PROSTHODONTICS-fundamentals-of-fixed-prosthodontics

Fig 5-2 The patient guides the earpieces v
the dentist inserts the bitefork shaft into the tc
under the facebow.

Fig 5-4 Firm pressure is placed on the end of the
n,ision relator and the thumbscrew is tightened.

mWhip Mix Facebow and Articvlator

and have the patient close lightly into the wax to obtain the front edge of the facebow (Fig 5-6). If you are using
shallow impressions of only the cusp tips Cool the wax a Model 8500 articulator, this information should be
and remove the bitefork from the mouth. Trim away recorded on the patient's data record to aid in setting the
excess wax. Any areas where soft tissue was registered articulator later. It is not necessary for the 2200 series
on the wax must be completely removed. instrument shown here, because it has a permanent non-
adjustable intercondylar width of 110 mm. This corre-
Set the maxillary cast in the bitefork registration to con- sponds to the "M" width shown on the facebow.
firm that the cast seats firmly in the index with no rocking
or instability. If the cast does not seat, first check the Loosen the thumbscrew and remove the plastic nasion
occlusal surfaces of the cast to make sure there are no relator. Then loosen the three thumbscrews on the top
nodules of stone. If there are none, then either the regis- surface of the facebow by one-quarter turn. As the
tration or the cast is distorted and should be remade. patient slowly opens the mouth, carefully remove the
entire assembly from the head. Recheck and securely
Place the bitefork back in the mouth and have the tighten the toggles. It is sometimes difficult to adequate-
patient close to hold it securely between the maxillary ly tighten these toggles while the facebow is on the
and mandibular arches. Ask the patient to grasp both patient's head.
arms of the facebow and guide the plastic earpieces into
the external auditory meati, much as one would guide the Mounting the Maxillary Cast
earpieces of a stethoscope (Fig 5-2). At the same time,
the operator should slide the toggle onto the shaft of the e the articL ator to receive the cast. Separate the
bitefork, making certain that the toggle is positioned and lower members of the articulator. Set the
above the shaft. Tighten the three thumbscrews on the
top of the facebow (Fig 5-3). Place the nasion relator on
the transverse bar of the facebow Extend the shaft while
adjusting the facebow up or down to center the plastic
nosepiece on the patient's nasion. Tighten the thumb-
screw (Fig 5-4)

Support the facebow with a firm, forward pressure and
slide the toggle lock on the bitefork shaft until it is near,
but not touching, the lips. Tighten it firmly with the hex
driver (Model 8600) or T-screw (Model 8645), and then
tighten the toggle on the vertical bar in the same manner
(Fig 5-5). For extra support and for peace of mind, the
patient can hold the side arms of the facebow. Be
extremely careful that the facebow does not tilt out of
position in any direction during these tightening proce-
dures Use your free hand to stabilize the assembly
against any torquing while tightening

The patient's approximate intercondylar distance of
"small," "medium," or "large" is indicated on the top of

Fig S-8 The three thumbscre1
The incisal guide pin has been

\ from the facebow and attached to a transfer base mount-
\ ed on the articulator base, is available. This permits the
facebow to be used on another patient even if the casts
\ for this patient have not yet been mounted.

condylar guides at "FB" in preparation for attachment of Hold the facebow firmly against the upper frame and
the facebow. If your articulator does not have this setting, tighten the three thumbscrews on the facebow. Place the
adjust the guides to an angulation of 30 degrees. Firmly upper frame and attached facebow back onto the lower
secure clean mounting plates to the upper and lower frame of the articulator with the fork toggle of the facebow
members of the articulator. Remove the incisal guide pin resting on the plastic incisal guide block (Fig 5-8)
The three thumbscrews on the top of the facebow should
be slightly loose for the next step. Hold the facebow in Soak the maxillary cast, tooth side up, in a plaster
one hand and the upper member of the articulator in the bowl. There should not be enough water to cover the
other. Guide first one and then the other pin on the outer teeth. Carefully seat the cast into the bitefork registration.
surfaces of the condylar guides into the holes on the Mix mounting stone (Whip Mix Corp) to a thick, creamy
inner surfaces of the plastic earpieces. Hold the facebow consistency Lift the upper frame of the articulator and
against your body while you are doing this (Fig 5-7). apply a golf-ball-sized mound of stone to the base of the
Alfow the front end of the member of the articulator to rest cast. Use one hand for support to prevent any movement
on the transverse bar of the facebow. of the facebow fork or cast, and close the upper frame
down until it touches the transverse bar of the facebow
An indirect transfer assembly, which can be removed (Fig 5-9). This will force the mounting plate into the soft
mounting stone.

The mounting stone should engage undercuts on the
base of the cast and the mounting plate If necessary,
add more mounting stone into these areas to insure ade-
quate retention for the mounting. When the stone has
completely set, remove the facebow from the articulator.

Mounting the Mandibular Cast

Replace the incisal guide pin in the upper frame of the
articulator with the rounded end down and set at a 2 0-
mm opening. (Align the second mark above the circum-
ferential line of the pin with the top edge of the bushing.)
Adjust the plastic incisal guide block slightly so that the
pin will rest in the dimple. This compensates for length-
ening the straight incisal pin. Snap the centric latch
closed at the rear center of the articulator (Fig 5-10).

Whip Mix Facebow and Arliculalor

Secure the bilateral elastic straps to the lateral, or outer, the teeth. Move the immediate lateral translation guide on
aspects of the vertical posts of the base frame, using the the front of each condylar guide outward to a setting of
thumb holding screws attached to the straps. "0" (Fig 5-11). This will prevent any lateral movement dur-
ing mounting of the mandibular cast
Place the upper frame of the articulator (with maxillary
cast attached) upside down on the laboratory bench with After the cast has soaked, reseat it into the record. Mix
the incisal guide pin extending over the front edge of the mounting stone to the consistency of thick cream and
bench. Set the centric relation interocclusal record on the place a golf-ball-sized mound of stone on the bottom of
maxillary cast. The teeth should seat completely into the the cast. Apply a small portion of stone to the mounting
depressions in the record. plate on the lower frame, and hinge the lower frame down
into the soft stone until contact is made between the
Now position the mandibular cast in the interocclusal incisal guide pin and the incisal guide block. Hold the
record and confirm that the teeth are fully seated. The mandibular cast with your fingers to steady it in the inter-
maxillary and mandibular casts should not contact any- occlusal record until the mounting stone has set (Fig 5-
where Remove the mandibular cast and soak it, tooth 12).
side up. in a plaster bowl for approximately 2 minutes.
There should not be enough water in the bowl to cover

Check these features: Remove the pieces of 28-gauge green wax from the
storage cup and carefully place them over the maxillary
1. Each condylar element should be against the posteri- cast. If the red dots show through the perforations in the
or and superior walls of its condylar guide. wax, the accuracy of the mounting procedure has been
confirmed. If they do not show through, recheck the pro-
2. The maxillary and mandibular casts should be com- cedure and correct the error.
pletely seated in the interocclusal record.
Remove both casts, with their respective mounting
3. The mounting stone should be engaged in the under- plates, from the articulator Mix more mounting stone and
cuts on both the base of the cast and on the mounting fill all voids between the casts and mounting plates. Use
plate. your finger to smooth over the mounting stone to give it a
neat appearance. There must be no stone on the surface
Allow the mounting stone to set completely. Then con- of the mounting plate that contacts the articulator frame.
firm the mounting accuracy by opening the articulator, The neatness of the casts (or the absence of same) will
removing the interocclusal record, and raising the incisal be interpreted by the technician and the patient as indi-
guide pin 2.5 cm (1 inch). Place a 5.0-cm (2-inch) strip of cators of how much you care about the work that you are
no. 10 red-inked silk ribbon between the posterior teeth doing.
on both sides and lightly tap the teeth with the condyles
retruded. This will leave red dots at CRCP.

Whip Mix Facebow and Articulate

Fig 5-16 The condylar in
increased until the condyle <
superior wall of the guide.

Setting Condylar Guidance lar cast in the indentations of the wax record. Be sure
they are seated completely. Support the articulator in this
Loosen slightly the medial pair of thumb clamp screws on position with one hand on the right side. Notice that the
the lop or back side of the upper frame of the articulator. left condylar element has moved downward, forward,
Set both condylar guides at 0 degrees (Fig 5-13). Now and inward. It is not touching the condylar guide at any
loosen the lateral translation clamp screws on the for- point (Fig 5-15).
ward aspect of each condylar guide and set the immedi-
ate lateral translation controls at their most open position Set the inclination of the left guide by releasing its
(Fig 5-14). Raise the incisal guide pin so that it will not clamp screw. Rotate the guide inferiorly until the superior
touch the plastic incisal stop in any position. wall again touches the condylar element (Fig 5-16).
Tighten the holding screw. Accommodate mandibular
Invert the upper frame, with cast attached, and seat lateral translation by releasing the lateral translation
the right lateral interocclusal record on the teeth of the clamp screw and sliding the lateral translation guide lat-
maxillary cast. Be sure that the teeth seat completely in erally until it touches the medial surface of the condylar
the wax indentations. Hold the upper frame in your left element (Fig 5-17). Retighten the clamp screw. Set the
hand and place the right condylar element in the right right condylar guidance by using the record for the left
condylar guide. Gently position the teeth ot the mandibu- lateral excursion and repeating these steps.

Articulation of Casts

Fig 5-18 The guidance provided by anterior teeth
ed in acrylic resin on the incisal guide block.

Once the lateral interocclusal records have been made lator to assess the anterior guidance. If there are non-
for the diagnostic mounting and the articulator has been working interferences on the casts, remove them to
set, the data are recorded on the patient's information enable the articulator to move freely while maintaining
card On the patient's casts, mark the correct articulator contact between the anterior teeth. Examine the anterior
settings for each side. Example: A condylar inclination of guidance to determine its adequacy If it is not adequate
40 degrees and a lateral translation of 0 3 mm would be because of wear, fracture, or missing teeth, restore it to
recorded as 40/0.3. When teeth are prepared at some an optimum form with inlay wax or denture teeth on the
future date and working casts are mounted on the artic- cast.
utator, it will not be necessary to make new lateral inter-
occlusal records. The recorded information from the Raise the mcisal guide pin (round end down) so that it
diagnostic mounting can be used to set the instrument. will miss contacting the plastic incisal guide by at least
1.0 mm in all excursions (Fig 5-19). Place one or two
Anterior Guidance drops of monomer on the plastic incisal guide. Mix one-
half scoop of tray acrylic resin in a paper cup. While it still
The influence of the temporomandibular joint on the flows freely, place a small amount on the incisal guide. As
occlusal scheme has been noted. The use of lateral inter- the uncured acrylic resin develops more body, add addi-
occlusal records in the setting of the condylar guides tional material to the block until there is approximately 6.0
enables us to transfer some of the influence from the tem- mm (1/4 inch) of resin on the plastic incisal guide (Fig 5-
poromandibular joint to the semiadjustable articulator. 20).
The influence of the incisors and canines (ie, anterior
guidance) on the occlusion during excursive movements Lubricate the round end of the incisal guide pin and
must also be taken into account.78 the functioning surfaces of the anterior teeth with petro-
latum. Close the articulator into full occlusion so that the
The guidance given to mandibular movements by the guide pin penetrates into the soft tray resin (Fig 5-21).
anterior teeth can be recorded and made part of the set- Move the articulator repeatedly through all the mandibu-
ting of the articulator (Fig 5-18). Anterior guidance can, in lar movements, making sure that the anterior teeth
effect, be transferred from the teeth to the incisal guide remain in contact at all times (Fig 5-22). The tip of the
block of the articulator. If crowns restoring the lingual incisal guide pin molds the acrylic resin to conform to the
contours of the anterior teeth are to be placed, it is various movements. Continue moving the articulator
extremely important that the anterior guidance be regis- through all the excursions until the tray resin has poly-
tered on the articulator. If this is not done, restorations merized.
may be made whose lingual contours or length will not
provide anterior guidance Trim off excess resin after it has polymerized. The tip of
the guide pin has acted as a stylus in forming a registra-
The mounted casts should be examined on the articu- tion of the anterior guidance (Fig 5-23). It will now be pos-
sible to duplicate the influence of the anterior teeth on the
movements of the casts, even if the anterior teeth are pre-
pared and the incisal edges shortened.

