient elasticity to permit the denture to be the final impression will help achieve a posterior
removed but is rigid enough to allow the fabrica- border seal. In addition, this part of the tray will act
tion of a custom tray. as a guiding stop to help position the tray properly
during the impression procedure (Figure 13-15, A).
FINAL IMPRESSIONS A wax spacer will not be used if a metallic oxide
impression paste has been selected for making the
A number of materials are available for making the final impression.
final impression. Plaster of Paris was once widely
used as a final impression material, but it is not The custom tray should be 2 to 3 mm thick,
“user friendly” and has been superseded by other with a stepped handle in the anterior region of the
materials. These include metallic oxide impression tray to facilitate removal from the mouth. The step
paste, polyether and silicone impression materials, should be of sufficient height to avoid distortion of
and irreversible hydrocolloids. the upper lip when the tray is in the mouth (Figure
13-15, B). The premise in prescribing a custom tray
Metallic oxide impression pastes are rigid when is that the proposed denture-bearing area of the
set and can be used only where there are no bony denture will be reflected in the tray’s extension.
undercuts. They are used in a close-fitting tray, and
so the overall bulk of the impression is kept to a Refining the Custom Tray
minimum. This is particularly useful where the
denture-bearing area is considerably reduced. In When the custom tray is removed from the prelim-
these circumstances, a close-fitting tray is easier to inary cast, the wax spacer is left inside the tray
locate correctly in the mouth compared with a (Figure 13-16). The spacer allows the tray to be
spaced tray. In addition, it is easier to avoid dis- properly positioned in the mouth during border
placing the limiting structures with a close-fitting molding procedures.
tray. Metallic oxide impression pastes should not
be used in patients with dry mouths because the Border molding is the process by which the
paste tends to adhere to the mucous membrane. shape of the border of the tray is made to conform
accurately to the contours of the buccal and labial
vestibules. This essential requirement of the tray’s
fit ensures an optimal peripheral seal. It begins
with manipulation of the border tissue against a

226 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

AB

Figure 13-15 A, Relief wax covers the basal seat area except for the posterior palatal
seal area and the labial and buccal reflections. B, The custom tray should be 2 to 3 mm thick
and the handle shaped so that it does not interfere with the position of the upper lip.

Figure 13-16 The custom tray covers the entire line is observed in the mouth as the patient says a
basal seat area. The wax spacer has been left inside the series of short “ahs.” The posterior border of the
tray to allow the tray to be properly positioned in the impression tray is marked with a disposable indeli-
mouth during border molding. ble marker, the palatal tissues are dried quickly, the
tray is placed in the mouth, and the patient is asked
moldable impression material that is properly to say “ah.” The tray is removed from the mouth,
supported and controlled by the tray. The amount of and the mark that has been transferred from the tray
support supplied by the tray and the amount of force to the mouth is compared with the vibrating line
exerted through the tissues vary according to the and the hamular notches. If it is underextended, the
resistance or viscosity of the impression material. length is corrected by the addition of modeling
compound.
For border molding to be carried out success-
fully, space must be created for the border molding The tray is now ready for border molding, dur-
material. Therefore the flanges of the custom tray ing which the borders of the tray are molded to a
should be reduced until they are 2 mm short of the form that will be in harmony with the physiologi-
reflections. Once the buccal and labial flanges of cal action of the limiting anatomical structures.
the custom tray have been adjusted, the posterior This may be carried out in sections either recording
palatal border is checked. The tray must contain one part of the border at a time or recording all
both hamular notches and extend approximately parts of the border simultaneously.
2 mm posterior to the vibrating line. The vibrating
Recording all of the border simultaneously has
two general advantages: first, the number of inser-
tions of the tray is reduced to one, and second,
developing all borders simultaneously avoids prop-
agation of errors caused by a mistake in one section
affecting the border contours in another.

The requirements of a material to be used for
simultaneous molding of all borders are that it
should (1) have sufficient body to allow it to
remain in position on the borders during loading of
the tray, (2) allow some preshaping of the form
of the borders without adhering to the fingers,
(3) have a setting time of 3 to 5 minutes, (4) retain
adequate flow while the tray is seated in the mouth,

