Modern endodontic planning part 1: assessing complexity and predicting success

Diagnostic prerequisites

It is essential to have a high quality periapical radiograph, taken using a parallelling device, as part of the diagnostic process. The radiograph must include the entire root and apical area. All practitioners should have a quality assurance programme in place to monitor the justification, diagnostic and processing quality of their radiographs. Parallax radiographs are helpful in multi-rooted teeth to differentiate anatomy. Recent developments have demonstrated that cone beam computed tomography (CBCT) may have a role in assessment of anatomy and pathology. There is evidence that CBCT has a higher diagnostic yield when assessing for periapical pathology than conventional periapical radiography.¹⁰ In addition, CBCT can help identify anatomical variations, patency, separated instruments, fractures, resorptive conditions and the quality and extent of pre-existing root canal filling.¹¹ CBCT delivers a significantly higher radiation dose than conventional radiography and should only be used to answer specific questions that may alter the decision to treat a tooth.¹² Therefore, all CBCT scans must be appropriately justified and practitioners must not view CBCT as a routine diagnostic tool for all patients.

Patient factors

Patients must be prepared to undergo lengthy and potentially expensive treatment if they wish to proceed with endodontic treatment. Multiple visits may be necessary. The management of a patient with a prominent gag reflex is potentially challenging, but the majority cope well once a rubber dam, isolating the mouth from instruments and medicaments, has been applied. Anxious/phobic patients may require adjunctive sedation. This service may not be readily available, especially for lengthy or complex procedures. Dentists should be honest about the clear difficulties which these patients present and consider extractions if the teeth are not of strategic significance or an appropriate referral.

There are very few medical conditions which contra-indicate endodontic therapy. It has been suggested that a patient with an ASA status 3 (Table 3) or greater should not be treated in general practice. Often it is not the patient's medical but physical condition that may preclude RCT, such as a difficulty in lying flat (for long periods), or involuntary muscular movements. Patients with significant learning difficulties may not be able to consent to treatment and, in these instances, a best interests decision should be made with the input of their next of kin or an independent mental capacity advocate.

There are a number of circumstances in which root canal treatment is preferable to extraction. These may include patients with a history of head and neck radiotherapy, the use of bisphosphonates or patients with coagulation defects (Figure 4). For many of these patients multidisciplinary care is required and this is most often achieved in a secondary or tertiary centre but this is not a reflection on the complexity of the root canal treatment per se but a management issue. With good support from a local consultant, practitioners can treat these cases in practice.

Mouth factors

The need for endodontic treatment must be placed in the context of the patient's oral disease status and general oral health. Complex care should be deferred if there is active caries and periodontal disease (Figure 5). When teeth are painful and the pulp irreversibly damaged this must be addressed by extirpation and dressing a tooth or extraction. Practitioners should not prescribe antibiotics unless there is evidence of systemic involvement (fever/malaise) and/or enlarging facial swelling that has not been controlled with local measures (RCT/extraction) alone.

Limited opening, poor access to affected teeth and an inability to place rubber dam all add to the potential difficulties of providing treatment (Figure 6). Mouth props may help, but if rubber dam cannot be placed this must be regarded as a contra-indication to endodontic treatment.

Tooth factors

Diagnostic complexity

Irreversible pulpal disease in a heavily restored dentition can make identification of the offending tooth difficult (Figure 7). Following the appropriate diagnostic tests, if doubt remains as to the source of the pain, it may be prudent to offer analgesics and defer intervention. If symptoms do not correlate with dental disease, the clinician must be more cautious. Unusual pain histories, when teeth are minimally restored, if pain crosses the midline or there is a history of extractions following previous similar presentations, the clinician should be alerted that such pain may not be dental. In these cases, rather than commence RCT, a referral for a second opinion to discount non-odontogenic pain is indicated.

It is a prerequisite that rubber dam can be placed and this may be tried prior to treatment. If the dam margins do not form a water-tight seal, treatment may need to be abandoned unless novel approaches can be used (Figure 8). Extensive caries which is inaccessible to complete removal should be considered a contra-indication to further treatment. If there is evidence of failed coronal seal or recurrent disease, consideration must be given to the removal of crown and bridgework in advance of treatment. This also allows a more thorough inspection of the underlying tooth structure and may facilitate access to the pulp chamber and root canal system (Figure 9). Access through crowns can be difficult; there is often impaired visibility. Furthermore, loss of anatomical markers and alterations in crown-root angulation may increase the likelihood of excessive tooth removal and perforation.

Assessment of restorability is often subjective

A tooth restorability index has been described.¹³ Though this remains unvalidated, it may serve as a more objective aid when assessing teeth.