Whip Mix Facebow and Articulator

Articulation of Casts

Fig 5-24 The compo Slidematic facebow are (top to Heat a sheet of baseplate wax in a bowl of hot water
bottom): a reference pl r, the bitefork assembly, and the until it can be easily molded. Adapt the wax to the bite-
facebow with pointer. fork to cover all portions of it. Place the wax-covered bite-
fork between the teeth, with the bitefork shaft to the
Denar Facebow and Articulator patient's right. Center the fork by aligning the index ring
on the fork with the patient's midline. Instruct the patient
The Denar Slidematic facebow (Teledyne Water Pik, Fort to bite lightly into the wax to produce shallow indenta-
Collins, CO) is another self-centering ear facebow that is tions of the cusp tips in the wax. Cool the wax and
easy to use (Fig 5-24). The technique for its use is remove the bitefork from the mouth. Trim any excess wax
described with the Mark II articulator, an arcon semiad- off the bitefork.
justable articulator. This articulator also allows inter-
changeability of articulated casts with other Mark II artic- Try the maxillary cast in the wax record to insure that it
ulators without a loss of accuracy. will seat without rocking. If the cast fails to seat, check
the occlusal surfaces of the cast for nodules of stone. If
Facebow Armamentarium none are evident, there is a distortion in the registration

1. Slidematic facebow (with bitefork, articulator index, rthec
reference pin, and reference plane indicator) Fasten the reference pin to the underside of the face-
bow by tightening the set screw with a hex driver (Fig 5-
2. Felt-tip marker 26). Recent models have finger screws rather than set
3. Denar Mark II articulator screws. The clamp marked "2" should be on the patient's
4. Plaster bowl right (your left as you look at the front of the instrument).
5. Spatula
6. Laboratory knife with no. 25 blade Place the bitefork in the mouth and have the patient
7. Trimmed maxillary cast hold it securely between the maxillary and mandibular
8. Pink baseplate wax teeth. The patient should grip both arms of the facebow
9. Mounting stone to guide the plastic earpieces into the external auditory
meati, in the same manner as one would place a stetho-
scope into the ears (Fig 5-27). While the patient is insert-
ing the earpieces, the operator should slide the clamp
marked "2" onto the shaft of the bitefork. The clamp
should be positioned above the shaft. Tighten the single
finger screw on the front of the facebow (Fig 5-28).

Extend the anterior reference pointer while moving the
facebow up or down. When the pointer is properly
aligned with the anterior reference point, tighten the fin-
ger screw (Fig 5-29). While continuing to support the
facebow, tighten the set screw on clamp " 1 " on the verti-
cal reference pin with a hex driver (Fig 5-30). Then tight-
en clamp "2" on the horizontal reference pin For added
stability and peace of mind, the patient can continue to
support the facebow by holding the side arms. Do not
allow the facebow to torque or tilt during the tightening
procedure.

Loosen the finger screw on the front of the facebow by
a quarter turn. As the patient opens the mouth, remove
the assembly from the head. Recheck and tighten the
clamps with a hex driver. Remove the bitefork assembly
from the underside of the facebow by loosening the set
screw on the clamp by a quarter turn. Only the bitetork
assembly need be used for mounting the maxillary cast.
The facebow is ready for use on another patient

Facebow Record Mounting the Maxillary Cast

Use the reference plane indicator to measure a point 43 Remove the incisal guide block from the articulator and
mm above the incisal edges of the maxillary incisors on replace it with the articulator index (Fig 5-31). Insert the
the right side. Mark this point with a felt-tip marker (Fig 5- vertical reference pin of the bitefork assembly into the
25). This will form the anterior, or third, reference point for hole on the top of the articulator index. The reference pin
the icebow transfer. has a flat side, which will match a flat side on the hole.

g 5-27 The dentist place • the bitcfork shaft
hile the patient inserts the i

Check to be sure that the numbers " 1 " and "2" on the ing plate up.
clamps of the bitefork assembly are upright. Use a hex Soak the maxillary cast, tooth side up, in a plaster bowl
driver to tighten the set screw in the front of the index.
containing only enough water to wet the sides and bot-
Secure clean mounting plates to the upper and lower tom of the cast. Seat the cast into the wax registration on
members of the articulator. Assemble the articulator by
placing the fossae over the condyles. Place the incisal the bitefork (Fig 5-32). Mix mounting stone (Whip Mix
pin at the zero position. The long incisal pin for the dim- Corp) to the consistency of thick cream. Apply a golf-
pled guide block will rest in the recessed center of the ball-sized mound of stone to the base of the cast and the
index. The short pin used for flat guide blocks will con- mounting plate. Assemble the articulator by placing the
tact the sliding metal piece in the middle of the index. fossae over the condyles. Close the upper member of the
The incisal pin with the adjustable foot sits on the poste- articulator into the soft mounting stone until the incisal
rior section of the index. Remove the upper member of guide pin contacts the appropriate spot on the articulator
the articulator and set it on the benchtop. with the mount- index. Lock the centric latch by pushing it into the down
position.

Articulation of Casts

Fig 5-29 Ihe fatebow h
one hand and extend the rt
with the other.

Fig 5-30 The clamps i
assembly ate tightened.

The mounting stone will engage undercuts in the that the centric latch is engaged. Place the centric rela-
mounting plate and cast. Additional stone can be added tion interocclusal wax record on the maxillary cast Check
if needed to secure the mounting. When the stone has to insure that the teeth seat completely into the record.
set completely, remove the transfer jig from the articula-
tor. Replace the incisal guide block in the articulator. Place the mandibular cast into the interocclusal record
and make sure that the teeth are fully seated. There
Mounting the Mandibular Cast should be no contact between the maxillary and
mandibular casts. Remove the mandibular cast and soak
Adjust the incisal pin for a 2.0-mm opening to accommo- the bottom and sides of it in a partially filled bowl of water
date the thickness of the interocclusal record. Invert the for about 2 minutes.
articulator with the attached maxillary cast, making sure
Reseat the soaked mandibular cast into the interoc-
clusal wax record. Mix some mounting stone to a thick,
creamy consistency and place a mound of stone on the
inverted bottom of the cast. Apply some mounting stone

Denar Facebow

Fig 5-32 The maxillary cast in the bite
is positioned by the articulator index.

to the mounting plate on the lower member of Ihe ariicu- 3. Mounting stone engages undercuts on both the base
lator and hinge it down into the soft stone on the cast until of the cast and the mounting plate
the incisal guide pin makes firm contact with the incisal
guide block. Stabilize the mandibular cast with your fin- When the mounting stone has set completely, confirm
gers to keep it securely in the interocclusal record until the accuracy of the mounting. Open the articulator,
the mounting stone sets (Fig 5-33). Rubber bands or remove the interocclusal record, and raise the incisal
sticky wax can also be used, but they are more likely to guide pins 1 inch. Place a 2-inch piece of no. 10 red-
slip and produce a mounting error. inked silk ribbon between the posterior teeth on both
sides. Tap the teeth together lightly with the condyles
Examine the casts and articulator for the following: against the posterior wall of the condylar guide, leaving
red dots that represent the contacts at centric relation
1. The condyle is located against the posterior and position.
superior walls of the condylar guide.
Retrieve the pieces of 28-gauge green wax that have
2. Both casts are completely seated in the interocclusal been stored in a cup and lightly place them on the teeth
record.

of the maxillary cast The accuracy of the mounting will Use one hand on the right side of the articulator to sup-
be confirmed if the red dots are visible through the per- port it in this position. The left condylar element will have
forations in the wax. If they are not visible, the procedure moved downward, forward, and inward. It should not be
should be rechecked and the error corrected. touching the condylar guide at any point (Fig 5-34).

Remove the casts and their mounting plates from the Increase the inclination of the right protrusive condylar
articulator. Mix additional mounting stone to fill any voids path by rotating the fossa until the superior wall makes
between the casts and their mounting plates. Smooth the contact with the condylar element (Fig 5-35, A). Tighten
mounting stone with your finger to give it a neat appear- the set screw on the back of the upper crossbar with a
ance. No stone should remain on the surface of the hex driver. Set the immediate lateral translation by mov-
mounting plate that will contact the articulator frame ing the medial wall of the fossa outward or laterally until it
Both the dental technician and the patient will form an contacts the medial surface of the condylar element (Fig
impression of you when they see these casts on the artic- 5-35, B). Retighten the set screw. The wax interocclusal
ulator Make sure that it is a positive one. record for the left lateral excursion is used to set the right
condylar guidance in the same manner.
Setting Condylar Guidance
After setting the articulator, record the data on the
With a hex driver, loosen the set screw on the underside patient's information card. Mark the articulator settings
of each fossa and set the medial side wall to a 6-degree for each side on the respective side of the patient's cast.
progressive lateral translation Release the lock screw on Example: A condylar inclination of 35 degrees and an
each end of the posterior aspect of the upper crossbar of immediate lateral translation of 0.6 mm would be record-
the articulator using a hex driver and set both condylar ed as 35/0.6. When teeth are prepared at some future
guides at 0 degrees. Then loosen the set screw on the time, working casts can be mounted on the articulator
top of each fossa as far as possible to the medial. Lift the without making new records. The instrument can be reset
incisal guide pin to prevent it from touching the plastic using the recorded information from the diagnostic
incisal stop in any position. Release the centric latch. mounting.

Seat the right lateral interocclusal record on the maxil- Anterior Guidance
lary cast attached to the inverted upper member of the
articulator. The teeth should seat completely in the wax Examine the mounted casts on the articulator. Remove
indentations. Hold the upper member of the articulator in any nonworking interferences from the casts so that the
the left hand and place the right condylar element in the articulator can move freely while the anterior teeth remain
right condylar guide. Seat the teeth of the mandibular in contact. If the guidance is inadequate for any reason,
cast gently but completely into the indentations of the restore it to an optimum configuration with a diagnostic
wax record wax-up.

