ENDODONTICS-Endodontics in Clinical Practice, 6e

Harty’s endodontics in clinical practice

Thermomechanical compaction coated condensor is operated in the canal, plasticized
gutta-percha is compacted onto the canal walls. Without
In this technique, an engine-operated compactor the reliance on friction to plasticize the gutta-percha, the
e.g. Gutta-Condensor (Dentsply Maillefer) (Fig. 6.35), condensor can be operated at a lower speed lessening the
designed with reverse turning screw threads, is rotated in risk of instrument fracture and potential heat damage to
a forward direction alongside a fitted gutta-percha point the periodontium.
or several points. The heat created by the friction plasti-
cizes the gutta-percha and, at the same time, the centrifu- Thermoplasticized injectable
gal forces generated compacts the gutta-percha onto the gutta-percha
canal walls. The higher the speed of rotation the greater
the heat generated.93 As the bulk of gutta-percha in the The concept of injecting softened gutta-percha into the
canal builds up, the compactor is forced out of the canal. root canal was introduced many years ago96 as a develop-
The result can be a well-condensed root canal filling that ment of vertical condensation. An example is the Obtura
is more homogeneous compared with lateral condensa- III Max (Obtura Spartan, Earth City, MO, USA) (Fig. 6.36),
tion.94 If the compactor is used accidentally in reverse, it a high temperature system capable of taking the tempera-
screws into the root canal and will break. Another disad- ture of gutta-percha in the heating chamber to 200°C. It
vantage is that it is possible to extrude gutta-percha consists of a delivery unit with an electrical cord connected
through the apex with this technique; to prevent this, the to a temperature control box with a digital display. The
hybrid technique was developed, in which an apical gutta- gutta-percha is loaded into the heating chamber. When
percha plug is first created by lateral condensation prior the trigger of the delivery unit is squeezed, the softened
to thermomechanical compaction.95 gutta-percha is extruded through a 20, 23 or 25 gauge
needle; the needles are reusable, bendable and sterilizable.
A modified technique of thermomechanical compac- Thermal protectors are used to insulate the heating unit
tion involves coating the condenser with already plasti- and to prevent burning the patient’s lip. This technique is
cized gutta-percha of a different viscosity (e.g. Microseal, useful when filling large and irregular canals. The root
SybronEndo). The ultra-low fusing gutta-percha for this filling produced is well adapted to the prepared canal.97 It
technique comes in cartridges, which are heated in an is also used for back filling canals after an apical plug has
oven and delivered with a syringe. A master gutta-percha been established.
point is placed beforehand and as previously, when the
Other manufacturers have brought out similar thermo-
plasticized injectable gutta-percha delivery devices
including a cordless version (HotShot, Discus Dental)
(Fig. 6.37) and a dual-function combination of a System
B-type heated spreader with a motor-driven warm gutta-
percha extruder (Elements Obturation Unit, SybronEndo)
(Fig. 6.38).

Figure 6.35  Gutta-Condensor (Dentsply Maillefer) for Figure 6.36  Obtura III Max thermoplasticized injectable
thermomechanical compaction of gutta-percha. gutta-percha system. The heated delivery gun extrudes
gutta-percha through the fine needle; the temperature is
88 controlled by the main unit.

Basic instrumentation in endodontics Chapter | 6 |

Figure 6.37  HotShot, a cordless thermoplasticized injectable
gutta-percha delivery device.

Figure 6.39  Thermafil obturator, a plastic carrier-based
device coated with gutta-percha.

Figure 6.38  Elements Obturation Unit, a combination of a root canal.98 The Thermafil obturators have a 0.04 taper,
System B-type heated spreader with a motor-driven warm V-shaped cross-section plastic core, which is coated with
gutta-percha extruder. alpha-phase gutta-percha that has excellent flow proper-
ties (Fig. 6.39). The obturators are colour-coded and come
Gutta-percha carrier devices in ISO sizes 20–140. The size of the Thermafil obturator
required is first determined with the aid of a set of Verifier
The Thermafil system (Dentsply Maillefer) is an example files. The chosen obturator is warmed by placement in a
of a gutta-percha carrier device. This commercial product special oven (ThermaPrep Plus oven). When warmed, the
originated from a technique of moulding heated gutta- obturator is removed from the oven and inserted, with
percha to a root canal file, which was then used to fill the force, into the root canal. After cooling, the handle, if
already pre-notched is twisted off; otherwise it is cut off
with a bur. A Thermafil Post Space bur is available if post
space preparation is required.

The Thermafil system is intended to make filling easier
and faster.99 However, a minor disadvantage of leaving a
plastic core filling material in situ is the problem of
removal, should retreatment be required. The retained

89

Harty’s endodontics in clinical practice

obturator is not easy to remove.100 Many rotary holder, with a snap-on finger ring handle (Fig. 6.41). Dis-
NiTi systems include similar carrier-based devices that posable wells (Gelwells) for medicaments and canal
correspond to the size of their instruments and are lubricants, may be attached to the sponge holder; there is
marketed as a comprehensive package (e.g. System GT also a ruler incorporated. The Endoring II system allows
obturators and ProTaper Universal obturators, Dentsply easy access to root canal instruments within the operating
Maillefer). field, eliminating the time-consuming action of picking up
instruments from the bracket table.

STORAGE AND STERILIZATION OF Sterilization of endodontic
ENDODONTIC INSTRUMENTS instruments

Instrument stands and Infection control is of paramount importance and the
storage systems responsibility of every member of the dental team. Recom-
mended, universal methods of infection control must be
Root canal instruments such as files, unless labelled sterile employed to prevent the risk of transmission of infection
when supplied, should be cleaned and sterilized before- within the dental surgery.101 All instruments and equip-
hand. They may be stored in small boxes with stands (e.g. ment must be cleaned thoroughly and sterilized. However,
Endo-Stand, Dentsply Maillefer), or in Pyrex glass test concerns regarding the re-use of endodontic instruments
tubes with different coloured covers for instrument iden- and the possible transmission of variant Creutzfeldt-Jakob
tification (Fig. 6.40). Complete sets of instruments can be Disease (vCJD) led to current United Kingdom guide-
pre-arranged, sterilized and kept, ready for use. Metal or lines102,103,104,105 advising dentists to ensure that endodon-
plastic boxes with lids, in a variety of sizes are available. tic files and reamers are treated as single use. Prions, the
Some can house all the basic instruments required for abnormal proteins associated with vCJD are more resistant
endodontic treatment; there is also a file stand, a medica- than other types of infectious agent to conventional clean-
ment dish and a cotton wool pellet container. Alter­
natively, instruments can be sterilized and stored in
transparent autoclave bags and laid out on an open plastic
tray, with a sponge for files.

Another instrument-holding device, the Endoring II
system (Jordco, Beaverton, OR, USA) comprises a triangu-
lar disposable sponge for root canal instruments, which is
inserted into an autoclavable thermoplastic resin sponge

A
B

Figure 6.40  (A) Plastic tray containing instruments in a Figure 6.41  Endoring II, comprising a sponge for
transparent sterile bag; (B) files can be stored and sterilized instruments in a plastic holder incorporating a ruler.
in Pyrex glass test tubes.

90

Basic instrumentation in endodontics Chapter | 6 |

Figure 6.43  Telescopes and portable headlight attached to
spectacle frame for enhanced vision and illumination.

Figure 6.42  Sterilized paper points, files and burs in blister
packs.

ing and sterilization procedures normally used to decon-
taminate dental instruments.106

For convenience, and if available, single-use, disposable
items are recommended. Sterile packs of files, burs
and blister packs of paper points are produced by many
manufacturers (Fig. 6.42) and are often available at no
extra cost.

LOUPES, FIBRE-OPTIC LIGHTS AND
OPERATING MICROSCOPES

Endodontic procedures are often performed in areas of Figure 6.44  Dental operating microscope provides a range
limited access and reduced visibility. The use of magnifica- of magnifications and improved illumination.
tion and better illumination can certainly be extremely
helpful in these situations. Magnifying binocular loupes • basic selection of instruments required for
(e.g. SurgiTel, Ann Arbor, MI, USA) (Fig. 6.43) can help
enhance vision while fibre-optic lighting provides better endodontic treatment
illumination. Dedicated dental operating microscopes
(e.g. Global Microscope, Global Surgical Corp., St. Louis, • reasons and equipment for rubber dam application
MO, USA) (Fig. 6.44) provide the combined benefits • instruments for root canal preparation
of magnification and illumination.107 They allow greater • devices for delivering root canal irrigants
magnification and facilitate canal orifice location in • instruments for retrieving broken instruments
difficult cases; they are widely used by specialist practi­
tioners. A fibre-optic endoscope, to provide magnified and posts
intracanal visualization was also developed for use in
endodontics.108 • instruments for filling root canals
• storage, sterilization and guidelines on re-use of
LEARNING OUTCOMES
endodontic instruments
At the end of this chapter, the reader should be able to
recognize and discuss the: • uses and advantages of magnification and additional

illumination.

91

Harty’s endodontics in clinical practice

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7Chapter  

Preparation of the root canal system

J.S. Rhodes

CHAPTER CONTENTS 97 SUMMARY
97
Summary 98 A major goal of root canal treatment is the removal of
Introduction 98 microorganisms from the root canal system. This chapter
Gaining access to the root canals 98 on preparation of the root canal system will cover gaining
98 access to the root canals, determining working length,
Pretreatment assessment preparation techniques including with rotary nickel-
Preparation of the tooth 98 titanium instruments, root canal irrigation and controver-
Rubber dam 100 sies associated with cleaning and shaping.
Removal of the pulp chamber roof and 100
coronal pulp tissue 101 INTRODUCTION
Creating straight-line access 102
Working length determination 103 It is widely accepted that microorganisms and their
Root canal irrigation 104 byproducts are the main aetiological factors in the initia-
Instrumentation techniques 104 tion and progression of pulpal inflammation and periapi-
Crown-down rationale 105 cal disease.1,2,3 The central focus of root canal treatment
Nickel-titanium instruments is, therefore, to eliminate microbes and their substrates
Crown-down technique 105 from the root canal system.4 This may involve the removal
Calcified canals 105 of necrotic pulp and tissue debris, removal of an inflamed
Controversies in root canal cleaning 105 pulp or, in elective treatment, the removal of healthy
and shaping pulp tissue. Retreatment of failing cases is addressed in
Where should the preparation end? 106 Chapter 14.
When should the preparation end?
What about the apical size of 106 Historically, a mechanistic approach to root canal treat-
preparation? ment was frequently adopted. However, there is now a
Should apical patency filing be 106 greater awareness of the microbiota and pattern of colo-
performed? 107 nisation within the complexities of an infected root canal
Should treatment be completed in one 107 system (Fig. 7.1). This has led to the development of
or multiple visits? newer techniques, instruments and materials and a
Learning outcomes biologically-based rationale for root canal treatment:
References 1. Removal of all tissues, microorganisms, their

© 2009 Elsevier Ltd, Inc, BV byproducts and substrates from the root canal
DOI: 10.1016/B978-0-7020-3156-4.00010-3 system.

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Harty’s endodontics in clinical practice

ture should never preclude the proper design and fulfil-
ment of the requirements of the access opening.5,6 On the
other hand, injudicious tooth removal should be avoided.
Pulp space anatomy and access cavities are covered in
Chapter 4.

Pretreatment assessment

The dimensions of the pulp chamber and the location of
the root canal orifice(s) will be influenced by the amount
and position of tertiary ‘irritation’ dentine that has been
deposited during the life of the tooth and in response
to ‘insults’ that the tooth had suffered since eruption.
Canal orifices may also become obstructed by pulp stones
and/or dystrophic calcifications. Such calcifications and
increased amounts of fibrotic tissue in the pulp chamber
will make identifying and negotiating the root canals more
challenging.

Figure 7.1  A root end which has been made transparent by Preparation of the tooth
clearing showing two lateral canals.
Caries and failing restorations must be completely
2. Shaping of the root canal system to facilitate removed prior to preparing the access cavity to prevent
placement of irrigants, medicaments and a root infected dentine and restorative material being inadvert-
canal filling. ently introduced into the root canal system, and to prevent
microleakage or reinfection. If there is any doubt regarding
3. Filling of the shaped canal system coupled with an the restorability of the tooth, the existing restoration
adequate and timely coronal restoration. should be completely removed7,8 to confirm that there is
sufficient tooth substance remaining. Removal of existing
The traditional ‘endodontic triad’ concept of cleaning, restorations and crowns may reveal caries, additional
shaping and filling may be modified. Considering that a canals or hairline cracks on one or more axial walls, which
major goal of root canal treatment is the removal of micro- may influence the prognosis and/or the design of the post-
organisms from the complex root canal system ‘shaping endodontic restoration (Fig. 7.2).
to facilitate cleaning and filling’ might be a more appro-
priately modified concept. Nevertheless, these three objec- Unsupported cusps should be removed or protected
tives must be achieved while ensuring conservation of by, for example, placing an orthodontic band around the
tooth structure and maintaining canal shape. tooth to prevent cusp fracture during and after treatment.
In some cases, following dismantling of the coronal
GAINING ACCESS TO THE restoration it may be necessary to place a provisional res-
ROOT CANAL SYSTEM toration to prevent microleakage, aid rubber dam isola-
tion and create a reservoir for the irrigant solution in the
The main function of an access cavity is to create an unim- access cavity.
peded pathway to the pulp space and the apical foramen
of the tooth. Good access cavity design and preparation is Rubber dam
imperative for quality treatment results, prevention of
iatrogenic problems and avoidance of technical failure of Isolation of the tooth with rubber dam is a necessary
root canal treatment. Conservation of coronal tooth struc- prerequisite for endodontic treatment. This topic is
covered in Chapter 6. In addition, excellent reviews on the
application of rubber dam have also been published.8,9,10

Removal of the pulp chamber
roof and coronal pulp tissue

The number of canals and their approximate positions can
be predicted from a sound knowledge of dentinogenesis

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Preparation of the root canal system Chapter | 7 |

AB

Figure 7.2  Retreatment case. (A) The cast restoration
was removed to reveal caries around the core material.
(B) Following caries removal the root filling material is
C visible. (C) Exploration of the pulp floor revealed the
second mesiobuccal canal (arrowed).

and the nature of root formation. The pulp chamber Maillefer, Ballaigues, Switzerland), frequent re-evaluation
and root canal space are always located in the cross- of the alignment visually and/or radiographically will help
sectional centre of the crown and root respectively.5 The reduce the risk of procedural errors. The direction of the
location of canal orifices is best achieved with good illu- search can then be adjusted if necessary (Fig 7.4).
mination and carefully drying the pulp floor. Magnifica-
tion with either loupes or an operating microscope is The roof of the pulp chamber should be penetrated at
beneficial and the latter is better for detecting canal a point where the roof and floor of the pulp chamber is
orifices.11 the widest, this commonly occurs at the point where the
pulp horn relating to the largest canal is situated, for
The design of the access cavity should reflect the antici- example, the palatal root in maxillary molars. Tungsten
pated position of the underlying root canal orifices. The carbide burs are ideal for cutting through metal. However,
relationship between the pulp chamber and the external a diamond bur should be used to map out the access in
anatomical outline is assessed from preoperative radio- porcelain fused to metal crowns, before using a tungsten
graphs. Careful alignment of the bur will reduce the pos- carbide bur, to reduce the likelihood of porcelain fracture.
sibility of perforation either vertically, through the floor For this reason, it is wise to warn the patient beforehand
of the chamber into the furcation, or laterally (Fig. 7.3). that a restoration may be irreversibly damaged and may
Occasionally, where an extracoronal restoration is severely need replacing following root canal treatment. Once the
tilted relative to the root, or in cases with sclerosed root roof of the pulp chamber has been breached, the bur will
canal systems, initial access may best be made prior to suddenly drop into the pulp chamber space. To prevent
rubber dam placement to permit more accurate orienta- damage to the floor of the pulp chamber a non-end-
tion of instruments. When using instruments such as long- cutting bur is then used to remove the entire roof of the
shank round burs or tungsten-carbide LN burs (Dentsply pulp chamber. The walls of the access cavity should be

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Harty’s endodontics in clinical practice

root canal system. Ultrasonically energized tips (Fig. 7.6)
are useful for breaking up calcific masses and aid removal
of gross debris.