If the coronal aspect of a tooth is not restorable, and capable of being isolated with rubber dam, the root(s) may still be used as an overdenture abutment. This allows preservation of alveolar bone, tactile proprioception, increased support for prostheses and, if root surface anchors are used, an increase in the retention of prostheses (Figure 10).

In the case of perio-endo lesions, all diagnoses with a primary periodontal disease origin carry an uncertain prognosis. It is imperative that endodontic therapy is undertaken parallel with periodontal treatment if outcomes are to be improved in teeth that have perio-endo lesions.

Root factors

If a root canal shows no evidence of radiographic patency this may increase the complexity, but many canals that appear sclerosed on a radiograph are not always sclerosed clinically¹⁴ (Figure 11). It is important to attempt orthograde treatment first but inform the patient that surgical treatment or an extraction may be the only solution should access prove futile. Access to the root canal can be difficult, especially when extensive cores have been placed or posts used (Figure 12). Techniques for accessing sclerosed canals are described later in this series.

With increased curvature comes an increased likelihood of iatrogenic damage, canal shortening, instrument fracture and inadequate cleaning and shaping. The basic curvature of the root can be calculated on an undistorted periapical radiograph by the intersection of a line passing through the long axis of the tooth and a line connecting the long axis and apical position (Figure 13). Double curves present even more difficulty (Figure 14). Complexity is also increased where complex root canal anatomy is evident, such as C-shaped canals and internal resorption.

An open apex results from incomplete root formation or external inflammatory resorption of the apex. This may necessitate the use of alternative obturation materials and techniques not commonly practised. Where there is incomplete root development, consideration must be given to using different techniques and materials, such as mineral trioxide aggregate. These will be described in later papers (Figure 15).

Previous RCT in a tooth invariably complicates subsequent attempts at root canal treatment. This may be due to the difficulties of removing old root canal materials and sealers or to iatrogenic deviations from the root canal system. Correction of errors of preparation, such as ledges, zipping and perforation, may be very difficult to undertake and require considerable skill and often additional equipment and materials (Figure 16). However, not all retreatments are difficult. It may be evident that primary treatment was not undertaken to a high standard with poorly compacted gutta percha and retreatment may not be challenging (Figure 17). Referral centres may reject these cases, suggesting that the primary care clinician attempts re-treatment.

The presence of fractured instruments may not preclude orthograde root and root canal re-treatment but may complicate it¹⁵ (Figure 18). As a general rule, if an instrument can be visualized, it may be possible to retrieve it. If it is beyond a curvature or in the apical portion of the tooth, retrieval may become impossible. In these instances, successfully bypassing the instrument is the only solution, but again this may not be possible. One must always consent patients to the risk of further iatrogenic damage when instrument removal is to be attempted.

The existence of additional pathology (eg root resorption) indicates that more specialized investigations, such as CBCT, and potentially different techniques may be required (Figure 19). See Table 4 for a summary of the key factors to be considered in decision-making.

Operator factors

Operator training is associated with improved success.⁶ Thus it is essential to work within one's competency. Access to loupes, an operating microscope, and more specialized equipment and materials is best practice for more complex cases. Indeed, some would argue that these are necessary for all cases!

Removable partial denture

These are simple, cost-effective and can restore both aesthetics and function. Unfortunately, many do not get worn and there may be both psychological and physiological costs related to removable prostheses.^21,22,23

Adhesive bridge

These are predictable and minimally invasive and can offer a good solution for missing teeth.²⁴ Evidence suggests successful retention of 7+ years.²⁵ Anterior adhesive bridges will survive longer than posterior bridges and both have more favourable outcomes than bridges replacing canines.²⁶

Conventional bridge

These have similar, if not improved, survival rates compared to adhesive bridges, but at an increased biological cost.⁵ Up to 63–72% of tooth structure is removed when a tooth is prepared for a metal-ceramic restoration.²⁷ Furthermore, 19% of such teeth may lose vitality.²⁸ When these bridges fail, the result is more detrimental to the remaining dentition.

Single tooth implant

These offer very good survival rates at 5 and 10 years at 94.5% and 89.2%.⁵ The aesthetics can be excellent and destruction of abutment teeth is not required. Bone grafting may be indicated to prepare the site for placement and anatomic structures may prohibit placement. In the posterior maxilla, the presence of the maxillary sinuses often means that there is insufficient bone volume for a dental implant. In the posterior mandible, implants may only be placed if there is sufficient bone volume above the inferior dental nerve. Implants can be prohibitively expensive and patients must be consented to the cost of ongoing maintenance.²⁹

Health economic evaluation has demonstrated that there is merit in attempting root canal treatment ahead of implant therapy.³⁰ The condition of the remaining dentition should be assessed and any pre-exisiting disease stabilized. It is important that the clinician should not focus on the missing tooth in isolation but consider it in context with the rest of the mouth and in accordance with the general wellbeing of the patient.