1 causes the left con
all (B) of the guide.
r

c

1A

Fig 5-34 The right I
away from the superk

Fig 5-35 To adjust the condylar guide: (A) the condylar inclination is increased
until the superior wall contacts the condyle and (B) the medial wall is moved into
contact with the condyle.

Raise the mcisal guide pin so that it will be at least 1.0 completely. The guide pin will penetrate the soft acrylic
mm off the plastic mcisal guide block in all excursions resin (Fig 5-38). Move the articulator through all excur-
(Fig 5-36). Moisten the surface of the guide block with sions repeatedly, keeping the teeth contacting at all
monomer. Mix one-half scoop of tray resin and, while it is times (Fig 5-39). The tip of the guide pin will mold the
still free-flowing, place a small amount on the incisal acrylic resin to record the pathway of the various move-
guide. As the polymerizing resin becomes stiffen add ments. Continue the movements until the resin is com-
more until there is about 1/4 inch of it covering the guide pletely polymerized. Trim off the excess. A record of the
block (Fig 5-37). Lubricate the end of the incisal guide anterior guidance has now been formed on the incisal
pin and all contacting surfaces of the anterior teeth with table (Fig 5-40).
petrolatum. Close the articulator so that the teeth occlude

Fig 5-38 The guide pin is allowed to close into the soft resin. Fig 5-39 The drtitulator is moved through .ill excursi

Fig 5-40 An anterior guidance record exists on the guide block.

Fig 5-41 The components of a Spring-Bo\
fatebow with orbital pointer and the bitefo:

Hanau Facebow and Articulator Cool the wax in the mouth with an air syringe Remove
the fork from the mouth and finish cooling it in a bowl of
The Hanau Spring-Bow (Teledyne Water Pik, Fort Collins, cold tap water. Trim off excess and any areas imprinted
CO) is an ear facebow that utilizes a one-piece spring- by soft tissue Seat the maxillary cast in the wax record to
steel bow (Fig 5-41). It is simple in design and can be be sure that it is stable If there is any rocking of the cast,
used either as a direct-mount or an indirect-mount device check the occlusal surfaces of the cast for nodules of
with the removable bitefork assembly and mounting plat- stone. If there are none, either the cast or the record is
form.9 The technique for its use is described with the distorted and must be remade.
Hanau Series 184 Wide-Vue Articulator, an arcon semi-
adjustable instrument. If the bitefork assembly is separate from the facebow,
insert the transfer (vertical) rod of the assembly into the
Facebow Armamentarium bow socket on the underside of the black centerpiece on
the front of the facebow. Make sure the flat surface on the
1. Spring-Bow (with bitefork assembly and mounting front of the rod faces you as you place it in the socket.
guide) The assembly should be to your right, with the knobs fac-
ing you (Fig 5-42). Tighten the thumbscrew on the front of
2. Hanau Wide-Vue articulator the centerpiece.
3. Plaster bowl
4. Spatula While the patient grips the bitefork between the maxil-
5 Laboratory knife with no. 25 blade lary and mandibular teeth, position the loosened bitefork
6. Trimmed maxillary cast clamp over the bitefork shaft 4,0 cm (1.5 inches). The
7. Pink baseplate wax facebow should be pointed upward during this action
8 Mounting stone (Fig 5-43) Open the bow by pulling outward on the arms
and swing it down into position, placing an earpiece gen-
Facebow Record tly into each external auditory meatus. Have the patient
adjust the earpieces to the most comfortable seated
Soften a sheet of baseplate wax in hot water and com- position (Fig 5-44).
pletely cover the bitefork with it. Position the wax-covered
bitefork against the maxillary teeth and have the patient Mark the orbitale (infraorbital notch) on the patient's
close until the mandibular teeth contact the wax on the face with a felt-tip marker to provide an anterior reference
underside of the fork. The shaft of the bitefork will be to point (Fig 5-45). Loosen the thumbscrew that holds the
the left of the patient's midline. orbital pointer and gently swing it in toward the reference
mark (Fig 5-46). Elevate the front of the facebow along
the transfer (vertical) rod of the bitefork assembly until
the pointer is at the plane of the anterior reference point.
Grasp the bow to resist torquing (Fig 5-47) and tighten
the three thumbscrews in order from left to right (Fig 5-
48):
1. Transfer (vertical) rod/transverse (horizontal) rod

Articulation of Casts

Fig 5-42 The vertical rod of ihe bitefork Fig 5-4
assembly is inserted into the bow socket. The
flat side should face you, with the empiy bite-
fork clamp to your riBht.

Fig 5-44 The patient should adj
earpieces should be checked to make

2. Transverse rod clamp (upper) Mounting the Maxillary Cast
3. Bitefork clamp (lower)
Prepare the articulator to accept the casts by setting the
Be sure that they are tight. Use an Allen wrench if nec- inclination of the enclosed condylar track mechanisms at
essary. 30 degrees on each side (Fig 5-49). The "Bennett angle"
ring for the progressive mandibular lateral translation
Now rotate the reference pointer back over the right should be set at 30 degrees (Fig 5-50).
temple of the bow and tighten the thumbscrew enough to
hold it there. Have the patient open while you grasp the Use petrolatum to lubricate the surfaces of the upper
ends of the bow and remove the earpieces from the audi- and lower members of the articulator around the thread-
tory meati Make sure that you have a firm hold, since the ed mounting studs Then firmly secure a clean mounting
bow is made of spring steel and could snap back. Slide plate to the mounting stud on the upper member of the
the bow away from the patient

Hanau Facebow and Articulator
Fig 5-46 The pointer is rotated toward the

articulator. Attach a mounting guide or platform to the Raise the upper member of the articulator and place a
lower member of the articulator. Loosen the thumbscrew golf-ball-sized mound of thick, creamy mounting stone
on the front of the facebow and remove the bitefork on the base of the cast. Swing the upper member of the
assembly. Place the vertical transfer rod of the assembly cast down until the incisal pin is resting on the mounting
into the hole at the front of the mounting guide and guide or the anterior table, depending on the type of
secure it by tightening the screw. Adjust the cast support guide used. Be sure that stone is engaging the cutouts in
to touch the underside of the wax on the bitefork (Fig 5- the top of the mounting plate. Add more stone if neces-
51). sary, and smooth off the top with a spatula. When the
stone has set completely, remove the bitefork assembly
Soak the maxillary cast in a plaster bowl, but do not and mounting guide from the articulator. Attach a clean
cover the teeth with water Carefully seat the maxillary mounting plate to the lower member of the articulator
cast into the imprints in the baseplate wax on the bitefork.

Articulation of Casts

Fig 5-51 The r llary cast is
articulator by ithe bitefork asisembly

mounting guide

Mounting the Mandibular Cast Remove the mandibular cast and soak it for about 2 min-
utes. To prevent any erosion of the teeth on the cast,
Extend the incisal guide pin 1 to 2 mm to compensate for make sure that they are not covered by water. Reseat the
the thickness of the interocclusal wax record. Tighten the soaked mandibular cast into the record. Swing the lower
centric lock on each enclosed condylar track mecha- member of the articulator up and back. Place a mound
nism to insure that the articulator is capable of nothing of thick, creamy mounting stone on the bottom of the
but a hinge opening. cast. Apply enough to the mounting plate on the lower
member to fill the cutout slots on either side of it Hinge
Invert the articulator on the benchtop, resting it on the the lower member of the articulator back over into the
three thumbnuts protruding from the upper member of soft mounting stone. The incisal guide pin should be rest-
the articulator. Place the centric relation interocclusal ing firmly against the incisal guide table. Use your hand
wax record on the teeth of the maxillary cast. Be sure that to steady the mandibular cast in the retruded position
the teeth seat completely into the wax record. wax registration until the mounting stone has achieved
an initial set (Fig 5-52).
Place the mandibular cast into the interocclusal record
and again confirm complete seating. There should be no
contact between the maxillary and mandibular casts

Hanau Facebow and Articulate!

Inspect the articulated casts; g 5-52 The mandibular cast is held s
hile the mounting stone sets.
1. The condyle is in the retruded position in its condylar
track mechanism. guide of the articulator. Slowly rotate the "Bennett angle"
ring outward (from 30 degrees toward 0 degrees) until
2. Both casts are seated completely in the interocclusal the flat side on the outer aspect of the condylar ball con-
wax record. tacts the inner surface of the sleeve on the condylar
shaft, forming a "brass to brass" contact (Fig 5-54).
3. Mounting stone is securely attached to both casts and Repeat the process on the right side.
mounting plates.
If a protrusive interocclusal wax record is used to
After the mounting stone has achieved a final set, cor- establish the condylar inclination, both condylar mecha-
roborate the accuracy of the mounting. Open the articu- nisms are rotated simultaneously in the same manner
lator and raise the incisal guide pin so that it will not described above for setting each condylar inclination
touch the incisal table when the teeth are contacting. separately. In this situation, the angle of mandibular lat-
Remove the interocclusal record and place a 2-inch eral translation is estimated by use of the "Hanau
piece of no. 10 red-inked silk ribbon between the poste- Formula," L = H/8 + 12, where "H" is the condylar protru-
rior teeth on both sides Tap the teeth together lightly, sive inclination. Since a change in condylar inclination
producing red marks on the teeth where they contact in from 20 to 50 degrees would produce less than a 4-
the retruded position. degree change in the "Bennett angle" by this calculation,
placing the "Bennett angle" ring at an arbitrary 15-
Retrieve the pieces of 28-gauge green wax and care- degree angle would produce a minimal error.
fully position them on the teeth of the maxillary cast. If the
cast mounting is correct, the red marks on the teeth will Enter the condylar inclinations in the patient's record.
be visible through the perforations in the wax. If they are Write the amount of condylar inclination for each condyle
not visible, recheck the procedure step by step and then on the corresponding side of the cast. When teeth are
correct the error. prepared at some future time, it will not be necessary to
make new interocclusal records to adjust the articulator.
Unscrew the mounting plates and remove the casts The settings developed during the diagnostic mounting
from the articulator. Soak the plates and attached mount- can be reused.
ing stone in water. Add more mounting stone wherever it
is needed to fill voids between the casts and the mount- Custom Anterior Guidance
ing plates. Smooth the additional stone as it sets to give
it a neat appearance. Be careful not to leave any stone A customized anterior guidance jig can be made for this
on the surface of the mounting plate that will contact the articulator by using a round-end incisal pin and a flat
articulator frame. It has been said that sloppy cast anterior table or an incisal cup. Acrylic resin is molded by
mountings are not an indication of a poor operator; they the end of the incisal pin in the same manner that the
are absolute proof. anterior guidance is recorded for the other articulators.
Examine the mounted casts on the articulato
Setting Condylar Guidance
orkiing infterfere .ThThe arttiiculator
Wax lateral or protrusive interocclusal records are used
for setting the condylar inclination of this instrument.
Loosen the thumbnut at the rear of each condylar track
mechanism so that it can be easily rotated. At this time,
however, leave the condylar inclination at 30 degrees.
The incisal guide pin should still be raised out of contact
with the incisal table.