Creating straight-line access

Once the canal orifice(s) have been identified it may be
necessary to refine or modify the outline of the access
cavity to allow endodontic files unimpeded, straight-line
access into the coronal third of the root canal system.
Straight-line access will reduce the likelihood of iatrogenic
problems such as zips, elbows and ledges being created by
large, and therefore, less flexible files as they attempt to
straighten, particularly, in curved canals. Straight-line
access will also allow unimpeded penetration of files for
root canal preparation.

Although nickel-titanium (NiTi) rotary files are very
flexible, poor straight-line access can still result in instru-
ment separation.

A well-designed access cavity permits:

• complete debridement of the pulp chamber
• visualization of the pulp floor
• unimpeded placement of instruments into the

root canals

• conservation of tooth tissue.

WORKING LENGTH DETERMINATION

Figure 7.3  Alignment of the bur on the preoperative Regardless of treatment philosophy on the desired final
radiograph will help indicate the position and depth of the end point of preparation, it is always necessary to ascertain
restoration and pulp chamber. the length of the root canal accurately.2,12,13,14 The most
widely accepted method of establishing working length
probed to ensure that the roof of the pulp chamber has has been with radiography. In this method,15 the working
been completely removed, i.e. no dentine ledges/lips are length is initially estimated by taking a measurement from
present (Fig 7.5). an undistorted, preoperative radiograph. A file, preferably
ISO size 15 or larger, so that it is easily discernible radio-
Careful inspection of the pulp chamber floor will reveal logically, is inserted into the canal to the estimated
subtle changes in the colour of the dentine, which aids working length and a working length radiograph exposed.
identification of the canal orifices. Dark developmental If the tip of the file is within 1 mm of the ideal location,
lines may be visible linking canal orifices, which will then the radiograph can be accepted as an accurate repre-
appear as a small area of opaque dentine against a sentation of the tooth length. If adjustments of 2 mm or
background of yellow/grey secondary dentine. A canal more are needed, the working length should be recon-
orifice will feel sticky when probed with a DG16 endo- firmed with an additional working length radiograph.16
dontic explorer or Micro-Opener (Dentsply Maillefer). In This method usually provides acceptable results but radio-
extensively calcified canals, transillumination or the use graphs are, frequently difficult to interpret especially with
of dyes may provide some guidance for canal orifice posterior teeth. More importantly, the apical foramen may
identification. be distant from the radiographic apex further confusing
interpretation. In such circumstances, additional methods
The pulp chamber is irrigated with sodium hypochlorite of working length determination should be utilized.
during access cavity preparation to dissolve tissue and aid
debridement. This will also reduce the inadvertent inocu- Modern electronic apex locators measure the imped-
lation of microorganisms from the pulp chamber into the ance of the root canal at different frequencies and have
been reported to be accurate to within 0.5 mm in >90%
of cases.17,18,19 Consequently, an apex locator can be
more reliable than a radiograph for determining working

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Preparation of the root canal system Chapter | 7 |

AB

Figure 7.4  In a tooth with an extensively calcified canal (A) a check radiograph with a probe in the base of the cavity will
provide guidance for instrument progression. (B) A later radiograph confirms that the file is in the root canal.

AB

Figure 7.5  Inadequate access: (A) the pulp horns have been mistaken for the canal orifices and the roof of the pulp chamber
is still in situ; (B) removal of the roof of the pulp chamber allows good visualization of the pulp floor.

length.20 The use of an apex locator allows for a reduction ROOT CANAL IRRIGATION
in the number of radiographs required during root canal
treatment. In a long-term retrospective study in which an Root canal treatment involves a chemomechanical
apex locator was used solely to determine working length approach; microorganisms are removed mechanically
in infected root canals with periapical lesions, a high during canal preparation and eradicated chemically using
success rate was achieved21 confirming its benefit. Not just irrigants. Microorganisms are present in the lumen of the
one method but the combination of the radiographic root canal in a planktonic form and as a biofilm adhering
method and the use of electronic apex locators will to the canal walls. Regardless of the instrumentation tech-
enhance the accuracy of working length determination.

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Figure 7.6  A selection of ultrasonic tips that can be used to tion, involving a dye and a diode light, and lasers have
break up calcific masses in the canal orifice. also been advocated for disinfection of the root canal
system28 but its superiority over sodium hypochlorite is
nique or system chosen, the use of irrigants is essential for yet to be proven.
thorough debridement of the root canal system.22
During root canal preparation a layer of ‘sludge’ is
The actions of an irrigant include: formed by the action of the instruments against the canal
walls. This material is deposited on the canal wall and is
• rinsing of debris called the ‘smear layer’. It has both organic and inorganic
• lubrication of the canal system which facilitates components and exists as a superficial, loosely bound
layer and a deeper adherent layer.29 Considerable debate
instrumentation has taken place as to whether or not the smear layer
should be removed. Complete removal of the smear layer
• dissolution of remaining organic matter may open up dentinal tubules to the passage of microor-
• antibacterial properties ganisms from the root canal into the dentine. On the other
• softening and removing the smear layer hand, failure to remove the smear layer will, possibly
• penetrating into areas inaccessible to instruments, allow bacteria to remain in the canal system and impair
the adaptation of the root filling to the dentine wall and
thereby extending the cleaning process. tubules.30,31 A very close adaptation of thermoplasticized
gutta-percha to the dentine wall has been shown following
Ideally, the irrigant should be non-toxic and have a low smear layer removal.32,33 Removal of the smear layer is best
surface tension, in addition to being stable, inexpensive achieved by irrigating the root canal system with sodium
and easy to use. A plethora of irrigants have been used. hypochlorite throughout the preparation procedure to
Currently, the most widely used irrigant is sodium flush out and prevent accumulation of debris on the canal
hypochlorite. It is highly effective at killing bacteria and walls. A final rinse with 17.5% ethylenediaminetetraacetic
breaking down organic material; various concentrations acid (EDTA), a chelating agent, is recommended for
of sodium hypochlorite, varying from 0.5% to 5.25%, removal of the inorganic component.34 The effects of
have been recommended.23 The effectiveness of sodium chelating agents such as EDTA are self-limiting.
hypochlorite has been shown to depend on the concentra-
tion and time of exposure. Higher concentrations of The irrigant is commonly delivered using specially
sodium hypochlorite have greater tissue-dissolving prop- designed endodontic needles and syringes. The needle is
erties24 but the higher the concentration, the more severe inserted into the canal to the level of the apical third.
the potential reaction if it is inadvertently forced into the However, during initial canal preparation, the needle may
tissues. Accidental extrusion of sodium hypochlorite into not reach this depth so it should be inserted to the binding
the periapical tissues may result in tissue damage accom- point, pulled out slightly so that it is loose in the canal
panied by varying degrees of pain, swelling and bruising. and then the irrigant delivered gently and passively. As
This topic is discussed in Chapter 14. canal preparation proceeds, the needle will gradually
reach deeper into the canal but at all times, the needle
The use of calcium hydroxide as an intracanal medica- must not be jammed into the canal and the irrigant
ment between visits has been shown to enhance disinfec- delivered with unnecessary force. Irrigants may also be
tion following the use of sodium hypochlorite. Other delivered using ultrasonic devices. The effectiveness of
irrigants used in root canal chemomechanical preparation ultrasonic irrigation is due to the creation of acoustic
include chlorhexidine,25 iodine potassium iodide26 and microstreaming and allows more effective delivery of irrig-
electrolytically-activated water.27 Irrigants such as chlo- ant to the apical part of the root canal system.35,36 A pas-
rhexidine and iodine potassium iodide have antibacterial sively vibrating ultrasonic instrument is more effective
properties but no tissue-dissolving properties. Apart from than one that is being dampened by the canal wall.37,38 For
the rinsing effect, local anaesthetic solution or saline have this reason, modern tips designed for this purpose are fine
none of the desired properties of a root canal irrigant and in size (ISO size 15) or even smooth, without cutting
their use is not recommended. Photoactivated disinfec- flutes. There is limited evidence to specify the ideal length
of time that passive ultrasonic irrigation should be acti-
vated within the canal.

INSTRUMENTATION TECHNIQUES

All root canal systems are curved in one or more planes
with the degree and extent of curvature varying from root
to root. Irrespective of the instrumentation technique

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Preparation of the root canal system Chapter | 7 |

used, the apical part of the root canal system is usually the Figure 7.7  The anatomy of the apical constriction must be
least well-cleaned and prepared. The morphology of the maintained during canal preparation.
apical root canal system is complex and highly variable.
This has been clearly demonstrated from clearing tech- preventing inoculation of periapical tissues with
niques and micro-computed tomography.39 contaminated debris

Preparation of the root canal system requires consider- • elimination of coronally-placed interferences that
able skill, particularly in cases with more severely curved
canals or other complex anatomical features. Despite might adversely influence instrumentation
advances in instrument design, the experience and tactile
skills of the operator remains important.40 There is no • early movement of large volumes of irrigant and
replacement for practical instructions on root canal prepa-
ration in order to acquire the necessary skills and compe- lubricant to the apical part of the canal
tency. Regardless of the instrumentation technique or type
of instrument used, the goals of shaping and cleaning of • facilitating accurate working length determination as
the root canal systems are:
coronal curvature is eliminated early in the
• thorough debridement of the root canal system preparation.
• development of a continuously tapering preparation
• avoidance of procedural errors. The essentials of the coronal-to-apical approach to root
canal cleaning and shaping are as follows:
Maintaining the anatomy of the apical constriction (Fig.
7.7) during canal shaping is essential for predictable • development of straight-line access from the occlusal
healing of the periapical tissues. Long-term studies have
shown improved success rates when instrumentation or lingual surface into the pulp chamber
and filling procedures are maintained within the canal
system, at approximately the level of the cemento-dentinal • removal of all overhanging ledges from the pulp
junction.41
chamber roof
Historical methods of canal preparation that encom-
passed a mechanistic approach have largely been super- • removal of lingual ledges or cervical bulges formed
seded. Canal preparation techniques can be broadly
divided into those that adopt an ‘apical-to-coronal’ due to the deposition of dentine in the cervical part
approach or those that adopt a ‘coronal-to-apical’ of the tooth
approach. Most endodontists would now advocate using
a crown-down (coronal-to-apical) approach to prepara- • development of divergent walls in the pulp chamber
tion with hand files manipulated in a balanced-force
action or nickel titanium rotary instruments in a hand- from the cavosurface margin to the chamber floor
piece. Numerous protocols have detailed the crown-down
approach, these include: the Crown-down pressureless • cutting of a funnel-shaped preparation, with its
technique,42 the Roane or Balanced-force technique,43 the
‘Double-flare’ technique,44 and the Modified double-flare narrowest part located in the tooth apically.
technique.45 In the Balanced-force technique, hand files of
a triangular cross-section are rotated a quarter-turn clock- The clinical benefits of the crown-down technique are:
wise to engage dentine of the root canal wall. Whilst
applying apical pressure, this is followed by a half turn of • ease of removal of pulp stones
the file in the counter-clockwise direction, which effec- • enhanced tactile feedback with instruments by
tively ‘cuts’ the dentine that was engaged. The process can
be repeated for two or three times before removing the removal of coronal interferences
instrument to clean the flutes and irrigate the canal. Unlike
many other techniques, files are not pre-curved when used • enhanced apical movement of instruments into the
in this manner.
canal
Crown-down rationale
• enhanced working length determination due to
There are several advantages with the crown-down
approach: minimal tooth contact in the coronal third

• elimination of debris and microorganisms from the • increased space for irrigant penetration and

more coronal parts of the root canal system thereby debridement

• rapid removal of pulp tissue located in the coronal

third

• straight-line access to root curves and canal junctions
• enhanced movement of debris coronally

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Harty’s endodontics in clinical practice

• decreased deviation of instruments in canal 2. NiTi flexibility enables manufacturers to produce
files with tapers greater than standard stainless steel
curvatures by reducing root wall contact hand files. Therefore, fewer instruments are generally
required.
• decreased canal blockages
• minimize instrument separation by reducing contact 3. NiTi instruments will efficiently taper a preformed
pilot channel, avoiding the need for stepping back.
with canal walls
4. The instruments tend not to deviate from the
• improved quality of canal shaping centre-point of the canal, and transportation of the
• improved quality of canal cleaning canal is uncommon.
• faster preparation, which may allow one-visit root
Disadvantages of NiTi instrumentation
canal treatment.
1. Instrument fracture can still be unpredictable.
The biological benefits of the crown-down technique are: 2. The instruments are flexible but are liable to fracture

• more rapid removal of contaminated, infected tissue when worked around curvatures with a small radius.
This risk increases with increasing file diameter.
from the root canal system 3. Overuse will still result in zipping and transportation
of the canal despite superflexibility.
• removal of tissue debris coronally, thereby 4. NiTi instruments tend to be more expensive.

