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2. CONSERVATION
DECISION-MAKING FACTORS AFFECTING OUTCOME
Periapical Periodontitis
The only factor that has consistently been proven to influence the outcome of
endodontic treatment is the presence of apical periodontitis. It has been shown that the
success rate for root canal retreatment is approximately 1520% higher in teeth without
periapical lesions than in those with apical periodontitis (Table 2.3).
Following a sound biological approach to root canal treatment, a success rate of 96%
was achieved for root canal treatment in teeth with no lesion, whereas the presence of apical
periodontitis resulted in a reduced success rate of 86%.21 In the same study, the success rate
for root canal retreatment was shown to be 62%. In another study the presence of
preoperative periapical radiolucency was shown to have a significant negative effect on theoutcome of root canal retreatment, although overall success rates were high (91%).22
One can assume that the presence of a periapical area normally indicates bacterial
infection of the root canal system. Retreatment cases often present with apical periodontitis
and may be more difficult to disinfect effectively both from a technical point of view and as a
result of the types of bacteria present. There is no room for missed canals, iatrogenic errors or
complacency if a high success rate is to be achieved when treating teeth with apical
periodontitis.
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Length of Instrumentation and Obturating Material
Healing was reported in 94% of root-filled teeth where preparation and root filling
ended within 02 mm of the radiographic apex.19 Preparations that were shorter showed only
68% success. Another study showed that 55% of over-filled roots with defective seals were
associated with apical periodontitis, whereas only 12% of root fillings that ended within 02
mm of the radiographic apex showed periapical radiolucency.23 The crux of the problem
may be whether or not an infected canal was present before primary treatment (Figures 2.23
2.25).
Figure 2.23
In this case the maxillary right premolar teeth have been root filled. The root-filling material is short of the root
apex in both teeth. There is a periapical radiolucency associated with the maxillary first premolar. However,
there is little evidence of periapical pathology associated with the maxillary second premolar.
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Figure 2.24
During root canal retreatment it was possible to regain patency in the root canals of the first premolar. This is
important as the root canals are undoubtedly infected and should be disinfected to their full extent if possible.
The second premolar was blocked apically and it was not possible to gain patency. This should not be of serious
concern, as the tooth is not associated with periapical pathology and optimistically there will be little chance of
residual bacteria in the apical portion.
Figure 2.25
The completed case shows the canals obturated with gutta percha. As expected, root-filling material is short in
the second premolar but the canals in the first premolar have been obturated to their full extent.
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As discussed previously, gutta percha is generally well tolerated by the tissues and
does not initiate an inflammatory response per se. However, over-filling often occurs
following over-preparation which, in the presence of an infected canal, may result in
extrusion of infected debris and obturating material into the tissues. Likewise, under-filling,
which may result from failing to instrument the canal completely, could result in bacteriaremaining in the root canal following treatment. Both situations could subsequently lead to
induction or persistence of periapical inflammation. In a recent study of teeth or roots with
signs of apical periodontitis, a millimeter loss in working length increased the chance of
treatment failure by 14%.24
The importance of thoroughly disinfecting the entire root canal system cannot be
underestimated in teeth with periapical periodontitis and infected root canals. Ledged or
blocked canals may prevent renegotiation of the canal and therefore adequate disinfection. A
2-year follow-up study showed a success rate of 86.8% for retreatment of teeth in which there
were morphological changes as opposed to 47% in canals that had been altered by the
previous treatment.25 Obstruction that prevents complete negotiation may not always affect
outcome.26
Size of Periapical Radiolucency
The host osteolytic response has not been directly correlated with the extent of canal
contamination by bacteria but it has been suggested that an increase in the size of periapical
radiolucency beyond 5 mm diameter may have a negative effect on the outcome of root canaltreatment.22,27 The converse has also been reported. This may be due to the fact that root
canal-treated teeth associated with large areas take longer to heal and require further
observation.
Technical Factors
Failure of root canal treatment following procedural inadequacies is often an
indication for root canal retreatment. However, technical factors can influence the difficulty
of completing root canal retreatment (Figures 2.26, 2.27).
Fractured Instruments andSilver Points
Instruments that have fractured coronally are easier to remove than those positioned
more apically. If the instrument is visible with good illumination and magnification, then
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removal is probably more likely. Nickeltitanium instruments tend to be more difficult to
remove than stainless steel files (Figures 2.282.32).