Seat the right interocclusal record on the teeth of the
mandibular cast. Gently lower the upper member of the
articulator until the maxillary teeth engage the wax
record. Adjust the left condylar guide by changing the
condylar inclination with the thumbnut located at the rear
of the guide. The teeth on the right side of the cast will
rock in and out of the record. If the condylar path is too
shallow, the anterior teeth will be drawn out of the wax
record (Fig 5-53, A). When the path becomes too steep,
the posterior teeth become unseated (Fig 5-53, B). The
correct condylar inclination has been determined when
the cast is seated completely in the wax record (Fig 5-53,
C). Tighten the nut at the rear of the condylar guide.

Loosen the thumbnut on the top of each condylar

Articulation ot Casts

Fig 5-53 To i a prattL rl al

;ondy r k d r

condylar inclinatii)ti is rocked up ;

down. When the a „

anterior teeth lift out oi th^ record (A).

When the inclination is too steep, the pos-

terior teeth lift out (Bl. When the cast i

completely seated, the inclination is correct

(Q, When lateral interocclusal records are

employed, the left record is used for the

right condylar inclination and the right

record for the lett condylar inclination

Hanau Facebow and Articulator

Fig S-S4 With the casts seated in a lat-
eral interocclusal record, there is a gap
between the condyle and sleeve (A).
When the "Bennett angle" ring (and
condylar track mechanisml are rotated,
the condyle contacts the sleeve (B). The
number on the scale is the angle of the

must be able to move freely with the anterior teeth in con- occluding surfaces of the anterior teeth with petrolatum.
tact. If the guidance is inadequate, rebuild it to an opti- Close the articulator to complete contact between the
mum configuration with a diagnostic wax-up. casts. The guide pin should sink into the soft acrylic resin
(Fig 5-57) Move the articulator through all excursions
Raise the incisal guide pin at least 1.0 mm off the plas- repeatedly, keeping the anterior teeth touching at all
tic incisai guide block in all excursions (Fig 5-55). times (Fig 5-58). The pathways of all the movements will
Moisten the surface of the guide block with monomer, Mix be imprinted by the tip of the guide pin in the acrylic resin
one-half scoop of tray resin and, while it is still free-flow- as a permanent record (Fig 5-59). Continue moving the
ing, place a little on the incisal guide. As the polymeriz- casts until polymerization is complete. Remove the
ing resin becomes stiffer, add more until there is about excess.
6.0 mm (1/4 inch) of it covering the guide block (Fig 5-
56). Lubricate the tip of the incisal guide pin and the

•tcutation of Casts

Fig 5-57 Ihe guide pi.

Mechanical Anterior Guidance

The guidance of mandibular movement imparted by the
anterior teeth also can be recorded on this instrument
with a mechanical incisal guide. Examine the mounted
casts. Remove any interferences from the casts that pre-
vent the anterior teeth from remaining in contact in all
excursions. Restore any inadequacies in the guidance
by building up an optimum configuration in a diagnostic
wax-up.

Loosen the lock nut under the incisal table at the front
end of the lower member of the articulator. The incisal pin
should be in contact with the incisal table.

Protect the casts from undue abrasion by lubricating
contacting surfaces with petrolatum. Gently move the
upper member of the articulator back to bring the maxil-
lary and mandibular teeth into an end-to-end position.
The incisal pin will be lifted off the incisal table. Rotate the
incisal guide to raise it posteriorly. Stop when it makes
contact with the pin (Fig 5-60, A). Tighten the lock nut to
maintain this inclination of the table.

Move the casts into a right lateral excursion. The pin
will move to the left side and will again be lifted off the
table. Loosen the small thumbnut under the left side of
the table and use the elevating screw to raise the left
wing of the table into contact with the corner of the guide
pin (Fig 5-60, B). Repeat the process by moving the
casts into a left lateral excursion. Raise the right wing of
the incisal table to contact the pin (Fig 5-60, C)

Hanau Facebow and Aniculator

Fig 5-60 To set the mechanical incisal
guide, the casts are moved into a protru-
sive relationship. The angulation of the
table is increased to contact the pin (A).
The casts are moved into a right lateral
excursion and the left wing of the incisal
table is raised (B). The casts are moved
into a left lateral excursion and the right
wing of the table is lifted to complete
the recording (C).

References 3. Schuylet CH: The function

1. Pruden WH: The role of study casts in diagnosis and treat- ance in oral rehabilitate
ment planning. JProsthet Dent 1960; 10:707-710. 1011-1030.
9. strohaver RA, Ryan JR N.
2. HickeyJC, LundeenHC, Bohannan HM: A new articulate* for
use in teaching and general dentistry J Prosthet Dent 1967; dental laboratory cooperal
18:425-437. 638-641.

3. Teteruck WR, Lundeen HC: The accuracy of an ear facebow
J Prosthet Denf\96B\ 16:1039-1045.

4. Gross MD, Gazit E: Articulators used in North American den-
tal schools. JDentEduc 1985; 49:710-711.

5. Cowan RD. Sanchez RA, Chappell RP, Glaros AG, Hayden
WJ: Verifying the reliability of interchanging casts with semi-
adjustable articulators. Int J Prosthodont 1991; 4:258-264.

Chapter 6

Treatment Planning for Single-Tooth Restorations

By using cast metal, ceramic, and metal-ceramic cess of the restoration. Many teeth are seemingly prime
restorations, large areas of missing coronal tooth candidates for cast metal or ceramic restorations, based
structure can be replaced while that which remains solely on the amount of tooth destruction that has previ-
is preserved and protected. Function can be restored, ously occurred. However, when these teeth are evaluat-
and where required, a pleasing esthetic effect can be ed from the standpoint of the oral environment, they may,
achieved. The successful use of these restorations is in fact, be poor risks for cemented restorations. If exten-
based on thoughtful treatment planning, which is mani- sive plaque, decalcification, and caries are present in a
fested by choosing a restorative material and a restora- mouth, the use of crowns of any kind should be carefully
tion design that are suited to the needs of the patient. In weighed. The design of a restoration should take into
account those factors that will enable the patient to main-
a time when production and efficiency are heavily tain adequate hygiene to make the restoration success-
stressed, it should be restated that the needs of the ful. The patient must be motivated to follow a regimen of
patient take precedence over the convenience of the brushing, flossing, and dietary regulation to control or
dentist. eliminate the disease process responsible for destruction
of tooth structure It may be desirable to use pin-retained
In what circumstances should cemented restorations amalgam "temporary" restorations to save the teeth until
made from cast metal or ceramic be used instead of the conditions responsible for the tooth destruction can
amalgam or composite resin restorations? The selection be controlled. This will give the patient the time neces-
of the material and design of the restoration is based on sary to learn and demonstrate good oral self-care. It will
several factors: also permit the dentist and staff to reinforce the skills
required of the patient and to evaluate the patient's will-
1 Destruction of tooth structure ingness and ability to cooperate. If these measures prove
2. Esthetics successful, cast metal, ceramic, or metal-ceramic
3. Plaque control restorations can be fabricated. Since these restorations
4. Financial considerations are used to repair the damage caused by caries and do
5. Retention nothing to cure the condition responsible for the caries,
they should not be used if the oral environment has not
Destruction of tooth structure: If the amount of destruc- been brought under control.
tion previously suffered by the tooth to be restored is
such that the remaining tooth structure must gain Financial considerations: Finances are a factor in all
strength and protection from the restoration, cast metal or treatment plans, because someone must pay for the
ceramic is indicated over amalgam or composite resin. treatment. That "someone" may be a government
agency, a branch of the military, an insurance company,
Esthetics: If the tooth to be restored with a cemented and/or the patient. If the patient is to pay, give your best
restoration is in a highly visible area, or if the patient is advice and then allow the patient to make the choice. A
highly critical, the cosmetic effect of the restoration must conscientious dentist must walk a fine ethical line. On the
be considered. Sometimes a partial veneer restoration one hand, you should not preempt the choice by select-
will serve this function. Where full veneer coverage is ing a less than optimum restoration just because you
required in such an area, the use of ceramic in some think that the patient cannot afford the preferred treat-
form is indicated. Metal-ceramic crowns can be used for ment. On the other hand, you also should be sensitive
single-unit anterior or posterior crowns, as well as for enough to the individual patient's situation to offer a
fixed partial dentures. All-ceramic crowns are most com- sound alternative to the preferred treatment plan and not
monly used on incisors, although they can be used on apply pressure.
posterior teeth when an adequate bulk of tooth structure
has been removed and the patient is willing to accept the Retention: Full veneer crowns are unquestionably the
possibility of more frequent replacement. most retentive12 (Fig 6-1). However, maximum retention
is not nearly as important for single-tooth restorations as
Plaque control: The use of a cemented restoration
demands the institution and maintenance of a good
plaque-control program to increase the chances for suc-

Treatment Planning tor Single-Tooth Restoratioi

Fig 6-1 A comparison Class lonomer
types of crowns (P= .05)
Small lesions where extensions can be kept minimal and
it is for fixed partial denture retainers It does become a where preparation retention will be minimal can be
special concern for short teeth and removable partial restored with this material. It is useful for restoring class
denture abutments. 5 lesions caused by erosion or abrasion (Fig 6-2). It also
can be employed for incipient lesions on the proximal
Twelve restoration types are presented in the following surfaces of posterior teeth by use of a "tunnel" prepara-
pages to provide a frame of reference for making a deci- tion, which leaves the marginal ridge intact (Fig 6-3).
sion whether to use a "plastic restoration" or a "cement-
ed restoration." The "plastic restoration" is inserted as a Glass ionomer has found a niche in the restoration of
soft, or plastic, mass into the cavity preparation, where it root caries in geriatric and periodontal patients (Fig 6-4).
will harden and be retained by mechanical undercuts or An occlusal approach may be precluded by the pres-
adhesion. The "cemented restoration," made of cast ence of an otherwise acceptable crown, or a convention-
metal, metal and ceramic, or ceramic material alone, is al restoration at such an apical level might require the
fabricated away from the operatory and is luted in or on destruction of an unacceptable amount of tooth struc-
the patient's tooth at a subsequent appointment. One ture. However, handpiece access may be too restricted
type can be better suited for a particular application than to create the needed retention for a small amalgam
the other, or their suitabilities may overlap. restoration. Glass ionomer also lends itself to rapid
placement well enough to serve as an interim treatment
Intracoronal Restorations restoration to assist in the control of a mouth with rampant
caries (Fig 6-5). This is further enhanced by the release
When sufficient coronal tooth structure exists to retain of fluoride by the material.
and protect a restoration under the anticipated stresses
of mastication, an intracoronal restoration can be Composite Resin
employed. In this circumstance, the crown of the tooth
and the restoration itself are dependent upon the in esthetically critical areas (Fig 6-6). While it can be .:
strength of the remaining tooth structure to provide struc- used in the restoration of incisal angles assisted by acid >
tural integrity. etching, a tooth that has received a class 4 resin restora- )
tion ultimately will require a crown. •;
j
Composite resin has been used in the restoration of |
posterior teeth with mined results. Sufficient abrasion I
resistance to prevent occlusal wear has b&en a problem. ]
Also, unless the resin is carefully applied in small incre-
ments, polymerization shrinkage will lead to leakage and
ultimately to failure. Its use probably should be restricted

icclusal restorations on first

premolars.
A technique devised to combat the problems of shrink-

age and leakage is the fabrication of a composite resin
inlay (Fig 6-7). This can be accomplished in the dental
office, using a fast-setting gypsum cast, or in a dental
laboratory. The resultant bench-polymerized inlay will
have greater hardness, and the thin layer of resin used
for affixing it to tooth structure will be less susceptible to
significant shrinkage at the margin than a restoration that
is bulk cured in situ

I Intracoronal Restorations

ireparaliun and gla^s ionomer can be used t(
in incipient lesion on the proximal surface of a posterio

Treatment Planning for Single-Tooth R

Fig 6-7 Indirect inlays of composite n
can be used for proxtmo-occlusal resti
tions on posterior teeth.