minimizing pushing debris apically Crown-down technique

• reduction in postoperative pain that may occur with The basic steps common to all ‘crown-to-apical’ tech-
niques involve early coronal and mid-root flaring and
apical extrusion of debris enlargement before proceeding to the apical part of the
canal. Early coronal flaring significantly reduces the change
• better dissolution of tissue with increased irrigant in working length during canal preparation.58 As an instru-
ment initially moves into the coronal third of the canal
penetration and as the pathway is enlarged, this facilitates further
movement of small instruments and allows passage of
• easier smear layer removal because of better contact irrigants deeper into the root canal. This entire process is
continued until the working length can be determined
with chelating agents easily. Instrument placement into the middle and apical
parts of the canal system is unimpeded. Irrigants and
• enhanced disinfection of canal irregularities due to lubricants will penetrate more easily and will facilitate
passage of instruments in an apical direction.
irrigant penetration.
When using NiTi instruments, larger instruments will
Nickel-titanium instruments make space for smaller instruments. This may involve
using an instrument with a greater taper before one with
Following the introduction of nickel-titanium (NiTi) alloy a smaller taper, or a series of instruments in decreasing tip
to endodontic instrument design,46 many new NiTi hand sizes. Some systems have been designed with variable
and rotary instruments have become available. The clini- tapers and as long as the instruments are used in sequence,
cal and mechanical properties of these NiTi instruments dentine will be selectively removed in a coronal-to-apical
have been compared with those of stainless steel instru- direction.
ments; these include the efficacy of canal preparation,
cleanliness of the canals after preparation, the shaping As a general rule, most systems consist of a series of
ability of the instruments and fracture properties of the shorter, more tapered instruments that are used for coronal
instruments.32,47–56 There is a general acceptance that rotary flaring followed by another series of longer, more flexible
NiTi instruments produce well-shaped canals in an effi- instruments meant to be used more apically. The final
cient manner with the creation of relatively fewer iatro- taper of the preparation is usually decided by the operator
genic problems than stainless steel files. However, direct depending on the dimensions and the degree of curvature
comparison between stainless steel and NiTi instruments of the original canal. Using micro-computed tomography
is difficult unless the instrument design is identical.57 it has been possible to see the changes to the internal
anatomy of the root canal as a sequence of instruments is
In addition, most testing procedures were carried out used during preparation and it is interesting to see that the
in vitro, frequently in plastic blocks with simulated files rarely contact the entire wall of the root canal and
canals, and long-term clinical evidence of the superiority actually remove relatively little dentine, especially in the
of one instrument type is unproven. Since NiTi is more
flexible than stainless steel, instruments can be manufac-
tured with greater tapers whilst retaining flexibility. A
canal of pre-determined, desired taper can be created using
the corresponding tapered instrument instead of relying
on a series of standardized lesser tapered files. This also
decreases the risk of iatrogenic problems during prepara-
tion as generally fewer instruments are required to prepare
the canal.

Benefits of NiTi instrumentation

1. Files are superflexible and able to work round
significant curvatures.

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Preparation of the root canal system Chapter | 7 |

Crown-down root canal preparation CONTROVERSIES IN ROOT CANAL
CLEANING AND SHAPING
Access:
Create an unimpeded pathway to the pulp space and the canal A number of issues remain unresolved concerning endo-
1 orifices using diamond or tungsten carbide fissure, round burs, dontic treatment procedures.
a non-cutting tip bur and/or specialized ultrasonic tips.
Where should the preparation end?
Coronal flaring:
Use Gates-Glidden burs or NiTi instruments designed to open This question was addressed succinctly in a short paper
2 the canal orifice and enlarge the coronal aspect of the root entitled ‘Where shall the root filling end?’.13 Current treat-
canal. Irrigate with sodium hypochlorite between each ment protocols used by many clinicians are frequently
instrument change and throughout canal preparation. based on opinion rather than fact, for example, there is
little or no evidence to support the belief that the presence
3 Working length: of sealer ‘puffs’ on a postoperative radiograph indicates
Establish working length using apex locator and/or radiograph. better quality of treatment. In fact, there is considerable
evidence for maintaining all instrumentation procedures
Glide path/pilot channel: and filling material within the root canal system.4,60,61,62,63,64
4 Use hand instruments and a filing or Balance-force action to There should be differentiation between vital teeth, those
with infected canals, and retreatment cases, when deciding
create a pathway to working length. where to terminate the instrumentation and filling.41
Based on biological principles and experimental evidence,
Apical preparation and finishing: instrumentation should terminate 2–3 mm from the radi-
ographic apex in vital cases. In cases where canals are
5 Canal preparation continues with hand or rotary NiTi infected, the position should be 0–2 mm from the apex,
instruments in sequence, to working length, until desired taper while in retreatment cases the ideal termination should be
at the apical foramen. However, irrespective of the preop-
and apical size achieved. erative condition of the canal system, it is recommended
that all instrumentation and filling procedures should not
Figure 7.8  A composite protocol for use with a ‘coronal-to- extend beyond the apical foramen.
apical’ root canal preparation concept.
Discussion on the ideal termination of the preparation
apical region.39,59 An example of a composite protocol for and filling procedures presupposes the existence of the
use with a ‘coronal-to-apical’ preparation concept is ‘ideal’ root apex as described by Kuttler.14 However, it has
shown in Figure 7.8. been found that this ideal apical terminus exists in less
than half of teeth.65 Instead, a number of apical anatomi-
Calcified canals cal configurations have been described (Fig. 7.9). No
apical constriction may be present especially in the pres-
The same basic principles apply to preparation of calcified ence of any resorptive process.66 Consequently, it is often
canals. However, the operator should proceed with very difficult or even impossible to locate either the apical
caution, irrigate frequently to keep dentine chips in sus- constriction or the apical foramen.
pension, flush them away and check for patency with a
small file between instruments. Ultrasound can be used to When should the preparation end?
loosen debris in the sclerosed canal orifice. The tip of
the ultrasonic instrument can be used either to activate the Removal of all microorganisms, tissue and debris is the
solution in the chamber or it can be placed into the aim of root canal treatment and hence this can be taken
calcified orifice in an attempt to provide some initial to be the end point of preparation. However, determining
patency. A small K-file, or a specific file designed for canal when this has been achieved remains difficult clinically.22
penetration (e.g. Pathfinder, SybronEndo or C-file, Dent- Historically, instrumentation procedures have taken little
sply Maillefer), can be used to begin canal penetration. At account of canal anatomy, such as fins, webs, anastomoses
this point, a small NiTi rotary instrument designed for or apical ramifications. Outdated standardized prepara-
coronal flaring can be used to taper the orifice and remove tion techniques in which the presence of white dentine
any constriction. The clinician can return to a small ultra- chips was used as a sign of canal cleanliness have been
sonic tip to penetrate further into the canal. Gates-Glidden shown to be unreliable.67
burs will not be beneficial as they have a non-cutting tip.
This procedure will take time and patience, and the temp-
tation to try to drill a canal into the root should be resisted
as this invariably leads to deviation and potential root
perforation.

105

Harty’s endodontics in clinical practice

four sizes larger than the initial apical file at working
length, then rotating the largest apical file again after final
irrigation and drying. Apical clearing is recommended
in canals which have been prepared with an apical
stop. However, apical clearing in teeth without an apical
stop would increase the chances of overpreparation and
overfilling.

Preparation should be carried out to produce sufficient
space for irrigants to be effective. This was achieved, his-
torically, by using files with a greater tip size. However,
modern NiTi instruments provide space by creating larger
tapers for a minimal apical size.

Figure 7.9  Five major apical morphological forms. Should apical patency filing
be performed?

‘Apical patency’ is described as the placement of small
files to and through the apical constriction during
preparation.36,73 The aim is to allow for creation of a prepa-
ration and filling extending fully to the periodontal liga-
ment. Evidence to support this concept is unavailable. It
is, however, important to make sure that the canal does
not become blocked apically with infected dentine chips
during preparation and, therefore, there is merit in reca-
pitulating with a small instrument to keep the canal
patent. Inoculating infected material beyond the apical
constriction could result in postoperative discomfort or
flare-ups.

Due to the complexities of canal anatomy, the emphasis Should treatment be completed in
has shifted to chemomechanical preparation of the root one or multiple visits?
canal system.22,68,69 Removal of the smear layer also
improves disinfection.22 The importance of an intracanal One-visit root canal treatment has assumed a position of
dressing such as calcium hydroxide has been demon- controversy for many reasons. Clinical studies have
strated as canals can be more reliably rendered bacteria- addressed the advantages and disadvantages.
free.69 An unanswered question is how long, ideally,
should the irrigant be left in the canal system to achieve The advantages of one-visit treatment are:
‘adequate’ disinfection of the canal? This concern has
fuelled a further controversy; namely can root canal • reduced number of appointments
treatment be completed in one visit or should it be carried • no risk of intra-appointment microbial
out in multiple visits?
recontamination
What about the apical size
of preparation? • use of canal space for immediate post-retention

There is controversy concerning the ideal diameter of the restorations.
apical preparation. Some authorities consider that dentine
should be removed apically to eliminate contamination The disadvantages are:
whilst others consider that a narrow preparation, com-
bined with a suitable flare to allow irrigant penetration • longer appointments may cause patient fatigue
is satisfactory.70,71,72 • inability to control exudates may prevent completion

Increasing the apical size of the preparation to allow of the procedure.
better debridement, irrigant penetration and making a
defined stop were discussed as the ‘apical clearing’ Whether completed in one or multiple visits, studies con-
concept.73 This involved sequentially rotating files, two to cerning postoperative pain74–82 as well as effective healing
rates82,83,84 have shown that outcomes are similar. However,
many of these studies have used older preparation tech-
niques, which have the potential for less effective canal
cleaning. There are some indications and contraindica-
tions that should be considered when contemplating
one-visit treatment.

106

Preparation of the root canal system Chapter | 7 |

The indications include: LEARNING OUTCOMES

• uncomplicated teeth with vital pulps Following completion of this chapter, the reader should
• fractured teeth where aesthetics is important and be able to:

extensive restoration is indicated immediately • appreciate the steps to undertake when gaining

• patient unable to return for additional appointments access to the root canals
• patient requires antibiotic prophylaxis or sedation.
• explain the methods of determining working length
Contraindications include: • understand the role of root canal irrigants
• explain the concepts of root canal preparation
• patients with acute apical periodontitis
• teeth with severe anatomical anomalies including the crown-down approach and use of NiTi
• molars with necrotic pulps and periapical rotary instruments

radiolucencies • tackle calcified canals
• discuss controversies associated with root canal
• root canal retreatment.62
preparation.
One-visit treatment does not sit easily with evidence on
effective and predictable canal disinfection in infected
cases22,68 so cases should be selected carefully.

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321–333. Journal 2000;33:219–226.

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8Chapter  

Intracanal medication

D. Ørstavik

CHAPTER CONTENTS 111 Pain of endodontic origin 119
112 Exudation and bleeding 120
Summary 112 Root resorption 120
Introduction 112 Tissue distribution of medicaments 120
History 112 120
Rationale and overview of applications 113 Diffusion and solubility 120
113 Penetration of dentine 121
Asepsis, antisepsis and disinfection 113 Effect of the smear layer
Secondary functions of medicaments 114 Tissue toxicity and biological 121
Microbiology of endodontic infections 114 considerations 121
Primary root canal infection 114 Suggested clinical procedures 121
Secondary root canal infection 114 Mechanical reduction of bacteria 122
Persistent root canal infection 114 Primary root canal infection
Extraradicular infection 115 Secondary and persistent root canal 122
Antimicrobial agents infections 122
Antibiotics 116 Temporary filling 123
Disinfectants Learning outcomes 123
Resistance of oral microbes to 116 References
medicaments 116
Concept of predictable disinfection in 117 SUMMARY
endodontics 117
Mechanical instrumentation 117 Endodontics may be considered the treatment or preven-
Antibacterial effect of irrigation tion of apical periodontitis, which translates into the
Effect of antibacterial dressing 117 elimination or control of root canal infection. Over the
Follow-up studies years, medicaments used for this purpose have changed
Adequate disinfection in single-visit 118 from strong and toxic chemicals to more selective and
endodontics 118 effective, yet tissue tolerant agents. Antibiotics have found
From controlled to predictable 119 limited use in root canal treatment, but may be useful in
disinfection the treatment of immature teeth. The bacterial flora of
Treatment of non-infected teeth different types of root canal infections is variable, and so
Induction of hard tissue formation is their susceptibility to conventional medicaments; this
has led to alternatives, or combinations of, medicaments

© 2009 Elsevier Ltd, Inc, BV 111
DOI: 10.1016/B978-0-7020-3156-4.00011-5

Harty’s endodontics in clinical practice

that show promise in managing persistent and recurrent to this category and remained popular for decades. For-
infections. A better understanding of factors influencing mulations with sulphonamides10 and later antibiotics
the local availability and potency of medicaments has were tried as intracanal medicaments; Grossman’s polyan-
helped facilitate improved means of application. Medica- tibiotic paste11 and Ledermix®12 (Haupt Pharma GmbH,
ments are also used with the intention of controlling pain Wolfratshausen, Germany) are examples of these types
and supporting the tissue healing process; however, they of dressings.
are always secondary to their main, antimicrobial func-
tion. While irrigation with sodium hypochlorite and The reduction of pain through pharmacological control
dressing with calcium hydroxide remain standard treat- of the inflammatory process has also been attempted in
ment protocol, chlorhexidine and iodine compounds are endodontics by the application of eugenol,13 and later
emerging as alternatives or supplements to these classical corticosteroids and other anti-inflammatory drugs,14 as
medicaments. dressings. The focus on the possible adverse toxic effects
of medicaments15,16 led to a more systematic selection
INTRODUCTION from the list of disinfectants available for use. Phenol
derivatives and iodine formulations gained popularity as
Endodontic success or failure is related to the absence or medicaments in endodontics; sodium hypochlorite was
presence of signs and symptoms of apical periodontitis.1 confirmed as a suitable irrigant.
Root canal treatment can, therefore, be considered the
prevention or cure of this disease.2 Apical periodontitis Calcium hydroxide, while advocated since 1930,17 has
includes periapical granuloma and radicular cyst as well gained popularity in endodontics in the last three decades.
as acute manifestations of inflammation. The aetiology of Calcium hydroxide has had success in a variety of clinical
apical periodontitis is, primarily, a bacterial infection of situations including pulpotomy, root resorption, root-end
the root canal system;3,4,5,6 consequently, the technical and closure, control of exudation and root canal infection.18
pharmacological aspects of prevention and treatment are
mainly aimed at controlling infection. Thus, preventive RATIONALE AND OVERVIEW
endodontics entails treatment of a tooth without previous OF APPLICATIONS
signs of apical periodontitis by aseptic pulp extirpation.
Curative endodontics is the chemomechanical elimina- The primary function of endodontic medicaments is to
tion of infection in the root canal system of a tooth with provide antimicrobial activity. In a few instances, other,
signs of apical periodontitis. Both procedures are com- secondary functions are desirable (Table 8.1). The ration-
pleted by the placement of a bacteria-tight filling to ale for applying intracanal medicaments in various clinical
prevent new infection. situations has been reviewed.19

