Abstract: Abstract: Objective To evaluate incisor root resorption of adults with skeletal class Ⅲ malocclusion through threedimensional reconstruction of cone beam computed tomography (CBCT) image using interacting medical imaging control sys⁃ tem (Mimics) and then offer guidance for labially tilted angle control in orthodontic treatment and distance of bone moving in surgery. Methods Adults of skeletal class Ⅲ malocclusion (n=30) who underwent orthodontic-orthognathic combination treatment were included in this study. CBCT images were then reconstructed three-dimensionally using Mimics 10.01. Each incisor were separated at cementum-enamel junction as crown and root. Labially tilted angle and root volumes of each inci⁃ sor were measured before and after operations. At last, the correlativity between root resorption and labially tilted angle was calculated through statistic analysis. Results The decrement of upper, lower and front incisors’root volumes upon treat⁃ ment is statistically significant. However, there is no statistically significant difference of incisor’s root volumes among eight incisors nor between different gender. There is linear correlation between root volumes and labially tilted angle when the lat⁃ ter changes 7° or more when they followed the fomular =-21.416+5.618X. Conclusion For adults with skeletal class Ⅲ malocclusion, orthodontic treatment before orthognathic surgery decrease incisor root volumes when labially tilted angle changes 7° or more.

Key words: malocclusion, angle class Ⅲ, tomography, X-ray computed, image processing, computer-assisted, root re? sorption, labially tilted angle