Types of Disease and Their Treatment

The statement, “Endodontists provide endodontic treatment to manage endodontic disease” is a gross oversimplification that masks important subtleties in recognition of the nature of the diseases and how best to address them. Endodontists manage inflammation of the specialized connective tissues within and surrounding the teeth; more specifically, they deal with inflammation that generally commences in the pulp tissue and progresses to the periradicular tissues via portals of communication that convey the neurovascular supply. Incipient or established pulpitis may be managed by vital pulp therapy when judged reversible, largely because a sufficient body of pulp tissue remains healthy and unaffected. More advanced pulpitis that approaches the foramina into the periodontal ligament may require root canal treatment. When pulpal inflammation, necrosis, or infection encroaches on the apical periodontal ligament, root canal treatment is required. Apical periodontitis that persists despite technically adequate root canal treatment may require root canal retreatment, periradicular surgery, or extraction to manage the source of the persistent disease. Endodontic treatment is therefore a collective and nonspecific term for a range of procedures directed at managing the spread of pulpal inflammation or infection. Endodontic treatment encompasses the following procedures:

• 1.

  Vital pulp therapy (indirect pulp therapy, direct pulp capping, pulpotomy, regenerative pulp therapy)

• 2.

  Nonsurgical root canal treatment

• 3.

  Nonsurgical root canal retreatment

• 4.

  Surgical retreatment

The ideal outcome for endodontic treatment consists of controlled reduction of inflammation, accompanied by healing through regeneration, although sometimes repair may follow instead. Unfortunately, none of the involved tissues are within the direct sight of the clinician, hidden as they are by their housings of hard tooth structure or alveolar bone and their gingival/mucosal coverings. Consequently, surrogate measures must be employed to evaluate the presence or absence of the disease process and its resolution. The evaluation process is further complicated by the lack of direct correlation between measures of the disease process and its clinical manifestation.

Types of Outcome Measures

In its broadest sense, an outcome measure for a treatment intervention may constitute any consistently anticipated and measurable consequence of the treatment. The prepared shape of the root canal system, bacterial load reduction, and technical quality of the root filling may all be regarded as outcome measures by this definition. But the ultimate clinical measure of a treatment outcome is assessing the prevention and resolution of disease.

The outcome of endodontic treatment may be assessed in four dimensions as in other medical disciplines. The first dimension is physical/physiologic and related to presence or absence of pulpal/periapical health/disease, pain, and function. The second dimension assesses longevity or tooth survival. The third dimension relates to economics and assesses direct and indirect costs. Finally, the fourth dimension examines psychologic aspects involving perceptions of oral health–related quality of life (OHRQoL) and aesthetics.

Effectiveness of Procedures

First, treatment procedures must be effective. Otherwise, there is no reason to recommend them to patients as a treatment option. The patient must be properly informed as to the risks, benefits, and potential outcomes of the offered treatment. The availability of pooled outcome data and consensus guidelines offers both patients and endodontists reassurance and confidence in the validity and predictability of the offered procedure. However, the pooled average outcome data may not pertain if the clinician does not have the requisite experience, skill, and personal outcomes matching at least these average figures of performance. Personal outcome data offer the patient more precise measures for comparison and expectation. It also aids practitioners in refining their technique and knowledge to further improve their outcomes and, ultimately, to help improve the overall pooled data. The treating clinician must assess his or her own personal outcome data and personal expectation of success. If the clinician is uncertain of a result or feels that the outcome could be enhanced by treatment from another clinician, then referral to someone else more qualified is paramount.

Factors Affecting Outcomes

Pooling data (that is preferably homogeneous) offers the potential to evaluate and prioritize the factors that exert a dominant influence on outcomes. In this way, protocols for treatment may be improved in a progressive fashion, bringing about the perfect meld of technical, clinical, and biologic insight necessary for the highest performance and most predictable outcome. Evaluation of factors affecting treatment outcomes arguably provides the strongest influence for making changes that will improve the clinical outcomes. Weighing the relative importance of individual factors should help to identify the key biologic factors at play and how best to manage them from a clinical or technical perspective.

Value for Prognostication

Prognostication, which could be defined as the prediction, projection, prophesizing, or foretelling the likely outcome of treatment, is not often well defined in endodontics. The overall prognosis of a tooth depends on the interaction among three individual and often independent variables, including endodontic, periodontal, and restorative prognoses. Each has a set of subsidiary factors that must be considered to derive an overall prognosis. Finally, the tooth in question must be considered from a strategic perspective, relative to its position in the dental arch and the contribution it makes in the dynamic occlusion.

A deeper analysis of the factors affecting outcomes as prognostic indicators is merited in order to clarify the degree of complexity inherent in the problem. A comparison may be made with the randomized controlled trial of a drug as a treatment intervention. The drug therapy is delivered as a clearly prescribed and standardized dose regimen delivered by specified timings to effect an anticipated blood or target tissue concentration for a specified duration. Data recording is confined to compliance with the prescription and possibly checking of actual blood levels achieved as well as the final outcome effect.

In stark contrast, a surgical intervention, regardless of any standardization of the described procedural protocol, is subject to enormous variation in its delivery dependent on interpretation and execution of the protocol by each operator. To add to the levels of complexity and variation, surgical protocols are often multistep, sequential procedures, each prospective step dependent on the previous for its efficacy. Even characterizing and accurately recording any variations in treatment protocols becomes a challenge because many aspects and steps must be documented. This leads to the next challenge, that of demonstrating compliance with the accuracy of such complex data gathering. Furthermore, it becomes important from an analytic perspective to not only consider the effect of individual steps (factors) alone but also any interactive effect between the multiple steps inherent in the procedure. Even when such comprehensive prospective outcome data are available, utilizing these data to individually calculate the prognosis in a particular scenario may be challenging. Clinically, there may be two distinct ways to estimate prognosis: (1) to apply heuristic principles and intuitively gauge the effect of dominant factors or, at the other end of the extreme, (2) to mathematically input comprehensive data into an algorithmic model to calculate the estimated outcome. An even more sophisticated approach may be to use mathematical modeling to calculate iterations on variations within the system. At present, the evidence base is insufficient to allow such a sophisticated approach.

It therefore follows that evaluating outcomes and the factors that affect them are fundamental to the creation of a suitable data foundation for future application to endodontic prognostication. The endodontic treatment option is in competition with other alternative therapies and therefore, for the discipline to survive and thrive, a suitable blend of efficacy, efficiency, utility, predictability, and cost-effectiveness data must be generated for its principal therapies. Achievement of such a goal will require a diligent and conscientious collection of data from many sources. Analyses of such powerful datasets will ultimately yield proper insight into outcomes of the procedures we use. Coupled with biologic insight of the problem, it will become possible to derive new therapeutic solutions necessary to deliver them.

