INTRODUCTION
The key factor in the
development of pulpal inflammation and apical periodontitis is the presence of
bacteria. It has been widely accepted that bacteria and/or their products are
the main aetiological factors in the initiation and progress of these diseases.
Consequently, the central focus of root canal treatment has been directed
towards the elimination of bacteria and their substrates from the pulp canal
system. This may involve removal of necrotic pulp and tissue debris, removal of
an inflamed pulp or, in elective treatment, the removal of healthy tissue.
Historically, a mechanistic approach to root canal treatment was frequently
adopted, but in recent years a greater awareness of the complexities of the root
canal system has led to the development of newer techniques, instruments and
materials. These new developments have greatly enhanced the clinician’s ability
to achieve the biologically-based objectives of root canal treatment, which
include:
1. Removal of all
tissue, bacteria and bacterial products and substrates from the root canal
system.
2. Shaping of the root
canal system to facilitate placement of a root canal filling.
3. filling of the
shaped canal system coupled with an adequate and timely coronal restoration.
A root end which
has been made transparent showing two lateral canals
Traditionally the ‘endodontic
triad’ concept of cleaning, shaping and
filling has been promulgated widely. However, considering that a major goal of
root canal treatment is removal of microorganisms from the complex root canal
system, it would therefore appear that ‘shaping to facilitate cleaning
and filling’ might be a more appropriate
concept. These objectives must be achieved while ensuring conservation of tooth
structure and maintaining canal shape.
PREOPERATIVE
ASSESSMENT
Once a diagnosis has confirmed the need for root canal treatment, then a
treatment plan that includes the marginal periodontal status and restorability
of the tooth is essential before treatment commences. In addition to the
clinical examination this assessment includes radiological evaluation of the
tooth. Good quality preoperative radiographs (preferably from two different
angles) are indicated. These films must not be distorted, and must be processed
properly to ensure a permanent record. Alternatively, digital radiographs
should be filed and a permanent copy stored. Use of a paralleling technique and
a film-holder will minimize distortion of the radiograph and facilitate
accurate preoperative, postoperative and review comparisons. Periapical films
are the radiographic views most frequently used during root canal treatment.
However, other intraoral and extraoral views can often contribute to the
overall preoperative assessment and to diagnosis. These additional films
include bitewing, panoramic and occlusal films. For example, a supplemental
bitewing radiograph may be useful in detecting suspected caries not readily
visible on the periapical radiograph or to determine the relationship of the
pulp chamber to the external surface of the tooth. The tooth to be treated
should be located centrally on the periapical film with at least 2 mm of
periradicular tissue visible beyond and around the apex. A subsequent film
should be exposed with the X-ray beam angled 15o–20o to the original exposure. This
shift in angulation results in an apparent change in the position of the roots
and is called the parallax effect. Both horizontal and vertical parallax techniques
can be used. A good quality film will provide information concerning the
general tooth form and the relationship of the tooth to the surrounding
structures. Furthermore it will reveal evidence about the number of roots,
their length, and the relationship of the roots to the crown of the tooth.
Moreover, it can provide details of previous dental disease and treatment, as
well as the resultant pulp reactions such as narrowing of the pulp
chamber and root canals or presence of pulp calcifications. However,
interpretation of radiographs can be misleading if certain concepts are not
understood; for example, teeth with irreversibly inflamed or necrotic pulps
frequently show no radiological changes. Likewise radiological evidence of
periradicular lesions may not become obvious until the dense cortical plate of
bone has undergone some resorption.
Two radiographs
of the maxillary second premolar taken from different angles: (a) a single
root canal filling is observed in the buccal root canal; (b) the two
root canals are superimposed on each other but the periapical radiolucency is
clearly seen
A bitewing radiograph (a) clearly shows dental caries on the distal surface of the maxillary second premolar, whereas it is far less clear on the periapical radiograph (b).
The radicular anatomy
of teeth is variable, as is the relationship of the roots to the surrounding
bone. Anumber of anatomical structures overlie the roots such as the zygomatic
arch, mandibular and maxillary tori and the maxillary sinus; they frequently
confuse radiological interpretation of the image. It must be appreciated that a
radiograph is merely a two-dimensional shadow of a threedimensional object. In
addition, interpretation of radiographs has been shown to be highly subjective.