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 227

(5) allow finger placement of the material into Figure 13-17 The polyether material is placed
deficient parts after the tray is seated, (6) not cause across the posterior palatal seal area and continued
excessive displacement of the tissues of the around the entire border of the tray.
vestibules, and (7) be readily trimmed and shaped
so excess material can be removed and the borders ward, and inward and moved backward
shaped before the final impression is made. and forward to simulate movement of the
frenum (Figure 13-18, B). Posteriorly,
Stick impression compound is ideally suited for the buccal flange is border molded by extend-
carrying out border molding in sections. However, ing the cheek outward, downward, and
it is unsuitable for recording all parts of the border inward. The patient is asked to open wide and
simultaneously because it is impossible to get the move the mandible from side to side.
material softened over the full length of the border. 7. When the impression material is set, the tray
Polyether impression materials are well suited for is removed from the mouth.
border molding as they meet all of the requirements 8. The border molding is examined to deter-
listed previously. mine that it is adequate (Figure 13-19). The
contour of the border should be rounded.
When border molding with polyether impres- Any deficient sites can be corrected with a
sion material, the following procedure should be small mix of polyether material added to
followed: the appropriate area. Overextensions are
readily detected because the tray will pro-
1. An adhesive for polyether impressions is trude through the polyether material and be
placed on the border of the tray, covering adjusted as necessary.
both the inside and outside of the border.
The wax spacer is left inside the tray but The technique is basically the same if stick impres-
should be cut away from the border to allow sion compound is used except that the border is
space for the impression material. molded in sections. The labial vestibule is molded
initially, then each buccal vestibule and finally the
2. The polyether material is mixed and intro- posterior palatal area. The tray with the addition of
duced into a plastic “impression” syringe. softened compound is placed in the mouth, with the
Slightly less catalyst should be used than wax spacer still inside the tray, and the appropriate
recommended by the manufacturers to pro- area is molded. The tray is carefully removed from
vide sufficient working time to complete the the mouth, and the impression compound is chilled
border molding. in cold water. There is no need to use an adhesive
to attach the impression compound to the tray.
3. The polyether material is syringed around
the border and across the posterior palatal If the custom tray is constructed on a cast
seal area (Figure 13-17). The material is taken from the optimized previous denture, it can
quickly preshaped to proper contours with
fingers moistened in cold water.

4. The tray is placed in the mouth, making cer-
tain that the lips are retracted sufficiently to
avoid scraping the material from the border.

5. The border is inspected to ensure that impres-
sion material is present in the vestibule. If
insufficient material is present, excess mate-
rial from an adjacent site should be transferred
with a finger moistened in the patient’s saliva.

6. Border molding is carried out. This is
accomplished in the anterior region when
the lip is elevated and extended out, down-
ward, and inward (Figure 13-18, A). In the
region of the buccal frenum, the cheek is
elevated and then pulled outward, down-

228 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

AB

Figure 13-18 A, Border molding in the anterior region is achieved by moving the lip
outward, downward, and inward. B, The left buccal flange is molded by moving the
cheek outward, downward, inward, and then backward and forward to simulate movement
of the frenum.

be presumed that the tray already reflects the bor- tissues will help the dentist determine whether
der molding developed with the tissue conditioner additional segmental border molding is required.
that has been used to reline the denture. Thus fur- Patients are able to wear complete dentures with
ther border molding is very likely unnecessary. apparent success even though the bases are not
This is assuming that the previous denture base extended correctly. Accepting an incorrectly
is correctly extended and that care has been extended base just because the denture has been
taken with the tissue conditioner to obtain the cor- worn previously is not good practice and excludes
rect border shape. A careful scrutiny of the tray’s the possibility of providing something better.
periphery in the mouth while moving the peripheral
Preparing the Tray to Secure the
Figure 13-19 Border molding has been com- Final Impression
pleted, including the posterior palatal seal area. The
relief wax is still in the impression tray. Space must now be created for the final impression
material; otherwise, the borders will be overex-
tended and the mucous membrane displaced
unnecessarily.

The spacer wax is removed from inside the tray
along with any border molding material that
has flowed over it. Any excess material on the out-
side of the tray also is removed. The thickness of
the border will vary from individual to individual,
but a thick border in the anterior region results in a
poor appearance. If necessary, the thickness of the
labial flange should be adjusted to approximately
2.5 to 3 mm in thickness from one buccal frenum
to the other. Material that extends into an undercut
is reduced because this allows the tray to be seated
more easily. Finally, a small amount of material is
removed from those parts of the border that have