Outcome Measures for Vital Pulp Therapy Procedures

The techniques used to maintain the vitality and health of pulps in teeth with extensive caries or those with traumatic/mechanical exposures include (1) indirect pulp capping with one-step or stepwise caries excavation; (2) direct pulp capping of exposed pulps; and (3) partial/full pulpotomy procedures for more extensively involved pulps. The surrogate outcome measures adopted in studies include (1) clinical success (pulp sensitivity to cold test and absence of pain, soft-tissue swelling, sinus tract, periradicular radiolucency, or pathologic root resorption), (2) patient satisfaction, (3) adverse events (pain, swelling, tooth fracture), and (4) tooth extraction. Although not providing a specific follow-up strategy, the quality guidelines of the European Society of Endodontology suggests “initial review at no longer than 6 months and thereafter at further regular intervals.” They also provide the criteria for judging the favorable outcome of vital pulp therapy ( Table 11-1 ). There are substantial differences in the criteria adopted in published clinical studies on outcomes of vital pulp therapy with few studies adopting all of the criteria. The frequency of radiologic review adopted in published studies also varies substantially, with some recommending the first review at 1 month followed by subsequent 3 monthly reviews. The relative benefit of acquired information versus unnecessary radiation to patients has been questioned. An initial assessment at 6 to 12 weeks, followed by a review 6 and 12 months after treatment, seems to have been accepted and is recommended. Some studies reported up to 10 years follow-up on case series demonstrating lower success rates, inferring the possibility of slow spread of pulpal inflammation and late failures. The conclusion is that longer follow-up periods are merited.

The process at each review consists of obtaining a history of symptoms, coupled with an examination to determine the presence or absence of tenderness to palpation of adjacent soft tissues, tenderness to pressure and percussion of the tooth, signs of radiographic pulpal, and periapical changes, and responses to pulp tests. The accuracy of pulp tests may be limited in pulpotomized teeth because of the distance of the remaining pulp tissue from the tooth’s surface. In the case of pulp capping and pulpotomy, additional tests include radiographic verification of the presence of the calcific barrier ( Fig. 11-1 ) and its integrity by removal of the dressing and direct probing. Although an initial examination at 6 weeks has been suggested, this can be modified for the radiographic assessment. If there is no evidence of complete bridge formation, the treatment is considered failed and root canal treatment should be considered. In addition, in the case of incompletely formed roots there should be radiographic evidence of continued root development ( Fig. 11-2 ).

Histologic view of intact calcific bridge formation following pulpotomy.

Immature maxillary right lateral and central incisors (A) showing continued root development following pulpotomies (B) .

Outcome Measures for Nonsurgical Root Canal Treatment and Retreatment

Root canal treatment may be employed either to prevent or resolve periapical disease. Given that periapical lesions develop as a result of interaction between bacteria (and their by-products) and the host defenses, it is clear that prevention or resolution of the disease process depends on preventing or terminating this interaction.

Prevention of apical periodontitis applies to the clinical situation where it is judged that the pulp is irreversibly inflamed, necrotic, or infected to the extent that vital pulp therapy would not resolve the problem, which therefore requires pulpectomy. The implication is that the procedure demands asepsis as a prime requirement. The precise technical details of the protocol may not be so important, as long as they are focused on effective and aseptic removal of the pulp tissue. This is validated by the high chance of retaining periapical health (judged by conventional radiography), regardless of the clinical protocol used.

Once the periapical lesion has become established, the challenge is a different one because the purpose now is to remove the bacterial biofilm and effect switching-off the periapical host response. The challenge seems to be greater still if the periapical lesion is larger as it is associated with a more diverse infection. A number of approaches (protocols) have been used to achieve this general aim. The periapical healing process that occurs after root canal treatment is less clear. Nevertheless, ideal healing would eventually result in regeneration and the formation of cementum over the apical termini, isolating the root canal system from the periapex ( Fig. 11-3 ); but this is not an inevitable result. Incomplete removal of the infection will reduce but not eliminate the periradicular inflammatory reaction, and in fact this is generally what happens. This implies that residual infection in the apical anatomy is typical following completion of root canal treatment and that an ongoing interaction continues between the residual infection, root filling material, and host defenses, which plays a definitive role in determining the final healing outcome.

Low-power view of healing by cementum formation when Sealpex is used (black particles are residual Sealapex and root filling material).

(Courtesy Prof. M. Tagger.)

The culture test has been used during root canal treatment as an interim measure of the efficacy of the chemomechanical procedure; however, it has fallen out of favor in contemporary practice for a variety of reasons. The outcome measures that quantitate healing subsequent to root canal treatment are the absence of clinical signs and symptoms of persistent periapical disease. The definitive outcome measure (in conjunction with the absence of signs and symptoms), however, is periapical healing, because the treatment is aimed at resolution of periapical disease ( Fig. 11-4 ). Clinical judgment of the outcome of treatment is based on the absence of signs of infection and inflammation, such as pain, tenderness to pressure/percussion of the tooth, tenderness to palpation of the related soft tissues, absence of swelling and sinus tract, and radiographic demonstration of reduction in the size of the periapical lesion (if sufficient time has lapsed), with a completely normal development of the periodontal ligament space. Although the majority of periapical lesions heal within 1 year, healing may continue for up to 4 years or longer.

Resolution of periapical disease after root canal treatment of the mandibular left molar with preoperative periapical radiolucency associated with mesial and distal roots (A) , delayed healing caused by extruded filling material from the distal canal (B) , and nearing complete healing as extruded material is resorbed (C) .

Absence of signs and symptoms of periapical disease with radiographic evidence of a persistent periapical radiolucency may indicate either fibrous repair ( Fig. 11-5 ) or persistent chronic inflammation or infection. Only time and acute exacerbation would identify the latter, whereas the former should remain asymptomatic.

Histologic view of fibrous periapical healing.

Longevity measures include survival of the root canal fillings or treatment and tooth retention or survival. The term functional retention was coined by Friedman in 2004 to mean retention of the tooth in the absence of signs and symptoms regardless of the radiographic presence of a lesion. The term functionality should further and more specifically cover the functional utility of the tooth—that is, some patients may complain that despite the absence of specific signs and symptoms of infection or inflammation, they find it impossible to use the tooth because it “feels” weak.

Modern definitions of health embrace a broader spectrum of measures including psychological well-being. Instruments to assess these aspects have been developed in general medicine and adapted for application to dentistry, such as the Oral Health Related Quality of Life instrument. There is no definitive instrument for measuring these aspects in endodontics as yet. Studies published so far have mainly adapted versions of the Oral Health Impact Profile (OHIP).

The periapical status of root-treated teeth has traditionally been assessed using two-dimensional conventional radiographic imaging. The use and limitations of two-dimensional radiographic images for assessing treatment outcome has been reviewed thoroughly and reported to suffer from low sensitivity, particularly in the posterior parts of the mouth. The development of digital imaging technology brought the possibility of image manipulation, including digital subtraction, densitometric analysis, correction of gray values, and the manipulation of brightness and contrast. However, none of these approaches has addressed the main deficiencies of accurately elucidating and quantitating the actual existence or progression of periapical bone loss.

Cone-beam computed tomography (CBCT), a new three-dimensional imaging technique requiring only 8% of the effective dose of conventional computed tomography, has been proposed as a means of overcoming the problem of superimposition of tissue layers and structures. The diagnostic values of periapical radiography and cone-beam computed tomography were compared on dogs’ teeth using histology as the comparative method of determining apical periodontitis 180 days after root canal treatment. CBCT was found to be significantly more accurate in detecting minor bone lesions compared with two-dimensional radiology. Other evidence to support the superior sensitivity of CBCT is available from studies using a variety of simulated defects created in bone in pig or human jaws. Although the validity of clinical outcome data derived using conventional radiographic techniques has been questioned, the routine use of CBCT is not recommended owing to its higher radiation dosage. The use of CBCT, which may be more sensitive for detection of periapical healing, may give lower healing rates and longer durations to complete healing.