During the preoperative assessment it may become evident that a tooth requires
coronal buildup, crown lengthening or extrusion before a rubber dam clamp can
be placed and root canal treatment started. Localized periodontal surgical
procedures or electrosurgery are recommended frequently when caries or
fractures extend more than 2–3mm subgingivally. Before the tooth can be
restored adequately, a sound dentine margin should protrude at least 1 mm above
the free gingival margin that is normally 1–2 mm from the sulcus depth. This
implies that the dentine margin should be approximately 3 mm above the crestal
bone. The combined connective tissue and epithelial attachment from the crest
of the alveolar bone to the base of the gingival sulcus is called the
biological width. It is important that restorations do not encroach on this normal
soft tissue attachment.
PREPARATION
OF THE CLINICAL CROWN
Preliminary procedures involve isolation of the tooth and removal of all
dental caries. Existing restorations may need to be removed completely
especially if defective. Even if dental caries does not dictate the complete
removal of the restoration, it is often beneficial to do so as hidden fracture
lines in the proximal areas become visible. If cast restorations are present,
it is important to assess the integrity of the restoration and its cement lute,
and to decide whether to retain or to remove the restoration. If the tooth is
at risk of fracture, a provisional crown or an orthodontic band should be
placed prior to treatment. Orthodontic bands provide an excellent option when
there has been extensive loss of coronal tooth tissue. These bands are supplied
in a wide variety of sizes and are readily adjusted and cemented to the
existing tooth structure. Failure to prepare the crown adequately prior to root
canal treatment can result in:
• Bacterial
contamination from saliva or caries during or between treatments;
• Displacement
of restorative materials into the canal;
• Fracture
of unsupported tooth structure between visits or after treatment.
The maxillary premolar (a) shows a crack in the floor of the mesial box after removal of the restoration and staining; (b) the mandibular molar shows a crack on the distal aspect after removal of the crown and staining.
Isolation of the tooth
with rubber dam is a necessary prerequisite for endodontic treatment. It is
essential for protection of the airway. The inhalation or swallowing of
instruments by a patient in the absence of rubber dam is a serious but
preventable accident and is indefensible. The rubber dam application technique
is a matter of choice for the individual clinician. A wide variety of clamps
are available but a skilled clinician will normally use a limited range. Winged
clamps are most suitable for the fast and efficient placement of rubber dam.
These winged clamps allow the dentist to place the clamp, dam and frame in one
action. In recent years an increasing number of reports of allergies to latex
have been reported and therefore non-latex rubber dam has been developed.
A complete dam
placement kit should include:
• Rubber dam;
• Rubber dam punch;
• clamp forceps;
• Selection of clamps;
• Dental floss;
• caulking agent.
Occasional
improvization is necessary when routine rubber dam placement proves difficult.
Examples include cases where the tooth in question has undergone extensive
coronal tissue loss or where the tooth to be treated is the abutment for a
fixed bridge. These situations frequently necessitate clamping an adjacent
tooth and stretching the dam over the tooth to be treated, using a ‘split-dam’
technique. Following placement, minor defects in the adaptation of the dam can
be corrected with a caulking agent such as OraSeal (Ultradent, Salt Lake City,
UT, USA) or cyanoacrylate. Excellent reviews of rubber dam placement have been
published. In general, rubber dam application prior to endodontic treatment
should be a simple procedure and will enhance both treatment and patient
comfort.
A winged clamp
allows fast and efficient placement of rubber dam, in this case on a mandibular
molar.
In the split-dam
technique the right central incisor has been clamped and the dam stretched over
the left lateral incisor to allow isolation of the left central incisor
ACCESS
CAVITY
The main function of
the access cavity is to create an unimpeded pathway to the pulp space and the
apical foramen of the tooth. Many problems encountered during root canal
treatment can be avoided or eliminated by a properly designed access opening.
