Grey areas in restorative dentistry: part 7. Managing a tooth with a sub-optimal root filling

Root canal treatment is a common procedure, and based on raw data from their study, Leon-Lopez et al¹ concluded that globally, 8.2% of teeth have been endodontically treated, and 55.7% of adults over the age of 18 years have at least one root-filled tooth.

Root canal treatment in the UK is predominately provided by general dental practitioners, with over 500,000 endodontic treatments completed annually in the NHS alone (pre COVID-19 2018/2019).² It is likely, therefore, that during an average day, a practitioner will come across several teeth that have been root treated.

According to the European Society of Endodontology:

‘Endodontic treatment encompasses procedures designed to maintain the health of all or part of the dental pulp. When the dental pulp is diseased or injured, treatment is aimed at preserving normal peri radicular tissues. When apical periodontitis has occurred, treatment is aimed at restoring the peri radicular tissues to health; this is usually carried out by root canal treatment, occasionally combined with surgical endodontics.’³

Furthermore, the society states that:

‘The root canal filling should consist of a (semi-) solid material in combination with a root canal sealer to fill the voids between the (semi-) solid material and root canal wall. The prepared root canal should be filled completely unless space is needed for a post. The prepared and filled canal should contain the original canal. No space between canal filling and canal wall should be seen. There should be no space visible beyond the endpoint of the root canal filling.’³

Endodontic treatment aims to remove the pulp or pulpal remnants from the root canals as close to the apical constriction as possible, to render the canals as bacteria and/or virus free as possible, and then to fill the created and shaped space with a suitable filling material. The apical constriction normally varies between 0.5 and 2 mm from the radiographic apex (Table 1).

Therefore, accurate diagnosis and assessment is essential for the successful management of the root filled tooth and this will embrace:

The routine use of cone-beam computed tomography (CBCT) for diagnosing the status of the peri-apical region and the root fillings is no longer recommended owing to its higher radiation dosage.⁴ However, CBCT does have a role in more complex situations, especially where peri-apical radiographs are not consistent with persistent clinical signs or symptoms. By producing 3D imaging of the totality of the tooth and alveolar bone, much is revealed beyond that of the 2D intra oral radiograph.

When analysing a long cone peri-apical radiograph, it is important to be aware that bone loss around the root of the tooth, whether apically or laterally, will only appear if cortical bone is lost (Figure 1). There can be considerable loss of cancellous bone without any indication on the radiograph. A series of laboratory experiments on dried mandibles illustrated this point very clearly.⁵ A mandible was sectioned and a large amount of cancellous bone removed without damage to the inner layer of the cortical bone. The mandible was then reconstructed and a further peri-apical radiograph taken. Despite the loss of bone, the post-experiment radiograph had the same appearance as the pre-operative radiograph. In a second experiment, a lower second molar was removed from a dried mandible and holes drilled into the cancellous bone at the base of each socket, representing peri-apical lesions. Lead balls were placed into these holes, the extracted tooth replaced in its socket and a subsequent radiograph clearly showed their position at the base of each root. The tooth was then removed again, the lead balls removed, and the tooth replaced in its socket again. A further radiograph did not reveal the loss of bone at the apices of the tooth. The important implication of this is that the visual absence of bone loss cannot be taken as true sign of a healthy situation. The appearance must be assessed together with the history, clinical examination and any further investigations, including radiographs (Table 2 and Figure 2).

While Figure 2 shows what would be an acceptable/optimum root filling, what it does not tell us is how many roots are present in the tooth because the rightangle view allows for overlap of the buccal roots against any lingual roots that may be present. To ascertain the number and distribution of roots, the parallax technique is the one that would be most useful in general practice as access to CBCT equipment is likely to be limited.

Kanasingham et al⁶ found that ‘the diagnostic accuracy of single digital peri-apical radiography was significantly better than single film peri-apical radiography. The inclusion of two additional horizontal (parallax) angulated peri-apical radiograph images (mesial and distal horizontal angulations) significantly improved detection of apical periodontitis although according to Davies et al,⁷ while two parallax radiographs detect significantly more root canals than a single radiograph, they did not increase detection of peri-apical lesions when compared to a single peri-apical radiograph.’

The SLOB rule (also known as the Clarke rule or buccal object rule) identifies the position of a root as lingual or buccal. With a shift in horizontal angulation, a root that appears on the second radiograph to move in the same direction as the head of the X-ray machine will be lingual, while a shift in the opposite direction will identify the root as buccal: same lingual opposite buccal.

The sub-optimal root filling challenges the practitioner to decide between accepting or modifying the current situation (Figures 3–5).

Conclusion

The discovery of a tooth with a sub-optimal root filling presents the practitioner with a choice, either to accept or to modify the situation. Where there are symptoms and signs, intervention will be necessary to bring the patient to health and comfort, and this may extend to extraction of the offending tooth. Where there is a desire to retain the tooth and enable it to become an aesthetic and/or functioning unit in the mouth, it is desirable to have a structured approach to assessing the situation to enable a care plan to be formulated having informed the patient of the risks and benefits of any treatment (or no treatment) proposed.

Clinical conundrums

For these clinical scenarios, what would be the aims of treatment, the range of interventions to achieve these, and how would you choose? List the risks and benefits for each option.

1. This UL4 had become tender to bite on over the previous 2 weeks. The crown was loose and there was buccal tenderness over the apex of the tooth. The tooth is in occlusion. There is pocketing of 3 mm.

What further investigations, if any, would you undertake and what would be your diagnosis?

What are the options available for treatment? How would you choose which option to proceed with?

2. This tooth was root filled with silver points in 1980. The patient is now 70 years old. The existing crown needs replacement because of carious dentine distally under the crown. The tooth is asymptomatic, and the periodontium shows 3–4-mm pocketing. The tooth is in occlusion with the upper natural teeth.

What observations can be made, what further investigations, if any, would you undertake, and what treatment options are available? How would you choose which option to proceed with?