Many studies consider the treatment successful only when both radiographic and clinical criteria are satisfied. It has been documented that a small proportion of cases present with persistent symptoms despite complete radiographic resolution of the periapical lesion. Comparison of success rates estimated with or without clinical examination revealed no or only a very small difference (1%).

The widely accepted definition for endodontic success and failure by Strindberg embraces both radiographic and clinical findings ( Table 11-2 ). Friedman and Mor preferred the terms healed, healing, and diseased instead of success and failure because of the potential of the latter to confuse patients. The “healed” category corresponds to “success” as defined by Strindberg, whereas “healing” corresponds to “success” as defined by Bender and colleagues (see Table 11-2 ).

The long duration of the periapical healing process coupled with the reduced recall rates at longer follow-up periods has provided opportunity for setting the thresholds of success at either complete healing or partial healing (reduced lesion size). The success criteria used for complete resolution have been described either as “strict” or “stringent,” whereas the criteria established for reduction in periapical radiolucency size has been described as either “loose” or “lenient.” The frequency of adoption of these two thresholds has been similar in previous studies; the expected success rates using “strict” criteria would be expected to be lower than those based on “loose” criteria. The literature finds the difference to vary from 4% to 48%.

A periapical index (PAI) consisting of five points on the scale was devised for measuring the periapical status and used in some studies. However, the studies only reported the increase or decrease in mean scores for the clinical factors under investigation coupled with the proportion of successful cases. This approach precluded direct comparison of their data with studies reporting conventional dichotomized outcomes. Other studies using the index dichotomized the scores into “healthy” (PAI 1 or 2) or “diseased” (PAI 3 to 5) categories, thus allowing the data to be compared directly with the more traditionally used binary outcomes of success or failure. In this system of designation, given that the PAI score 2 represents periodontal ligament widening, it effectively signals adoption of the “loose” threshold. The longitudinal follow-up of 14 cases presenting with widened apical periodontal ligament (PAI score at 2) for 10 years revealed unfavorable future healing in only a small proportion of the cases (28%, 4/14).

Outcome Measures for Periapical Surgery

Nonsurgical root canal treatment alone may fail to resolve apical periodontitis in a small proportion of cases because it may not allow access to the infection or resolution of the cause of the infection (i.e., root fracture or crestal bone communication to the periapical infection). Where the cause is microbial persistence, the infection may be localized intraradicularly (in the apical canal anatomy [ Fig. 11-6 ] or in the apical dentinal tubules [ Fig. 11-7 ] or extraradicularly [ Fig. 11-8 ]). In these instances, a surgical approach to the periapex may be required in addition to the nonsurgical approach to removing such microbes (see Fig. 11-7 ).

Axial sections through the surgically removed apical portion of the root with a therapy-resistant periapical lesion (GR). Note the cluster of bacteria (BA) visible in the root canal. Parts B – E show serial semithin sections taken at varying distances from the section plane of (A) to reveal the emerging (B) and gradually widening (C–E) profiles of an accessory root canal (AC). Note that the accessory canal is clogged with bacteria (BA). Original magnification: A ×52; B – E ×62.

(From Nair PN, Sjogren U, Krey G, Sundqvist G: Therapy-resistant foreign body giant cell granuloma at the periapex of a root-filled human tooth, J Endod 16:589, 1990.)

A, Adequate root filling demonstrated on radiograph. B, View of the periapical surgery and root resection of the tooth shown in (A) shows stained root dentine. C, Resected root showing stained/infected dentine. D, Histologic view of the root end shown in (C) showing infected dentinal tubules (S).

Actinomyces in the body of a human periapical granuloma. The colony (AC in B) is magnified in B . The rectangular area demarcated in B is magnified in C . Note the starburst appearance of the colony with needle-like peripheral filaments surrounded by few layers of neutrophilic granulocytes (NG), some of which contain phagocytosed bacteria. A dividing peripheral filament (FI) is magnified in the inset. Note the typical Gram-positive wall (CW): D = dentine. Original magnification: A ×60; B ×430; C ×1680; inset ×6700.

(From Nair PR, Schroeder H: Periapical actinomycosis, J Endod 10:567, 1984.)

The success of periapical surgery has been assessed with the same clinical and radiographic criteria as for nonsurgical root canal treatment. However, the radiographic criteria for successful periapical healing are different from those for nonsurgical root canal treatment ( Table 11-3 ; Figs. 11-9, 11-10, and 11-11 ). Moreover, periodontal attachment loss in the form of marginal gingival recession is an additional criterion for measuring the outcome of periapical surgery.

A, A maxillary right central incisor having undergone periapical surgery. B, Incomplete periapical healing at 1 year postoperatively. Complete healing at 3 (C) and 4 years (D) postoperatively.

Example of incomplete healing with isolated scar tissue.

Example of uncertain healing. Periapical radiographs of a maxillary left central incisor taken immediately after periapical surgery (A) , at 2 years postoperatively (B) , and at 3 years postoperatively (C) .

Now that the parameters have been discussed as to the variables that need to be considered when assessing healing or nonhealing outcomes, the following discussion will describe the expected outcomes of the various endodontic procedures.

Indirect Pulp Capping (One-Step versus Stepwise Excavation)

The most conservative management for extensive caries is indirect pulp capping using either the one-step or the stepwise excavation approach. The stepwise excavation approach with initial partial caries removal was advocated to reduce the risk of pulpal exposure and is generally considered to be associated with poorer outcomes. The clinical outcomes of the one-step or stepwise approaches have been compared in three randomized controlled trials on permanent teeth with deep caries. Stepwise excavation was found to be associated with a lower rate of pulp exposure and higher chance of long-term clinical success than the one-step excavation approach ( Table 11-4 ). Maltz and colleagues, however, found the contrary, and they attributed the low long-term clinical success rate of the stepwise approach to patients being noncompliant in returning for scheduled completion of treatment. Interestingly, comparison of the cost-effectiveness of the one-step versus the stepwise excavation techniques using health-economic modeling involving simulated treatment of a molar tooth with deep caries in a 15-year-old patient revealed the one-step procedure to accrue lower long-term costs as well as longer tooth retention and pulp vitality.

Meta-analyses of data from studies listed in Table 11-4 revealed that the weighted pooled success rate for indirect pulp capping using the one-step approach (81.7%; 95% confidence interval [CI]: 72.7%, 90.6%) ( Fig. 11-12 ) was similar to that for the stepwise approach (81.9%; 95% CI: 72.1%, 91.7%) ( Fig. 11-13 ).

Forest plot showing individual study and weighted pooled probabilities of success for one-step indirect pulp capping.

Forest plot showing individual study and weighted pooled probabilities of success for stepwise indirect pulp capping.