The major consideration in all access openings is that conservation of coronal
tooth structure should never preclude the proper design and purpose of the
access opening. The design of the access cavity to the pulp chamber should
reflect the anticipated position of the underlying root canal orifices. The
relationship between the pulp chamber and external anatomical outlines must be
assessed on the preoperative radiographs. Careful analysis of the radiographs
and careful alignment of the bur will reduce the possibility of mishaps during
access preparation. Inadvertent overextension of a bur either vertically through
the floor of the chamber into the furcation or laterally can be prevented by
taking these precautions. Occasionally, in cases where an extracoronal restoration
is severely tilted relative to the roots or in cases with sclerosed root canal
systems, access to the pulp canal chamber may best be created prior to placing
rubber dam to permit more accurate orientation of the rotary instruments to the
root outline. The pulp chamber must be completely unroofed. The pulp chamber
dimensions can vary enormously and reflect the nature of the ‘insults’ that the
tooth suffered since eruption. In addition, mineralized deposits are frequently
found in the chamber and root canal system. A well-designed access cavity
permits:
• complete debridement of
the pulp chamber;
• Visualization of its
floor;
• Unimpeded placement of
instruments into the root canals;
• Conservation of tooth
tissue.
Coronal and cervical
obstructions that may have a restrictive effect on canal exploration and
instrumentation need to be eliminated.
Irrigation of the pulp
chamber with sodium hypochlorite (NaOCl) during access cavity preparation is
used to dissolve tissue and aid in debridement of the chamber. This will also
reduce the opportunity for the inadvertent inoculation of microorganisms from
the pulp chamber into the root canal system. Ultrasonically energized tips are
useful adjuncts during debridement of the pulp chamber to break up calcific
masses with relative safety and to facilitate removal of debris. These
instruments are contra-angled to enhance access.
Alignment of the bur on the preoperative radiograph will indicate the position and depth of the restoration and pulp chamber.
There are mineralized deposits in the pulp chambers of the canine and first premolar
ROOT CANAL ORIFICES
A sound knowledge of
the anatomy of the tooth is very important to the practice of predictable and
successful endodontics. The number of canals and their approximate positions
can be predicted from a knowledge of dentinogenesis and the nature of root
formation. No technological advances or innovations can fully compensate for a
lack of understanding of the anatomical features of the pulp chamber, which
along with the root canal space are always located in the cross-sectional
centre of the crown and root respectively. The location of canal orifices is
best achieved with good illumination and a dry pulp floor. Magnification with
either loupes or a microscope is usually considered beneficial; however the
microscope is better for detecting orifices. Careful inspection of the floor
will usually reveal anatomical ‘guidelines’ that will facilitate identification
of the orifices even in calcified cases. If the orifice is not immediately
apparent, a sharp DG 16 probe can be used to explore along the anatomical
landmarks on the pulp floor. Reassessment of the relationship of the internal
anatomical features to the external outlines will also help with orientation
during a search for orifices that are difficult to locate. In extensively
calcified canals transillumination or the use of dye may provide some guidance
for orifice identification and instrument progression. Even extensively
calcified canals may contain pulp tissue and judicious use of a variety of
instruments usually facilitates entry into the canal system. A number of
ultrasonically energized instruments have been designed for this purpose.
Despite being relatively safe, care must be taken if perforation of the root is
to be avoided. Radiographs taken with radiopaque markers in the chamber can
help confirm the direction of instrumentation. When using rotary instruments
such as Müller burs or long-shank small round high-speed tungstencarbide burs,
frequent re-evaluation of bur position visually and/or radiographically will
reduce procedural errors. The direction of search can then be adjusted if necessary
and the procedure continued.
Furthermore,
enlargement of the canal orifices prior to instrumentation facilitates mid-root
and apical instrumentation, and enhances irrigation.
WORKING LENGTH DETERMINATION
Planning a final point
for instrumentation and filling depends on the philosophy of treatment, while
establishment of this point can be determined in a number of ways. It is
necessary to establish the length of the tooth accurately during root canal
treatment. The most widely accepted method for establishing working length has
been the use of radiographs.
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.
