Analysis of Radiographic Signs to Predict the Risk of Damage to the Inferior Alveolar Nerve Following Impacted Mandibular Third Molar Extraction among Sinhalese Population

Aims: This study aimed to define the panoramic criteria can be used in predicting the direct contact between impacted mandibular third molar (MTM) and the inferior alveolar nerve (IAN).

Study Design: A prospective cross-sectional study.

Place and Duration of Study: This study carried out at Unit B in National Dental Teaching Hospital, Ward Place, Colombo 07 from July 2019 to February 2020.

Methodology: Both orthopantomography (OPG) and cone beam computed tomography (CBCT) images of 107 impacted MTMs were assessed to record the radiographic signs for each impacted tooth. The angulation and the position of impaction, Rood & Shehab signs including superimposition, mandibular canal (MC) position relative to the MTM roots, proximity of MTM roots to MC, and the changes of cortical plates due to impacted MTM roots were recorded with sex and age. The Chi-square and Fishers’ exact tests were used for comparison.

Results: The most common position of impaction was position B, most common impaction angulation was mesial angulation, most common OPG sign was interruption of white line, and most common MC position was lingual position relative to the MTM roots. Position A, and position B, A-vertical impaction type, B-horizontal impaction type, darkening of roots, sign combinations of darkening and superimposition, and darkening and interruption, and lingually located MC relative to the MTM roots were significantly correlated with direct contact between impacted MTM and the MC (P<0.05). The signs of superimposition and narrow root were significantly correlated with lingually positioned MCs (P<0.05). The sign of darkening of roots was significantly correlated with lingual and buccal cortical plates thinning (P<0.05).

Conclusion: With superimposition and darkening or darkening and interruption, or B-horizontal type of impaction, there is a risk of IAN damage during the surgical removal of impacted MTM. With A-vertical type of impaction, there was no risk of damage to IAN. The sign combination of superimposition and darkening has a high positive predictive value for predicting contact MTM roots to MC than buccal plate thinning.