The use of intracanal medicaments is an adjunct to the Asepsis, antisepsis and disinfection
prevention, and essential for, the treatment of apical peri-
odontitis. The primary function is to prevent root canal Asepsis is the assurance that no pathogenic microorgan-
infection where none is present, and/or to inactivate bac- isms are present in the field of operation. It entails the use,
teria already infecting the root canal space. Intracanal not only of clean, but also of sterile or disinfected instru-
medicaments would include any agent with intended ments and utensils, liquids, etc. In the course of treating
pharmacological action introduced into the root canal teeth with no signs of root canal infection, maintaining
space. Antibacterial and other active compounds currently asepsis is the primary means of preserving a bacteria-free
used as irrigating solutions during instrumentation rightly
belong in this category. Intracanal dressings more con- Table 8.1  Functions of intracanal medicaments
cisely describe medicaments left in the root canal space to
exert their effects over a longer time period. Primary function: antimicrobial activity

HISTORY Antisepsis

The role of microorganisms in pulpless teeth was recog- Disinfection
nized more than a century ago,7 and strong, caustic anti-
septics were popular as intracanal medicaments at the Secondary functions
turn of the twentieth century. Formaldehyde-containing
materials, e.g. formocresol,8 and iodoform pastes9 belong Hard tissue formation

Pain control

Exudation control

Resorption control

112

Intracanal medication Chapter | 8 |

canal. Antisepsis is the endeavour to prevent or arrest the Control of inflammatory root resorption
growth of microorganisms on living tissue. In vital pulp
extirpation, antiseptic measures are necessary to prevent Trauma to the teeth may result in various forms of resorp-
infection in case there is a breach in the chain of asepsis. tive damage; inflammatory root resorption being the most
Irrigating solutions and interappointment dressings need aggressive and destructive. Inflammatory root resorption
to be antibacterial in action to prevent any microorgan- is normally associated with infection of the root canal
isms, which may contaminate the root canal system, from combined with physical damage to the cementum; again,
multiplying and establishing themselves. a primary function of treatment is to eliminate infection
in the root canal system. Secondarily, medicaments may
Disinfection is the elimination of pathogenic microor- influence the resorption process itself.
ganisms, usually by chemical or physical means. Disinfec-
tion by antiseptic agents is what is attempted in the Induction of hard tissue formation
treatment of infected teeth. Sterilization, on the other
hand, implies the use of irradiation or heat to reach a state It is often considered desirable to allow hard tissue
of complete freedom from live microbes and cannot be to form, to continue apical root development, to close a
applied to root canal treatment. Disinfection entails wide foramen, or to create a mechanical barrier at a frac-
mechanical removal of tissue and debris containing ture line. Although the mechanism of action is largely
microbes, irrigation and dressing with antiseptic agents; unknown, dressings are available with claims of inducing
also, surgical removal of an infected apex contributes to hard tissue formation (see later).
the antiseptic efforts of treatment. The presence of radio-
logically discernible apical periodontitis is a sign that the MICROBIOLOGY OF
root canal system is infected.6 This state of pre-existing ENDODONTIC INFECTIONS
infection also has a negative influence on prognosis.20 In
these cases, bacterial reduction, and effective disinfection, Following pulpal necrosis, sooner or later, the entire root
of the root canal system is a prerequisite for successful canal system will become infected. A long-standing infec-
treatment. tion will have bacteria not only in the main, but also in
accessory canals, and for a distance into the dentinal
Secondary functions of tubules.21 If apical periodontitis has progressed to the
medicaments point where resorption of the cementum occurs, bacteria
may be found throughout the length of the dentinal
Root canal treatment is sometimes associated with clinical tubules.22
features only indirectly related to infection of the root
canal system. Pain during and after treatment may occur, The source of the infecting bacteria may be dental caries,
and the associated tissue reactions include exudation, salivary contamination through fractures, cracks or leaking
transudation, swelling and resorption. Each of these phe- fillings, or contamination of the pulp space during dental,
nomena, either singularly or in conjunction with infec- including endodontic, treatment. The microbial flora
tion, has been a target for attempts at medication during, will vary with the clinical condition, and endodontic
between and after treatment sessions. infection may be one of three types: primary, secondary,
or persistent infection. Infected canals typically contain
Pain control 2–10 different cultivable species; the total number of
microorganism ranging from 103 to 107.23 The exact
Pain is mostly associated with infection, and the primary number of microorganisms is not known as they vary
means of pain control in endodontic treatment is infec- from tooth to tooth, and because of a lack of established
tion control. Pharmacological agents that result in pain quantitative methods of determination.
reduction through a decrease in the tissue responses
to inflammation may have a role in further alleviating Primary root canal infection
clinical pain from both infectious and aseptic pulpal-
periodontal inflammation. With increasing time and depth, a primary root canal
infection, i.e. one in existence prior to any intervention,
Control of exudation or bleeding the microbial flora changes from a predominantly faculta-
tive, Gram-positive flora to an almost completely anaero-
Persistent exudation in the root canal may occur, despite bic and mainly Gram-negative set of microorganisms.24
apparently successful technical treatment. Exudation Strains belonging to the genera Tannerella, Dialister, Fuso-
reflects inflammation, however, and residual infection bacterium, Prevotella, Porphyromonas, Peptostreptococcus,
should be suspected. Therefore, treatment is aimed at and Treponema are frequently found in teeth with apical
dealing with potential infection as well as drying, or coag- periodontitis.25 Other microorganisms not found by
ulating the exudating site.

113

Harty’s endodontics in clinical practice

normal culturing techniques may be present. Facultative There are three main concerns about the local use of anti-
streptococci are also common. These same types of micro- biotics in the root canal:
organisms are found in exacerbations or periapical
abscesses.26 In addition, infections involving other micro- • Sensitization. Topical application of an antibiotic
organisms, e.g. streptococci, Eubacterium, Veillonella27 and
Actinomyces/Arachnia28 frequently occur.29 increases the risk of the patient becoming allergic to
it.38 Life-threatening anaphylactic reactions may
In most infected teeth, several species are recovered occur from the administration of antibiotics to
from the root canals.25 Many of the dominating species, sensitized individuals. Induced allergy to an
e.g. Fusobacterium, Prevotella and Porphyromonas, may antibiotic may limit the options for treatment of
require the presence of some other synergistic species for more severe infections, which would, otherwise,
their survival and propagation. It may be noteworthy in be curable with that particular drug.
this context that these same species have not been found
in dentinal tubules, which when infected harbour less • Development of bacterial drug resistance. The drug
fastidious microorganisms, such as lactobacilli and
streptococci.30 kinetics of antibiotics applied in the root canal is not
well known.39 Conditions may become favourable
Secondary root canal infection for the development of antibiotic-resistant microbial
strains, causing an infection, which in turn is more
The microbial flora in retreatment cases, a secondary difficult to treat.40 Moreover, beyond the scope of
root canal infection, occurring during or after treatment, treatment of the individual patient, the widespread
has been shown to differ significantly from microorgan- use of antibiotics causes a general increase in
ism in primary apical periodontitis. Typically, retreatment pathogenic and indigenous microorganisms that
cases show enterococci, streptococci, and anaerobic cocci are resistant to a variety of antibiotics.41
in high frequencies;31,32 enteric rods and Candida are
also relatively more frequent than in primary apical • Limited spectrum. No one antibiotic is efficacious
periodontitis.33,34,35,36
against all endodontic microorganisms.42 Given
that most endodontic infections are caused by a
combination of species, the chance of one antibiotic
achieving effective bacterial inhibition or elimination
is small.

Persistent root canal infection Sulpha preparations

A similar flora is found in persistent root canal infection. Sulphathiazole as part of a dressing was advocated in the
Here, a pre-existing infection has withstood the antimicro- 1950s and 1960s.10 While irrefutably antibacterial, varia-
bial effects of treatment, and a selection of species sur- ble results were shown in comparative clinical studies.43,44
vived, having adapted to the new environment in the root Moreover, although effective against many Gram-negative
canal system. In these cases, dependent on the healing and Gram-positive microorganisms, sulpha drugs are inef-
response after non-surgical root canal treatment, follow- fective against enterococci and Pseudomonas aeruginosa.
up surgery may be necessary.
Penicillin
Extraradicular infection
Grossman’s polyantibiotic paste contained penicillin as
Some organisms, notably Actinomyces and Propionibacte- an important ingredient. Beta-lactamase produced by
rium species, but also others, are known to survive and several microbial species found in the root canal makes
propagate in soft tissues and also at the periapex as extra- them resistant to penicillin. This includes P. aeruginosa and
radicular infection.37 These infections may be one of the several anaerobic Gram-negative rods.
causes of what has been termed ‘treatment-resistant cases’.
Intracanal medicaments are of little use in extraradicular Metronidazole
infections; surgery is indicated.
Metronidazole has good effect against several Gram-
ANTIMICROBIAL AGENTS negative anaerobic microorganisms.45 It has been sug-
gested for use in irrigating solutions,46 as an intracanal
Antibiotics dressing47 and for parenteral applications in combination
with other antibiotics, particularly penicillin.37 It has
The successful use of various antibiotics, both systemically limited activity against enterococci.48
and topically, in other areas of medicine made them likely
candidates for antibacterial action in the root canal system. Tetracycline

Tetracycline shows affinity for hard tissues and may be
retained on tooth surfaces.49 It is used locally in periodon-

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Intracanal medication Chapter | 8 |

tics with good clinical and bacteriological results,50 and Table 8.2  Root canal disinfectants
the derivative, doxycycline, forms the antibiotic ingredient
in Ledermix.51 However, its antimicrobial spectrum is Halogens
quite narrow, and it may be ineffective against several
oral and endodontic pathogens. The fact that resistance to Chlorine
tetracycline occurs through the formation of transferable Irrigating solution: sodium hypochlorite 0.5% in 1%
R factors also suggests caution in its application. sodium bicarbonate as Dakin’s solution; or 0.5–5.25% in
aqueous solution.
MTAD (BioPure MTAD, Dentsply Tulsa Dental, Tulsa,
OK, USA) is an irrigant containing a mixture of tetracy- Iodine
cline, an acid and a detergent. The tetracycline component, Irrigating solution and short-term dressing: 2% iodine in
doxycycline is retained in the dentine after application. 5% potassium iodide aqueous solution; iodophors.
Apart from the criticism that doxycyline is bacteriostatic Field disinfection: 5% iodine in tincture of alcohol.
and not bacteriocidal, another disadvantage is the poten-
tial iatrogenic staining of teeth when sodium hypochlorite Chlorhexidine
reacts with MTAD with alternating usage.52
Chlorhexidine gluconate
Clindamycin Field disinfection and irrigating solution: 0.12–2.0%
aqueous solution.
One study has reported on the use of clindamycin as an Irrigation and dressing: 1–5% gel.
inter-appointment dressing, but only limited antibacterial
efficacy could be demonstrated.53 An experimental deliv- Calcium hydroxide
ery device for clindamycin in the root canal has been
reported,54 and in vitro experiments suggest that clindamy- Dressing: aqueous, viscous or oily suspension/paste with
cin may penetrate deep into dentinal tubules.55 varying amounts of salts added. Other antibacterial
agents (iodine, chlorophenols, chlorhexidine) may be
Antibiotic combinations added.

While the traditional polyantibiotic pastes11 have been Aldehydes
largely discontinued, a new combination of three or four
antibiotic compounds has received interest,56,57 Successful Formocresol
revascularization, with hard tissue formation in the pulp Dressing: 19% formaldehyde, 35% cresol, 46% water
and complete root formation, has been observed in imma- and glycerine.
ture, permanent teeth with pulp necrosis and apical peri-
odontitis after application of this mixture.58,59,60 dures in primary teeth,61 but its toxic and mutagenic prop-
erties are of concern. It is no longer favoured and it has
Disinfectants been suggested that its use should be discontinued.62

While antibiotics work through biological interference Paraformaldehyde is the polymeric form of formalde-
with essential biochemical processes, disinfectants (Table hyde, best known for its inclusion in some root canal
8.2) are a group of chemicals that act by direct toxicity to filling materials, e.g. N2 and Endométhasone. It slowly
the microbes. Their action is thus quicker and more decomposes to release its monomer, formaldehyde; its
general, and they usually have a broader antibacterial toxic, allergenic, and genotoxic properties are as for
spectrum than antibiotics. On the other hand, they may formaldehyde.
be more toxic to host tissues, and their action is generally
more dose dependent. Halogens

Aldehydes Halogens include chlorine and iodine, which are both
used in various formulations in endodontics. They are
Formaldehyde, paraformaldehyde and glutaraldehyde potent oxidizing agents with rapid bactericidal effects.
have been widely used in dentistry including endodontics. Chlorine is released from sodium hypochlorite and from
They are water-soluble, protein-denaturing agents and are chloramine. The latter releases active chlorine at a lower
among the most potent disinfectants. Aldehydes have rate, and has been used for short-term dressing of the root
applications in the disinfection of surfaces and medical canal. Sodium hypochlorite is currently the irrigating solu-
equipment that cannot be sterilized, but they are quite tion of choice. It is used clinically in concentrations from
toxic and allergenic, and some may be carcinogenic. 0.5–5.25%. Both in vitro and in vivo bacteriological
studies support its application. Necrotic tissue and debris
Formocresol is an aqueous solution containing cresol, are dissolved by sodium hypochlorite,63 a property
formaldehyde, and glycerine, used for pulpotomy proce-