In this method, an estimated working length is
initially established by measuring from an accurate, non distorted,
preoperative radiograph. A file, preferably ISO size 15 or greater, is then
placed to the estimated working length and a second radiograph is exposed. If
the tip of the file is within 1 mm of the ideal location then the radiograph
can be accepted as an accurate representation of the tooth length. If
adjustments of 2 mm or more need to be made, working length should be
reconfirmed with a new radiograph. This method usually provides acceptable
results. However, radiographs are frequently difficult to interpret especially
in posterior teeth. In addition it is widely accepted that the apical foramen
may be distant from the radiographic apex further confusing interpretation. Electronic
apex locators work on the principle that the impedance between the periodontal
membrane and the oral mucosa is constant at 6.5 k
.
Recent apex locators
(Root ZX, AFA, Justy, Endex- Plus) have been reported to be accurate to within 0.5
mm in >90% of cases. The apex locator is significantly more reliable than
the radiograph for determining working length. As a consequence of their
accuracy, apex locators allow for a reduction in the number of radiographs
necessary to determine the working length especially in teeth where the apex is
difficult to visualize on the radiograph. These findings indicate that apex
locators should be regarded as the primary means of determining the working
length during endodontic procedures. Moreover, in a recent long-term
retrospective study in which an apex locator was the sole determinant of
working length in infected root canals with periradicular lesions, a high
success rate was achieved.
ROOT CANAL IRRIGATION
Regardless of the
instrumentation technique or system used, the use of irrigants is essential for
debridement of the canal system. Consequently the preparation of root canal
systems involves both mechanical and chemical components; hence the concept of
‘chemomechanical’ preparation. Irrigation with appropriate solutions
contributes to the cleaning of the canal system in several ways
Including:
• rinsing of debris;
• Lubrication of the canal
system which facilitates
Instrumentation;
• Dissolution of remaining organic
matter;
• Antibacterial properties;
• Softening and removing
the smear layer;
• Penetrating into areas
inaccessible to instruments thereby extending the cleaning processes.
Ideally the irrigant should be non-toxic and have a low surface tension in addition to being stable, inexpensive and easy to use. Aplethora of irrigants have been used. Currently, the most widely used irrigant is NaOCl, which has both antibacterial and tissue-dissolving properties.
The effectiveness of this
irrigant has been shown to depend on its concentration and time of exposure. Higher
concentrations of NaOCl have greater tissue-dissolving properties. However, the
greater the concentration, the more severe the potential reaction should some
of the irrigant be inadvertently forced into the tissues; hence, various concentrations
of NaOCl, varying from 0.5% to 5.25%, have been recommended. Those using the
lower concentrations are attempting to minimize the postoperative sequelae
should irrigant be inadvertently introduced into the tissues, whilst those
using the higher concentrations are attempting to maximize the tissue-dissolving
and antibacterial properties of the NaOCl. Accidental extrusion of NaOCl into
the periradicular tissues may result is tissue damage accompanied by varying degrees
of pain, swelling and bruising. To prevent
Procedural errors with NaOCl:
• avoid forceful injection
of the irrigant;
• Use specially designed
side-venting needles;
• Use carefully in the presence
of resorbed or open apices and perforations.
The use of calcium hydroxide as an intracanal medicament between visits has been shown to enhance disinfection following use of NaOCl. This synergism has beneficial effects for the chemomechanical preparation of the canal system. Other irrigants used in root canal chemomechanical preparation include chlorhexidine, iodine potassium iodide (IKI) and electrolytically activated water. During root canal preparation a layer of ‘sludge’ is formed by the action of the instruments against the canal walls. This material is deposited on the canal wall and is called the ‘smear layer’. The smear layer has both organic and inorganic components and exists as a superficial loosely bound layer and a deeper adherent layer. Considerable debate has occurred as to whether or not the smear layer should be removed. Complete removal of the smear layer may open up dentinal tubules to the passage of microorganisms from the root canal into the body of the dentine. On the other hand, failure to remove the smear layer will possibly allow bacteria to remain in the canal system and impairs the adaptation of the root filling to the dentine wall by preventing the movement of filling material into the dentine tubules. Removal of the smear layer is beneficial to root canal sealing , and significantly less microleakage occurs when these ‘smear-free’ canals are filled with thermoplasticized gutta-percha. A very close adaptation of thermoplasticized gutta-percha to the dentine wall has been shown following smear layer removal. Removal of the smear layer is best achieved by irrigating the canal system with NaOCl throughout the preparation procedure to prevent accumulation of debris on the canal walls and to flush out the canal system. A final rinse with 17.5% ethylene diamine tetra-acetic acid (EDTA) is recommended for removal of the inorganic component; EDTA is also produced commercially in a paste form for lubrication during the instrumentation procedure. The effects of chelating agents such as EDTA are self-limiting.