Calcium hydroxide cement was the preferred lining material for the pulpal surface, whereas zinc oxide–eugenol–based cement was the preferred base material in most studies. Recently, resin-modified-glass-ionomer liner has also been used, but the type of lining material did not influence the outcome (see Table 11-4 ). The age of patients, presence of preoperative pain, and pulpal exposure during excavation were significant negative prognostic factors.

Direct Pulp Capping

Direct pulp capping is performed on teeth with pulp exposures caused by caries, caries excavation, or traumatic injuries. Most studies investigating the clinical outcome of direct pulp capping on permanent teeth had excluded teeth with signs and symptoms of irreversible pulpitis and apical pathosis ( Table 11-5 ). Saline, sodium hypochlorite, and chlorhexidine have been reportedly used to irrigate the exposed pulp and to achieve hemostasis. Calcium hydroxide paste and mineral trioxide aggregate (MTA) were the commonly used capping materials (see Table 11-5 ).

A meta-analysis of data from studies * listed in Table 11-5 revealed the weighted pooled success rate to be 70.1% (95% CI: 59.9%, 80.2%) ( Fig. 11-14 ). The patient’s age and sex; tooth location and type; pulp exposure type, size, and its location; and the restoration type, size, and quality did not have a significant influence on success. Although the outcome of direct pulp capping of teeth with immature versus mature apices has not been systematically compared in individual studies, indirect comparison of pooled data from different studies revealed that teeth with immature roots were associated with significantly more successful outcomes.

Forest plot showing individual study and weighted pooled probabilities of success for direct pulp capping.

The type of capping material was another significant prognostic factor, with MTA performing superiorly to calcium hydroxide in a randomized controlled trial and in a systematic review.

* Please see the following references: .

Pulpotomy

Earlier studies on the outcome of partial pulpotomy (specifying varying degrees of coronal pulp removal) had only included teeth with vital traumatic pulp exposures; however, more recent studies have also included teeth with carious pulp exposures. Teeth with spontaneous or severe pain and signs and symptoms of apical pathosis were excluded ( Table 11-6 ). On the other hand, the outcomes of full pulpotomies (completely removing the coronal pulp and retaining the radicular pulp) had only been investigated in teeth with carious exposures ( Table 11-7 ). Saline irrigation has been preferred for achieving hemostasis, whereas calcium hydroxide and more recently MTA were the preferred pulp capping materials (see Table 11-6 ).

A meta-analysis of data from studies listed in Tables 11-6 and 11-7 revealed the weighted pooled success rate to be 79.3% (95% CI: 66.7%, 91.8%) for partial pulpotomies ( Fig. 11-15 ) and 82.4% (95% CI: 69.3%, 95.4%) for full pulpotomies ( Fig. 11-16 ).

Forest plot showing individual study and weighted pooled probabilities of success for partial pulpotomy.

Forest plot showing individual study and weighted pooled probabilities of success for full pulpotomy.

The effects of potential prognostic factors for pulpotomy have not been explored systematically except for the pulp capping material. Randomized controlled trials revealed that MTA achieved similar outcomes in partial or full pulpotomies when compared with calcium hydroxide.

Summary of Prognostic Factors for Vital Pulp Therapy

In summary, vital pulp therapy performed under guideline standards with optimal coronal seal achieved promising long-term success in teeth with carious, mechanical, or traumatic exposures of healthy pulps.

The most important factors affecting the outcome of vital pulp therapy are preexisting health of the pulp, adequate removal of infected hard or soft tissues, careful operative technique to avoid damage to residual tissues, and elimination of microbial leakage around the final restoration. It can be difficult to gauge the health of the residual pulp as it is a matter of subjective assessment and relies on experience in pulp diagnosis. The degree of pulp bleeding upon exposure is a more reliable tool to judge the status of the pulp than the preoperative clinical signs and symptoms. Continued bleeding after 10 minutes, even after rinsing with sodium hypochlorite solution, may suggest that the residual pulp was still heavily inflamed and a complete pulpectomy may be a more effective treatment modality. Removal of infected tissue is a matter of subjective experience but may be aided by various dyes. The final factor relies on the correct choice of restorative material and its adequate manipulation to prevent leakage.

Factors such as age and health of the patient, size and nature (carious or traumatic) of pulp exposure, and its duration of exposure to the oral environment (up to 48 hours) do not in themselves compromise outcomes of vital pulp therapy.

Factors Affecting Periapical Health or Healing Following Root Canal Treatment

The factors influencing the maintenance of periapical health or periapical healing of preexisting lesions following root canal treatment may be broadly classified into patient factors (age, sex, general health, tooth anatomy, preoperative pulpal and periapical status), treatment factors (operator variables, canal enlargement, irrigation, medication, culture test, and obturation), and restorative factors. Some factors had a profound impact on success rates, whereas others showed a negligible effect. Patient factors characterizing the nature of the disease showed the most significant effect (periapical status), whereas most of the treatment factors were found to exert a less significant effect; the exceptions were the apical extent of root canal treatment relative to the root canal terminus. In addition, the quality of the postoperative restorative care also exerted a profound influence on outcome of treatment.

Patient Factors

Patient’s age and sex consistently had no significant effect on outcome, whereas some specific health conditions (diabetes, compromised immune response ) apparently had a significant influence. The evidence for the effect of host immune response characterized by the general health of the patient is, however, weak. Emerging evidence indicates that the host response measured by polymorphisms of various genes involved in periapical healing may have an effect on outcomes ( Table 11-8 ). The importance of the host response to maintenance of periapical health or periapical healing was also supported by the statistically significant clustering effect of multiple teeth within the same patient in a prospective study.

The widespread perception that single-rooted teeth with less complicated anatomy should benefit with more predictable and favorable outcomes proves to be untrue. Having accounted for potential confounding factors such as the presence of periapical disease, tooth type does not seem to exert a strong influence on success rates. This would appear to be counterintuitive but may be explained by the logical inference that canal complexities in the apical anatomy probably play a more dominant role than other complexities such as the number and curvature of canals.

The presence and size of a periapical lesion seem to have the most negative effect on periapical health/healing; it therefore follows that these factors must be accounted for when analyzing the influence of any other factor. The profound change in success rates once a periapical lesion becomes established is interesting, as it is correlated with the establishment of infection in the apical canal anatomy. This seems to suggest that once the apical canal complexities become infected, it may be much more difficult to eradicate the infection. The negative influence of large periapical lesions has a reasonable biologic explanation: the diversity of bacteria (by number of species and their relative abundance) is greater in teeth with larger periapical lesions. An endodontic infection is more likely to persist in canals with a higher number of bacteria present preoperatively. In addition, larger lesions may represent longer-standing root canal infections that may have penetrated deeper into dentinal tubules and accessory anatomy in the complex canal system where mechanical and chemical decontamination procedures may not be so effective. Larger lesions may also represent cystic transformation. Finally, the host response may also play a part, as patients with larger lesions may innately respond less favorably to residual bacteria. This speculation may crystallize into distinct questions for further biologic research into the nature of interactions among host, bacterial infection, and treatment intervention.