115

Harty’s endodontics in clinical practice

exploited in biomechanical cleansing of root canals.64,65 Its of a paste, it physically restricts bacterial colonization of
toxicity is low; however, its bleaching properties can be a the canal space. Calcium hydroxide is applied as a thick,
nuisance if spilled onto a patient’s clothes, its smell is creamy suspension in sterile water, saline, and a variety of
objectionable to some patients, and it may cause severe other, viscous or oily vehicles.82,83
symptoms if accidentally injected beyond the apex.66
Calcium hydroxide with
Iodine is used mainly as iodine potassium iodide and antimicrobial additives
in iodophors, which are organic iodine-containing com-
pounds that release iodine over time. Iodine is also a very Complete disinfection by calcium hydroxide cannot be
potent antibacterial agent of low toxicity, but may stain expected in all cases.84 Moreover, in root filled teeth the
clothing if spilled. As iodoform (triiodomethane), it was flora may contain microorganisms relatively resistant to
used in a paste formulation as a permanent root canal its action. Numerous attempts have been made to mix
filling.9 Iodine compounds are used as an irrigating solu- calcium hydroxide with other aqueous and non-aqueous
tion and short-term dressing as 2% solution of iodine in disinfectants.85 Parachlorophenol, camphorated parachlo-
4% aqueous potassium iodide. It has also been added to rophenol,82 metacresol,86 and iodoform87 have all been
gutta-percha points for root canal filling.67,68 Some patients added to calcium hydroxide suspensions. Combinations
may be allergic to iodine compounds, and their use in of calcium hydroxide with chlorhexidine have also been
these patients is contraindicated. tested in vitro.88,89,90

Phenol derivatives RESISTANCE OF ORAL MICROBES
TO MEDICAMENTS
Phenol itself is no longer used in endodontics because of
its high toxicity, but the derivative paramonochlorophe- In some cases, bacteria persist and produce symptoms of
nol has been a very popular component of interappoint- inflammation despite apparently optimal cleansing and
ment dressings. It has been used both in aqueous solution69 disinfection procedures.91 They may either be inaccessible
and in combination with camphor (as camphorated to the cleaning instruments or to the medicaments, or they
monochlorophenol); it was long recognized as the dress- may be resistant to the medicaments used.57 Special inter-
ing of choice for infected teeth. Thymol, similarly, enjoyed est has recently focussed on streptococci, enterococci and
widespread popularity, but is less antibacterial than the yeasts in persistent infections; these have been shown to
chlorophenol compounds. be relatively resistant to calcium hydroxide84,90,92,93 and
occur in high frequency in retreatment cases.27,33,94 Organic
Eugenol is frequently used as a dressing for temporary and inorganic debris in the root canal system will also
control of pain after vital pulp exposure.70 It has a well- affect and limit the antimicrobial activity of irrigating
documented, but limited, antimicrobial effect and is solutions and interappointment dressings.95
applied primarily for its pain-relieving effect.71
CONCEPT OF PREDICTABLE
Chlorhexidine DISINFECTION IN ENDODONTICS

Chlorhexidine has been widely used in periodontology.72 Given the infectious nature of apical periodontitis,
Its substantivity (persistence in the area of interest), its rel- any clinical procedure should be based on the ability
atively broad spectrum of activity, and its low toxicity may of each step to prevent contamination and to eliminate
make it well suited for irrigation and as dressings in endo- infection. A standard procedure should, furthermore, be
dontics. Results of in vitro studies pointed to the suitability based on a worst-case scenario, which would be the
of chlorhexidine in endodontics73–77 and some in vivo bac- infected root canal with associated chronic apical perio-
teriological data are emerging.36,78 Effective concentrations dontitis. Individual treatment steps have been assessed for
are in the 0.2–2% range. Innovative attempts to utilize the their efficacy in eliminating bacteria from infected root
disinfecting properties of chlorhexidine include its inclu- canals23,91,96,97,98,99,100 (Fig. 8.1).
sion in gutta-percha points for root canal filling.68
Mechanical instrumentation
Calcium hydroxide
Even in the absence of an antibacterial irrigating solution
Calcium hydroxide has reached a unique position as and subsequent dressing, there is still a dramatic decrease
a dressing in endodontics.79 After its successful clinical
application for a variety of indications,18,80 multiple
biological functions have been ascribed to calcium
hydroxide.81 Its primary function is probably antibacterial
in most clinical situations, with the added benefits of
cauterizing activity and high pH; also in the consistency

116

Intracanal medication Chapter | 8 |

Vital Infected pulp; Mechanical Irrigation and Filled and Complete

pulp apical periodontitis instrumentation dressing healing healing

Root canal infection/disinfection

Time

Figure 8.1  Apical periodontitis develops when the root canal system becomes infected. Treatment entails the reduction of
bacteria by mechanical instrumentation and antibacterial irrigation. The antibacterial dressing, if effective, eliminates infection.
Total disinfection allows for complete healing of the tooth with apical periodontitis following root canal filling.

in bacterial numbers in a root canal from mechanical in fully instrumented canals between visits.84,102,106,107
cleansing alone.23,101,102,103 However, in the majority of Calcium hydroxide has been found to be more effective
cases, bacteria, which are left in the canal, have the poten- than camphorated monochlorophenol in comparative
tial to multiply between appointments23 and after root experiments,84 but the added effect on the reduction from
canal filling.94 instrumentation and irrigation is variable.79 Attempts at
potentiating the antimicrobial effect of calcium hydroxide
Antibacterial effect of irrigation by the addition of other medicaments in the dressing has
met with some,108 but limited success.109
The addition of sodium hypochlorite as an antibacterial
irrigating solution increases the number of bacteria-free Follow-up studies
canals substantially.96 The use of 5% rather than 0.5%
sodium hypochlorite appears slightly more effective, and Teeth treated as described above have been followed for
the reduction in the number of infected teeth has been periods of up to 7 years, a successful outcome (definite
shown to be even greater, when ethylenediaminetetraace- signs of healing of apical periodontitis) shown in more
tic acid (EDTA) was alternated with sodium hypochlo- than 90% of the cases.91 While success rates from different
rite,96,97 and when ultrasonic instrumentation of the canal studies may be difficult to compare, it would appear that
was performed.100 Increasing the temperature of sodium these clinical results are better than most, if not all, previ-
hypochlorite also increases its efficacy.104 Chlorhexidine ous reports.110
(applied as a 2% gel) has been shown to be similarly or
even more effective than sodium hypochlorite in reducing Adequate disinfection in
intracanal bacteria during instrumentation.105 single-visit endodontics

Effect of antibacterial dressing Single-visit (‘one-step’) endodontics implies shaping,
cleaning and disinfection of the root canal in the course
The number of bacteria-free canals may be further of one treatment session. This is followed by permanent
increased when a dressing of calcium hydroxide is placed

117

Harty’s endodontics in clinical practice

root canal filling at the same appointment. Immediate 100
root canal filling of teeth that are not infected is not
controversial and, in principle, probably preferable to Percent bacteria-free canals 75
treatment in multiple appointments; if asepsis is main-
tained, there is no need for a disinfecting dressing 50
between appointments and the risk of leakage. The debat-
able issue is whether the time duration and the type of 25
medicament that can be applied during one appointment
endodontics will provide predictable disinfection and, 0 181 135 109 80
subsequently, healing of infected teeth with apical perio- 147 105 Post irrigation (average)
dontitis. It is highly desirable to achieve effective disinfec-
tion quickly, and data from clinical studies have shown Preoperative Post medication
that treatment in one visit may be as effective, and as
predictable, as procedures utilizing an interim dress- Figure 8.2  Percentage reduction in canals positive for
ing.111,112 However, some clinical follow-up studies suggest bacterial growth after instrumentation/irrigation and dressing
better treatment outcome after dressing-based disinfection of initially infected root canals. Numbers beneath bars refer
compared with single-visit procedures.113,114 Human and to the articles cited.
animal histological studies have also reported the pres-
ence of residual bacteria and inflammation in teeth treated
in one visit.115,116

From controlled to Figure 8.3  Inflammation-free extirpation wound of a mature
predictable disinfection central incisor (monkey) after two weeks of dressing with
calcium hydroxide.
Scientific data from clinical studies should be the basis
for a rational, evidence-based approach to treatment of serves any purpose in the treatment of teeth with non-
infected teeth.117Clinical experiments have documented infected pulps.
controlled disinfection by advanced bacteriological tech-
niques. When applied to clinical practice, adherence to Other principles of treatment may have the potential
the principles of mechanical instrumentation, irrigation for equal or better efficacy and success rates. However,
with sodium hypochlorite and EDTA, and dressing with the extensive literature with clinical and bacteriological
calcium hydroxide, would be expected to produce predict- controls, and clinical and radiological follow-ups makes
able disinfection (bacteria-free canals) in a very high the above guidelines a standard of reference. Alternative
percentage of cases (Fig. 8.2), and in turn, a very high rate methods and medicaments should be tested and
of clinical and radiological evidence of healing of apical compared similarly prior to receiving general clinical
periodontitis. Indeed, large series of follow-up studies acceptance.
using this treatment regimen for infected teeth have borne
out the high success rate.118 A need for routine chairside
bacteriological control of procedures is not implied in
clinical practice.

Treatment of non-infected teeth

None of the steps advocated for the treatment of the
infected tooth place in jeopardy the success of treatment
of a tooth with an initially non-infected pulp. Vital pulp
extirpation followed by instrumentation with sodium
hypochlorite and a dressing of calcium hydroxide give a
clean pulp wound with minimal or no inflammation (Fig.
8.3). Therefore, as a means of securing the absence of
microbes in these cases, the same treatment principles
should apply. One exception is when permanent root
canal filling is possible at the first appointment; then there
is no need for a period of canal dressing for the purpose
of disinfection. Also, it may be questioned whether EDTA

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Intracanal medication Chapter | 8 |

PAIN OF ENDODONTIC ORIGIN

Figure 8.4  Formation of a hard tissue barrier (B) at the Endodontic pain is mainly associated with both inflam-
apex of an immature central incisor (monkey). The pulp was mation and infection.124–129 The inflammatory responses
extirpated and a dressing of calcium hydroxide placed for to the trauma of pulp extirpation and instrumentation
three weeks. may elicit pain of lesser magnitude and duration than pain
following bacterial activity.29,130 The rationale behind pain
INDUCTION OF HARD control by interappointment dressings is thus, primarily,
TISSUE FORMATION to combat infection. This is reflected also in the finding
that interappointment pain is significantly more frequent
The process of creating a hard tissue barrier at an in infected, necrotic teeth than in vital cases.131,132 There
open apex or at a grossly over-instrumented apex is are strong psychological components to the clinical
termed root end closure or apexification.119,120 When expression of pain of endodontic origin.133,134 Clinical
calcium hydroxide is used in long-term treatment of trau- pain is further confounded by the concomitant presence
matized young permanent incisors and infection is con- of microbial and iatrogenic and other factors. The quanti-
trolled, a barrier of bone/cementum-like tissue at the apex fication of pain clinically is also very difficult to standard-
is formed with a high degree of predictability120,121 (Fig. ize for comparative purposes.
8.4). This barrier allows mechanical compression of the
root filling, and any toxic responses of the tissues to the The incidence of interappointment or post-treatment
filling materials are minimized by this intervening barrier. pain seems to be very much dependent on the criteria
While it may not be essential that calcium hydroxide be defining pain.135,136,137 As an operating definition, the inci-
used as a dressing for this purpose, its clinical application dence of patients requiring an extra, non-scheduled visit
is the most extensively documented. Similar principles following self-reported pain may have some merit. It
apply in the formation of a hard tissue barrier more coro- would not include the discomfort sometimes associated
nally, e.g. at the line of a horizontal root fracture or at a with, the practical necessities of the treatment itself (local
pulpotomy or pulp-capping wound surface.122 Mineral tri- anaesthetic injection, rubber dam clamp placement, sever-
oxide aggregate (MTA) is now the material of choice for ance and laceration of the pulp). By such criteria, no sig-
these purposes; it is a filling or sealant material rather than nificant advantage of one medicament over another has
a medicament, and thus falls outside the scope of this been reported.138,139,140,141
chapter123 but is covered elsewhere in this book (see
Chs 9 & 12). Due to the lack of precise knowledge of the source of
pain in individual cases, the introduction of medicaments
in dressings to alleviate inter- and post-treatment pain
has been by theoretical considerations, and by trial and
error, rather than by clinical research. Most interest has
focused on the use of corticosteroids in the interappoint-
ment dressing; particularly, the use of Ledermix contain-
ing triamcinolone, has been popular.12,51,142,143 It is
doubtful whether initial concerns about the systemic
effects of locally administered corticosteroids are justified;
there is no indication that harmful side-effects are associ-
ated with its use in dentistry, and the doses applied are
rather small compared with other medical indications.144
However, while concerns for side-effects may have been
exaggerated, the clinical benefits, if any, over calcium
hydroxide medication remain questionable.143 Non-
steroidal anti-inflammatory drugs have also been tested
clinically as intracanal dressings,14 but any clinical advan-
tages again remain obscure.

For the control of pain, little seems to be gained
either by the prophylactic addition to dressings or by the
routine prescription of parenteral drugs.137 It seems that
endodontic pain may be better dealt with on a case-
by-case approach, providing relief with pain control
medication and by treatment appropriate for the indi-
vidual patient.