Types of Filling Material
Pastes usually offer the least resistance to removal, but some cements, such as phenolresins, are extremely difficult to remove. Silver points are easier to remove when an extension
has been left in the access cavity but can be much more difficult when there is restricted
access or the head of the point is buried subgingivally. Single cone gutta percha fillings are
generally easier to remove than well-compacted thermoplasticized fillings. Plastic Thermafil
carriers can be removed relatively easily but those with a metal carrier can be more difficult.
Figure 2.26
A maxillary first molar has been root filled using a single cone technique but remains symptomatic. The canals
are under-prepared and the filling material is short in all of them. As there is a technical deficiency in the
primary treatment, root canal retreatment should have a good prognosis.
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Figure 2.27
A missed second mesiobuccal canal was located during root canal retreatment. All the other canals were
successfully renegotiated, shaped, cleaned and obturated. The patient is now symptom-free.
Figure 2.28
Leaving a tag of silver point in the core material should make removal considerably easier
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Figure 2.29
Removing a fractured instrument from the orifice of a root canal should be relatively simple. In this mandibular
left molar, a fractured orifice opener can be seen in one of the mesiobuccal canals. It should be relatively simple
to remove using ultrasonics. The tilting of the tooth made access more difficult.
Figure 2.30
The previous case root canal retreated. The fragment of instrument was removed uneventfully and the root
canals retreated.
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Figure 2.31
A fragment of file is retained in the apical part of a mesial canal of this mandibular right molar. The mesial
canals have also been ledged. Root canal retreatment will be extremely difficult. It may not be possible to
remove the fractured instrument. As there is a periapical area associated with this root, it is important to try to
disinfect the canal as thoroughly as possible. There could potentially be an indication for endodontic surgery in
this instance or an alternative such as fixed bridgework or an implantbased solution.
Figure 2.32
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Fortunately, root canal retreatment was successful using a non-surgical approach. The ledges in the mesial
canals were negotiated and the fragment of instrument removed. In the distal canal what initially appeared to be
two separate canals was in fact one larger canal, and this has been completely prepared to the full length of the
root.
Perforations
Successful treatment of perforations depends on the operators ability to seal the
defect and prevent infection. The size, position and time of perforation all affect successful
treatment. The earlier a perforation can be repaired, the better, and the possibility of infection
must be kept to a minimum. Large perforations are most difficult to seal (>0.5 mm) and are
associated with more tissue destruction. Perforations in close proximity to the gingival sulcus
can lead to contamination by bacteria from the oral cavity. Perforations located below crestal
bone have a better prognosis, as do those in the floor of the molar pulp chamber away from
canal orifices. The introduction of Mineral Trioxide Aggregate has improved the outcome of
perforation repair (Figures 2.332.36).28
Restoration
The general state of restorations in the mouth may affect the decision as to whether
root canal retreatment is advisable. Patients presenting with gross caries will require a
preventative approach to avoid the demise of new restorations. They may be better off with
an alternative to complex root canal retreatment. Since root canal retreatment is often time-
consuming, requiring dismantling of previous restorations and the removal of root-filling
material before disinfecting the root canal system, it is important to make an assessment of
the restorability of a tooth prior to embarking on prolonged and often expensive treatment.
Alternatives to root canal retreatment, such as the placement of a fixed prosthesis or perhaps
an implant-supported restoration, may offer a better longterm prognosis and should be
considered at the
treatment planning stage.
It has been reported that the quality of restoration and coronal seal may influence the
outcome of endodontic treatment29,30 and it is considered likely that many failures resultfrom coronal microleakage. The ability of a well-prepared and filled root canal to resist frank
and long-standing exposure by caries, fracture or loss of restoration may be considerably
better than first thought.31,32
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Figure 2.33
This mandibular molar presented with a buccal sinus tract and significant gingival recession exposing the
furcation. An access cavity has been cut in the occlusal surface; however, the root canals had not been located.
Figure 2.34
Under microscopic magnification, the temporary filling material in the access cavity was removed.
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Figure 2.35
Using a bur, the superficial filling material was removed and the remainder carefully retrieved using ultrasonic
tips.
Figure 2.36
A view of the pulp floor unfortunately showed a large perforation. Hyperplastic gingival tissue had extended
through the defect. The perforation site encompassed one of the root canals and the defect would therefore have
been extremely difficult to seal. As there is direct communication between the pulp chamber and the furcation
region of the tooth, coronal leakage and reinfection could be possible. Therefore, the prognosis for successful
retreatment in this tooth was considered poor and it was extracted.