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 229

not already been adjusted. Approximately 0.5 mm The final impression material of choice is
is removed from the inner, outer, and top surface of mixed according to the manufacturer’s instructions
the border. and uniformly distributed within the tray. All bor-
ders must be covered. The tray is then positioned in
Stick impression compound is adjusted with the mouth, as described previously, and border
a scalpel; the polyether is adjusted with either a molding is performed.
scalpel or a bur. The material over the posterior
area is not adjusted. This serves three functions. When the final impression material has set, the
First, it slightly displaces the soft tissues at the dis- tray is removed from the mouth and inspected for
tal end of the denture to enhance posterior border acceptability. If it needs to be remade, the impres-
(palatal) seal. Second, it serves as a guide for posi- sion material is removed with particular care to
tioning the tray properly for the final impression. preserve the border molding. Assuming the tray
Third, it helps prevent excess impression material was formed properly, faulty positioning is the most
from running down the patient’s throat. frequent reason that a final impression must be
remade. A number of reasons for remaking final
Finally, holes can be placed in the palate of the impressions are described in the next chapter.
impression tray with a medium-sized round bur to
provide escape ways for the final impression mate- Boxing Impressions and Making the Casts
rial, and the adhesive material is applied. The holes
furnish relief during the making of the final Great care is taken when making the final impres-
impression so that the mucous membrane over the sion to record the functional width and depth of the
medial palatal raphe and in the anterolateral and sulcus. It is essential that this be preserved in the
posterolateral regions of the hard palate is not dis- final cast. The procedure for preserving this form is
placed excessively. Holes are also preferably called boxing.
placed over residual ridge sites where the soft tis-
sues are mobile and displaceable. The objective is A strip of boxing wax is attached all the way
to avoid recording denture-bearing tissues in a dis- around the outside of the impression approximately
placed or distorted position. 2 to 3 mm below the border and sealed to it with a
spatula (Figure 13-20, A). The strip must be main-
Making the Final Impression tained at its full width, particularly at the distal end
of the impression, to hold the vertical walls of the
As with any impression, the correct positioning of boxing away from the impressions and provide
the tray in the patient’s mouth is essential if the final space for adequate thickness of the cast in this
impression is to be achieved successfully. The pro- region. A thin sheet of modeling wax is then
cedure for placing the tray is the same as that used attached to the outside of the boxing strip to form
when making preliminary impressions. The tray is the vertical wall of the boxing (Figure 13-20, B).
centered as it is carried to position on the upper The vertical wall should extend 10 to 15 mm above
ridge. This is most easily achieved by observing the the impression so that the base of the cast at its nar-
position of the labial frenum relative to the labial rowest point will be of this thickness. The sheet of
notch in the tray. When the frenum is positioned wax should extend completely around the impres-
within the notch, the index fingers of each hand are sion and be sealed to the boxing wax strip to pre-
shifted to the first molar region, and with alternat- vent the escape of artificial stone when this is
ing pressure the tray is carried upward, without dis- poured into the impression. Also, the impression
placement of the front end of the tray downward, should be supported in a level position by the box-
until the posterior palatal seal of the tray fits prop- ing. Boxing procedures cannot be used on impres-
erly in the hamular notches and across the palate. sions made in hydrocolloid materials because the
The tray is held in position with a finger placed in wax will not adhere to the impression.
the palate immediately anterior to the posterior
palatal seal. This procedure should be practiced Artificial stone is mixed according to the man-
with the empty tray until the dentist feels confident ufacturer’s instructions. The stone is poured into
of the proper position of the tray in the mouth. the boxed impression level with the top of the ver-
tical wall of the boxing and allowed to set. After

230 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

AB

C

Figure 13-20 A, Boxing wax has been attached just below the borders of the final
impression. B, The vertical wall of the boxing is securely attached to the boxing strip. The
height of the wall will allow the base of the cast to be from 10 to 15 mm thick. C, The cast
provides an accurate positive record of the basal seat and reflections. The thickness and form
of the cast permit easy adaptation of the materials used in making the occlusion rims.

the final impression is separated from the cast, the 2. Make preliminary impressions.
cast must be shaped to maintain the form of the a. Use a stock tray, modified with wax around
borders of the impression and yet be easily accessi- the border, and irreversible hydrocolloid
ble for adaptation of the materials used in making impression material.
the occlusion rims (Figure 13-20, C). b. Use a stock tray with impression com-
pound material or silicone putty impression
SUMMARY material.
c. On the impression’s border, identify the
1. Ensure the tissues of the mouth are healthy. peripheral outline of the proposed custom
a. Optimize the present dentures with tissue tray. This will conform to a line between the
conditioners and occlusal adjustments. attached and unattached mucous membrane.
b. Encourage the patient to leave the dentures Make a laboratory stone cast.
out as much as possible. d. If the denture has been optimized, that is,
c. Instruct the patient in oral and denture functionally border molded with a tissue con-
hygiene and to massage the denture-bearing ditioner, regard it as the preliminary impres-
tissues. sion. Make a laboratory cast in stone or
d. Prescribe any necessary preprosthetic surgery. silicone putty.

Chapter 13 Developing an Analogue/Substitute for the Maxillary Denture-Bearing Area 231

3. Fabricate a custom tray. 5. Make final impression with preferred impres-
a. Cover the basal seat area with wax except for sion material.
the posterior palated seal area and the labial
and buccal reflections 6. Master cast preparation.
b. Construct a custom tray that extends just past a. Box and pour the final impression.
the identified junction of the attached and b. Trim the cast.
unattached mucosa.
Bibliography
4. Refine the custom tray.
a. Try the tray in the mouth and adjust the bor- Jani RM, Bhargave K: A histologic comparison of palatal
ders as necessary. The flanges should be 2 mucosa before and after wearing complete dentures,
mm short of the reflection and extend J Prosthet Dent 36:254–260, 1976.
approximately 2 mm beyond the vibrating
line. Laney WR, Gonzalez JB: The maxillary denture: its palatal
b. Develop the borders of the tray with either an relief and posterior palatal seal, J Am Dent Assoc
incremental technique with stick tracing 75:1182–1187, 1967.
compound or a one-step technique with a
polyether impression material. Lye TL: The significance of the fovae palatini in complete den-
c. If the tray has been constructed on a cast ture prosthodontics, J Prosthet Dent 33:504–507, 1975.
taken from the optimized previous denture,
then border molding may not be necessary. Martone AL: Clinical applications of concepts of functional
d. Place relief holes in the tray as required. anatomy and speech science to complete denture prostho-
dontics, J Prosthet Dent 13:4–33, 1963.

