LAUSR

Objective The aim of this study was to predict the risk of lingual plate fracture during mandibular third molar (M3) extraction. Materials and methods Cone beam computed tomography (CBCT) data from 264 mandibular M3s (erupted and impacted) from 264 patients (104 males and 160 females; age range, 17–75 years) were retrospectively analyzed. Lingual plate thicknesses at the levels of the mid-root and root apex of the M3s were measured and defined as “thicker” (bone thicker than 1 mm), “thinner” (bone thinner than 1 mm), or “perforated” (bone perforated by the M3 root). These measurements were correlated with potential risk factors for thinner and perforated lingual plates: tooth position of the mandibular M3, morphology of the lingual plate, and patient characteristics (age and sex). Results The mean thickness of the lingual plate was 1.49 ± 1.38 mm at the mid-root of the M3s, and 2.35 ± 2.03 mm at the root apex. Multivariate regression analyses revealed that mesioangularly and horizontally impacted M3s were significantly associated with thinner and perforated lingual plates at the mid-root ( P  < 0.001), whereas the M3s in infra-occlusion positions (in infra-occlusion when compared with the adjacent second molar) had thinner lingual bone at the root apex ( P  = 0.022 and P  = 0.027, depending on the level of impaction). Female patients were less likely to have lingual plate perforation ( P  = 0.036). Conclusions Mesioangulation, infra-occlusion, and male sex were risk factors for lingual plate fracture. Clinical relevance When the risk of lingual plate fracture is high, a sufficiently large flap, osteotomy, and tooth section by bur or piezosurgery are recommended to create a good operative field and avoid excessive pressure on the lingual plate.