Objective: To measure and compare EARR of the maxillary central and lateral incisors after MARPE, and to evaluate risk factors of root resorption after expansion. Methods: CBCT images of total 60 patients were taken before expansion(T1) and 3 to 6 months after expansion(T2). Tooth length(L), root length(r), crown length(c) were measured. Resorption length(RL) and resorption volume(RV) was defined as the difference in tooth length(L) and volume(V) between T1 and T2 period. Resorption length and volume percentage was calculated. Center of Resistance(Cre) was calculated as distance from both maxillary first molars' bifurcation point. The amount of expansion(E) was defined as the difference in Cre measured between T1 and T2 period. Results: There was a significant difference in tooth length and volume of central and lateral incisors before and after expansion. Resorption index(RL, RLp, RV, RVp) was significantly higher in central incisor than in the lateral incisor. There was a significant correlation between age and RLp of central incisors, amount of expansion and RVp of central incisors, tooth length of the central incisors and RL , RLp of the central incisors, root/crown ratio of central incisors and RL of the central incisors, tooth length of the lateral incisors and the RL of the lateral incisors. Conclusions: There is a significant maxillary incisor's root resorption after MARPE. Root resorption after MARPE was significantly higher in central incisors than in lateral incisors. Order initial age, larger amount of expansion, initial tooth length and root/crown ratio were risk factors of EARR after MARPE.

Keywords: Expansion, Root resorption, CT, Microimplant