Abstract: Objective: To evaluate the bony and dental characteristics of mandibular second molar impaction and to provide reference for clinical treatment. Methods: Pretreatment CBCT records of 53 subjects of impacted mandibular second molar were selected as impaction group, and the same number of fully erupted mandibular second molar as eruption group. Mimics 19.0 software was used to observe and measure the indexes like SNA, SNB, ANB, Co-Gn, Co-Go, Go-Gn, W, Co-Go-Gn, retromolar space, tooth size and posterior tooth crowd. Independent t test and binary linear regression were analyzed and significant difference was identified with P＜0.05. Results: The impaction and eruption group didn’t differ significantly in respect to the bony measurements. Retromolar space was significantly shorter, and second molar was wider in the impaction group. Posterior tooth crowd of third molar in impaction group was statistically bigger than in the eruption group. Conclusions: Mandibular second molar impaction seemed to be relevant to retromolar space, mesiodistal width of the second molar, and the posterior tooth crowd.

Key words: second molar impaction, cone beam CT, retromolar space, posterior tooth crowd