Watson IB, MacDonald DG: Oral mucosa and complete den-
tures, J Prosthet Dent 47:133–140, 1982.

Watson IB, MacDonald DG: Regional variations in the
palatal mucosa of the edentulous mouth, J Prosthet Dent
50:853–859, 1983.

14C H A P T E R

Developing an Analogue/Substitute for
the Mandibular Denture-Bearing Area

David M. Davis

THE MANDIBLE of resisting occlusal forces than the maxillae are,
and extra care must be taken if the available
The mandibular denture poses a great technical chal- support is to be used to advantage.
lenge for the dentist and often a significant manage-
ment challenge for the patient. Nonetheless, the Crest of the Residual Ridge
fundamental principles for mandibular impressions
are similar to those for maxillary impressions. Both The crest of the residual alveolar ridge is covered
the support or stress-bearing area and the peripheral by fibrous connective tissue, but in many mouths
or limiting area will be in contact with the denture’s the underlying bone is cancellous and without a
fitting or impression surface. The denture base must good cortical bony plate covering it (Figure 14-1).
extend as far as possible without interfering with
the health or function of the tissues. The support The mucous membrane covering the crest of
for a mandibular denture comes from the body of the residual ridge is similar to that of the upper
the mandible. The peripheral seal is provided by the ridge insofar as in the healthy mouth, it is covered
form of the denture’s border as determined by the by a keratinized layer and is attached by its submu-
macroscopic and microscopic anatomy of the limit- cosa to the periosteum of the mandible. The extent
ing structures. However, the presence of the tongue of this attachment varies considerably. In some
and its individual size, form, and activity complicate people, the submucosa is loosely attached to the
the impression procedure for the lower denture and bone over the entire crest of the residual ridge, and
also the patient’s ability to manage the denture. the soft tissue is quite movable. In others, the sub-
Consequently, the retention of a mandibular denture mucosa is firmly attached to the bone on both the
is constantly threatened by tongue movements. crest and the slopes of the lower residual ridge.

ANATOMY OF SUPPORTING The mucous membrane of the crest of the lower
STRUCTURES residual ridge, when securely attached to the under-
lying bone, is capable of providing good soft tissue
Support for the lower denture is provided by the support for the denture. However, because underly-
mandible and the soft tissues overlying it. The total ing bone is often cancellous, the crest of the resid-
area of support from the mandible is significantly ual ridge may not be favorable as the primary
less than from the maxillae. The average available stress-bearing area for a lower denture.
denture-bearing area for an edentulous mandible is
14 cm2, whereas for edentulous maxillae it is 24 The Buccal Shelf
cm2. This means that the mandible is less capable
The area between the mandibular buccal frenum
and the anterior edge of the masseter muscle is

232

Chapter 14 Developing an Analogue/Substitute for the Mandibular Denture-Bearing Area 233

E

B F
C
D
A

Figure 14-1 A, The crest of the residual ridge is often composed of cancellous bone.
B, The buccal shelf consists of cortical bone. C, The mental foramen. D, The genial tubercles.
E, The coronoid process. F, When the alveolar ridge resorbs, it results in a basal seal that
becomes wider and larger. This change occurs because as resorption moves the crest of the
ridge inferiorly, the width of the mandible becomes greater than that of the alveolar process
at the time the teeth were removed.

known as the buccal shelf (Figure 14-2). It is bound brane overlying the crest of the residual ridge.
medially by the crest of the residual ridge, laterally However, the bone of the buccal shelf is covered by
by the external oblique ridge, and distally by the a layer of cortical bone. This, plus the fact that the
retromolar pad. The total width of the bony founda- shelf lies at right angles to the vertical occlusal
tion in this region becomes greater as alveolar forces, makes it the most suitable primary stress-
resorption continues. The reason is that the width of bearing area for a lower denture (Figure 14-3).
the inferior border of the mandible is greater than
the width at the alveolar process (see Figure 14-1). Shape of the Supporting Structure

The mucous membrane covering the buccal shelf The configuration of the bone that forms the
is more loosely attached and less keratinized than the support for a mandibular denture varies consider-
mucous membrane covering the crest of the lower ably among individuals. Factors that influence this
residual ridge and contains a thicker submucosal form are listed in the previous chapter. Many eden-
layer. The inferior part of the buccinator muscle is tulous mandibles are extremely flat, and indeed, the
attached to the buccal shelf, and its fibers are found bearing surface can become concave, allowing the
in the submucosa immediately overlying the bone. attaching structures, especially on the lingual side
of the ridge, to fall over onto the ridge surface.
The mucous membrane overlying the buccal Such conditions require displacement of these
shelf may not be as suitable histologically to provide
primary support for the denture as the mucous mem-

234 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

B

C

A

Figure 14-2 The buccal shelf is shown by the dotted line. It extends from the buccal
frenum (A) to the retromolar pad (B) and from the external oblique ridge of the mandible to
the crest of the residual alveolar ridge (C).