Simple Amalgam Complex Amalgam

The simple amalgam, without pins or other means of aux- Amalgam augmented by pins or other auxiliary means of
iliary retention, for decades has been the standard one- retention can be used to restore teeth with moderate to
to three-surface restoration for minor- to moderate-sized severe lesions in which less than half of the coronal
lesions in esthetically noncritical areas (Fig 6-8). It has dentin remains (Fig 6-9) Amalgam used in this manner
received a "bum rap" from an ill-informed, sensationaliz- can be employed as a final restoration when a crown is
ing press in recent years. Approximately 100 million or contraindicated because of limited finances or poor oral
more simple amalgam restorations are placed annually.3 hygiene. It can be used in the restoration of teeth with
They are best used where more than half of the coronal missing cusps, or endodontically treated premolars and
dentin is intact. molars—teeth that ordinarily would be restored with
mesio-occluso-distal (MOD) onlays or other extracoronal
Tooth preparation size for incipient lesions has dimin- restorations. In such situations, amalgam is used to
ished in recent years as the concept of "extention for pre- replace or overlay the cusp to provide the protection of
vention" has waned. This move toward less destructive occlusal coverage. It does produce good strength in the
preparations has been augmented by the development restored tooth.5 Ideally, however, a crown should be con-
of smaller instruments and stronger amalgams. structed over the pin-retained amalgam, using it as a
Nonetheless, even a minimal preparation for an amalgam core, or foundation restoration
restoration significantly weakens the structural integrity of
the tooth."

Metal Inlay MOD Onlay

Minor io moderate lesions on teeth where the esthetic This design can be used for restoring moderately large
requirements are low can be restored with this restoration lesions on premolars and molars with intact facial and lin-
type (Fig 6-10) While usually made of softer gold alloys, gual surfaces (Fig 6-12). It will accommodate a wide isth-
metal inlays can also be fabricated of etchable base mus and up to one missing cusp on a molar. If a cast
metal alloys if a bonding effect is desired.67 The prepa- metal restoration is needed on a premolar with both mar-
ration isthmus should be narrow to minimize stress in the ginal ridges compromised, it should include occlusal
surrounding tooth structure. Premolars should have one coverage to protect the remaining tooth structure. This
intact marginal ridge to preserve structural integrity and restoration also can be considered an extracoronal
minimize the possibility of coronal fracture. restoration because of the occlusal coverage that over-
lays and protects the tooth cusps.
The additional bulk of tooth structure found in a molar
permits the use of this restoration type in an MOD con- The MOD onlay does not have the necessary resis-
figuration. The indications for this type of restoration are tance to be used as a fixed partial denture retainer.
much the same as those for an amalgam, since this Although ordinarily fabricated of a gold alloy, this restora-
restoration only replaces lost tooth structure and will not tion design has been used with cast glass and other
protect remaining tooth structure. Because of the amount types of ceramics. Ceramic MOD onlays should be used
of destruction of tooth structure required by this restora- very cautiously. Without generous occlusal thickness,
tion, it is not recommended for incipient lesions. these restorations are susceptible to fracture.

Ceramic Inlay Extracoronal Restorations

This restoration is utilized to restore teeth with minor- to If insufficient coronal tooth structure exists to retain the
moderate-sized lesions that will permit a narrow prepara- restoration within the crown of the the tooth, an extra-
tion isthmus in an area of the mouth where the esthetic coronal restoration, or crown, is needed. It may also be
demand is high (Fig 6-11). Premolars should have one used where there are extensive areas of defective axial
intact marginal ridge, but MOD ceramic inlays can be tooth structure, or if there is a need to modify contours to
used in molars Because this type of restoration can also refine occlusion or improve esthetics.
be etched to enhance bonding, there is some evidence
that the structural integrity of the tooth cusps may be sta-
bilized by bonding.8 The relatively large size of the cavi-
ty preparation required for this restoration mitigates its
use in the treatment of incipient lesions.

Treatment Planning lor Single-Tooth Restoi

Partial Veneer Crown esthetic requirements. It can be used as a fixed partia
denture retainer where full coverage and a good cos
This is a crown that leaves one or more axial surfaces metic result must be combined.
unveneered (Fig 6-13). Therefore, it can be used to
restore a tooth with one or more intact axial surfaces with All-Ceramic Crown
half or more of the coronal tooth structure remaining. It
will provide moderate retention and can be used as a When full coverage and maximum esthetics must be
retainer for short-span fixed partial dentures. If tooth combined, this crown is the choice (Fig 6-16). All-ceram-
destruction is not excessive, a partial veneer crown with ic crowns are not as resistant to fracture as metal-ceram-
a minimally extended preparation and carefully finished ic crowns, so their use must be restricted to situations
margins can satisfy moderate esthetic demands in the likely to produce low to moderate stress. They are usual-
maxillary arch. ly used for incisors, although cast glass ceramics are
also employed in the restoration of posterior teeth.
Full Metal Crown Preparations for this type of restoration on premolars and
molars do require the removal of large quantities of tooth
The conventional full crown can be used to restore teeth structure.
with multiple defective axial surfaces (Fig 6-14). It will
provide the maximum retention possible in any given sit- Ceramic Veneer
uation, but its use must be restricted to situations where
there are no esthetic expectations. This will usually limit Because all-ceramic and metal-ceramic crowns require
it to second molars, some mandibular first molars, and the removal of such large quantities of tooth structure,
occasionally mandibular second premolars. Because there has been considerable interest in less destructive
less tooth structure must be removed for its preparation alternatives. The ceramic veneer has emerged as a
than for crowns with a ceramic component, and its fabri- means of producing a very cosmetic result on otherwise
cation is the simplest of any crown, this restoration intact anterior teeth that are marred by severe staining or
should remain among those designs considered in plan- developmental defects restricted to the facial surface of
ning single-tooth restorations on molars as well as pos- the tooth (Fig 6-17). This restoration also can be used to
terior fixed partial dentures. restore moderate incisal chipping and small proximal
lesions. The use of a veneer requires only a minimum
Metal-Ceramic Crown tooth preparation, so it offers an alternative to crowns
that is attractive to patient and dentist alike.
This crown can also be used to restore teeth with multi-
ple defective axial surfaces (Fig 6-15). It too is capable The features and capabilities of the 12 types of single-
of providing maximum retention, but it also will meet high tooth restorations described in this chapter are shown in
Table 6-1.

Table 6-1 Attributes of Single-Tooth Restorations

amalgam Poor to
Metal inlay Adequate-

inlay Moderate t Poor to
MOD onlay Large Adequate'

Large Poor to
Large Adequate*
Large
Large Modera
Good
Good

SMayof

Class 5 Nn J

Clas No Class 5 No
All | Yec-t
Adequate No No
Class 5 Nr
No§ Class 2 Poor Class 5 Yes
No§
Class 2 Adequate No
ate
d Good No
d
Good Poor
Good Good
Adequate Good
Poor Good

it Planning for Single-Tooth Restor

18—| Fig 6-18 Comparison of the estimated
16- longevity of 12 types of restorations, based
8 14- on a survey of 36 dentists. ANOVA was per-
£ 12- formed, with P= .OS. G1R = glass-ionomer
CO 10- restoration, COM = composite resin restora-
tion, VEN = ceramic veneer, CIN = ceramic
Type of Restoration inlay, ACC = all-ceramic crown, CAM =
complex amalgam restoration, MCR =
metal-ceramic crown, MIN = metal inlay,
PVC = partial veneer crown, SAM = simple
amalgam restoration, MOD = metal MOD
only, FMC = fufl metal crown.

Restoration Longevity Clinical studies of restoration longevity have produced
widely disparate figures. As a general rule, cast restora-
Every dentist would like to be able to answer the patient's tions will survive in the mouth longer than amalgam
question, "How long will my restoration last?" Logical restorations, which in turn will last longer than composite
though this question may be, unfortunately it is impossi- resin restorations.9 A compilation of five studies of 676
ble to answer directly. We cannot predict the life span of patients concluded that amalgam restorations exhibit a
a pair of shoes or a television set, and these everyday 50% failure rate between 5.5 and 11.5 years, with an
items are not custom made, nor do they perform their extrapolated life expectancy of 10 to 14 years.10
service in a hostile biological environment, submerged in
water. Meeuwissen et al11 reported a 10-year survival rate of
58% for amalgam restorations in Dutch military patients;
Arthur et al1? reported an 83% survival rate for the same

time span in a US military population. Qvist et al13 found mRestoration Longevity
that 50% of the amalgam restorations in a group of
Danish patients had failed at 7.0 years. Christensen14 dontic restorations was 10.3 years.™ Walton and associ-
estimated a 14-year longevity for amalgam restorations. ates, evaluating a group of 424 restorations, found full
In selected populations, amalgam restorations of crowns lasting 7.1 years, partial veneer crowns 14.3
unspecified types or sizes in one study9 have shown 10- years, metal-ceramic crowns 6.3 years, inlays and onlays
year survival rates as high as 72.0%. A 15-year survival 11.2 years, and porcelain jacket crowns 8.2 years 31
rate of 72 8% was reported for simple amalgams in
another study.15 The dentists responding to Christensen's survey esti-
mated the longevity of crowns to be from 21 to 22
A survey of 571 fixed prosthodontists, nonspecialist years.14 The estimates supplied by the respondents to a
restorative dentists, and dental school faculty projected survey by Maryniuk and Kaplan were 12.7 years for
an average life span of 11 2 years for simple amalgams metal-ceramic crowns and 14.7 years for all-gold restora-
and 6.1 years for complex amalgams.16 In fact, one tions.16 Kerschbaum, examining German insurance
group of 125 complex amalgams was reported to have a records, found 91.5% of gold crowns still in the mouth
76% survival rate at 15 years,15 while another group of after 8 years.K In a review of records in 40 Dutch dental
171 complex amalgam restorations exhibited a 50% sur- offices, Leempoel et al told of 10-year survival rates of
vival rate at 11.5 years.17 98% and 95.3% for full crowns and metal-ceramic

