Radiographic prediction of mandibular third molar eruption and mandibular canal involvement based on angulation

The aim of our study was to identify and predict patients at risk of impeded mandibular third molar eruption and potential relation between the third molar roots and the mandibular canal, based on molar angulations in an early development stage.

A total of 1011 adolescent orthodontic patients were included in this longitudinal study.

We analysed pre-eruptive rotational changes and root development of mandibular third molars on 2022 panoramic radiographs (two time-points). Five variables were evaluated: third molar eruption level, development stage, risk of relation between the third molar and the mandibular canal, the molar angulations and orthodontic treatment. The relation between early third molar angulation and mean annual angulation change was assessed using a linear mixed model. Logistic regression was applied to investigate a potential correlation of the radiographic variables with the eruption potential and risk of developing a relation between the third molar and the mandibular canal.

Mandibular third molar follicles with an initial angulation exceeding 27.0° relative to the second molar tend to progressively increase their angulation during further development. A significant correlation was found between the hemimandibular molar angulations and the probability of eruption (P < 0.0001). The second to first molar angulation was predictive for potential development of a relation with the mandibular canal (P = 0.005).

From the present data, it appears that severely angulated mandibular third molars (>27.0°) have a minimal chance of future eruption and a maximal risk of developing a relation with the mandibular canal.