Relationship between eruption status of mandibular third molars and thickness of the lingual bone

PURPOSE To estimate the relationship between the eruption status of the mandibular third molars and the thickness of the lingual bone. METHODS Cone-beam CT (CBCT) data of 187 patients who underwent mandibular third molar extraction from Jan 2016 to Dec 2018 were selected. Lingual bone thickness at the levels of mid-root and root-apex of the third molars were measured using GALIEOS Viewer software, and the relationship between the eruption status of the mandibular third molars and the thickness of the lingual bone was estimated. SPSS 22.0 software package was used for Wilcoxon test, univariate and multivariate logistic regression analysis. RESULTS The mean thickness of the lingual bone at the mid-root of the third molars was significantly less than that at the root apex (P<0.01). There was a significant correlation between the thickness of the lingual bone at the mid root and the mesiodistal angulations of the third molars. The thickness of the lingual bone at the mid root of mesioangularly and horizontally impacted third molars were significantly thinner (P<0.01). There was a significant correlation between the thickness of the lingual bone at the root apex and the impaction depth of the third molars. The thickness of the lingual bone at the root apex of medium and low positioned third molars were significantly thinner (P<0.05). CONCLUSIONS The thickness of the lingual bone is associated with the eruption status of the mandibular third molars. Mesially angulated and lower positioned third molars are considered as the risk factors for the thinner lingual bone, so that lingual plate fracture should be prevented during tooth extraction.