En-masse Retraction of Upper Anterior Teeth when Using power Arms in Corticotomy-assisted Orthodontic Treatment in Bimaxillary Protrusion Patients

Abstract

Introduction: Bimaxillary protrusion patients is a condition characterized by protrusive and proclined upper and lower anterior teeth and an increased procumbency of the lips. Almost orthodontic treatment plan is removal of 4 first premolars and retracting the anterior teeth. Orthodontic tooth movement more than anatomical limits mat cause many side effects. In 2001, Wilcko et al. developed a new treatment method that can reduce these side effects called as the Periodontally Accelerated Osteogenic Orthodontics (PAOO). From previous studies the center of resistance of six upper anterior teeth was moved apically after corticotomy, it was interesting that whether the apically moved distance of the center of resistance of the six upper anterior teeth after corticotomy effected the type of tooth movement or not and how much of it? Also whether en-masse retraction using power arms in height of 13.5 mm from incisal edge of upper central incisor caused the bodily movement of upper anterior teeth or not. Objectives: To evaluate and compare the effect of en-masse retraction in corticotomy-assisted orthodontic treatment with conventional orthodontic treatment in bimaxillary protrusion patients. Methods: 22 non-growing patients with class bimaxillary protrusion were divided into 2 groups, corticotomy group (experimental group) and conventional group (control group). Both groups had the same orthodontic treatment plan that required 4 first premolars extraction for anterior teeth retraction, resulting in decreased lips protrusion. In experimental group, the samples were treated with decortication and bone graft in area of anterior teeth before en-masse retraction. The amount of anterior teeth retraction in both horizontal and vertical dimensions and angulation of upper anterior teeth were analyzed by superimposition of two lateral cephalometric radiographs that taken before en-masse retraction and after retraction 4 months. The ratio between the moved distance of the most apical point and the moved distance of the most incisal point, the change of angulation of upper anterior teeth and the retraction rate were calculated. T-test and Mann-Whitney test were used for comparison between two groups. Paired t-test and Wilcoxon Signed Rank test were used for comparison between before and after retraction in each group. Results: There is no statistically significant different in upper anterior tooth movement between two groups. After retraction the upper central incisor was retroclined 3.5 ± 3.5 degree, the ratio between the moved distance of the most apical point and the moved distance of the most incisal point was 0.64 ± 0.26, there was no significant change in vertical dimension of upper central incisor and the retraction rate was 0.99 ± 0.32mm/month in corticotomy group that is faster than conventional group about 1.5 times. Conclusions: En-masse retraction with 13.5 mm height of power arms results in combination between controlled tipping and bodily movement of upper anterior teeth in both groups and there is no different in upper anterior tooth movement between two groups. Retraction rate in corticotomy group is faster than conventional group about 1.5 times.