Most of the other investigated preoperative factors (pain, tooth tenderness to percussion, soft tissue tenderness to palpation, soft tissue swelling and sinus tract, periodontal probing defect of endodontic origin, root resorption) are in fact different clinical manifestations of periapical disease. They may therefore act as surrogate measures or complement “presence and size of periapical lesion” in measuring the effect of severity of periapical disease within a broad continuous spectrum. Of these, only presence of preoperative pain, sinus tract, swelling, and apical resorption have been found to be significant prognostic factors that have been associated with significantly reduced success rates in root canal treatment.

The biologic explanation for the negative impact of sinus tract and swelling, either in the acute or chronic form, on periapical healing is interesting, as both represent suppuration and the proliferation of microbiota into the periapical tissues, with the inference being that the host tissues must have become locally overwhelmed. The precise reasons for reduced success rates under these conditions remain unclear but must somehow be related to the nature of the host-microbial interaction.

Treatment Factors

Operator

Although the impact of operator qualification and skill has not been specifically investigated, systematic review has shown that the involved clinicians may be grouped into undergraduate students, general practitioners, postgraduate students, and specialists. Studies show a clear trend in superior outcomes by greater experience and training. Clearly technical skills play an important role, but this is difficult and often impossible to quantify. In addition, the technical abilities must be augmented by the overall understanding of the biologic issues and the quest for superior treatment by the operator. If clinicians do not feel they can do optimal treatment, it is incumbent upon them to refer the patient to a more qualified practitioner.

Isolation

The use of rubber dams in modern root canal treatment is widely accepted, and the justification seems almost empirical. One study on retreatment analyzed the influence of rubber dam use compared to cotton roll isolation and found significantly higher success rates with the former approach. Another study reported a significantly higher success rate of root canal–treated teeth when a rubber dam was employed during post placement compared to when it was not. Perhaps as a consequence, the principal justification for rubber dam use is based on medicolegal implications of root canal instrument ingestion or aspiration by the patient.

Magnification and Illumination

Endodontists have repeatedly reinforced the value of magnification and illumination during root canal treatment, but a systematic review failed to draw any objective conclusions on their influence as no article was identified in the current literature that satisfied their inclusion criteria. A prospective study investigated this factor, but researchers found only an insignificant influence on the final outcome. Use of a microscope may sometimes assist location of the second mesiobuccal canal in maxillary molars, but this only made a small difference to the success rates associated with mesiobuccal roots, when a periapical lesion was present. The true benefit of a microscope can only be verified through a randomized controlled trial. However, canal negotiation with less tooth structure removal and fewer procedural accidents is favorable and seems intuitively more consistent with the use of superior magnification and illumination.

Mechanical Preparation: Size, Taper, Extent, and Procedural Errors

The root canal system may be mechanically prepared to a requisite size and taper using a variety of instruments of different cutting designs, tips, tapers, and materials of construction. Their efficacy is often tested in laboratory studies, and the instruments and their utility may have well-characterized properties. Investigation of the influence of type of instrument used for canal enlargement has been undertaken in one nonrandomized prospective study, but the outcome is likely subjective because of many factors, including the protocol adopted for teaching technical skills. In this study, the better success rates for hand or rotary NiTi instruments compared with stainless steel instruments were attributable to the fact that tactile skills training was achieved through a preliminary focus on the use of stainless steel files to develop tactile sensitivity and consistency. Only on demonstration of this competency did the trainees progress to NiTi instruments. More important, such senior students may also have had a better understanding of the biologic rationale for root canal treatment. The ability to gain and maintain apical patency as well as to avoid procedural errors was better instilled in the senior students, whereas in selected cases, NiTi instruments appear capable of achieving the same in primary root canal treatment undertaken by undergraduates.

A key tenet of the European Society of Endodontology (ESE) guidelines is that root canal debridement must be extended to the terminus of the canal system, which is expressed variously as extension to the “apical constriction,” or to “0.5 to 2 mm from the radiographic apex,” or to the “cementodentinal junction.” This guideline is broadly supported by the fact that outcome of treatment is compromised by canal obstruction or failure to achieve patency to the canal terminus. Ng and colleagues reported a twofold reduction in the success of treatment when the patency to the canal terminus was not achieved. It could be speculated that the lack of mechanical negotiability of canals may be due to the presence of obstructions caused by “denticles,” tertiary dentine, acute branching or a fine plexus of apical canals, or dentine/organic debris.

The continued debate on the optimal size of apical preparation remains topical in the absence of definitive evidence; the findings from relevant in vitro and clinical studies have been previously reviewed. So far, four clinical outcome studies have considered this issue or have systematically investigated the effect of apical size of canal preparation on treatment outcome. One randomized controlled trial revealed that enlargement of the canal to three sizes larger than the first apical binding file was adequate (the mean final size was ISO #30). The observational studies had not designed their investigation with apical canal size as their principal focus and neither had they found a statistically significant influence from this factor; nevertheless, they all reported the same inverse trend of decreasing success rates with an increase in size of apical preparation. It was speculated that canal preparation to larger apical sizes may compromise treatment success by generation of more apical dentine debris, which in the absence of an adequate irrigation regimen serves to block apical canal exits that may still be contaminated with bacteria. Continued generation of dentine debris, in the absence of sufficient irrigation, may lead to what is termed dentine mud, which ultimately creates a blockage. The impatient or neophyte clinician fails to resist the temptation to force the instrument back to length, resulting in the classically described procedural errors of apical transportation, canal straightening, and perforation. An alternative mechanism is required to explain the higher failures in initially large canals; it is likely that immature roots present a different debridement challenge, where the canal shape is not amenable to planing of the main portions of the canal by conventional instruments. Perhaps an intracanal brush may be a more suitable cleaning device in such teeth. The findings from these studies therefore do not concur with views that more effective bacterial debridement may be achieved with larger apical preparations.

The issue of apical preparation size should be considered together with that of the size and taper of the rest of the canal preparation. Again, there is a paucity of sufficient direct evidence for the influence of degree of canal taper on root canal treatment outcome. The ESE guidelines recommend only that canal preparation should be tapered from crown to apex without stipulating any particular degree of taper. Three studies have analyzed the influence of canal preparation taper on primary treatment and retreatment outcome, although again, none had focused their investigation primarily on this factor. Smith and coworkers, using loose criteria for determination of success, found that a “flared” preparation (wide taper) resulted in a significantly higher success rate compared with a “conical” preparation (narrow taper); the exact degree of taper was not reported and the effects of other treatment and nontreatment parameters were not controlled. In contrast, Hoskinson and associates and Ng and colleagues, using strict criteria, did not find any significant difference in treatment outcome between narrow (.05) and wide (.10) canal tapers. The controlled use of stainless steel instruments in a step-back technique may create .05 (1 mm step-back) or .10 (0.5 mm step-back) tapers, although, of course, uncontrolled use of such instruments may generate a variety of shapes. Ng and colleagues also compared these (.05 and .10) preparation tapers with .02, .04, .06, and .08 tapers (generally achieved by using greater taper nickel-titanium instruments) and found no significant effect on treatment outcome. They cautioned that their investigation of the influence of canal preparation taper without randomization could be influenced by the initial size of the canal, the type of instrument used, and operator experience.