Delivery of the
irrigant is usually achieved by placing a side-venting needle 1–2 mm short of
the working length of the canal. Alternatively, ultrasonically energized files
can be used. Their effectiveness is due to the creation of acoustic micro
streaming and to the effective delivery of irrigant to the apical part of the
root canal system.
INSTRUMENTATION TECHNIQUES
Access to the apical
part of the root canal will largely depend on adequate coronal preparation. All
root canal systems are curved in one or more planes with the degree and extent
of curvature varying from root to root. Elimination of coronal obstructions
will greatly enhance the instrumentation procedures in the apical part of the
root. Irrespective of the instrumentation technique used, the apical part of
the canal system is invariably the least well-cleaned and prepared part of the
root canal system. Contrary to the idealized picture depicted in many texts,
the morphology of the apical canal system is complex and highly variable. Five
major apical morphological forms have been described. Experimental clearing of
roots has confirmed these variations and underscores the importance of a
chemomechanical approach to preparation especially in the apical third of the
canal system.
Preparation of the
root canal system requires considerable skill, particularly in cases with more
severely curved canals or complex anatomical features. Despite advances in
instrument design, the experience and tactile skills of the operator remain
important. Considerable efforts have been devoted to the study of instrument
design and metallurgy in an attempt to produce an ideal instrument. The
advances in design have been driven, in part by development of new alloys, and
in part by an increase in understanding of the anatomy of the root canal
system.
Five major apical morphological forms are shown.
Regardless of the instrumentation procedure or instrument type used, the goals of shaping and cleaning of the root canal systems are:
• Debridement of the root
canal system;
• Development of a
continuously tapering preparation;
• Avoidance of procedural
errors.
Maintaining the
anatomy of the apical constriction during canal shaping is essential for
predictable healing of the apical tissues, in addition to mechanically
retaining the filling material within the confines of the canal system.
Long-term studies have shown improved success rates when instrumentation and
filling procedures are maintained within the canal system approximately at the
level of the cemento-dentinal junction.
Historically, canal
preparation techniques have included the standardized and serial preparation
techniques that focus on achieving a round apical preparation with either a
small or minimal taper from apex to coronal aspect of the preparation. In
recent decades the concept of the ideal preparation has altered to take into
consideration a greater understanding of the natural anatomy of the root canal
system moving away from the more rigid mechanistic approach. Canal preparation
techniques can be broadly divided into those that adopt an ‘apical to coronal’
preparation procedure and those that adopt a ‘coronal to apical’ approach.
Crowndown technique
Most recently many
clinicians have used coronal to apical techniques to clean and shape root
canals.
There are several
advantages:
• Elimination of debris and
microorganisms from the more coronal parts of the root canal system thereby
preventing inoculation of apical tissues with contaminated debris;
• Elimination of coronally
placed interferences that might adversely influence instrumentation;
• Early movement of large
volumes of irrigant and lubricant to the apical part of the canal;
• Facilitation of accurate
working length determination as coronal curvature is eliminated early in the
preparation.
The crowndown and
stepback techniques of preparations aim to produce a similar result, i.e. a
flared preparation with small apical enlargement. The essentials of the coronal
to apical approach to root canal cleaning and shaping are as follows:
• Development of
straight-line access from the occlusal or lingual surface into the pulp
chamber;
• Removal of all
overhanging ledges from the pulp chamber roof;
• Removal of lingual ledges
or cervical bulges that form due to the deposition of dentine in the
Cervical part of the
tooth;
• Development of divergent
walls in the pulp chamber from the cavosurface margin to the chamber floor;
• cutting of a
funnel-shaped preparation, with its narrowest part located in the tooth
apically, in a stepwise manner in the coronal, middle and apical parts of the
root canal.