tissues by the impression and make the lingual lous patients. Anteriorly, the mylohyoid ridge, with
flange of the denture more difficult to adapt. its attached mylohyoid muscle, lies close to the infe-
rior border of the mandible. Posteriorly, after resorp-
The maxillae resorb upward and inward to tion, it often lies flush with the superior surface of
become progressively smaller because of the direc- the residual ridge (Figure 14-5). The mucous mem-
tion and inclination of the roots of the teeth and the brane over a sharp or irregular mylohyoid ridge will
alveolar process. The longer the maxillae have been be easily traumatized by the denture base, unless
edentulous, the smaller their bearing area is likely relief is provided in the denture base. The area under
to be. The opposite is true of the mandible, which the mylohyoid ridge is undercut.
inclines outward and becomes progressively wider
according to its edentulous age. This progressive Mental Foramen As resorption takes place, the
change of the edentulous mandible and maxillae mental foramina will come to lie closer to the crest
makes many patients appear prognathic (Figure of the residual ridge (see Figure 14-1). In these cir-
14-4). cumstances, the mental nerves and blood vessels
may be compressed by the denture base unless
In addition, there are a number of anatomical relief is provided. Pressure on the mental nerve can
features that influence the shape of the supporting cause numbness of the lower lip.
structure.
Genial Tubercles Like the mental foramina, the
Mylohyoid Ridge Soft tissue usually hides the genial tubercles usually lie well away from the crest
sharpness of the mylohyoid ridge. The shape and
inclination of the ridge vary greatly among edentu-

Chapter 14 Developing an Analogue/Substitute for the Mandibular Denture-Bearing Area 235

A
B

Figure 14-3 The crest of the residual alveolar ridge consists of cancellous bone (A). Its
porosity and roughness make it unsuitable as the primary stress-bearing area. Therefore the
buccal shelf (B) is selected as the primary support area.

AB AB AB

Figure14-4 Progressive resorption of the maxillary and mandibular ridges makes the
maxillae narrower and the mandible wider. The lines A and B represent the centers of the
ridges. Notice how the distance between them becomes greater as the mandible and
maxillae resorb.

236 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

AA

B

Figure 14-5 An edentulous ridge with a flat residual alveolar ridge. A, The mylohyoid
ridges lie flush posteriorly with the crest of the alveolar ridge. The mylohyoid ridges are
sharp and the area beneath them is undercut. B, The genial tubercles that come to lie closer
to the crest of the alveolar ridge as resorption occurs.

of the ridge. However, with resorption, the genial side must be considered, as well as those around the
tubercles become increasingly prominent (see labial and buccal surfaces of the denture. The struc-
Figure 14-5). tures on the lingual side of the mandible are more
complicated to control than those on the buccal and
Torus Mandibularis The torus mandibularis is a labial sides. The problem is the greater range of their
bony prominence usually found bilaterally and lin- movement and the speed of their actions.
gually near the first and second premolars midway
between the soft tissues of the floor of the mouth Labial Vestibule
and the crest of the alveolar process. In edentulous
mouths, where considerable resorption has taken The labial vestibule runs from the labial frenum to
place, the superior border of the torus may be flush the buccal frenum (Figures 14-7 and 14-8). The
with the crest of the residual ridge (Figure 14-6). length and thickness of the labial flange vary with
The torus mandibularis is covered by an extremely the amount of tissue that has been lost. The extent
thin layer of mucous membrane. It often needs to of the denture flange in this area often is limited
be removed surgically because it can be difficult to because of the muscles that are inserted close to the
provide relief within the denture for the torus crest of the ridge. The mentalis muscle is a partic-
without breaking the border seal. ularly active muscle in this region. The depth of the
flange will be determined by the turn of the muco-
ANATOMY OF PERIPHERAL OR labial fold, which is the line of flexure of the
LIMITING STRUCTURES mucous membrane as it passes from the mandible
to the lip.
The influence of the limiting structures in the
mandible is more difficult to record than in the max- The mandibular labial frenum contains a band
illae. The reason is that the structures on the lingual of fibrous connective tissue that helps attach the
orbicularis oris muscle. Therefore the frenum is

Chapter 14 Developing an Analogue/Substitute for the Mandibular Denture-Bearing Area 237

X
X

AB

Figure 14-6 Tori mandibulari (X). Surgical reduction of these will be necessary before a
satisfactory seal can be developed.

9 10 9

8 7
8
7

10 6 13
6 13 4
11
5 12
4

12 5
3

3

11 2 1 2

A 1

B

Figure 14-7 Correlation of anatomical landmarks. A, Intraoral drawing of the
mandibular arch: 1, labial frenum; 2, labial vestibule; 3, buccal frenum; 4, buccal vestibule;
5, residual alveolar ridge; 6, buccal shelf; 7, retromolar pad; 8, pterygomandibular raphe;
9, retromylohyoid fossa; 10, tongue; 11, alveololingual sulcus; 12, lingual frenum; 13, region
and premylohyoid eminence. B, Mandibular final impression showing the corresponding
denture landmarks: 1, labial notch; 2, labial flange; 3, buccal notch; 4, buccal flange;
5, alveolar groove; 6, buccal flange, which covers the buccal shelf; 7, retromolar pad;
8, pterygomandibular notch; 9, lingual flange with extension into retromylohyoid fossa; 10,
inclined plane for the tongue; 11, lingual flange; 12, lingual notch; 13, premylohyoid
eminence. (Adapted from Martone AL: J Prosthet Dent 13: 4-33, 1963.)