Composite resin restorations have not been included Several of the restorations described in this chapter
m many longevity studies. A study of dental school have not been in widespread use for a long enough peri-
patients did incorporate them, reporting a 10-year sur- od of time to have been included in longevity studies.
vival rate of 55.9%.9 Another report, done on a general Thirty-six restorative dentists and prosthodontists with a
patient population, described a shorter life span for com- mean experience of 19.2 years were surveyed to provide
posite resin restorations, with 50% of them having failed a basis for estimates of the life expectancies of some of
in 6.1 years.18 the newer restorations discussed in this chapter (Fig 6-
18).24 The longevities given are only opinions, based on
Mount1* disclosed an overall success rate of 93% for extensive experience with some restoration types and
1,283 glass-ionomer restorations for up to 7 years, with only limited experience with others. A compilation of
the rate varying from 2% to 36% depending on the class longevities from this survey and from other studies cited
of cavity and the brand of cement. In that study, the in this chapter is presented in Table 6-2.
patients evaluated had been treated by only two dentists,
and not all of the restorations had been in place for the The question of longevity is an important one to con-
full 7-year span of the study While promising, these fig- sider when deciding on treatment for a patient. The more
ures must be assessed cautiously until longer studies of destructive the preparation required for the restoration,
a broader population have been completed. the greater the potential risk tor the tooth, and ultimately
the greater expense It has been estimated that if a crown
Schwartz et al, after studying a group of 791 failed were placed in a patient's mouth at age 22, at a fee of
restorations, reported mean life spans, at failure, of 10.3 $425, attendant sen/ices and replacements of that crown
years for full crowns, 11.4 years for three-quarter crowns, will have cost the patient nearly $12,000 considering an
and 8.5 years for porcelain jacket crowns (anterior all- average life expectancy of 75 years.25
ceramic crowns). The mean life span for all fixed prostho-

Table 6-2 Longevity of Single-Tooth Restorations

Type of No. of Composite Simple Complex
study respondents
Investigatot(s)

_ 10yetoa 14
58.0% at
50% 10 yea
at 6.1
10 yea s
50
at 7 0

Marymuk and 61
Kaplan'1' 'ears

Robtains and 50%
Summit17 t 11.5

Mount'9

Kersctibaum22 Clinical

Leempoel et al?3 Clinical

Shiilingburg-'1 Survey

12.7
years

_

References i. Qvist V, Thylstrup A, M|o
and longevity of amalgarr
1. Potts RG, Shillmgburg HT, DuncE
resistance ol preparations for ca: 1986; 44:343-349.
Oenf1980; 43:303-307.
k Christensen GJ: The practicability of compacted golds in
2. Kishimoto M, Shillingbutg HT, Dur inson MG: Influer general practice—A survey. J Colo Dent Assoc 1971; 49:

prepar retenti' md resistance F 18-22.

MOD onlays. J Prosthet Dent 1< 13, 49:35-39. j Smales RJ. Longevity of cusp-covered amalgams: Survivals

3, JW: In defer sofai gam. Oper Dent 199 after 15 years. Oper Den! 1991; 16:17-20.

4. Mondelli J, Steagall I, Ishikiriama A, Navi o MF, Soars !. Maryniuk GA, Kaplan SH: Longevity of restorations: Survey
Fracture strength of human teeth with cavity preparations J results of dentists' estimates and attitudes JAm DentAssoc
Prosthet Dent 1980, 43:419.
1986; 112:39-45.
5. Reagan SE, Scriwandt NW, Duncanson MG: Fracture resis-
' Robbins JW, Summit! JB. Longevity of complex amalgam
with and without amalgam cuspal coverage. Quintessence
Inf\989; 20469-472. restorations. Oper Dent 1988; 13:54-57.
6. Kent WA, Shillingburg HT, Duncanson MG, Nelson EL:
Fracture resistance of ceramic inlays with three luting mate- !. Qvist V, Thylstrup A, Mjor
rials. J Dent Res 1991; 70:561. and longevily of resin rt
7. Livaditis GJ: Etched metal resin-bonded intracoronal cast 1986; 44:351-356.
restorations. Part II: Design criteria for cavity preparation. J
Prosthet Dent 1986; 56:389-395. !. Mount GJ: Longevity of glass ionomer cements. J Prosthet
DenM986; 55:682-685.
8. Bodell RW, Kent WA, Shillingburg HT, Duncanson MG:
Fracture resistance of intracoronal metallic restorations and ) Schwartz NL, Whitsett LD, Berry TG, Stewart JL:
three luting materials. J Dent Res 1991, 70.562. Unserviceable crowns and fixed partial dentures: life span
and causes for loss of serviceability. JAm Dent Assoc 1970;
9. Bentley C, Drake CW: Longevity of restorations in a dental 811395-1401
school Clinic. J Dent Educ 1985; 50:594-600.
. Walton JN, Gardner FM, Agar JR: A survey of crown and
10. Maryniuk GA: In search of treatment longevity—A 30-year fixed partial denture failures: Length of service and reasons
perspective. JAm DentAssoc 1984; 109:739-744. for replacement. J Prosthet DenM986; 56:416-421.

11. Meeuwissen R, Elteren P, Eschen S, Mulder J: Durability of ! Kerschbaum T. Uberlebenzeiten von kronen- und brucken
amalgam restorations in premolars and molars in Dutch ser- zahneratz heute. Zahnaertzi Mitt 1986; 76:2315-2320.
vicement. Community Dent Health 1985; 2:293-302
i. Leempoel PJB, de Haan AFJ, Reintjes AGM: The survival
12. Arthur JS, Cohen ME, Diehl MC: Longevity of restorations in rate of crowns in 40 Dutch practices J Dent Res 1986;
a U.S. military population. J Dent Res 1988; 67:388. 65:565.

I. Shillingburg HT: Unpublished research
>. Cohen BD, Milobsky SA: Monetary damages in dental-miury

cases Trial Lawyers Quarterly 1989; 20 80-81.

Chapter 7

Treatment Planning for the
Replacement of Missing Teeth

The need for replacing missing teeth is obvious to that will serve the patient's needs and still be reasonable
the patient when the edentulous space is in the to accomplish. At such times, the restorative dentist, or
anterior segment of the mouth, but it is equally prosthodontist, is the one who should manage the
important in the posterior region. It is tempting to think of sequencing and referral to other specialists. He or she
the dental arch as a static entity, but that is certainly not will be finishing up the treatment and should act as "the
the case. It is in a state of dynamic equilibrium, with the quarterback." Communicate and be open to sugges-
teeth supporting each other (Fig 7-1). When a tooth is tions, but don't allow someone else to dictate the restora-
lost, the structural integrity of the dental arch is disrupt- tive phase of the treatment, leaving you with a treatment
ed, and there is a subsequent realignment of teeth as a plan you do not think will work. You will be doing the
new state of equilibrium is achieved. Teeth adjacent to or restoration and the patient will return to you if it fails, so
opposing the edentulous space frequently move into it be sure you are comfortable with the planned treatment.
(Fig 7-2). Adjacent teeth, especially those distal to the The following guidelines are not "laws," and they are not
space, may drift bodily, although a tilting movement is a absolute. However, when a preponderance of these
far more common occurrence. items is used in the consideration of the planning for one
arch or one mouth, a more compelling reason exists for
If an opposing tooth intrudes severely into the edentu- the selection of the type of prosthesis described.
lous space, it is not enough just to replace the missing
tooth (Fig 7-3). To restore the mouth to complete function, Removable Partial Denture
free of interferences, it is often necessary to restore the
tooth opposing the edentulous space (Fig 7-4). In severe A removable partial denture is generally indicated for
cases, this may necessitate the devitalization of the edentulous spaces greater than two posterior teeth, ante-
supererupted opposing tooth to permit enough shorten- rior spaces greater than four incisors, or spaces that
ing to correct the plane of occlusion. include a canine and two other contiguous teeth; ie, cen-
tral incisor, lateral incisor, and canine; lateral incisor,
Selection of the Type of Prosthesis canine, and first premolar; or the canine and both pre-
molars.
Missing teeth may be replaced by one of three prosthe-
sis types: a removable partial denture (RPD), a tooth- An edentulous space with no distal abutment will usu-
supported fixed partial denture (FPD), or an implant-sup- ally require a removable partial denture. There are
ported fixed partial denture (Table 7-1). Several factors exceptions in which a cantilever fixed partial denture can
must be weighed when choosing the type of prosthesis be used, but this solution should be approached cau-
to be used in any given situation. Biomechanical, peri- tiously. See the section on cantilevers later in the chapter
odontal, esthetic, and financial factors, as well as the for a more detailed description of this type of restoration.
patient's wishes, are some of the more important ones. It Multiple edentulous spaces, each of which may be
is not uncommon to combine two types in the same arch, restorable with a fixed partial denture, nonetheless may
such as a removable partial denture and a tooth-sup- call for the use of a removable partial denture because of
ported fixed partial denture, or implant-supported and the expense and technical complexity. Bilateral edentu-
tooth-supported fixed partial dentures. lous spaces with more than two teeth missing on one
side also may call for the use of a removable prosthesis
In treatment planning, there is one principle that should instead of two fixed prostheses.
be kept in mind: treatment simplification. There are many
times when certain treatments are technically possible The requirements of an abutment for a removable par-
but too complex. Something must be done to cut through tial denture are not as stringent as those for a fixed par-
the possibilities and come up with a recommendation tial denture abutment. Tipped teeth adjoining edentulous
spaces and prospective abutments with divergent align-

Treatment Planning for the Replacement of Missing Teeth
in between teeth (L

ments may lend themselves more readily to utilization as for anything other than a single pontic prosthesis. An
RPD rather than FPD abutments. Periodontally weakened insufficient number of abutments may also be a reason for
primary abutments may serve better in retaining a well- selecting a removable rather than a fixed partial denture.
designed removable partial denture than in bearing the
load of a fixed partial denture. It is also possible to If there has been a severe loss of tissue in the edentu-
design the partial denture framework so that retentive lous ridge, a removable partial denture can more easily
clasps will be placed on teeth other than those adjacent be used to restore the space both functionally and
to the edentulous space. esthetically. For successful removable partial denture
treatment, the patient should demonstrate acceptable
Teeth with short clinical crowns or teeth that are just oral hygiene and show signs of being a reliable recall
generally short usually will not be good FPD abutments candidate.