Triangulation of the data on the effects of canal preparation size and taper on treatment outcome may intuitively lead to the conclusion that as far as current best evidence indicates, it is not necessary to over-enlarge the canal to achieve periapical healing. An apical preparation size of ISO 30 with a .05 taper for stainless steel instrumentation or .06 taper for NiTi instrumentation is sufficient. Precisely what biologic and hydrodynamic mechanisms underpin such sufficiency is more difficult to define based on available evidence. Although a number of laboratory studies have investigated the interaction between canal dimensions and irrigation or obturation dynamics, the precise physical, chemical, or biologic mechanisms that ultimately enable periapical healing remain unknown, although collaborations with fluid dynamics specialists and (micro)biologists may ultimately yield a clearer picture.

Procedural errors during root canal preparation include canal blockage, ledge formation, apical zipping and transportation, straightening of canal curvature, tooth or root perforation at the pulp chamber or radicular level, and separation of instruments. Instrument separation during treatment has been found to reduce the success rate significantly ; however, the reported prevalence of instrument separation was low (0.5% to 0.9%) in these studies, precluding an analysis of causative factors. A case-control study revealed no significant difference in success rates between periapically involved teeth with or without retained separated instruments. The stage of canal debridement at which instrument separation occurred and the justification for their retention may have implications on the outcome. The coronoapical location of a separated instrument and whether the instrument was successfully bypassed were found to have no effect on treatment outcome.

Irrigant

Different chemical agents have been used as irrigants for root canal treatment, singly or in various combinations, both in clinical practice and in the studies reviewed. They have included water, saline and solutions of local anesthetic, sodium hypochlorite, iodine, chloramine, sulfuric acid, EDTA, hydrogen peroxide, organic acid, Savlon, urea peroxide, and Biosept (a quaternary ammonium compound). Most of the studies had used sodium hypochlorite as an irrigant regardless of whether it was primary treatment or retreatment. This is consistent with the ESE guidelines for irrigation, which recommend a solution possessing disinfectant and tissue-dissolving properties.

One prospective study systematically investigated the effect of the irrigant on the success rates of root canal retreatment, which, although not a randomized controlled trial, revealed interesting new findings on the effects of irrigants. Even though a higher concentration of sodium hypochlorite made negligible difference to treatment outcome, the additional use of other specific irrigants had a significant influence on success rates. The finding of a lack of improvement in periapical healing with the use of a higher concentration NaOCl solution is consistent with previous clinical/microbiologic findings. Comparing 0.5% to 5.0% NaOCl solution for irrigation, it was found that the concentration of solution, per se, did not appear to increase the proportion of teeth rendered culture-negative or associated with greater periapical healing. As iodine and sodium hypochlorite are both halogen-releasing agents and attack common key protein groups, the finding that the additional use of 10% povidone-iodine for irrigation had no additional influence on treatment success was as expected. Surprisingly, however, the additional use of 0.2% chlorhexidine solution for irrigation was found to reduce the success of treatment significantly. This finding was in complete contrast to previous reports on its equivalent or superior in vivo antibacterial efficacy when compared with sodium hypochlorite solution. The use of chlorhexidine as a final irrigant following sodium hypochlorite irrigation had been recommended and was justified on several grounds, including its substantivity in root dentin (i.e., prolonged antibacterial effect), relative lack of toxicity, and broad-spectrum efficacy. Not until recently has alternate irrigation with sodium hypochlorite and chlorhexidine solution raised serious concerns because of their interaction product. The interaction product is thought to be an insoluble precipitate containing para-chloroaniline, which is cytotoxic and carcinogenic. Apart from mutually depleting the active moiety in the two solutions for bacterial inactivation, the precipitate may cause persistent irritation to the periapical tissue and block dentinal tubules and accessory anatomy, possibly explaining the observed lower success rate when chlorhexidine was used as an additional irrigant.

Ng and associates also found that the additional use of EDTA had a profound effect on improving radiographically observed periapical healing associated with root canal treatment (OR = 1.5 [1.1, 2.0]). In contrast, the observed synergistic effect of sodium hypochlorite and EDTA had been previously demonstrated in terms of bacterial load reduction but not periapical healing. The long-term (≥ 2 years) outcome of their cases stratified by canal disinfection protocols did not support their microbiologic findings. Their reported success rate for alternate irrigation with sodium hypochlorite and EDTA solutions (67%) was low when compared to the success rate for irrigation using saline (91%), 0.5% sodium hypochlorite (92%), or 5% sodium hypochlorite (86%) solutions. The reported outcome data were unexpected, as preobturation negative bacterial culture was achieved in all cases. Given the complexity of their study design (clinical and microbiologic), their sample size was restricted to 11 to 15 teeth per group, limiting their outcome data. The synergistic effect of the two disinfectants has been attributed to the chelating properties of the sodium salts of EDTA, and their roles have been reviewed by Zehnder. EDTA solution assists negotiation of narrow or sclerosed canals by demineralization of root dentine and helps in the removal of compacted debris from noninstrumented canal anatomy. It may also facilitate deeper penetration of sodium hypochlorite solution into dentine by opening dentinal tubules and removing the smear layer from the instrumented surface. Lastly, it may help detach or break up biofilms adhering to root canal walls.

Medicament

Most previous treatment outcome studies have not standardized the type of root canal medicament used in the interappointment period, but the use of several different medicaments has been reported. The list was consistent with that recommended in the ESE guidelines for a medicament with disinfectant properties and included calcium hydroxide, creosote, and iodine solutions. However, there is an absence of studies investigating the influence of this factor on treatment outcome.

The use of a mixture of calcium hydroxide and chlorhexidine has been tested based on the speculation that the mixture would be more effective against E. faecalis.

Root Canal Bacterial Culture Results Prior to Obturation

In the past, in various centers of endodontic excellence, completion of root canal treatment by obturation would only be acceptable after a negative culture test was obtained from the canal, confirming the absence of bacteria in the part of the root canal system that could be sampled. This practice has fallen out of clinical favor because of the perceived predictability and good prognosis of root canal treatment without microbiologic sampling. Sampling procedures are considered lengthy, difficult, often inaccurate, requiring laboratory support and having low benefit-to-cost ratio. A preobturation negative culture result may increase treatment success twofold ( Fig. 11-19 ). One large study helped contribute to the demise of the canal-culture test; however, even this study showed a 10% difference in success in favor of the negative culture test when periapical disease was present. The outcome is even worse when a positive culture test result combines with the presence of a periapical lesion.

Forest plot showing pooled and individual study’s odds ratio (OR) for periapical health of teeth undergoing root canal treatment with preobturation negative versus positive culture test results (pooled OR = 2.1; 95% CI: 1.5, 2.9).

Numerous studies * have evaluated the effect of different stages of root canal treatment on the intraradicular microbiota, both qualitatively and quantitatively ( Table 11-9 ). Some studies merely report positive culture tests, whereas others have identified and quantified intraradicular microbiota before and after various stages of treatment.

* Please see the following references: .

The effect of the “mechanical preparation” of the canal(s) on the microbiota has been tested using only water or saline as the irrigant. Taken collectively, the studies show that negative cultures were achieved on a weighted pooled average in 31% of the cases (range 0 to 79%). When sodium hypochlorite (concentration range 0.5% to 5%) irrigation supplemented the “mechanical preparation,” the frequency of negative cultures immediately increased to a weighted pooled average of 52% (range 13% to 95%) (see Table 11-9 ).