238 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

F I
E

D H
C G

B

A

Figure 14-8 A completed final impression with border outline landmarks. A, Mandibular
labial notch. B, Mandibular labial flange. C, Mandibular buccal notch. D, Buccal flange. E,
Area influenced by the masseter. F, Retromolar pad area. G, Lingual notch. H, Premylohyoid
eminence. I, Retromylohyoid fossa. Notice the S curve of the lingual flanges and also that in
the molar region, the flanges slope toward the tongue and extend below the attachment of
the mylohyoid muscles on the mylohyoid ridges. The slope of the lingual flanges allows the
mylohyoid muscles to contract and raise the floor of the mouth without displacing the lower
denture. The length of the lingual flange in the molar region allows it to reach the
mucolingual fold of tissue in the floor of the mouth to maintain the seal of the lower
denture. The posterior end of the lingual flange bends laterally toward the mandible to fit
into the retromylohyoid fossa. This part of the denture guides the tongue onto the top of the
lingual flange.

quite sensitive and active, and the denture must be jaw. The epithelium is thin and nonkeratinized, and
fitted carefully around it to maintain a seal without the submucosa is formed of loosely arranged con-
causing soreness. nective tissue fibers mixed with elastic fibers and
muscle fibers, depending on the site of histological
The muscles of the lower lip pull actively examination.
across the denture border, polished surfaces, and
teeth. When the patient’s mouth opens wide, the Buccal Vestibule
orbicularis oris muscle becomes stretched, narrow-
ing the sulcus. This would displace the mandibular The buccal vestibule extends posteriorly from
denture if the flange was unnecessarily thick. the buccal frenum to the outside back corner of the
Mandibular dentures and, hence, impressions will retromolar pad. The buccal flange, which starts
always be narrowest in the anterior labial region immediately posterior to the buccal frenum, swings
(see Figures 14-7 and 14-8). wide into the cheek and is nearly at right angles to
the biting force. The impression is always widest in
The mucous membrane lining the labial this region (see Figures 14-7 and 14-8).
vestibule and all limiting structures in the mandible
is similar to that lining the vestibule in the upper

Chapter 14 Developing an Analogue/Substitute for the Mandibular Denture-Bearing Area 239

The extent of the buccal vestibule is influenced Distal Extension
by the buccinator muscle, which extends from the
modiolus anteriorly to the pterygomandibular The distal extension of the mandibular denture is
raphe posteriorly and has its lower fibers attached limited by the ramus of the mandible, by the bucci-
to the buccal shelf and the external oblique ridge. nator muscle fibers that cross from the buccal to the
The external oblique ridge does not govern the lingual side as they attach to the pterygomandibular
extension of the buccal flange because the resist- raphe and the superior constrictor muscle, and by the
ance, or lack of resistance, encountered in this sharpness of the lateral bony boundaries of the
region varies widely. The buccal flange may extend retromolar fossa, which is formed by a continuation
to the external oblique ridge, up onto it, or even of the internal and external oblique ridges ascending
over it, depending on the location of the mucobuc- the ramus. If the impression extends onto the ramus,
cal fold. However, palpation of the external oblique the buccinator muscle and adjacent tissues will be
ridge is a valuable landmark in helping to ascertain compressed between the hard denture border and the
the relative amount of resistance, or lack of resist- sharp oblique ridges. This will not only cause sore-
ance, of the border tissues in this region. ness but also limit the function of the buccinator
muscle. The desirable distal extension is slightly to
The denture should cover completely the the lingual of these bony prominences and includes
buccal shelf, despite the fact that it will rest directly the pear-shaped retromolar pad, which provides a
on fibers of the buccinator muscle. The bearing of soft tissue border seal (Figure 14-9).
the denture on muscle fibers would not be possible
except for the fact that the fibers of the buccinator The retromolar pad is a triangular soft pad of
muscle run parallel to the base and, hence, its pull, tissue at the distal end of the lower ridge. Its mucosa
when in function, is parallel to the border and not is composed of a thin, nonkeratinized epithelium,
at right angles to it. Thus its displacing action is and in addition to loose alveolar tissue, its submucosa
slight. More resistance is encountered in this region contains glandular tissue, fibers of the buccina-
when the denture is first inserted than is manifested tor and superior constrictor muscles, the pterygo-
a few weeks after the denture has been worn. Thus mandibular raphe, and the terminal part of the
it is possible to stretch and displace these tissues tendon of the temporalis muscle. The action of
and so increase the area available for support and these muscles limits the extent of the denture and
stability. prevents placement of extra pressure on the distal
part of the retromolar pad during impression pro-
The distobuccal border, at the end of the buccal cedures. Because of this, the denture base should
vestibule, must converge rapidly to avoid displace- extend approximately one half to two thirds over
ment by the contracting masseter muscle, whose the retromolar pad.
anterior fibers run outside and behind the buccina-
tor muscle in this region (see Figure 14-8). When Lingual Border
the masseter muscle contracts, it pushes inward
against the buccinator muscle and produces a bulge The lingual tissues under the tongue exhibit less
into the mouth. The extent to which the masseter direct resistance than the labial and buccal borders
muscle influences the distobuccal edge of the do and are distorted easily when the impression is
mandibular impression and, hence the denture, being made. Such extension will cause tissue sore-
varies from individual to individual. If the ramus of ness and dislodgement of the denture by tongue
the mandible has a perpendicular surface and the movements. For success to be achieved with a
origin of the muscle on the zygomatic arch is situ- lower impression, it is important to understand the
ated medially, the muscle pulls more directly across action of the mylohyoid muscle.
the distobuccal denture border. This forces the buc-
cinator muscle inward, reducing the space in this Mylohyoid Muscle The floor of the mouth is
area. If the opposite is true, greater extension is formed by the mylohyoid muscle, which arises
allowed on the distobuccal portion of the mandibu- from the whole length of the mylohyoid ridge. This
lar impression. The extent of its effect will be ridge is sharp and distinct in the molar region and
recorded only when the masseter muscle contracts. becomes almost indiscernible anteriorly. Medially,