The benefits of using
the crowndown technique are multiple and greatly influence the achievement of
predictable success with root canal treatment. The clinical benefits of the
crowndown technique are:
• Ease of removal of pulp
stones;
• Enhanced tactile feedback
with instruments by removal of coronal interferences;
The anatomy of the apical constriction must be maintained during canal preparation
• enhanced apical movement
of instruments into the canal;
• Enhanced working length
determination due to minimal tooth contact in the coronal third;
• Increased space for
irrigant penetration and 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;
• Decreased deviation of
instruments in canal curvatures by reducing root wall contact;
• Decrease in canal
blockages;
• Minimization of
instrument separation by reducing contact with canal walls;
• Predictable quality of
canal shaping;
• Predictable quality of canal
cleaning;
• Faster preparation which
may allow one-visit root canal treatment.
The biological benefits of the crowndown technique are:
• Rapid removal of
contaminated, infected tissue from the root canal system;
• Removal of tissue debris
coronally, thereby minimizing pushing debris apically;
• Reduction in
postoperative pain that may occur with apical extrusion of debris;
• Better dissolution of
tissue with increased
irrigant penetration;
• Easier smear layer
removal because of better contact with chelating agents;
• Enhanced disinfection of
canal irregularities due to irrigant penetration.
The basic steps common
to all ‘crown to apical’ techniques involve early coronal and mid-root flaring
and enlargement before proceeding to the apical part of the canal. The initial
coronal flaring can be completed most efficiently with either Gates- Glidden
burs or with rotary NiTi instruments, such as orifice shapers (Dentsply Tulsa
Dental, Tulsa, OK, USA) designed specifically for this purpose. Early coronal
flaring significantly reduces the change in working length during canal
preparation. As an instrument initially moves into the coronal third of the
canal, the pathway is enlarged; the approach permits rapid irrigant penetration
and facilitates further movement of small instruments deeper into the root
canal. This entire process is continued until the working length can be
determined easily. This then allows unimpeded placement of instruments to the
middle and apical parts of the canal system. Irrigants and lubricants will
penetrate more easily and will facilitate passage of instruments in an apical
direction. ‘Crown to apical’ instrumentation techniques that have been proposed
include the crown-down pressureless technique, the Roane technique, the ‘double
flare’ technique [25], and the modified double-flare technique. Numerous
protocols have been detailed for use with a crown-down preparation technique. A
composite protocol for use with a ‘coronal to apical’ preparation is:
1. Access development
to remove cervical bulges in posterior teeth or lingual bulges in anterior
teeth.
2. Eliminate pulp
chamber obstructions.
3. Gates-Gliddens
sizes 4, 3, 2, or orifice shapers to enlarge canal orifices; irrigate.
4. Coronal to mid-root
enlargement using instruments from large to small; irrigate.
5. Explore canal and
establish working length with small instrument (size 10 or 15) using apex
locator and/or radiograph; irrigate.
6. Sizes 10, 15, 20
hand instruments to working length; irrigate.
7. Introduce large
files to coronal part of canal; when apical resistance is met the file is
removed and cleaned; irrigate.
8. Introduce
progressively smaller files deeper into the canal again until resistance is
encountered; irrigate.
9. Establish apical
preparation size; irrigate.
10. Complete
preparation to achieve desired taper.
Stepback technique
The most widely used
preparation technique until recently has been the stepback or telescope
technique first described in the 1960s and later modified. It replaced earlier
non-tapering preparation techniques and aimed to reduce instrument
transportation in the apical part. It has been effectively superseded by
crowndown techniques. The following are the stages of a stepback preparation.
Stage 1
1. Access.
2. Establish working length
with a pathfinder instrument.
3. Lubricate a fine
instrument and place to length with a ‘watch-winding’ motion (a watchwinding
motion implies a gentle clockwise and anti-clockwise rotation of a file with
minimal apical pressure); irrigate.
4. Place the next larger
size file to length; instrument circumferentially; irrigate.
5. Repeat the process until
a size 25 K-file (or a file two to three sizes larger than the first file that
binds at the apex) reaches working length.
Recapitulate between files
by placing a small file to working length.
This completes the apical
preparation; stage 2 involves flaring of the preparation.