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Patient Expectation
The patient should be included in the decision-making process. Following an
explanation of the problem, possible treatment options, disease risk and likely cost of
alternatives, the patient may decide not to have treatment. The patients wishes must be
respected as, medicolegally, patients must give consent to treatment before it starts. The finaldecision should be recorded with the clinicians advice.
Sometimes, patients expectations can be unrealistic. They may be desperate to save a
tooth that has an extremely poor prognosis and that should really be extracted. It is often
unwise to embark on treatment in this case, as the problems only become compounded when
things start to fail.
If patient expectations are commensurate with the clinicians expectations and
experience, then a happy outcome should be achieved.
Cost
Although a clinician will endeavour to avoid the removal of any functional natural
tooth, this may not be an option because alternative treatment is too costly. The costbenefit
ratio of any treatment has to be weighed against all the alternative options.
Root canal retreatment and a new crown may be less expensive than the replacement
of a tooth with a bridge or implant. Addition to an existing denture may be more cost-
effective than complex root canal retreatment. It can be a difficult ethical dilemma to balance,
but cost is an inevitable factor of modern dental practice.
Risk
There are many potential risks involved in carrying out root canal retreatment. For example,
there is the potential to damage an existing restoration when access is made through it. The
patient will need to be informed that a new restoration could be required. Iatrogenic errors
could occur during the process of removing the previous root-filling material or the root canal
wall could be perforated while attempting to remove a fractured instrument. The clinician
weighs up the risk of doing nothing, and therefore the potential of further pathology or pain,
against the likelihood of achieving a better result and healing of an endodontic lesion.
Because non-surgical root canal retreatment is better able to eliminate root canal
infection, is minimally invasive compared with surgery and is associated with fewer
postoperative complications, the riskbenefit ratio would appear to favour a non-surgical
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approach. For these reasons, root canal retreatment is normally considered the primary
approach for post-treatment disease.33
TREATMENT PLANNING
Following the decision-making process, no active treatment or review may beconsideredappropriate. The incidence of the possibility of acute exacerbation per year from
teeth with chronic apical periodontitis has been estimated as 5%. In other words, over a 10-
year period 50% will flare up.34 In cases where there is little or no periapical pathology
present and the root filling is deficient but there are no clinical signs or symptoms,
monitoring appears to result in complications in only a small percentage of cases.19 Not
providing treatment is only appropriate if there is a good coronal restoration, and the patient
is aware of the potential risk of acute exacerbation.
General patient attitudes will influence treatment planning. The motivation to retain
teeth, to pursue the best long-term treatment option and to spend time and money will vary
between patients. This may be a primary consideration in the treatment planning process. For
example, if a patient is not motivated to save teeth, extraction may be appropriate. If patients
are aware that non-surgical treatment will offer the best long-term prognosis but cannot
devote sufficient time or have financial concerns, they may accept a surgical approach or
extraction.33 Once a decision has been made to carry out retreatment, the clinician must
decide whether a surgical, non-surgical or combined approach is most appropriate. The
chance of teeth with no periapical pathology remaining sympto free following root canal
treatment or nonsurgical retreatment has been shown to be 9298%. When evidence of apical
periodontitis is present, this is reduced to 7486%. The chance of the teeth remaining
functional is 9197%. For root end surgery, the chance of teeth healing has been cited as an
average of 70% and remaining functional as 8692%.35 Conservative endodontic therapy,
both nonsurgical and surgical, is therefore definitely justified and should be attempted when a
good restorative and periodontal prognosis is projected, unless the patient is not motivated
to retain the tooth. There is little evidence in the literature to recommend a surgical approach
over a non-surgical approach, and the long-term success rates for surgical endodontics appear
to be no better than a conventional approach.36 But, surgical intervention is a far more
radical procedure, generally demanding more expertise and resulting in a shortening of the
clinical root length. The majority of endodontic failures occur as a result of infection within
the root canal system. It is a futile exercise to attempt to incarcerate these organisms by
carrying out root end surgery and placing an apical seal. Unless the reservoir of infection is
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eliminated, it is likely to continue causing persistent periapical inflammation or failure of
treatment. A surgical approach is normally reserved for situations in which, despite a good
attempt at non-surgical retreatment, the tooth still presents with signs and symptoms (Figure
2.37).
CONCLUSION
The consensus would therefore suggest that non-surgical root canal retreatment is
often the most appropriate means of treating failed root-filled teeth in the first instance and
that teeth should be permanently restored soon after retreatment to increase the chance of
success.37
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