Can lower third molar position indicate the need for preoperative cone beam computed tomography exploration of retromolar canal?

Abstract

This study aims to reveal whether and which position of lower third molar (M3), assessed on a 2D image, indicates or potentially exclude the need for the CBCT exploration of the retromolar canal (RMC). We hypothesized that some positions of M3 are associated with overall higher incidence of the RMC, and particularly clinically relevant ones, thus justifying additional CBCT diagnostics. CBCT exam of 186 hemi-mandibles with present M3 were selected for the study. Explorations were made during the 2-year period from January 1th 2018 to December 31th 2019 with Scanora 3Dx Sorodex (Tussula, Finland). The following variables were assessed: the presence and width of the RMC, eruption status, and angulation of the M3. The RMC presence in relation to the M3 eruption status and angulation was analyzed using appropriate statistical tests. RMC was present in 89 (47.8%) out of 186 hemi-mandibles. Mean canal width was 1.51mm. 22.5% of detected canals had the diameter exceeding 2mm. Third molar's eruption status showed no statistical correlation with the occurrence of RMC. We observed significantly higher occurrence of RMC in the hemi-mandibles containing distally angulated M3 in comparison to other orientations (p = 0.025). Based upon our findings, we recommend preoperative CBCT in cases where distal angulation of M3 is observed on 2D images, for the purpose of RMC exploration. Lower resolution CBCT mode and limited field of view (XS or S) are sufficient for the visualization of potentially clinically relevant RMCs, with as much reducing the patient dose.