Stage 2
1. Place the next file in
the series to a length 1 mm short of the working length; instrument
circumferentially, irrigate and recapitulate.
2. Repeat this process
placing the next larger file in the series to 2 mm short of the working length;
instrument circumferentially, irrigate and recapitulate.
3. Repeat the process with
successively larger files at 1 mm increments from the preceding file. It is
important not to omit any instrument in the sequence.
4. Complete the coronal
preparation with Gates- Glidden burs.
Variations to the classic
technique include:
• Initial enlarging of the
coronal aspect with Gates-Glidden drills;
• Use of small Gates-Glidden
burs in the mid-root level;
• Use of Hedstrom files to
flare the preparation.
The stepback approach
allowed creation of a small apical preparation with larger instruments used at
successively decreasing lengths to create a taper. The taper could be altered
by changing the interval between the stepback positions. In other words, the
taper of the final preparation could be increased by reducing the stepback
intervals from 1 to 0.5mm between each file. The stepback technique has been
considered to minimize procedural errors, such as transportation, ledging and
apical perforation, over previous techniques.
However despite the advances
of the stepback preparation over the standardized preparation in producing a
tapered preparation, these ‘apex to coronal’ techniques tended to result in
significant apical extrusion of debris. Apical blockage, canal deviation and
alteration of working length have also been frequently encountered with the
stepback technique. In addition, apical extrusion of debris during root canal
instrumentation has been associated with postoperative pain or discomfort.
Calcified canals
The basic principles apply
to preparation of calcified canals. As with patent canals, once the access
cavity to a calcified canal is completed, the pulp chamber is rinsed with
NaOCl. If the orifices are identified as being calcified, an ultrasonically
energized tip can be used to loosen debris in the orifice. The tip of the
ultrasonic instrument can be used either to activate the solution in the
chamber or it can be placed into the calcified orifice in an attempt to provide
some initial patency. The use of either a NaOCl or EDTA soak for up to 10
minutes along with the use of an ultrasonic tip in these cases may remove some
of the mineralized or partially mineralized tissue in the orifices. A small
K-file, or a specific file designed for canal penetration (e.g. Pathfinder,
Kerr Sybron), can be used to begin canal penetration. At this point, a small
orifice shaper can be used to provide a tapered orifice penetration that
facilitates further irrigant penetration and allows for the continued use of
small K-files, or in some cases a size 15 0.04 tapered instrument, to penetrate
further into the canal. The clinician can return to a small ultrasonic tip to
penetrate further into the canal. Gates- Glidden burs will not be beneficial as
they have a non-cutting tip. This procedure will take time and patience, and
the clinician should resist the temptation to try to drill a canal into the
root, as this invariably leads to deviation and potential root perforation.
NICKEL-TITANIUM INSTRUMENTS
Following the introduction
of nickel-titanium (NiTi) alloy to endodontic instrument design, many new NiTi
hand and rotary instruments have become available. The clinical and mechanical
properties of these NiTi instruments have been compared with those of
stainless-steel instruments; various aspects of instrument performance in canal
preparation such as the efficacy of canal preparation, cleanliness of the
canals after preparation, the shaping ability of the instruments and fracture
properties of the instruments have been examined. There is a general acceptance
that rotary NiTi instruments produce well-shaped canals in an efficient manner
with the creation of fewer iatrogenic problems than stainless- steel files.
However, direct comparison between stainless-steel and NiTi instruments is
difficult unless the instrument design is identical. In addition, most testing
procedures have been done in vitro, frequently in plastic simulated
canals, and longterm clinical evidence of the superiority of one instrument
type is unavailable.
CONTROVERSIES IN ROOT CANAL
CLEANING AND SHAPING
A number of issues remain
unresolved concerning endodontic treatment procedures; these include:
• Where should the preparation
end?
• When should the
preparation end?
• Should apical patency
filing be performed?
• Should treatment be
completed in one or multiple visits?
Where should the preparation end?
This question was addressed
succinctly in a short paper entitled ‘Where should the root filling end?.
