Correlation of darkening of impacted mandibular third molar root on digital panoramic images with cone beam computed tomography findings

TLDR

Darkening of the lower third molar root on panoramic radiographs signals a close relationship between the root and the mandibular canal. This study aimed to examine the anatomical relationship that causes this panoramic darkening by reviewing 253 impacted lower third molars with both digital panoramic radiography and cone‑beam CT. Panoramic images were scored for root darkening where the canal overlapped, while CBCT images were assessed for root grooving and cortical plate thinning or perforation, and logistic regression was used to correlate the findings. Cortical thinning or perforation on CBCT was significantly associated with root darkening (80 % of cases, P < 0.001), indicating that darkening reflects cortical compromise rather than root grooving.

Abstract

Darkening of the lower third molar root on panoramic images is known to indicate an intimate relationship between the root and mandibular canal. The objective of this study was to investigate the anatomical relationship between the third molar root and its surrounding structures that leads to this panoramic finding.Imaging findings of 253 impacted lower third molars examined by both digital panoramic radiography and cone beam CT were reviewed. Panoramic images were evaluated to detect the presence or absence of darkening of the root where the mandibular canal was superimposed. Cone beam CT images were evaluated for the presence or absence of the following two findings: (1) grooving of the root and (2) thinning or perforation of the cortical plate by the root. The correlation between the panoramic and cone beam CT findings was examined using logistic regression analysis.80 (32%) third molars showed a panoramic finding of darkening of the root. Between cone beam CT findings, cortical thinning or perforation alone was significantly correlated with this panoramic finding (80%, P < 0.001).The panoramic finding of mandibular third molar root darkening was considered to reflect cortical thinning or perforation rather than grooving of the root.