PURPOSE: The objective of this study was to determine the relationship between the mandibular third molar tooth (Md3) and the adjacent lingual cortical bone and determine the incidence of lingual cortex perforation by Md3s . PATIENTS AND
METHODS: This retrospective study was designed and implemented from 100 cone-beam computed tomographic scans (CBCTs) of patients with age ranging from 18 to 65 years old . The primary outcome was to assess the incidence of mandibular third molars (Md3s) with existing lingual cortex perforation by their roots . Perforation was assessed at the level of root apex and the most lingual portion on the apical half of the root . Other outcome variables included average thickness of covering lingual bone in the nonperforation group, lingual cortex morphology, impaction, and demographics . Descriptive statistics were computed .
RESULTS: More than half the radiographs showed lingual cortex perforation at the level of root apex and most lingual portion on the apical one half of the root (51.2% and 52.8%, respectively). The average thickness of the covering lingual bone was 1.25 mm around the root apex and 0.93 mm around the most lingual portion on the apical half of the root . The most common lingual cortex morphology was the undercut shape . There was statistically significant association between the presence of Md3 impaction and perforation at both root levels (P value <.001, Effect size = 0.378) and (P value <.001, Effect size = 0.445).
CONCLUSIONS: Perforation of the lingual cortex by Md3s, whether erupted or impacted, was found in> 50% of patients as determined by a preoperative CBCT scan . Therefore, the finding of lingual cortex perforation after removal of Md3s is likely to be evidence of a pre-existing condition rather than a result of surgery.