119

Harty’s endodontics in clinical practice

EXUDATION AND BLEEDING weeks),149 longer-term placement of calcium hydroxide
remains a clinically proven procedure in the treatment of
Purulent exudate is a clear sign of infection. A serous resorption.150
exudate (‘the weeping canal’) is a more elusive clinical
condition. It may also be associated with a relatively large It has been suggested that because Ledermix inhibits the
apical foramen or an over-instrumented, patent foramen. spread of dentinoclasts,151 it may provide added benefits
Both conditions are usually controlled by instrumentation in the control of inflammatory root resorption,152,153 par-
and dressing with calcium hydroxide. The application for ticularly when mixed with calcium hydroxide.39 More
a few minutes of dry calcium hydroxide packed against the experimental is the use of calcitonin, a hormone that
exuding surface may succeed in desiccating or necrotizing inhibits osteoclastic bone resorption, in canal dressings
the site to the point where seepage is controlled and treat- for inflammatory root resorption.154
ment may continue. However, an interim dressing with
calcium hydroxide may be necessary to control the exuda- TISSUE DISTRIBUTION OF
tion more effectively. MEDICAMENTS

To the extent that exudation is associated with inflam- There is limited knowledge of the actual distribution,
mation, and it may be reduced by local corticosteroids, in hard and soft tissues, of medicaments applied to
it would be rational in these cases to include steroid- the root canal.155,156,157 Several barriers limit the penetra-
containing dressings.142 Given the limited nature of this tion of chemical agents from the pulp canal space through
problem, clinical studies are hard to design and carry out, tooth structures and into the periapical tissues.92,158 There
and data are lacking to support this suggested mode of is also limited knowledge on the localization of microor-
treatment. ganisms, inflamed tissues and cells targeted by the
medicaments.159,160
Bleeding from the canal is usually easily controlled by
simple occlusion of the bleeding site with paper points, Diffusion and solubility
dry or moistened with 3% hydrogen peroxide. Calcium
hydroxide packed onto the bleeding site is also effective The ability of a medicament to dissolve and diffuse in the
in stopping bleeding within a few minutes. predominantly aqueous periapical environment may be
essential for its action. Lipid soluble substances may have
ROOT RESORPTION difficulty reaching targets at a distance in the tissues.
Amphipathic drugs may have particular benefits; it may
Root resorption is a complication of root canal infection not be coincidental that aldehydes and phenol derivatives
and trauma, in some instances with deleterious conse- have had clinical success.161 Thus, aqueous solutions of
quences to the tooth.145 The external apical root resorption paramonochlorophenol may penetrate further and have
associated with chronic apical periodontitis is self-limiting greater antimicrobial activity than the more concentrated
and stops when the root canal infection is adequately lipid solute.25 The low but significant solubility in water
controlled. It is likely that this resorption occurs to elimi- of calcium hydroxide has the dual advantage of limiting
nate necrotic and/or infected cementum and dentine at its toxic effects while the depot of the compound in sus-
the apex. pension at the same time provides continuous release of
the agent.
Traumatic tooth injuries, particularly luxations and
avulsions followed by replantation, frequently lead to Penetration of dentine
resorptive processes. Surface resorption is self-limiting and
followed by repair of cemental damage induced by the Studies in vivo have found the raised pH effect of calcium
trauma. Ankylosis or replacement resorption, however, hydroxide to pervade the width of dentine,157 but to
may be progressive in nature. Inflammatory resorption of decrease rapidly in the tissues beyond. However, precise
the root surface occurs in response to a necrotic and measurements of dentinal pH following application of
infected root canal system, and may be extremely rapid calcium hydroxide in the root canal ex vivo show that the
causing tooth loss in months if left untreated.146 Root pH in apical dentine is only moderately elevated.162 The
canal treatment is essential when inflammatory root application of calcium hydroxide on a dentine surface in
resorption is evident or imminent, and calcium hydroxide turn significantly reduces its permeability.163 Nevertheless,
is currently the medicament of choice for this purpose.147,148 calcium hydroxide is slower than many other medica-
Prolonged use of calcium hydroxide with multiple changes ments in killing bacteria in experimentally infected
of the dressing may lead to necrosis of cells trying to rec- dentinal tubules.92 Similarly, the active ingredients in
olonize the cementum surface. While this finding may Ledermix show a gradient in dentine decreasing from the
suggest that the duration of treatment with calcium site of application to the cementum surface.39 Eugenol, a
hydroxide in these cases should be kept short (1–2

120

Intracanal medication Chapter | 8 |

constituent in several root canal sealer formulations, CT
decreases in concentration 100-fold over 1  mm of
dentine.71 Moreover, intact cementum appears to be an BS
effective, if not complete, barrier to medicament penetra-
tion.158 Both the organic and the inorganic components of BC
dentine may also interact with medicaments and reduce
their antibacterial properties.164 Figure 8.5  Theoretical zones of bactericidal (BC),
bacteriostatic (BS) and cytotoxic (CT) activity from an
Effect of the smear layer antiseptic in the root canal.

Bacteriological data, both in vitro76,165 as well as in vivo,84 reported, however, of patients experiencing extremely
indicate that medicaments penetrate and act more effec- painful reactions to sodium hypochlorite inadvertently
tively, when applied in a root canal that has been treated placed or injected into the periapical tissues.66,169
to remove the smear layer. In infected teeth with chronic
apical periodontitis, it may be assumed that bacteria are Calcium hydroxide is, by virtue of its extremely
lodged peripheral to the main canal where the medica- high pH, potentially quite toxic. However, applied on
ments are applied.21,22 The removal of the smear layer vital tissue, the damage is limited to a narrow zone
through the use of EDTA seems prudent in these cases. of superficial necrosis with the potential for complete
Following complete disinfection, however, or in the treat- regeneration.170 Misplaced or placed in areas where diffu-
ment of a non-infected tooth, retention or recreation of sion of the ions may reach soft tissues in high concentra-
the smear layer may be advantageous in adding to the tions, calcium hydroxide may cause necrosis.171
sealing off of the canal by the final root canal filling,
although there are conflicting reports on the effects of the SUGGESTED CLINICAL PROCEDURES
smear layer on root canal fillings.166
Mechanical reduction of bacteria
TISSUE TOXICITY AND BIOLOGICAL
CONSIDERATIONS Mechanical instrumentation is the main factor in reducing
most bacteria infecting the root canal system. Rubber dam
Endodontic medicaments can cause tissue damage, which is essential in preventing the root canal system from sali-
will lead to inflammatory responses in soft tissues. These vary infection. All efforts should be made to complete the
responses may interfere with the healing of apical perio- mechanical phases of cleaning and shaping early in treat-
dontitis or serve as a locus for colonization by microorgan- ment, preferably at the first appointment. Any caries must
isms, to create a lesion where none existed. Any antiseptic be completely excavated, defective restorations removed,
will have a concentration gradient in the tissues with bac- and the tooth and surrounding rubber dam surface thor-
tericidal and then bacteriostatic activity, but the cytotoxic oughly disinfected. All instrumentation should be carried
effects will always be wider-ranging (Fig. 8.5). Experi- out in the presence of an irrigating solution. The clinical
ments with cell-culture techniques and toxicity tests in studies with bacteriological control have employed master
animals have aided the selection of chemicals and medica- apical file sizes of ISO 40 or larger, which exceed the
ments for endodontic use.15 Moreover, the allergenic and general recommendations in many current treatment pro-
genotoxic properties of medicaments must form part of tocols. Clinical experiments indicate that more bacteria
the selection criteria.167,168 are removed when canals were prepared to larger files
sizes,102,172 while other studies did not find an effect,173 and
The very strong tissue toxicity, as well as the allergenicity
and mutagenicity of aldehydes, have been part of the
reason why these agents are no longer recommended for
routine use. Similarly, phenols are strongly cytotoxic and
can hardly be recommended for use by current stand-
ards.15 Although toxicity is reduced by the addition of
camphor, the toxicity/efficacy ratio is still very high. In
recommended concentrations, halogen compounds have
high antibacterial activity combined with low tissue toxic-
ity. This forms part of the reason why sodium hypochlo-
rite is the irrigating solution of choice and why iodine
potassium iodide has been an attractive alternative for
short-term intracanal dressing.107 Cases have been

121

Harty’s endodontics in clinical practice

the type of file or instrumentation technique may not be
relevant.174,175,176

Primary root canal infection Figure 8.6  The root canal of a maxillary left central incisor
filled with calcium hydroxide. The radiopacity of the thick
Irrigation: Sodium hypochlorite has the best clinical and suspension of calcium hydroxide is close to that of dentine
laboratory documentation. It may be applied, as a 1–5% and an effective dressing gives the appearance of a
aqueous solution, in a sterile syringe with a short 12– completely filled canal.
25 mm needle with an outer diameter as low as practical
(0.25  mm). Care should be taken to prevent the needle Dressing: A mixture of calcium hydroxide with aqueous
from being wedged in the canal so as to prevent the acci- chlorhexidine has been tested in vitro88,89 and in vivo.179
dental injection of sodium hypochlorite into the periapi- Chlorhexidine may also be used in a gel form in concen-
cal tissues. Fresh solution is introduced and the exhausted trations of 2–5%. Given the predominance of streptococci
suctioned off between each change of files. Syringes of and enterococci in secondary and persistent root canal
10  mL capacity are practical for this purpose. Sodium infections, chlorhexidine preparations may be indicated in
hypochlorite may also be used with ultrasonic equipment, these cases.
and the alternate use of sodium hypochlorite and EDTA
will further reduce the number of bacteria. EDTA should Temporary filling
be the final rinse if adhesive root filling materials are used.
A bacteria-tight temporary filling is of paramount impor-
Dressing: Prior to the application of a dressing to disin- tance in preventing secondary contamination and infec-
fect an infected root canal, the canal is flushed with a tion of the root canal system. There are increasing numbers
15–17% neutral aqueous solution of EDTA. After allowing of complex endodontic cases as more and more people
the chelating agent to act for 1–2 minutes, it is suctioned seek conservative restorative treatment rather than extrac-
off and the canal is dried with paper points. tions. In these cases, treatment in two or several appoint-
ments is usually the rule rather than the exception. It may,
Calcium hydroxide has clearly the best record and fulfils reasonably, be assumed that a significant proportion of
most, if not all, indications. It may be applied with a apical periodontitis developing after pulp extirpation are
Lentulo spiral filler or a syringe. Care must be taken to caused by reinfection through coronal leakage and, there-
avoid overfilling. Paper points may be used to suck up fore, the quality of the seal afforded by the temporary
excess fluid, and root canal pluggers of suitable dimen- filling should be given careful attention.
sions may be used to ensure that the suspension or paste
reaches the apical part of the canal. More material may be The pulp chamber should be free of medicament and
added if needed and the packing procedure repeated until cleaned to receive the temporary filling. The dressing
a homogeneous filling is obtained (Fig. 8.6).

There are many commercially available calcium hydrox-
ide products; some are in injection syringes for ease of
application. In teeth with large root canals, as in very
young maxillary incisors, the syringe may suffice for
placement.

Secondary and persistent
root canal infections

Irrigation: The microbial flora may be resistant to conven-
tional medicaments, and an even greater antimicrobial
effort may be warranted. Following removal of the previ-
ous root canal filling by mechanical and/or chemical (e.g.
chloroform) means, the root canal system is irrigated
with sodium hypochlorite and EDTA as in primary cases.
Towards the end of each appointment and as instrumenta-
tion is nearing completion, chlorhexidine (0.2–2% in
aqueous solution or as a gel) is applied during the final
stages. EDTA should precede the chlorhexidine applica-
tion, as mixing sodium hypochlorite with chlorhexidine
may lead to the precipitation of a brown-coloured floc-
culate, suspected of being an aniline.177,178 EDTA should
be the final rinse if adhesive root filling materials are used.

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should be protected from saliva by a 3–4 mm thick layer leakage resistance and good physical properties making it
of sealing material. When the temporary filling is at par- the temporary filling material of choice in most clinical
ticular risk of fracture or dislodgement, extra precautions situations.
should be considered. A dual filling (‘the double seal’) is
then advisable: one internal, sealing the dressing and LEARNING OUTCOMES
designed to remain even if the external part breaks off, and
one external, designed to withstand occlusal function and/ Having read and understood this chapter, the reader
or for aesthetic reasons. Should the temporary filling fail, should be able to:
the root canal system is at risk of recontamination, so
defeating the purpose of placing a medicament. • distinguish and know the mode of action of the

Materials for temporary sealing of endodontic access different types of disinfectants and antibiotics used
cavities include reinforced zinc oxide-eugenol and calcium in endodontics;
sulphate-based materials. There is very limited data on the
true clinical efficacy of these materials, and the results are • recognize the most important species of
very variable, with one product type being superior in one
experiment, while falling short in another study.180,181 In a microorganisms associated with different types of
clinical study of bacterial penetration along temporary root canal infection, their differential susceptibility
fillings placed in vivo, calcium sulphate and reinforced to medicaments and intracanal factors that may limit
zinc oxide-eugenol cements performed equally well and the efficacy of medicaments;
better than a resin-based material.182 Given the greater
strength and resistance to dissolution and disintegration, • assess the overall importance of medicaments in root
reinforced zinc oxide-eugenol cements combine optimum
canal treatment;

• critically evaluate the efficacy of newer medicaments

as root canal dressings and irrigants.

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Villemure C, Bushnell MC. 143. Ehrmann EH, Messer HH, Clark extended extra-oral dry time.
Psychological State and Pain RM. Flare-ups in endodontics and Dental Traumatology 2008;24:
Perception. In: Sessle BJ, Lavigne their relationship to various 74–78.
GJ, Lund JP, Dubner R, editors. medicaments. Australian
Orofacial Pain: From Basic Endodontic Journal 2007;33: 153. Pierce A, Lindskog S. The effect of
Science to Clinical Management. 119–130. an antibiotic/corticosteroid paste
2nd edn. Chicago, Il, USA: on inflammatory root resorption
Quintessence; 2008. 144. Abbott PV. Systemic release of in vivo. Oral Surgery, Oral
corticosteroids following Medicine, Oral Pathology
135. Oguntebi BR, DeSchepper EJ, intra-dental use. International 1987;64:216–220.
Taylor TS, et al. Postoperative Endodontic Journal 1992;25:
pain incidence related to the type 189–191. 154. Pierce A, Berg JO, Lindskog S.
of emergency treatment of Calcitonin as an alternative
symptomatic pulpitis. Oral 145. Andreasen JO, Andreasen F. Root therapy in the treatment of
Surgery, Oral Medicine, Oral resorption following traumatic root resorption. Journal of
Pathology 1992;73:479–483. dental injuries. Proceedings of the Endodontics 1988;14:459–464.
Finnish Dental Society 1992;88:
136. Tammaro S, Berggren U, 95–114. 155. Abbott PV, Hume WR, Heithersay
Bergenholtz G. Representation of GS. The release and diffusion
verbal pain descriptors on a 146. Donaldson M, Kinirons MJ. through human coronal dentine
visual analogue scale by dental Factors affecting the time of onset in vitro of triamcinolone and
patients and dental students. of resorption in avulsed and demeclocycline from Ledermix
European Journal of Oral replanted incisor teeth in paste. Endodontics and Dental
Sciences 1997;105:207–212. children. Dental Traumatology Traumatology 1989;5:92–97.
2001;17:205–209.
137. Torabinejad M, Cymerman JJ, 156. Ciarlone AE, Pashley DH.
Frankson M, et al. Effectiveness 147. Flores MT, Andersson L, Medication of the dental pulp:
of various medications on Andreasen JO, et al. International a review and proposals.
postoperative pain following Association of Dental Endodontics and Dental
complete instrumentation. Traumatology. Guidelines for the Traumatology 1992;8:1–5.
management of traumatic dental