Current treatment protocols used by many clinicians are frequently based on
opinion rather than fact. An illogical belief exists that the quality of treatment
provided is determined by the presence of sealer ‘puffs’ visible on a
postoperative radiograph: the more the better! There is little or no
evidence to support this belief; in fact there is considerable evidence for
maintaining all instrumentation procedures and filling material within the root
canal system. There should be differentiation between vital teeth, those with
infected canals, and retreatment cases, when deciding where to terminate the
instrumentation and filling. Based on biological principles and experimental
evidence instrumentation should terminate 2–3 mm from the radiographic apex in
vital cases. In cases where canals are infected, the position should be 0–2mm from
the apex, while in retreatment cases the ideal termination should be at the
apical foramen. However, irrespective of the preoperative condition of the
canal system, it is recommended that all instrumentation and filling procedures
should not extend beyond the apical foramen.
Discussion on the ideal
termination of the preparation and filling procedures presupposes the existence
of the ‘ideal’ root apex as described by Kuttler; however it has been
found that this ideal apical terminus exists in less than half of teeth.
Instead, a number of apical anatomical configurations have been described. No
apical constriction may be present especially in the presence of any resorptive
process. Consequently, it is often very difficult or even impossible to locate
either the apical constriction or the apical foramen.
When should the preparation end?
Removal of all microorganisms,
tissue and debris is the aim of root canal treatment and hence this can be
taken to be the end point of preparation. However, determining when this has
been achieved remains difficult clinically. Historically instrumentation procedures
have taken little account of canal anatomy, such as fins, webs, anastamoses or apical
ramifications. Outdated standardized preparation techniques aimed to enlarge
the canal to a predetermined size and circular cross-sectional shape. The
presence of white dentine chips has been used as a sign of canal cleanliness;
however, a lack of correlation between their presence and the cleanliness of
the canal has been demonstrated.Because of the complexities of canal anatomy,
the emphasis has shifted to chemomechanical preparation of the canal system.
Removal of the smear layer improves disinfection. The import ance of an
intracanal dressing of calcium hydroxide has been demonstrated as canals can be
rendered bacteria-free. An unanswered question is how long should the irrigant
be left in the canal system to achieve adequate disinfection of the canal. This
concern has fuelled a further controversy; namely can root canal treatment be
completed in one visit or should it be done in multiple visits?
Should apical patency filing be performed?
There are two concepts of
patency filing. The first and original concept aimed to remove debris collected
during instrumentation from the apical part of the canal. This involved sequentially
rotating files two to four sizes larger than the initial apical file at working
length, then rotating the largest apical file again after a final irrigation
and drying. This was called ‘apical clearing’, and aimed to achieve:
• Better debridement;
• Enhanced filling;
• A more defined apical
stop.
Apical clearing is
recommended in canals which have been prepared with an apical stop. Further, apical
clearing in teeth without an apical stop would increase the chances of
overpreparation and overfilling.
The second concept of
patency filing refers to the placement of small files to and through the apical
constriction. The aim is to allow for creation of a preparation and filling extending
fully to the periodontal ligament. Evidence to support this concept is
unavailable.
Should treatment be completed in one or multiple visits?
One-visit root canal treatment
has assumed a position of controversy for many reasons. Clinical studies have
addressed the advantages and disadvantages.
The advantages of one-visit
treatment are:
• Reduced number of
appointments;
• No risk of
intra-appointment microbial recontamination;
• Use of canal space for
immediate post-retention.
The disadvantages are:
• Longer appointments may
cause patient fatigue;
• Inability to control
exudates may prevent completion of the procedure.
Those studies concerning
postoperative pain as well as effective healing rates have shown that outcomes
are similar, whether completed in one or multiple visits. Many of these studies
have used older preparation techniques, which have the potential for less
effective canal cleaning. There are some indications and contraindications that
should be considered when contemplating this approach to treatment. The indications
are:
• Uncomplicated teeth with
vital pulps;
• Fractured teeth where
aesthetics is important and extensive restoration is indicated;
• Patient unable to return
for appointments;
• Patient requires
antibiotic prophylaxis or sedation.
Contraindications are:
• Patients with acute apical
periodontitis;
• Teeth with severe
anatomical anomalies;
• Molars with necrotic pulps
and periradicular radiolucencies;
• Root canal retreatment.
One-visit treatment does not
sit easily with evidence on canal disinfection in infected cases.
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