Table 7-1 Replacement of Missing Teeth

Removable partial dentil

• Posterior spans longer than
teeth

• Anterior spans longer than

Span configuraten teeth • Usually has distal abutmen
but can be used with short
" N o distal abutment
• Multiple or bilateral edentulous cantilever pontic

spaces

Abutment alignme;nt • Tipped abutments can be • Less than 25° inclination ca
tolerated
be accommodated by
• Widely divergent abutment preparation modification
alignment

Abutment conditic>n • Short clinical crowns • Good if abutments need cr
Occlusion • Insufficient abutments • Nonvital teeth can be used

is sufficient coronal tooth s

• More adaptable to irregularities in • Favorable loading (magnitu
a healthy opposing natural dentition direction, frequency, durati

Periodontal condil ion • Can use alternate (secondary • Good alveolar bone suppo
abutments) when primary • Crown-root ratio 1:1 or bett
abutments are weakened • No mobility
* Favorable root morphology
Ridge form • Gross tissue loss in residual ridge * Provides rigid stabilization
General features
• Dry mouth poor RPD risk • Moderate resorption
• Limited patient finances • No gross soft tissue defect
• Acceptable oral hygiene
• Reliable recall candidate • Dry mouth high caries risk
• Treatment simplification
• Advanced age • Muscular discoordination
• Systemic health problems • Mandibular tori
• More adaptable to dentition in • Palatal soft tissue lesions
• Large tongue
transition to edentulous state • Exaggerated gag reflex
• Unfavorable attitude toward
• Patient can't cope with agin

• Favorable opposing occlus
removable prosthesis or
periodontally weakened na
dentition may permit FPD in
tfian optimal situations

• Must be within dentists skil

Implant-supported fixed par
dl

nt • Abutments mesial and distal • No distal abutment
t to pontic • Pier in 3 + pontic span
• All abutments at ends and as
an • Less than 15° inclination
mesiodistally pier(s) of long span
rowns
d if there • Should be in same faciolingual plane • Need for implant/abutment
structure • Preparations are not easily modified alignment requires close
ude, coordination between surgeon
on] because of minimal reduction and restorative dentist

• Defect-free abutments • Defect-free abutments
• Incisor, premolar replacements requiring no restoration

• Cannot be used for incisor • Occlusal forces must be as
replacement in presence of deep nearly vertical as possible to
vertical overlap prevent unfavorable lateral
loadinq of implants
ort • No mobility
ter • Periodontal splints (with auxiliary • Dense bone

resistance in tooth preparation)
y

• Moderate resorption • Broad, flat ridge
ts • No gross soft tissue defects
• Able to survive in dry mouth
• Well suited for young patients • May be better choice if teeth
• Can be used for replacing
will require extensive treatment
molars if masticatory muscles and will still be weak
are not too well developed questionable abutments
• Unfavorable attitude toward
d RPD RPD
ng, • Must be within dentist's skills

sion.

atural
n less

lls

Treatment Planning tor the Repla<

Patients oi advanced age who are on fixed incomes or an abutment both mesial and distal to the edentulous
have systemic health problems may require special treat- space.
ment simplification efforts, either to cut down on the
amount of appointment time required to restore the This prosthesis utilizes a standard pontic form, accom-
mouth or to make the treatment affordable Cajoling modating an edentulous ridge with moderate resorption
patients of limited means into overinvesting their and no gross soft tissue defects. Because it requires a
resources is not in their best interest shallow preparation that is restricted to enamel, the resin-
bonded fixed partial denture is especially useful in
A large tongue is a good reason to avoid a removable younger patients whose immature teeth with large pulps
prosthesis if at all possible, as is muscular discoordina- are poor risks for endodontic-free abutment preparations.
lion. An unfavorable attitude toward a removable partial
denture also makes it a poor choice. Tilted abutments can be accommodated only if there is
enough tooth structure to allow a change in the normal
Conventional Tooth-Supported alignment of axial reduction. This is limited by the need to
Fixed Partial Denture restrict most of the reduction to enamel. Rarely can a
mesiodistal difference in abutment inclination greater
When a missing tooth is to be replaced, a fixed partial than 15 degrees be accommodated. There can be little
denture is preferred by the majority of patients. The usual or no difference in the inclination of the abutments facio-
configuration for a fixed partial denture utilizes an abut- lingually.
ment tooth on each end of the edentulous space to sup-
port the prosthesis. If the abutment teeth are periodon- The resin-bonded prosthesis cannot be used for
tally sound, the edentulous span is short and straight, replacing missing anterior teeth where there is a deep
and the retainers are well designed and executed, the vertical overlap. Reduction deep into the underlying
fixed partial denture can be expected to provide a long dentin of the abutment teeth will be required in this situa-
life of function for the patient. Several factors have an tion, so a conventional fixed partial denture should be
influence on the decision whether to fabricate a fixed employed.
partial denture, what teeth to use as abutments, and what
retainer designs to use (see Table 7-1). Although this type of prosthesis has been described for
periodontal splints, it should be used with extreme care in
There should be no gross soft tissue defect in the those situations. Preparations will demand additional
edentulous ridge. If there is, it may be possible to aug- resistance features, such as long, well-defined grooves.
ment the ridge with grafts to enable the construction of a Abutment mobility has been shown to be a serious haz-
fixed prosthesis This treatment is reserved for patients ard in the successful use of this type of restoration.
who are both highly motivated and able to afford this spe-
cial procedure. If this is not the case, a removable partial Implant-Supported Fixed Partial Denture
denture should be considered.
Fixed partial dentures supported by implants are ideally
A dry mouth creates a poor environment for a fixed suited for use where there are insufficient numbers of
partial denture. The margins of the retainers will be at abutment teeth or inadequate strength in the abutments
great risk from recurrent caries, limiting the life span of to support a conventional fixed partial denture, and when
the prosthesis. However, an absence of moisture in the patient attitude and/or a combination of intraoral factors
mouth also will hinder the successful wearing of a remov- make a removable partial denture a poor choice,
able partial denture. In either case, the patient must be Implant-supported fixed partial dentures can be
made aware of the high risk involved. The risk may be employed in the replacement of teeth when there is no
minimized through home fluoride application and fre- distal abutment. Span length is limited only by the avail-
quent recall, but it cannot be eliminated. ability of alveolar bone with satisfactory density and
thickness in a broad, flat ridge configuration that will per-
Resin-Bonded Tooth-Supported mit implant placement.
Fixed Partial Denture
A single tooth can be replaced by a single implant,
The resin-bonded fixed partial denture is a conservative saving defect-free adjacent teeth from the destructive
restoration that is reserved for use on defect-free abut- effects of retainer crown preparations. A span length of
ments in situations where there is a single missing tooth, two to six teeth can be replaced by multiple implants,
usually an incisor or premolar. A single molar can be either as single-unit restorations or as implant-supported
replaced by this type of prosthesis if the patient's mus- fixed partial dentures. An implant can be used as a pier
cles of mastication are not too well developed, thus in an edentulous span three or more teeth long. There is
assuring that a minimum load will be placed on the some risk involved in using an immovable implant abut-
retainers The resin-bonded fixed partial denture requires ment in the same rigid prosthesis with natural teeth. In
such a situation, it is preferred that implants serve as the
abutments at both ends and as the pier(s) of a long span.
In fact, an entire arch can be replaced by an implant-
supported complete prosthesis, but that type of restora-
tion lies outside the realm of this discussion.

Abutment Evstu&tio*

The retainers used for most implant systems require a Abutment Evaluation
greater degree of abutment alignment precision than do
the retainers for a tooth-supported fixed partial denture. Every restoration must be able to withstand the constant
If implants are placed by someone other than the restor- occlusal forces to which it is subjected. This is of partic-
ing dentist, implant/abutment alignment demands close ular significance when designing and fabricating a fixed
coordination between surgeon and restorative dentist. partial denture, since the forces that would normally be
The abutments should be positioned so that the occlusal absorbed by the missing tooth are transmitted, through
forces will be as nearly vertical to the implants as possi- the pontic, connectors, and retainers, to the abutment
ble to prevent destructive lateral forces. teeth. Abutment teeth are therefore called upon to with-
stand the forces normally directed to the missing teeth, in
Implants should be better able than natural teeth to addition to those usually applied to the abutments.
survive in a dry mouth Implants may be a better choice
for FPD abutments if prospective tooth abutments will If a tooth adjacent to an edentulous space needs a
require endodontic therapy with or without dowel cores, crown because of damage to the tooth, the restoration
periodontal surgery, and possibly root resections to sup- usually can double as an FPD retainer. If several abut-
port a long-span, complex, and expensive prosthesis ments in one arch require crowns, there is a strong argu-
whose success is dependent on "feet of clay." ment for the selection of a fixed partial denture rather
than a removable partial denture.
No Prosthetic Treatment
Whenever possible, an abutment should be a vital
If a patient presents with a long-standing edentulous tooth. However, a tooth that has been endodontically
space into which there has been little or no drifting or treated and is asymptomatic, with radiographic evidence
elongation of the adjacent or opposing teeth, the ques- of a good seal and complete obturation of the canal, can
tion of replacement should be left to the patient's wishes. be used as an abutment. However, the tooth must have
If the patient perceives no functional, occlusal, or esthet- some sound, surviving coronal tooth structure to insure
ic impairment, it would be a dubious service to place a longevity. Even then, some compensation must be made
prosthesis. This in no way contradicts the recommenda- for the coronal tooth structure that has been lost. This can
tion that a missing tooth routinely should be replaced. be accomplished through the use of a dowel core, or a
The teeth adjoining an edentulous space usually move, pin-retained amalgam or composite resin core.
but they do not always move. When you meet the occa-
sional patient who has beaten the odds, recognize it for Teeth that have been pulp capped in the process of
what it is, congratulate the patient for being fortunate, preparing the tooth should not be used as FPD abut-
and tend to his or her other needs. ments unless they are endodontically treated. There is
too great a risk that they will require endodontic treatment
Case Presentation later, with the resultant destruction of retentive tooth
structure and of the retainer itself. This is a situation that
In cases where the choice between a fixed partial den- is better handled before the fixed partial denture is made.
ture and a removable partial denture is not clear cut, two
or more treatment options should be presented to the The supporting tissues surrounding the abutment teeth
patient along with their advantages and disadvantages. must be healthy and free from inflammation before any
The dentist is in the best position to evaluate the physical prosthesis can be contemplated. Normally, abutment
and biological factors present, while the patient's feelings teeth should not exhibit mobility, since they will be carry-
should carry considerable weight on matters of esthetics ing an extra load. The roots and their supporting tissues
and finances. should be evaluated for three factors:

Both dentist and patient must agree on the definitive 1. Crown-root ratio
treatment plan. If the patient understands and is willing to
accept the risks associated with treatment that is your 3. Periodontal ligament area
second choice, it is prudent to make a notation to that
effect and have it signed by the patient. If you are con- Crown-Root Ratio
vinced that a particular type of treatment is absolutely
wrong for a given situation, try to educate the patient to This ratio is a measure of the length of tooth occlusal to
the reasons for your opinion. If the patient remains the alveolar crest of bone compared with the length of
unconvinced, you would do well to refer the patient to root embedded in the bone. As the level of the alveolar
someone else. Life is too short for the aggravation that bone moves apically, the lever arm of that portion out of
may follow if you do not. bone increases, and the chance for harmful lateral forces
is increased. The optimum crown-root ratio for a tooth to
be utilized as a fixed partial denture abutment is 2:3. A
ratio of 1 • 1 is the minimum ratio that is acceptable for a
prospective abutment under normal circumstances (Fig
7-5).