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157. Tronstad L, Andreasen JO, 166. Saleh IM, Ruyter IE, Haapasalo Acta Odontologica Scandinavica
Hasselgren G, et al. pH changes M, Ørstavik D. Bacterial 2007;65:167–170.
in dental tissues after root canal penetration along different root
filling with calcium hydroxide. canal filling materials in the 175. Dalton BC, Ørstavik D, Phillips
Journal of Endodontics 1981;7: presence or absence of smear C, et al. Bacterial reduction
17–21. layer. International Endodontic with nickel-titanium rotary
Journal 2008;41:32–40. instrumentation. Journal of
158. Abbott PV, Hume WR, Heithersay Endodontics 1998;24:763–767.
GS. Barriers to diffusion of 167. Nunn JH, Smeaton I, Gilroy J.
Ledermix paste in radicular The development of formocresol 176. Shuping GB, Ørstavik D,
dentine. Endodontics and Dental as a medicament for primary Sigurdsson A, Trope M. Reduction
Traumatology 1989;5:98–104. molar pulpotomy procedures. of intracanal bacteria using
ASDC Journal of Dentistry for nickel-titanium rotary
159. Molven O, Olsen I, Kerekes K. Children 1996;63:51–53. instrumentation and various
Scanning electron microscopy of medications. Journal of
bacteria in the apical part of root 168. Ørstavik D. Endodontic materials. Endodontics 2000;26:751–755.
canals in permanent teeth with Advances in Dental Research
periapical lesions. Endodontics 1988;2:12–24. 177. Basrani BR, Manek S, Sodhi RN,
and Dental Traumatology et al. Interaction between sodium
1991;7:226–229. 169. Hülsmann M, Hahn W. hypochlorite and chlorhexidine
Complications during root canal gluconate. Journal of Endodontics
160. Nair PN, Luder HU. Wurzelkanal irrigation—literature review and 2007;33:966–969.
und periapikale Flora: eine licht- case reports. International
und elektronenmikroskopische Endodontic Journal 2000;33: 178. Bui TB, Baumgartner JC, Mitchell
Untersuchung. Schweizerische 186–193. JC. Evaluation of the interaction
Monatsschrift fur Zahnmedizin between sodium hypochlorite
1985;95:992–1003. 170. Schröder U, Granath LE. Early and chlorhexidine gluconate and
reaction of intact human teeth to its effect on root dentin. Journal
161. Wesley DJ, Marshall FJ, Rosen S. calcium hydroxide following of Endodontics 2008;34:
The quantitation of formocresol experimental pulpotomy and its 181–185.
as a root canal medicament. Oral significance to the development
Surgery, Oral Medicine, Oral of hard tissue barrier. 179. Zerella JA, Fouad AF, Spångberg
Pathology 1970;29:603–612. Odontologisk Revy 1971;22: LS. Effectiveness of a calcium
379–396. hydroxide and chlorhexidine
162. Teixeira FB, Levin LG, Trope M. digluconate mixture as
Investigation of pH at different 171. Bramante CM, Luna-Cruz SM, disinfectant during retreatment of
dentinal sites after placement of Sipert CR, et al. Alveolar mucosa failed endodontic cases. Oral
calcium hydroxide dressing by necrosis induced by utilisation of Surgery, Oral Medicine, Oral
two methods. Oral Surgery, Oral calcium hydroxide as root canal Pathology, Oral Radiology,
Medicine, Oral Pathology, Oral dressing. International Dental Endodontics 2005;100:756–761.
Radiology, Endodontics Journal 2008;58:81–85.
2005;99:511–516. 180. Mayer T, Eickholz P.
172. Yared GM, Dagher FE. Influence Microleakage of temporary
163. Pashley DH, Kalathoor S, of apical enlargement on restorations after thermocycling
Burnham D. The effects of bacterial infection during and mechanical loading. Journal
calcium hydroxide on dentin treatment of apical periodontitis. of Endodontics 1977;23:
permeability. Journal of Dental Journal of Endodontics 1994;20: 320–322.
Research 1986;65:417–420. 535–537.
181. Scotti R, Ciocca L, Baldissara P.
164. Haapasalo HK, Siren EK, Waltimo 173. Coldero LG, McHugh S, Microleakage of temporary
TM, et al. Inactivation of local MacKenzie D, Saunders WP. endodontic restorations in
root canal medicaments by Reduction in intracanal bacteria overdenture tooth abutments.
dentine: an in vitro study. during root canal preparation International Journal of
International Endodontic Journal with and without apical Prosthodontics 2002;15:479–482.
2000;33:126–131. enlargement. International
Endodontic Journal 2002;35: 182. Beach CW, Calhoun JC, Bramwell
165. Guignes P, Faure J, Maurette A. 437–446. JD, et al. Clinical evaluation of
Relationship between endodontic bacterial leakage of endodontic
preparations and human dentin 174. Aydin C, Tunca YM, Senses Z, temporary filling materials.
permeability measured in situ. et al. Bacterial reduction by Journal of Endodontics 1996;22:
Journal of Endodontics 1996;22: extensive versus conservative root 459–462.
60–67. canal instrumentation in vitro.

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9Chapter  

Root canal filling

N.P. Chandler

CHAPTER CONTENTS 131 Coronal restoration 150
131 Follow-up 151
Summary 132 Treatment outcome 151
Introduction 132 Learning outcomes 151
Canal anatomy References 151
Access and canal preparation 132
SUMMARY
Criteria for filling 133
Over the past decade several newer root canal filling mate-
Materials used to fill root canals 133 rials have been introduced, the focus being to improve on
the perceived deficiencies of gutta-percha and to achieve
Sealers 133 savings in both time and cost. Most of these developments
134 aimed to replace gutta-percha with a variety of new resins
Zinc oxide-eugenol sealers 134 as the core filling material. Newer root canal sealers have
Calcium hydroxide sealers 134 also been introduced to complement these systems. Gutta-
Resin-based sealers 134 percha and the newer core materials are now made to
Glass ionomer sealers 135 match the size and taper of modern root canal preparation
Silicone-based sealers 135 instruments. Single-cone, matched root fillings may
Calcium silicate-based sealers provide an acceptable result in carefully selected cases.
Smear layer 135 Mineral Trioxide Aggregate is finding an increasing role as
a root canal filling material, following its successful appli-
Gutta-percha 135 cation in immature teeth. The ideal root canal filling mate-
136 rial is yet to be developed and some root canal shapes
Canal filling with gutta-percha 141 remain challenging to fill irrespective of the method used.
Cold gutta-percha techniques 145 The aim of this chapter is to describe the fundamental
Heat-softened gutta-percha techniques 146 principles of canal filling using gutta-percha and to provide
Solvent-softened gutta-percha a brief overview of relevant alternative methods.
Other methods of root canal filling 146
146 INTRODUCTION
Mineral Trioxide Aggregate 147
Hydrophilic polymers 148 The entire root canal system should be filled following
Monoblocks 149 cleaning and shaping. The objectives of root canal
Non-instrumentation technology 149 filling are:
Silver points
Paste fillers

© 2009 Elsevier Ltd, Inc, BV 131
DOI: 10.1016/B978-0-7020-3156-4.00012-7

Harty’s endodontics in clinical practice

1. To prevent microorganisms which remain in the root with irrigants and minimal removal of dentine from
canal system after preparation from proliferating and canal walls. However, achieving the correct canal shape
passing into the periapical tissues via the apical invariably requires additional effort to create the flowing,
foramen and other pathways. flared preparation demanded by most root canal filling
techniques. Inappropriate access and root canal prepara-
2. To seal the pulp chamber and root canal system tion can leave microorganisms, pulpal remnants and
from leakage via the coronal restoration in order to dentine debris within the root canal system. These will,
prevent passage of microorganisms and/or toxins invariably, affect proper adaptation of the root filling to
along the root canal and into the periapical tissues the canal walls, and the physical properties of the sealer
via the apical foramen and other pathways. will determine the effectiveness of the seal produced. Fur-
thermore, creation of an inappropriate canal shape will
3. To prevent percolation of periapical exudate and make it difficult to introduce root filling materials along
possibly microorganisms into the pulp space via the the length of the canal, resulting in a poorly condensed
apical foramen and other pathways. filling with voids. Thus, the ability to fill canals predictably
is, significantly, dependent on the adequacy of access and
4. To prevent percolation of gingival exudate and the quality of the root canal preparation.
microorganisms into the pulp space via lateral/
furcation canals opening into the gingival sulcus or The method of root canal filling will be dictated by the
through exposed, patent dentinal tubules around the preparation technique and the shaping objectives. Some
neck of the tooth. operators prefer to create an apical stop at the dentine-
cementum junction where a natural apical constriction is
The quality of the root canal filling depends on the com- believed to exist; in this way instrumentation does not
plexity of the root canal system, the efficacy of canal prepa- extend beyond the apical foramen.4 With this shape
ration, the materials and techniques employed, and the of canal, the filling technique of choice is cold lateral
skill and experience of the operator. Filling of the canal condensation of gutta-percha. Other operators create a
does not represent the end of root canal treatment, as continuously tapering canal shape where the smallest
restoration of the clinical crown to prevent leakage of diameter is at the foramen.5 With this shape, a variety of
fluids and oral microorganisms into the pulp space is criti- warm gutta-percha techniques are more appropriate; the
cal to long-term success.1 There is mounting evidence that lack of an apical stop will predispose the master gutta-
the quality of the coronal seal affects the prognosis of root percha cone, used in lateral condensation, to being dis-
canal treatment.2 torted and pushed beyond the foramen when a spreader
is introduced.
Many materials and techniques have been used to fill
root canals.3 The current material of choice is gutta-percha
combined with a sealer, because it is versatile and can be
used in a variety of techniques.

CANAL ANATOMY CRITERIA FOR FILLING

Pulp anatomy is complex with many root canals having Root canal filling is often delayed for one or more visits
apical deltas, lateral canals and other aberrations; acces- following preparation to allow interappointment medica-
sory canals, fins, and anastomoses are not uncommon, ments placed in the canal to act on the microbial flora and
especially in posterior teeth. These, together with the con- for signs and symptoms to resolve.6,7 Unfortunately, delay-
sequences of physiological and pathological dentine dep- ing root canal filling may lead to loss of, or microleakage,
osition and procedural problems during canal preparation, through provisional restorations. Also, all medicaments
present challenges. The inherent anatomy of the root canal have limited antimicrobial activity7 and duration of effec-
system has a major influence on the techniques used to tiveness. Under the right circumstances, modern root
fill canals and on the quality of the final result. canal preparation techniques are effective in eliminating
microorganisms so in selected cases root canal preparation
ACCESS AND CANAL PREPARATION and filling may be completed in one visit.

The aims of preparation are to clean and shape the root The decision as to when to fill root canals is controver-
canal system. Access and preparation have been discussed sial and debatable. Advocates for immediate filling of
in Chapters 4 and 7 respectively. It should be emphasized canals following preparation believe that their regimen for
that time and care spent during access and canal prepara- eliminating microorganisms by preparing a continuously
tion will facilitate root canal filling. As well as removing tapering canal shape5 and the extensive use of sodium
microorganisms and debris from the root canal system, hypochlorite and ethylenediaminetetraacetic acid (EDTA)
preparation produces the desired canal shape to receive or alternative irrigation is effective. It was argued that the
the root filling. Cleaning of the canal may be achieved root canal system is likely to be sufficiently cleared of
microorganisms and substrate to allow filling to proceed
immediately.8 Meanwhile, there is strong evidence that

132

Root canal filling Chapter | 9 |

delaying root canal filling and the use of an intracanal • non-irritating to periapical tissues
medicament will reduce the microbial population further9 • insoluble in tissue fluids
and enhance the long-term outcome, particularly if • dimensionally stable
the root canal is infected. It will encourage more rapid • hermetic sealing ability
resolution of apical periodontitis and an improved • radiopaque
prognosis.10,11 To further confuse the issue, there is research • bacteriostatic
reporting no difference between the outcome of one-visit • sticky and good adhesion to canal wall when set
or two-visit root canal treatment incorporating calcium • easily mixed
hydroxide medication.12 • non-staining to dentine
• good working time
Logically, teeth with non-infected pulps and no sign of • readily removable if necessary.
apical periodontitis can be prepared and filled in one visit,
whereas infected cases with apical periodontitis should be No current material satisfies all these requirements but
treated cautiously, with additional appointments to allow many work well in clinical practice. As well as providing
an intracanal medicament to further reduce the microbial a satisfactory seal, it must be well tolerated by the periapi-
population. Unfortunately, research in this area is difficult cal tissues and be relatively easy to handle. Sealers are toxic
and time-consuming and so far, a definitive answer is when freshly prepared;17 however, their toxicity is reduced
lacking.13 Irrespective of the number of treatment visits, it substantially after setting.18 Thus, although sealers produce
is essential that the root canal can be thoroughly dried varying degrees of periapical inflammation, it is normally
prior to filling, otherwise it will influence the effectiveness only temporary and depending on composition, it does
of the seal. not appear to prevent tissue healing.19

MATERIALS USED TO FILL Most sealers are absorbed to some extent when exposed
ROOT CANALS to tissue fluid,20 so the volume of sealer must be kept to a
minimum with the core material forming the bulk of the
Many materials have been used to fill root canals. Histori- root filling. The core material should force the sealer into
cally, these range from feathers and wood sticks through inaccessible areas and into irregularities along the root
a range of precious metals to amalgam and dental cements. canal walls. Excess sealer should ideally flow backwards
The requirements for a root canal filling material have and into the access cavity, but some gutta-percha tech-
been specified for many years.14 A large number of materi- niques tend to force sealer apically and laterally via the
als have proved to be inadequate, impractical or biologi- foramen and accessory canals.21,22 The passage of sealer
cally unacceptable. into the periapical tissues is not encouraged. However,
there is equivocal evidence that it will reduce the success
SEALERS rate of treatment provided that canal preparation and
filling have been performed with care. Clinical experience
A root canal sealer (cement) is used in combination with suggests that most excess sealer in the periapical region is
the core root canal filling material, e.g. gutta-percha. The absorbed with time but large volumes of extruded sealer
primary role of the sealer is to obliterate the irregularities must be avoided.
between the root canal wall and the core material. Almost
all of today’s root canal filling techniques use a sealer to Sealers in use today can be divided into five groups
enhance the seal of the root canal filling.15 based on their constituents:

Root canal sealers are used for the following purposes: • zinc oxide–eugenol sealers
• calcium hydroxide sealers
• cementing (luting, binding) the core material to the • resin sealers
• glass ionomer sealers
canal • silicone-based sealers.