Most studies report culture reversals during the interappointment period when active antibacterial dressing is not used in the root canal system between appointments. The reversals are due to regrowth of residual bacteria or recontamination by bacteria from coronal restoration leakage. When active interappointment antibacterial dressing is used, negative cultures in the subsequent visit were achieved on average in 71% of cases (range 25% to 100%) (see Table 11-9 ).

Effect of Persistent Bacteria on Root Canal Treatment Outcome

The bacteria present in preobturation cultures have included Enterococcus , Streptococcus , Staphylococcus , Lactobacillus , Veillonella , Pseudomonas , Fusobacterium species, and yeasts. Studies have been variable as to the relationship between individual species and treatment failure. Although the overall failure rate for cases with positive cultures was 31%, teeth testing positive for Enterococcus species had a failure rate of 55%, and teeth with positive cultures for Streptococcus species had 90% failures. In another study, good-quality root canal treatment on 54 teeth with asymptomatic periapical disease gave an overall success rate of 74%, but teeth with positive cultures for Enterococcus faecalis achieved a success rate of only 66%. The success rate for teeth with no bacteria was 80%, whereas that for teeth with bacteria in the canal before obturation was 33%. These associations cannot be regarded as direct cause-and-effect associations, but they further emphasize the need to determine a relationship between microbial diversity and treatment outcome.

A monkey-model study used a four- or five-strain infection to test the effect of debridement and obturation procedures on outcome. When bacteria remained after chemomechanical debridement, 79% of the root canals were associated with nonhealed periapical lesions, compared with 28% when no bacteria were found to remain. Combinations of several residual bacterial species were more frequently related to nonhealed lesions than were single strains. When no bacteria remained at the end of chemomechanical debridement, healing occurred independently of the quality of the root filling. In contrast, when bacteria remained in the canal system, there was a greater correlation with nonhealing associated with poor-quality root fillings than in technically well-performed fillings. In root canals where bacteria were found after removal of the root filling, 97% had not healed, compared with 18% for those root canal systems with no bacteria detected upon removal of root filling. The study emphasizes the importance of reducing bacteria below detection limits before permanent root filling in order to achieve optimal healing conditions for the periapical tissues. It also reinforces the view that obturation does indeed play a role when residual infection is present.

Regardless of the technique used for obtaining a sample for a canal culture, the presence of a negative culture seems to have a positive impact on treatment outcome. The association of specific species with treatment failure is not well established but the identity of the small group of species isolated from positive cultures is relatively constant and may hold answers to treatment resistance and failure. However, it is important to understand that there are many other factors that can influence root canal treatment outcome.

Root Filling Material and Technique

The interrelationship among the core root filling material, sealer (for filling the gaps between the core material and canal surface), and technique for their placement complicates the investigation of the effect of obturation and technique on treatment outcome. In previous studies on treatment outcome, the most commonly used core root filling material was gutta-percha with various types of sealer or gutta-percha softened in chloroform (chloropercha). The sealers used may be classified into zinc oxide–eugenol–based, glass ionomer–based, and resin-based types. Materials such as Resilon, SmartSeal, and MTA have been adopted but have not significantly penetrated the market, except for the use of MTA in surgical repairs or repairs for immature apices. In any case, there is no evidence to show that the nature of root filling material and the technique used for placement has any significant influence on treatment outcome.

Apical Extent of Root Filling

Of the many intraoperative factors associated with success and failure of root canal treatment, the apical extent of the root canal filling material has been the most frequently and thoroughly investigated. In these previous studies, the apical extent of root fillings has been classified into three categories for statistical analyses: more than 2 mm short of radiographic apex (short), 0 to 2 mm within the radiographic apex (flush), and extended beyond the radiographic apex (long). The apical extent of root filling was found to have a significant influence on the success rates of treatment, regardless of the periapical status. Flush root fillings were associated with the highest success rates, whereas long root fillings were associated with the lowest success rates.

Most previous retrospective studies could not distinguish between the effects of apical extent of instrumentation versus the apical extent of obturation; however, the London Eastman study was able to separate the effect of these two factors and found them both to independently and significantly affect periapical healing. The factors correlated with each other, consistent with the fact that canals are normally filled to the same extent as canal preparation.

Extrusion of cleaning, medication, or filling materials beyond the apical terminus into the surrounding tissues may result in delayed healing or even treatment failure due to a foreign body reaction. Magnesium and silicon from the talc-contaminated extruded gutta-percha were found to induce a foreign body reaction, resulting in treatment failure. An animal study has shown that large pieces of subcutaneously implanted gutta-percha in guinea pigs were well encapsulated in collagenous capsules, but fine particles of gutta-percha induced an intense, localized tissue response. The inference that perhaps extrusion of large pieces of gutta-percha may not impact on periapical healing was not supported by data from previous studies. The discrepancy may possibly be accounted for by bacterial contamination of the extruded gutta-percha in the clinical data.

The radiographic evidence of “sealer puffs” extruding through the main apical foramina and lateral/accessory canals has been pursued with vigor by some endodontists based on the undaunted belief of its value as “good practice.” Their perception is that this represents a measure of root canal system cleanliness, and they ardently argue that healing would follow, albeit with some delay. The published evidence on the effects of sealer extrusion into the periapical tissues has been contradictory. Friedman and colleagues found that extrusion of a glass ionomer-based sealer significantly reduced success rates. In contrast, Ng and associates reported that extrusion of a zinc oxide–eugenol based–sealer had no significant effect on periapical healing. The discrepancy may be attributed to the difference in sealer type and the duration of treatment follow-up. The radiographic assessment of the presence or resorption of sealer may be complicated by the radiolucent property of its basic components and the insufficient sensitivity of the radiographic method used to detect small traces of it. It is possible that, in some cases, the radiographic disappearance of extruded sealer may simply be due to resorption of the radio opaque additive, barium sulfate, or its uptake by macrophages, still resident in the vicinity.

Extruded glass ionomer–based zinc oxide–eugenol–based, silicone-based sealers or endomethasone were not found to be resorbed/absorbed by periapical tissues after 1 year. Traces of calcium hydroxide–based sealer (Sealapex) could still be detected after 3 years. In the latter study, treatments were carried out on primary molar teeth and the canals were obturated with Sealapex without gutta-percha. With longer duration of follow-up, complete resorption of extruded zinc oxide–eugenol–based sealers (Procosol, Roth Elite) and a resin-based sealer (AH Plus, Dentsply/DeTrey, Konstanz, Germany) was demonstrated in 69% and 45% of the cases after 4 and 5 years, respectively. Ng and associates advanced two explanations for the difference between the effect of extruded core gutta-percha and the zinc oxide–eugenol sealer: the latter is antibacterial and may kill residual microorganisms, whereas it is also more soluble and readily removed by host cells compared to gutta-percha.

