Risk factors for lingual plate fracture during mandibular third molar extraction

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.