• filling the discrepancies between the root canal walls Zinc oxide-eugenol sealers

and core material Most of the zinc oxide-eugenol sealers are based on Gross-
man’s formula.23 Commercial products include Tubli-Seal
• acting as a lubricant (SybronEndo, Orange, CA, USA), Pulp Canal Sealer
• acting as an antimicrobial agent (SybronEndo) and Roth Sealer (Roth International Ltd,
• acting as a marker for accessory canals, resorptive Chicago, IL, USA). Modified formulations with extended
working times are also available.
defects, root fractures and other spaces into which
the main core material may not penetrate. Once set, zinc oxide-eugenol sealers are relatively
weak and porous, and are susceptible to decomposition
The requirements and characteristics of an ideal sealer in tissue fluids, particularly when extruded into the
are:16

133

Harty’s endodontics in clinical practice

periapical tissues.24 All zinc oxide-eugenol cements are is bonding between the root filling, sealer and the root
cytotoxic and the cellular response may last longer than canal dentine. Other resin sealers include Hybrid Root
those produced by other materials.18 However, these prob- SEAL (Sun Medical Co. Ltd., Moriyama City, Shiga, Japan)
lems are not usually apparent clinically, and zinc oxide- or MetaSEAL (Parkell, Edgewood, NY, USA), both of the
eugenol materials are, probably, the most commonly used same chemical formulation and based on 4-methacryloe-
sealers. The various zinc oxide-eugenol sealers have a thyl trimellitate anhydride(4-META).
range of setting times and flow characteristics so the choice
of formulation is dependent on the case. Difficult canals Glass ionomer sealers
that need some time to fill require a sealer with an
extended working time. If heat is applied during root canal The ability of glass ionomer cement to adhere to dentine
filling, its influence on the setting time of sealers should would appear to provide a number of potential advantages
also be taken into account. over conventional sealers. Its endodontic potential was
recognized soon after its introduction as a restorative
Calcium hydroxide sealers material31 but it was many years before a product for
endodontic use was formulated. The results of a multicen-
Calcium hydroxide-based sealers have been developed on tre clinical trial evaluating its performance32 suggested that
the assumption that they preserve the vitality of the pulp it was similar to traditional sealers, but this sealer is no
stump and stimulate healing and hard tissue formation at longer available.
the apical wound. Laboratory research has demonstrated
their sealing ability to be similar to zinc oxide-eugenol Activ GP glass ionomer sealer (Brasseler, Savannah,
sealers25 although it remains to be seen whether during Georgia, USA) was recently introduced for use with Activ
long-term exposure to tissue fluids they maintain their GP points (Brasseler). The surface of these gutta-percha
integrity, since calcium hydroxide is soluble and may points is coated with glass ionomer. The sealer is meant
leach out and weaken the remaining cement.24 to adhere chemically and micromechanically to the Activ
GP points and also bond to the root canal dentine.
Commercial products include Sealapex (SybronEndo),
a calcium hydroxide-containing polymeric resin, Apexit Silicone-based sealers
Plus (Ivoclar Vivadent, Schaan, Liechtenstein) and epoxy-
based Acroseal (Septodont, Saint-Maur Cedex, France). RoekoSeal (Coltène/Whaledent, Cuyahoga Falls, OH,
USA) is a polydimethylsiloxane-based sealer. The manu-
Resin-based sealers facturer stated that this silicone-based sealer expands
slightly on setting (0.2%) and is highly radiopaque; the
Resin-based materials have been available for many claimed advantages include good sealing ability33 and
years but they remain less popular than zinc oxide- excellent biocompatibility.34 However, in a histopatho-
eugenol sealers. The first resin sealer, AH 26 (Dentsply logical study on periapical healing in dog’s teeth, no dif-
DeTrey, Konstanz, Germany), a powder and a liquid, ferences were noted between RoekoSeal and AH Plus.35
consisted of an epoxy resin base which set slowly
when mixed with an activator. It has good sealing26 and GuttaFlow (Coltène/Whaledent), introduced in 2004,
adhesive properties, and antibacterial activity. However, is a modification of RoekoSeal. GuttaFlow contains parti-
it produces an initial severe inflammatory reaction18 cles of gutta-percha less than 30 µm in size and and also
which subsides after some weeks and the material is then expands slightly (0.2%) on curing according to the manu-
well tolerated by the periapical tissues. The resin has a facturer. The material is considered to be almost insoluble.
strong allergenic and mutagenic potential27 and cases of It is used with a single master gutta-percha cone, without
contact allergy and paraesthesia28 have been reported. The mechanical compaction, although lateral or vertical con-
material releases formaldehyde29 which may explain densation are acceptable. Its flow is significantly better
its strong antibacterial effect.30 AH 26 has largely been into lateral grooves and depressions in the apical regions
superseded by AH Plus (Dentsply DeTrey), a two paste of root canals than lateral condensation or warm compac-
system formulated to polymerize without the release of tion with AH 26 sealer.36 Its sealing qualities are similar
formaldehyde; this sealer is also marketed as TopSeal to lateral compaction or the System B technique with AH
(Dentsply Maillefer, Ballaigues, Switzerland). AH Plus is 26.37 All traces of irrigants must be thoroughly rinsed from
also less cytotoxic, with a thinner film thickness and lower the canal with water or isopropyl alcohol prior to intro-
solubility. ducing the material. GuttaFlow has a working time of 15
minutes and a setting time of about 30 minutes; Gutta-
EndoREZ (Ultradent, South Jordan, UT, USA) is a ure- Flow FAST has a 5 minute working time and a 10 minute
thane dimethacrylate (UDMA) based resin sealer. It is rec- set. A potential concern is extrusion of material beyond
ommended for use with EndoREZ points (Ultradent), the apex36,37 although its cytotoxicity is lower than some
methacrylate resin coated gutta-percha points so that there other sealers.

134

Root canal filling Chapter | 9 |

Calcium silicate-based sealers microorganisms trapped in the tubules to escape45 or to
proliferate within the tubules and, potentially, increase
An advantage with these, newer types of sealer is their leakage.46 Nevertheless, the present consensus is that the
potential bioactive property. Similar to other tricalcium removal of the smear layer is beneficial and desirable,
silicate and dicalcium silicate-containing biomaterials, particularly when treating infected teeth.
calcium hydroxide is produced on reaction with water. It
is anticipated that release of calcium and hydroxyl ions In laboratory studies, a number of methods have been
from the set sealer will result in the formation of apatites shown to be effective in removing the smear layer.40 The
as it comes into contact with phosphate-containing fluids. key method involves 17% EDTA as a chelating agent
together with sodium hypochlorite to dissolve the organic
ProRoot Endo sealer (Dentsply Tulsa Dental, Tulsa, OK, component.42
USA) is a calcium silicate-based endodontic sealer that is
designed to be used in conjunction with a root filling GUTTA-PERCHA
material in either the cold lateral, warm vertical or carrier-
based filling techniques. The major components of the Gutta-percha has been used to fill root canals for over 130
powder are tricalcium silicate and dicalcium silicate, with years and is the most widely used and accepted root filling
the inclusion of calcium sulphate as a setting retardant, material. Gutta-percha is a form of rubber obtained from
bismuth oxide as a radiopacifier and a small amount of tropical trees of the Sapotaceae family. It is a trans isomer
tricalcium aluminate. The liquid component consists of of polyisoprene, which exists in two crystalline forms, the
a viscous aqueous solution of a water-soluble polymer α- and β-phases. The α-phase occurs naturally and the β-
(polyvinyl-pyrrolidone homopolymer). Other calcium phase arises during refining; the two are interchangeable
silicate-based sealers on the market include iRoot SP sealer depending on temperature. Gutta-percha is mixed with
(Innovative Bioceramix Inc., Vancouver, BC, Canada) and other materials to produce a blend that can be used effec-
Endosequence BC sealer (Brasseler); the same product tively within the root canal. Commercial gutta-percha
marketed under different names in different countries. cones contain gutta-percha (19–22%), zinc oxide (59–
75%), various waxes, colouring agents, antioxidants, and
SMEAR LAYER metal salts to provide radiopacity. There is considerable
variation in the stiffness, brittleness and tensile strength
The smear layer, comprising both organic and inorganic of commercially available gutta-percha cones and obturat-
components, is found on the root canal walls after endo- ing products.47
dontic instrumentation.38,39,40 It is composed largely of
particulate dentine debris created by endodontic instru- Gutta-percha cones are:
ments during root canal preparation but also contains
pulpal remnants and microorganisms. With further instru- • inert
mentation the material is forced against the canal walls • dimensionally stable
forming a friable and loosely adherent layer. The smear • non-allergenic to almost all individuals
layer is typically 1–2 µm thick, although it can also be • antibacterial
found within the dentinal tubules for up to 40 µm.38 • non-staining to dentine
• radiopaque
The smear layer has received much attention, not only • compactible
because it may harbour microorganisms already in the • softened by heat
canal but it may create an avenue for leakage of microor- • softened by organic solvents
ganisms and act as a substrate for microbial proliferation. • removable from the root canal when necessary.
It may also be broken down by bacterial action41 to
provide a pathway for leakage. In addition, the smear layer However, the disadvantages are:
has the potential to interfere with the adaptation of sealer
against the root canal walls and prevent tubular penetra- • lack of rigidity
tion of sealer, thereby increasing the likelihood of • do not adhere to dentine.
leakage.1,42 Indeed, it has been shown that most leakage
occurs between the sealer and the wall of the root canal.43 Canal filling with gutta-percha

Smear layer removal prior to filling would appear to be The objective of root canal filling is to completely fill the
desirable as it would eliminate microorganisms and allow canal system in an attempt to seal the canal from leakage
for better adaptation of sealer. However, this procedure apically and coronally. Gutta-percha is versatile and can
has been questioned since opening the tubules might be used in a variety of techniques, but a sealer is always
increase the diffusion of potentially irritant root filling necessary to cement the material to the canal wall and to
materials through the tubules to the root surface,44 allow fill minor irregularities.

135

Harty’s endodontics in clinical practice

Over the years, a large number of newer filling tech- Figure 9.1  Maxillary left first premolar with a short, single
niques have been described, accompanied by claims of cone filling in one canal and an untreated second canal.
greater efficacy, reduced leakage or time and money
saving. Unfortunately, new does not necessarily mean
better, and sadly there is little evidence from clinical trials
to suggest that there are significant differences between
root canal filling techniques and treatment outcome.
Caution is required when considering newer filling tech-
niques and it is prudent to wait for the published results
of laboratory and clinical studies before investing in and
learning a newer technique.

Methods for filling canals using gutta-percha can,
broadly, be divided into three main groups:

• cold gutta-percha
• heat-softened gutta-percha
• solvent-softened gutta-percha.

Cold gutta-percha techniques

Cold gutta-percha techniques are relatively simple to
master as they are not complicated by the need to soften
the material with heat or solvents, hence they do not
require expensive devices or equipment. However, cold
gutta-percha cannot be effectively compacted into all the
irregularities in a root canal system so this is the role of
the sealer. Lateral condensation is the most popular
method of root filling with cold gutta-percha.

Lateral condensation Figure 9.2  Gutta-percha cones, 0.06 taper with standardized
15–40 tip sizes.
With the advent of the standardized preparation tech-
nique,48 the method of filling root canals with a single, full
length gutta-percha cone and sealer became popular. The
concept was simple and attractive; the root canal was pre-
pared to a round cross-sectional shape of a standard size
with reamers and filled with a gutta-percha cone of the
same diameter. Unfortunately, a round canal shape was
rarely achieved, especially in curved roots,49,50 and the
single cone required large amounts of sealer to fill the
intervening gaps resulting in increased leakage.51 It was
also clear that discrepancies in size52 and taper between
gutta-percha cones and equivalent numbered instruments
were prevalent. While many clinicians appreciated these
problems and adopted other filling techniques, others
continued to fill canals using this method (Fig. 9.1).

Current canal preparation techniques produce a flared
canal with a flowing conical shape and cannot be filled
adequately with a single 0.02 taper gutta-percha cone.
Gutta-percha cones with ISO standardized tip sizes but
with varying tapers, e.g. 0.04 or 0.06 tapers are available
(Fig. 9.2). These cones with increased taper can fill funnel-
shaped canals more effectively because they are more
likely to correspond to the canal shape created by instru-
ments with similar taper. In a laboratory study on curved
canals, a single tapered cone technique has been found to
be comparable with lateral condensation in terms of the

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Root canal filling Chapter | 9 |

Figure 9.3  Mandibular right first molar. The mesial canals Figure 9.4  Maxillary central incisor filled with laterally
are filled with 0.04 taper, size 40 gutta-percha cones and condensed gutta-percha.
the distal canal with a 0.06 taper, size 40 cone. Canal
entrances covered with IRM and an amalgam intraradicular
core for the coronal restoration. Reproduced courtesy
of D Violich.

amount of gutta-percha occupying the root canal space; result will be considerably less leakage than if the spreader
the technique is also faster than lateral condensation.53 A had only entered part of the way into the canal.55 The
clinical example shows radiographically acceptable results need to advance the spreader well into the root canal is
(Fig. 9.3). one of the main reasons why canals are flared. A narrow,
parallel shape will not allow the spreader to influence
Lateral condensation of cold gutta-percha is taught the adaptation of the apical region of the master gutta-
and practised throughout the world and is the technique percha cone. Narrow canal preparations also risk remov-
of choice for many clinicians. It is simple and rapid to ing the master gutta-percha cone when withdrawing the
carry out. It can be used in virtually all cases where canal spreader, as it might pierce the cone instead of condensing
preparation results in an apical stop, and is the standard the material.
against which most newer techniques are compared
(Fig. 9.4). Lateral condensation involves the placement The requirements for successful lateral condensation
of a master (primary) gutta-percha cone to the terminus are:
of the preparation followed by placing additional (acces-
sory) gutta-percha cones alongside (Fig. 9.5). The use of a • a flared canal preparation with an apical stop
standardized master cone provides the possibility of a • a well-fitting master gutta-percha cone
predictable fit at the apex, while the accessory cones fill • speader/s of the appropriate size and shape
the intervening space, produced as a result of the flared • accessory cones which match the dimensions of the
canal shape. The root filling, therefore, consists of numer-
ous cones cemented together and to the canal wall by spreader/s
sealer; there is no merging of the cones into a homogene-
ous mass of gutta-percha (Fig. 9.6). The technique is • an appropriate sealer.
not recommended when the canal has no apical stop and
files can easily pass through the foramen (when the canal The master gutta-percha cone must fit to the full length of
has a continuous taper with the foramen being the the preparation, be tight at the end-point of the canal
narrowest). preparation (ideally present some resistance to withdrawal
or ‘tug-back’), and it must not be able to pass through the
A spreader is inserted alongside the master cone to foramen.
improve its adaptation at the terminus of the preparation
and to create the space for the accessory gutta-percha The size of the master gutta-percha cone should corre-
cones. When inserted to within 1  mm of the terminus spond to the master apical file used to prepare the apical
to condense the master cone apically54 and laterally, the stop. The selected gutta-percha cone is held with tweezers
at the correct length, equivalent to the working distance
and then inserted into the canal. Ideally, the gutta-percha
cone should:

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