Quality of Root Filling

Another much investigated parameter of obturation in retrospective studies has been the radiographic measure of the “quality of root filling.” The rationale for complete obturation of the root canal system is to prevent recontamination by colonization from the residual infection or newly invading bacteria. Both are supposedly prevented by a “tight” seal with the canal wall and an absence of voids within the body of the material. Quality of root filling may therefore be regarded either as poor root-filling technique or as a surrogate measure of the quality of the entire root canal treatment, because good obturation relies on properly executed preliminary steps in canal preparation. A systematic review reported that the criteria for judging the quality of root fillings have not been well defined in previous studies. An unsatisfactory root filling has been defined as “inadequate seal,” “poor apical seal,” or “radiographic presence of voids.” Nevertheless, satisfactory root fillings were found to be associated with significantly higher success rates than unsatisfactory root fillings.

Acute Exacerbation During Treatment

The causes for interappointment “flare-up” or pain have not been precisely determined, and several hypothetical mechanisms involving chemical, mechanical, or microbial injury to the periradicular tissues, as well as psychological influences, have been suggested as contributory to postpreparation pain or swelling. Although these factors have not been specifically studied in the context of periapical healing, acute “flare-ups” during treatment were not found to be significantly associated with periapical healing in two studies. In contrast, the London Eastman study found that pain or swelling occurred in 15% of cases after chemomechanical debridement and was found to significantly reduce success as measured by periapical healing. This interesting finding may be explained by the hypothesis that “flare-ups” were caused by extrusion of contaminated material during canal preparation. Such material may elicit a foreign body reaction or (transient) extraradicular infection, resulting in treatment failure in a proportion of such cases. Alternatively, acute symptoms may be the result of incomplete chemomechanical debridement at the first appointment, leading to a shift in canal microbial ecology favoring the growth of more virulent microorganisms, leading to further postpreparation pain and treatment failure. The exact biologic mechanisms of failure in these cases remain obscure and warrant further investigation.

Number of Treatment Visits

The number of treatment visits for completing root canal treatment and its effect on periapical healing remains an ongoing controversy. Generally, the argument for single-visit treatment centers around better patient acceptability and cost-effectiveness versus the preference of multiple-visit treatments based on biologic rationale. The premise for multiple-visit treatments has been that primary debridement is not completely effective in eliminating all the adherent bacterial biofilm and the residual bacteria may multiply and recolonize the canal system. Therefore, the proponents consider it desirable to use the interappointment period to dress the canal with a long-lasting or slow-release antibacterial agent capable of destroying or incapacitating residual bacteria, as well as to take the opportunity to gauge the initial periapical response before root filling. Calcium hydroxide has served in this capacity for many years because of its ability to dissolve organic tissue, kill bacteria, detoxify antigenic material, and act as a slow-release agent because of its low solubility-product in an aqueous environment. However, its antibacterial ability has come under close scrutiny, with advocates suggesting that the material is not suitable for this purpose. A final resolution to this debate is awaited based on robust clinical evidence. Most of the published randomized controlled trials found no significant influence of healing attributable to number of treatment visits, but they all lacked robust statistical power.

The debate about the merits of single- or multiple-visit treatments will continue unabated given the respective strengths of the motivational drivers among the opposing groups. The issue may only be resolved by properly documented, large randomized controlled trials (which are currently unavailable) because undocumented variables (i.e., operator skill, biologic or technical case complexity, and patient compliance) would continue to bias the outcome.

Post Root Canal Treatment Restorative Factors

Effect of Quality and Type of Restoration

The placement of a coronal restoration after root canal obturation is the final step in the management of teeth undergoing root canal treatment. It has been shown to have a major influence on endodontic outcomes. Teeth with satisfactory coronal restorations were found to have significantly better periapical healing compared with those with unsatisfactory restorations (OR = 3.31; 95% CI: 1.07, 10.30). The term satisfactory restorations has been defined as a restoration with no evidence of marginal discrepancy, discoloration, or recurrent caries with absence of a history of decementation.

Given that one of the roles of coronal restorations is to prevent postoperative root canal reinfection via coronal leakage, the criteria for unsatisfactory restoration given by Hoskinson and colleagues could not infer coronal leakage when the inner core was still intact. Consequently, the London Eastman study adopted a different classification and definition for unsatisfactory restorations in order to illustrate obvious and potential coronal leakage more accurately. The two groups of unsatisfactory restorations were defined as those with (1) obvious signs of exposed root filling and (2) potential leakage indicated by marginal defects and history of de-cementation. It is perhaps this strategy that contributed to the finding of a profound effect (OR = 10.7; 95% CI: 3.7, 31.5) of coronal leakage on the endodontic outcome.

A number of investigations have been performed based on comparisons between the types of post root canal treatment restorations, including permanent versus temporary restorations, crown versus acrylic restorations, presence versus absence of posts, and nonabutment versus abutment. Teeth that had been permanently restored were associated with significantly higher success rates than their temporarily restored counterparts in some studies but not in others. The type of permanent restoration was found to have no significant influence on the outcome of treatment.

It has often been recommended that it would be wise to provide a subseal over the root filling in case of loss of a permanent or temporary restoration; the subseal would be glass ionomer (GIC) or zinc oxide–eugenol cement. The placement of a GIC or zinc oxide–eugenol (IRM) cement lining coronal to the gutta-percha filling and underneath the permanent core in order to provide an additional antibacterial coronal seal was found in a prospective study to have no beneficial effect on treatment success.

In summary, the preceding findings overall support the ESE guidelines that an adequate restoration should be placed after root canal treatment to prevent subsequent bacterial recontamination. Therefore, the provision of a good-quality coronal restoration, regardless of type, should be considered the final part of the root canal treatment procedure following obturation.

Use of Root Treated Teeth as Abutments for Prostheses and Occlusal Contacts

Mechanical stress on restorations is a function of the role of individual teeth in the occlusal scheme. The pattern of occlusal loading both in static and dynamic occlusion is dictated by whether the teeth are involved as single units or abutments (bridge/denture) and whether they have holding or guiding contacts. It is reasonable to expect that bridge and denture abutments may be placed under unfavorable loads, as may last-standing teeth in the dental arch. These teeth may therefore be expected to have lower success rates because of a potential increase in the development of cracks and fractures due to fatigue. This observation has been confirmed for teeth functioning as bridge abutments compared with those restored as individual units following root canal treatment.

Summary of Factors Influencing Periapical Healing Following Nonsurgical Root Canal Treatment

The following factors are considered as having a major impact on periapical health subsequent to root canal treatment:

• ♦

  Presence ( Fig. 11-20 ) and size ( Fig. 11-21 ) of periapical lesion

  

  Forest plot showing pooled and individual study’s odds ratio (OR) for periapical health of teeth undergoing root canal treatment with preoperative nonvital pulps and absence of periapical radiolucencies versus teeth with nonvital pulps and presence of periapical radiolucencies (pooled OR = 2.4; 95% CI: 1.7, 3.5).

  

  Forest plot showing pooled and individual study’s odds ratio (OR) for periapical health of teeth undergoing root canal treatment with preoperative large (> 5 mm) versus small (< 5 mm) periapical radiolucencies (pooled OR = 2.2; 95% CI: 1.3, 3.7).

• ♦

  Patency at the canal terminus (achieving patency significantly increased the chance of success twofold)

• ♦

  Apical extent of chemomechanical preparation in relation to the radiographic apex ( Fig. 11-22 )

  

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