JAPANESE JOURNAL OF ORAL & MAXILLOFACIAL SURGERY

Vol. 55 No. 1       2009

ISSN: 0021-5163      UBIC: 151-J

ABSTRACT

To prevent the mandibular third molar from dropping into the pterygomandibular space after extraction of this tooth, it is important to understand the local anatomy. We studied the lingual cortical bone in patients with impacted mandibular third molars on CT scans and classified the bone into three groups: Group I cortical bone defect; Group II, cortical bone thinning; and Group III, normal cortical bone. Among 134 impacted mandibular third molars studied, 15 (11.2 %), 36 (26.9 %), and 83 (61.9 %) were classified into Groups I, II, and III, respectively. In Groups I and II (38.1 %), the risk of the mandibular third molar dropping into the pterygomandibular space was considered high. The relation between the state of the lingual cortical bone and the depth of the impacted molar was examined on 114 panoramic radiographs. According to Winter's classification of molar depth, the numbers of molars in A, B, and C position were 15, 23, and 10, respectively, among the 48 impacted mandibular third molars in Groups I and II. There was no correlation between the state of the lingual cortical bone and molar depth. In conclusion, CT is useful for preventing the mandibular third molar from dropping into the pterygomandibular space during extraction of impacted mandibular molars. Key words: impacted mandibular third molar, lingual cortical bone of mandible, depth of impacted molar, Winter's classification.

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