Trosttvcnt Planning for the Rept3C6ffl6nt of Missing Tes

n f\ \ V

h r\\ fD \ (7) \ \ A'
\\
AB B
M
Fig 7-6 Although the root surface area of these te A
the toot configuration of the maxillary premolar (A), \
faciolingual dimension, makes it a superior abutmei

However, there are situations in which a crown-root fully support a fixed partial denture if the opposing occlu-
ratio greater than 1:1 might be considered adequate. If sion is composed of mobile, periodontally involved teeth
the occlusion opposing a proposed fixed partial denture than if the opposing teeth are periodontally sound. The
is composed of artificial teeth, occlusal force will be crown-root ratio alone is not an adequate criteria for eval-
diminished, with less stress on the abutment teeth The uating a prospective abutment tooth/
occlusal force exerted against prosthetic appliances has
been shown to be considerably less than that against Root Configuration
natural teeth: 26.0 Ib for removable partial dentures and
54.5 Ib for fixed partial dentures versus 150 0 Ib for nat- This is an important point in the assessment of an abut-
ments suitability from a periodontal standpoint. Roots
For the sai ;, an abutment tooth with a less
than desirabl

4 5 0 ROOT SURFACE AREAS ^ ^
OF MAXILLARY TEETH A
>•.
400

350

273

(1.5) ?*i

3 250 - 204 1 1 111 2 2 0
p i i ^ i , (1.2)
11.1) 179
g 200
(l.Q)

Fig 7-8 Comparative root surface 1100 f] /I f /]S 150
areas of maxillary teeth. The figure in
parentheses above each tooth is the M 0150
ratio between the root surface area of u uh H /l Hn
the respective tooth and the root surface
area of the smallest tooth in the arch, the O 1^
lateral incisor (based on data by

ROOT SURFACE AREAS „ nl ,1,2oi
OF MAND BULAR TEETH
—-— ——
„ 350

268

(1.7)

Fig 7-9 Comparative root surta _:-i 168 207
areas of mandibular teeth. The figure 154 n , . ISO (1.3)
parentheses above each tooth the (1.0)
ratio between the root surface 1 150 (1.2)
the respective tooth and the root
area of the smallest tooth in the a ch, the 11/ li100 n' n 1
central incisor (based on d Q0
Jepsen^).
U IN

that are broader labiolingually than they are mesiodtstal- Periodontal Ligament Area
ly are preferable to roots that are round in cross section
(Fig 7-6). Multirooted posterior teeth with widely separat- Another consideration in the evaluation of prospective
ed roots will offer better periodontal support than roots abutment teeth is the root surface area, or the area of
that converge, fuse, or generally present a conical con- periodontal ligament attachment of the root to the bone.
figuration (Fig 7-7). The tooth with conical roots can be Larger teeth have a greater surface area and are better
used as an abutment for a short-span fixed partial den- able to bear added stress. The areas of the root surfaces
ture if all other factors are optimal. A single-rooted tooth of the various teeth have been reported by Jepsen,3 and
with evidence of irregular configuration or with some cur- are shown in Figs 7-8 and 7-9. The actual values are not
vature in the apical third of the root is preferable to the as significant as the relative values within a given mouth
tooth that has a nearly perfect taper and the ratios between the various teeth in one arch.
When supporting bone has been lost because of peri-

jf Planning for the Replace

Fig 7-10 The combined root ., ...^ _^cond premolai Fig 7-11 The combined root s -face area of the first premolar
and the second molar (fyp+ rthan that of the firsi and the second molar aoutmer 1 <A1p+A2m) is approximately
molar being replaced (Aiplj). equal to that of the teeth being n

Fig 7-12 The combined root surface area of the canine and second

molar {Ac+A2m) is exceeded by that of the teeth being replaced
^ T D + J ^ 2 D + ^ 1 m^ A fixed partial denture would be a poor risk in this

odontal disease, the involved teeth have a lessened of the teeth to be replaced by pontics surpasses that of
capacity to serve as abutments. Millimeter per millimeter, the abutment teeth, a generally unacceptable situation
the loss of periodontal support from root resorption is exists (Fig 7-12).
only one-third to one-half as critical as the loss of alveo-
lar crestal bone.4 The planned treatment should take this It is possible for fixed partial dentures to replace more
into account. than two teeth, the most common examples being ante-
rior fixed partial dentures replacing the four incisors.
The length of the pontic span that can be successfully Canine to second molar fixed partial dentures also are
restored is limited, in part, by the abutment teeth and possible (if all other conditions are ideal) in the maxillary
their ability to accept the additional load Traditionally, arch, but not as often in the mandibular arch. However,
there has been general agreement on the number of any fixed prosthesis replacing more than two teeth
missing teeth that can be restored successfully. Tylman should be considered a high risk.
stated that two abutment teeth could support two pon-
tics.^ In a statement designated as "Ante's Law" by As a clinical guideline, there is some validity in the
Johnston et al,e the root surface area of the abutment concept referred to as "Ante's Law." Fixed partial den-
teeth had to equal or surpass that of the teeth being tures with short pontic spans have a better prognosis
replaced with pontics.7 than do those with excessively long spans. It would be an
oversimplification to attribute this merely to overstressing
According to this premise, one missing tooth can be of the periodontal ligament, however. Failures from
successfully replaced if the abutment teeth are healthy abnormal stress have been attributed to leverage and
(Fig 7-10). If two teeth are missing, a fixed partial denture torque rather than overload ' Biornechamcal factors and
probably can replace the missing teeth, but the limit is material failure play an important role in the potential for
being approached (Fig 7-11). When the root surface area failure of long-span restorations.

Biomechanical Considerati

There is evidence that teeth with very poor penodontal ture on short rnandibular teeth could have disappointing
support can serve successfully as fixed partial denture results Longer pontic spans also have the potential for
abutments in carefully selected cases. Teeth with severe producing more torquing forces on the fixed partial den-
bone loss and marked mobility have been used as fixed ture, especially on the weaker abutment. To minimize flex-
partial denture and splint abutments.8 Elimination of ing caused by long and/or thin spans, pontic designs with
mobility is not the goal in such cases, but rather the sta- a greater occlusogingival dimension should be selected.
bilization of the teeth in a status quo to prevent an The prosthesis may also be fabricated of an alloy with a
increase of mobility.9 higher yield strength, such as nickel-chromium.

Abutment teeth in these situations can be maintained All fixed partial dentures, long or short, flex to some
Iree of inflammation in the face of mobility, if the patients extent. Because of the forces being applied through the
are well motivated and highly proficient in plaque pontics to the abutment teeth, the forces on castings
removal.10 Crowns that anchor rigid prostheses to mobile serving as retainers for fixed partial dentures are different
teeth do require greater retention than do crowns in magnitude and direction from those applied to single
attached to relatively immobile abutments, however.11 restorations.14 The dislodging forces on a fixed partial
Follow-up studies of these patients with "terminal denti- denture retainer tend to act in a mesiodistal direction, as
tions" indicate a surprisingly low failure rate—less than opposed to the more common buccolingual direction ol
8% of 332 fixed partial dentures exhibited technical fail- forces on a single restoration. Preparations should be
ure in a time span that averaged slightly more than 6 modified accordingly to produce greater resistance and
years. '2 structural durability. Multiple grooves, including some on
the buccal and lingual surfaces, are commonly
What is the impact of the success of this type of treat- employed for this purpose (Fig 7-18).
ment on fixed partial dentures for the average patient?
The successful restoration of mouths with severe peri- Double abutments are sometimes used as a means of
odontal disease does have significance in everyday overcoming problems created by unfavorable crown-root
practice. It emphasizes the extreme importance of care- ratios and long spans. There are several criteria that must
fully evaluating the strengths and weaknesses of the be met if a secondary (remote from the edentulous
remaining dentition on an individual basis. space) abutment is to strengthen the fixed partial denture
and not become a problem itself. A secondary abutment
This should not be a signal for every dentist with a must have at least as much root surface area and as
handpiece to start using severely periodontally involved favorable a crown-root ratio as the primary (adjacent to
teeth as abutments. Bear in mind that the successful the edentulous space) abutment it is intended to bolster.
treatments that have been cited are of the work of well- As an example, a canine can be used as a secondary
trained and highly skilled clinicians on selected, highly abutment to a first premolar primary abutment, but it
motivated patients. would be unwise to use a lateral incisor as a secondary
abutment to a canine primary abutment. The retainers on
This type of heroic treatment C'herodontics," if you will) secondary abutments must be at least as retentive as the
is very demanding technically, and expensive as well. retainers on the primary abutments. When the pontic flex-
Performed by a well-trained, skilled clinician on an es, tensile forces will be applied to the retainers on the
informed, motivated patient who dreads tooth loss, under- secondary abutments (Fig 7-19). There also must be suf-
stands the patient's role in the success of the treatment, ficient crown length and space between adjacent abut-
and accepts the risk (and expense) of failure, it can be a ments to prevent impingement on the gingiva under the
good service. "Sold" by a practitioner without special
qualifications to an unmotivated and ill-informed patient, Arch curvature has its effect on the stresses occurring
this type of treatment easily could result in a lawsuit. in a fixed partial denture. When pontics lie outside the
interabutment axis line, the pontics act as a lever arm,
Biomechanical Considerations which can produce a torquing movement. This is a com-
mon problem in replacing all four maxillary incisors with
in addition to the increased load placed on the peri- a fixed partial denture, and it is most pronounced in the
odontal ligament by a long-span fixed partial denture, arch that is pointed in the anterior. Some measure must
longer spans are less rigid Bending or deflection varies be taken to offset the torque. This can best be accom-
directly with the cube of the length and inversely with the plished by gaining additional retention in the opposite
cube of the occlusogingival thickness of the pontic. direction from the lever arm and at a distance from the
Compared with a fixed partial denture having a single- interabutment axis equal to the length of the lever arm
tooth pontic span (Fig 7-13), a two-tooth pontic span will (Fig 7-20).1S The first premolars sometimes are used as
bend 8 times as much (Fig 7-14). A three-tooth pontic will secondary abutments for a maxillary four-pontic canme-
bend 27 times as much as a single pontic (Fig 7-15).13 to-canine fixed partial denture. Because of the tensile
forces that will be applied to the premolar retainers, they
A pontic with a given occlusogingival dimension will must have excellent retention.
bend (Fig 7-16) eight times as much if the pontic thick-
ness is halved (Fig 7-17). A long-span fixed partial den-

Treatment Planning for the Replacement of Missing Teeth

Fig 7-17 There will be 8 times as much deflection (8X1 if the
thickness is decreased by one-half (Ml).

Fig 7-18 The walls of facial and lingual grooves Fig 7-19 l"he retainers on secondary abutments will be placed in
mesiodiital torque resulting from force applied to the p. tension when the pontics flex, with the primary abutments acting

^nds in the opposite directio

Special Problems for all situations requiring a fixed prosthesis An edentu-
lous space can occur on both sides of a tooth, creating
Some problem situations occur often enough to deserve a lone, freestanding pier abutment (Fig 7-21).
mention Some of the commonly used solutions to the Physiologic tooth movement, arch position of the abut-
problems are also presented. ments, and a disparity in the retentive capacity of the
retainers can make a rigid five-unit fixed partial denture a
Pier Abutments less than ideal plan of treatment.

Rigid connectors (eg, solder joints) between pontics and Studies in periodontometry have shown that the faci-
retainers are the preferred way of fabricating most fixed olingual movement ranges from 56 to 108 |im,1fl and
partial dentures. A fixed partial denture with the pontic intrusion is 28 ujn.17 Teeth in different segments of the
rigidly fixed to the retainers provides desirable strength arch move in different directions.16 Because of the curva-
and stability to the prosthesis while minimizing the stress- ture of the arch, the faciolmgual movement of an anterior
es associated with the restoration. tooth occurs at a considerable angle to the faciolingual
movement of a molar (Fig 7-22).
However, a completely rigid restoration is not indicated
These movements of measurable magnitude and in
divergent directions can create stresses in a long-span
prosthesis that will be transferred to the abutments.