240 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures
X

Figure 14-9 The retromolar pad (X) is the posterior landmark for a mandibular denture.

the fibers join those from the mylohyoid muscle of anterior region and so does not affect the border of
the opposite side, and posteriorly they continue to the denture in this region except indirectly.
the hyoid base (Figure 14-10). The muscle lies deep
to the sublingual gland and other structures in the However, the posterior part of the mylohyoid
muscle in the molar region affects the lingual impres-

A B CD
A B CD

Figure 14-10 Relationships of the mylohyoid muscle in various regions. The letters with
prime signs denote cross sections of the designated areas. A, Canine region. B, Premolar
region. C, First molar. D, Third molar. At point D, notice that the mylohyoid ridge approaches
the level of the alveolar crest. The angle of the posterior lingual flange in the molar region is
affected by this muscle; anteriorly, only the length of the flange is affected.

Chapter 14 Developing an Analogue/Substitute for the Mandibular Denture-Bearing Area 241

sion border in swallowing and in moving the tongue. and so can move back toward the body of the
During swallowing, the mylohyoid muscles contract, mandible producing the typical S curve of the lingual
raising the floor of the mouth. During impression flange (see Figures 14-7 and 14-8).
taking, it is very easy to carry the impression mate-
rial into the undercut below the mylohyoid ridge The retromylohyoid fossa is bounded by the
because the mylohyoid muscle is a thin sheet of retromylohyoid curtain. The posterolateral portion
fibers that, in a relaxed state, will not resist the impres- of the retromylohyoid curtain overlies the superior
sion material. Extension of the lingual flange under constrictor muscle, and the posteromedial portion
the mylohyoid ridge cannot be tolerated in function covers the palatoglossal muscle plus the lateral
because it will interfere with the action of the mylo- surface of the tongue. The inferior wall overlies the
hyoid muscle when it contracts, and this will displace submandibular gland, which fills the gap between
the denture, causing soreness. For the denture to the superior constrictor muscle and the most distal
be successful, the flange must be made parallel to the attachment of the mylohyoid muscle. The denture
mylohyoid muscle when it is contracted. border should extend posteriorly to contact the
retromylohyoid curtain when the tip of the tongue
Fortunately, in this posterior region, the lingual is placed against the front part of the upper residual
flange can go beyond the mylohyoid muscle’s ridge. Protrusion of the tongue causes the retromy-
attachment to the mandible because the mucolin- lohyoid curtain to move forward.
gual fold is not in this area. Thus the impression
may depart from the stress-bearing area of the The medial pterygoid muscle lies behind the
lingual surface of the ridge, moving away from the superior constrictor muscle (Figure 14-11). Contrac-
body of the mandible to be suspended under tion of the medial pterygoid muscle can cause a
the tongue in soft tissue on both sides of the mouth, bulge in the wall of the retromylohyoid curtain
thereby reaching the mucolingual fold of soft tissue in the same way that contraction of the masseter
for a border seal (see Figures 14-7 and 14-8). The muscle can cause a bulge in the buccinator muscle.
distance that these lingual borders can be away
from the bony areas will depend on the functional Sublingual Gland Region
movements of the floor of the mouth and by the
amount that the residual ridge has resorbed. In the premolar region, the sublingual gland rests
above the mylohyoid muscle. When the floor of the
An extension of the lingual flange well beyond mouth is raised, this gland comes quite close to the
the palpable position of the mylohyoid ridge, but crest of the ridge and reduces the vertical space avail-
not into the undercut, has other advantages. The able for the extension of the flange in the anterior part
lack of direct pressure on the sharp edge of the of the mouth (Figure 14-12). The sublingual gland
ridge will eliminate a possible source of discom- may be pushed down and laterally out of position by
fort. If the impression is made with pressure on or resistant impression material. This can be avoided by
slightly over this ridge, displacement of the denture shaping this part of the flange of the tray to slope
and soreness are sure to result from lateral and ver- inward toward the tongue and making the final
tical stresses. On the other hand, if the border stops impression with a low-viscosity impression material.
above the mylohyoid ridge, vertical forces will
cause soreness, and the border seal will be easily The lingual frenum area is also rather shallow.
broken. If the flange is properly shaped and It should be registered in function because at rest
extended, it will provide border seal and guide the the height of its attachment is deceptive. In func-
tongue to rest on top of the flange. tion, it often comes quite close to the crest of the
ridge, even though when at rest it is much lower.

