Management of an incidental radiographic finding of a severely infraoccluded primary molar

Background

Infraocclusion, or submergence as it is commonly referred to, occurs when a tooth is no longer able to maintain its position adjacent to other teeth in the developing dentition. It usually occurs in the mixed dentition. The term ‘infraocclusion’ relates to the failure of continued eruption of a tooth which, following the continued occlusal eruption of the surrounding dentition, eventually leads to the tooth being positioned below the level of the occlusal plane.^1,2,3

There is a wide range in the reported prevalence of infraocclusion, ranging from 1.3–35.3%.^4-7 This large variation can be attributed to the use of differing diagnostic criteria, along with an inconsistency in the age of children included in the numerous studies. Mandibular first primary molars have been identified as the most commonly affected tooth, followed by the mandibular second primary molar and the maxillary primary molars.⁸ Severe infraocclusion is observed in only 2.5–8.3% of cases.⁸

Infraocclusion is widely associated with ankylosis,^1,9,10,11 which involves the failure of the periodontal ligament to separate cementum and dentine from the surrounding bone. The cementum and dentine are replaced by bone, and thus the tooth becomes fused to the bone. This correlation has also been reported in numerous histological studies which have demonstrated that ankylosis is strongly associated with teeth that are clinically submerged.^3,7,12 Changes in the position and shape of the cell rests of Mallassez have been thought to influence the likelihood of ankylosis and root resorption.¹³

A multitude of aetiological theories have been postulated for the occurrence of ankylosis. The traumatic theory suggests that it is due to the presence of defects, or any other discontinuity of the periodontal ligament, as a result of injury to either the bone or the periodontal ligament itself. Such damage is thought to be accompanied by a regenerative process leading to ankylosis. However, this theory was undermined following the findings of in vivo studies, which failed to elicit ankylosis.¹⁴

The disturbed local metabolism theory relies on the assumption that, in normal development, root resorption precedes the diminishment of the periodontal ligament. A disruption of this normal process, with the disappearance of the periodontal ligament prior to root resorption, results in direct contact between the tooth surface and the surrounding alveolar bone, leading to ankylosis.¹⁵

Alternatively, infraocclusion could be related to a genetic predisposition. This is supported by data from studies reporting 46% prevalence of ankylosis in siblings, compared to 1.3% in the control group.^4,16

Overall, extrinsic causative factors, such as trauma leading to damage of the Hertwig's epithelial root sheath, chemical or thermal irritation and deficient eruptive forces, are now thought to have a negligible influence.¹¹ Seemingly of greater importance are intrinsic factors such as the aforementioned genetic predisposition.^1,4,5,11

More severely infraoccluded teeth are often extracted to avoid potential problems. Indications for extraction include deep infraocclusion below the gingival margin, severe tipping of adjacent teeth and ectopic eruption of the permanent successor without resorption of the deciduous roots.¹² Owing to the aforementioned increased difficulty of extraction, often they involve raising a muco-periosteal flap and sectioning of the tooth. This frequently necessitates a general anaesthetic, especially for the child patient.

A number of sequelae of infraoccluded teeth have been described in the literature, most of which have orthodontic implications. Infraocclusion can cause a delay in the normal exfoliation of a deciduous tooth. When the permanent successors are present, the loss of the deciduous tooth can be delayed by 6–12 months compared to the contralateral unaffected side.⁷ Extraction of the infraoccluded tooth can also be more difficult, leading to frequent retention of root fragments. However, the absence of a permanent successor is associated with the retention of the infraoccluded primary tooth which, in the long term, will elicit orthodontic and restorative implications. Infraocclusion can also cause resorption of the proximal surfaces of the adjacent teeth and a reduction of the alveolar bone support. Teeth adjacent to an infraoccluded tooth are susceptible to tipping, whilst over eruption of the opposing teeth may also occur. In addition, caries and abscess formation can occur in association with the submerged tooth. A common consequence is the deviation of the dental centreline towards the affected side. Infraoccluded teeth have been reported to be associated with a significantly high frequency of lateral openbites and crossbites.⁹

The degree of infraocclusion is significantly influential on the complexity of its management and can be classified from slight to severe, according to the following parameters outlined by Brearley and McKibben:⁵

The diagnosis of infraocclusion is predominately reliant on the clinical presentation of a tooth that appears to be submerged relative to its adjacent teeth. This can be supplemented with additional diagnostic assessments, such as percussion of the suspected tooth. However, this method is dependent on the extent of ankylosis present. Studies have reported that a high pitched tone is best heard when at least 20% of the tooth's root surface is ankylosed.^17,18,19 As such, percussion has been deemed an inconsistent test.²⁰ The mobility of a tooth is also a commonly utilized diagnostic assessment. However, evidence has demonstrated that a lack of mobility requires more than 10% of the tooth's root surface to have been ankylosed¹⁸ and therefore is not a robust indicator. Routine radiographs may also be used to aid diagnosis. Yet, several studies comparing radiographic diagnosis, based on the absence of the periodontal ligament space with histological confirmation, have elicited a poor correlation,^5,20 and this can be attributed to the two dimensionality of plain radiographs.²⁰

Treatment decision-making models based on the management of infraoccluded primary teeth place significant emphasis on early diagnosis in an attempt to avoid the occurrence of the aforementioned complications associated with infraocclusion. Early diagnosis and intervention is generally associated with simpler treatment plans.⁹ Early diagnosis is usually accompanied by conservative treatment in the form of regular monitoring, which involves space measurements and study models and allows for accurate comparison. Intra-oral photographs can also be used as a monitoring tool.⁹

This report describes the process of diagnosis and subsequent management of a case that was not diagnosed early. The infraoccluded upper second primary molar tooth was a late incidental finding.