Retromylohyoid Fossa Alveololingual Sulcus

The retromylohyoid fossa, as its name implies, is The alveololingual sulcus, which is the space
the area posterior to the mylohyoid muscle. As the between the residual ridge and the tongue, extends
lingual flange moves into this fossa, it ceases to be from the lingual frenum to the retromylohyoid
influenced by the action of the mylohyoid muscle curtain. Part of it is available for the lingual flange

242 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures

RM M
MP
SC PR
B
RMC

Figure 14-11 Diagram shows the relationship of the medial pterygoid muscle to the
superior constrictor muscle. B, Buccinator muscle; M, masseter muscle; MP, medial pterygoid
muscle; PR, pterygomandibular raphe; RM, ramus of the mandible; RMC, posterolateral

portion of the retromylohyoid curtain formed by the mucous membrane covering the
superior constrictor muscle (SC).

B
C

A
Figure 14-12 The lingual side of the mandible shows the positions of the sublingual
gland relative to the mylohyoid muscle, at rest (A) and when contracted (B). The mylohoid
ridge is denoted by C.

Chapter 14 Developing an Analogue/Substitute for the Mandibular Denture-Bearing Area 243

of the denture. From the preceding discussion on 3. The posterior region. Here the flange passes
the functional anatomy of the floor of the mouth, into the retromylohyoid fossa. As it does, it
the shape of the lingual border of the denture is no longer influenced by the action of the
should now be clear. mylohyoid muscle, and so the flange can
turn laterally toward the ramus to fill the
The border can be considered in the following fossa and complete the typical S form of the
three regions: correctly shaped lingual flange (see Figures
14-7 and 14-8).
1. The anterior region. This extends from the
lingual frenum back to where the mylohyoid MANDIBULAR IMPRESSION
ridge curves above the level of the sulcus. PROCEDURES
Here a depression, the premylohyoid fossa,
can be palpated and a corresponding promi- The same principles of impression making are used
nence, the premylohyoid eminence, seen on for lower impressions as for upper impressions (see
impressions (see Figures 14-7 and 14-8). Chapter 13). As for the upper jaw, it is essential that
The lingual border of the impression in this the oral tissues are healthy before impressions are
anterior region should extend down to make made.
contact with the mucous membrane floor of
the mouth when the tip of the tongue touches Making the Preliminary Impression
the upper incisors. The lingual flange will be
shorter anteriorly than posteriorly. At the The space available in the mouth for the lower
premylohyoid fossa, the flange becomes impression is studied to determine the general form
larger as it extends below the level of the and size of the basal seat. An edentulous stock tray
mylohyoid ridge. is selected that will provide for approximately
5 mm of bulk of impression material over the entire
2. The middle region. This part extends from basal seat area. Posteriorly, the retromolar pads
the premylohyoid fossa to the distal end of should be covered by the tray. The tray is raised
the mylohyoid ridge, curving medially from anteriorly for observation of the relation between
the body of the mandible. This curvature is the lingual flanges and the lingual slope of the
caused by the prominence of the mylohyoid lower residual ridge (Figure 14-13). If the stock
ridge and the action of the mylohyoid tray is made from metal, the lingual flanges can be
muscle (see Figures 14-7 and 14-8). reshaped, if necessary, by bending to allow for the
When the middle of the lingual flange is action of the mylohyoid muscle (Figure 14-14).
made to slope toward the tongue, it can extend Any areas of underextension need to be corrected
below the level of the mylohyoid ridge. In this with soft boxing wax before the impression is
way, the tongue rests on top of the flange and made. A common site for stock trays to be under-
aids in stabilizing the lower denture on the extended is over the retromolar pads and down into
residual ridge. In addition, this slope of the the retromylohyoid fossae. In addition, soft boxing
lingual flange provides space for the floor wax can be used to line the entire border of the
of the mouth to be raised during function stock tray to create a rim, which helps adapt the
without displacing the lower denture. The seal borders of the tray to the limiting tissues (see
of the lower denture is maintained during Figure 14-14).
these movements because the lingual flange
remains in contact with the mucolingual fold Before the preliminary impression is made, it is
in the alveololingual sulcus. Therefore in this advisable to practice placing the tray in position
area, the flange rests not on mucous mem- and to rehearse with the patient. The patient is
brane in contact with bone but on soft tissue. asked to open the mouth halfway, and the tray is
When the mylohyoid muscle is relaxed, there rotated into the mouth in the horizontal plane with
is a space between the flange and the floor of the handle (see Figure 14-13) until it is centered over
the mouth, but contact is reestablished when the residual ridge, with the tongue raised slightly so
the floor of the mouth is raised.