The report also demonstrates the value of utilizing cone beam computed tomography (CBCT) as a diagnostic adjunct (Figure 1).

Case history

A 12 years 3 month-old Caucasian female was referred to the Orthodontic Department within the University Dental Hospital of Manchester by her general dental practitioner. She complained of mild pain in the upper right quadrant with an associated partially erupted, palatally displaced upper right second premolar (UR5). Her medical history was unremarkable and she was a regular dental attender.

A comprehensive orthodontic examination was undertaken with the following findings:

Radiographic investigation

Initially, a long cone periapical in the region of the partially erupted UR5 was requested. The periapical radiograph taken confirmed the impeded eruption of the UR5, showing it to be tilted distally and contacting the mesial aspect of the UR6. Incidentally, a radio-opacity was noted apically in relation to the crown of the UR5. In light of the radiographic findings, the patient was referred to the Radiology Department for limited field of view cone beam computer tomography (CBCT) of the upper right quadrant to aid diagnosis and for surgical planning.

The provisional diagnoses relating to the apparent radio-opacity in the region of the partially erupted impacted UR5 were as follows:

Infraoccluded upper right second deciduous molar (URE);

Supernumerary tooth;

Odontome.

The CBCT showed that the partially erupted upper right second premolar (UR5) was disto-angularly impacted on the palatal aspect of the alveolus and against the upper right first molar, but that there was no resorption of this tooth. It also demonstrated that the pericoronal radiolucency associated with the upper right second premolar (UR5) was an infraoccluded upper right second deciduous molar (URE), lying at the level of the floor of the maxillary sinus. The imaging also suggested that there had been extensive resorption of the infraoccluded tooth and that it was likely ankylosed in places, with thickening of the mucosal lining of the maxillary sinus. The most unusual finding of the CBCT was that the upper right second deciduous molar (URE) was seemingly submerging above the erupted upper right second premolar (Figures 2 and 3).

Orthodontic treatment

From the outset, the patient was reluctant to undergo orthodontic treatment, despite the rotated upper right first premolar (UR4) and molar (UR6), and the planned loss of the upper right second premolar (UR5). On review, 18 months following the extractions, the upper right first molar had uprighted well and the buccal segment was fairly well aligned with a Class II molar relationship on the right-hand side (Figure 4). The patient was not keen on proceeding with orthodontic treatment and was therefore discharged from the department.

Discussion

The literature indicates a low prevalence of severely infraoccluded upper primary second molars with a reported prevalence as low as 2.5–8.3%.¹⁰ Submergence of an upper deciduous molar superior to an erupted upper second premolar is unusual, with no similar reported cases in the literature. The pattern of the submergence may have been due to the palatal eruption pathway of the premolar.

Earlier recognition and management may have prevented the prevailing malocclusion and the extensive surgical intervention that was required.

Early intervention entails routine interval monitoring with accompanied clinical measurements of space and radiographic assessment for any further root resorption. Regular assessment allows for the identification of any further progression of infraocclusion or pathological developments,²⁰ along with the possibility of the loss of arch length. Such sequelae encourages interventive treatment, such as the early extraction of the primary tooth (advisable prior to the tooth infraoccluding below the gingivae) accompanied by space maintenance to allow for the subsequent eruption of the permanent successor. This option would have been worthwhile in this case.

A more conservative early treatment option for an ankylosed primary tooth involves the composite build-up of the tooth or the use of a stainless steel crown to prevent tipping of the adjacent teeth and to restore the occlusion to the correct height, thereby preventing the tooth of the opposing arch from over-erupting.

Such early interventions may have allowed the permanent successor to erupt normally and to have also prevented the tipping and rotating of the adjacent teeth. Similarly, earlier extraction would have likely been much more straightforward, removing the need for such a significant surgical procedure and the oro-antral communication that resulted from it.

Ideally, submerged teeth should be regularly monitored, with intervention occurring as soon as potential issues are observed. If the permanent successor is present and in a normal position, ankylosed teeth should exfoliate within 6 months of the contralateral side.

This case highlights how CBCT can be used to aid diagnosis and surgical planning in cases in which severe infraocclusion is present and where surgical intervention is required.

Conclusion

Overall, the importance of monitoring the developing dentition cannot be over emphasized. Tools, such as the ‘treatment decision-making model for infraoccluded molars’⁹ encourage clinicians actively to monitor the transition from primary to adult dentition, with the underlying intention of early diagnosis and intervention for any abnormality such as infraocclusion.