Research Of Incisor Root Resorption After Preoperative Orthodontic Treatment For Adults With Skeletal Class Ⅲ Using CBCT

Objective:Adults with skeletal class III malocclusion is a kind of complex cranial and dentofacial deformity,the patients always need orthodontic-orthognathic treatment in order to improve facial coordination.The maxillary incisors and mandibular incisors’ labially tilted angle may have obvious change after preoperative orthodontic treatment,wich is a risk factor resulting in root resorption. The study sample comprised adult patients with skeletal class Ⅲ malocclusion who need to have orthognathic surgery,then reconstructed three-dimensional images of CBCT image and described morphology change through Mimics 17.0. The study aims at evaluating and forecasting incisor root resorption,offering reference for distance of bone moving in surgery and labially tilted angle control in orthodontic decompensation treatment,finally decreasing root resorption and attaining facial aesthetics and stable function.MethodsThirty permanent dentition adult patients with skeletal class Ⅲ malocclusion(n=30,age 22.32±2.40,13 males,17 females) were included in Tianjin stomatological hospital from May 2009 to November 2014. All the objects were scanned by cone-beam CT,three-dimensional reconstructionn and mensurement by Mimics17.0.Statistical comparison of volume change between pre-treatment and post-treatment was performed by using a paired-samples t-test.Difference between sex and among incisors’ position was detected by using independent samples t-test and One-Way ANOVA.Pearson coefficient was performed to check the correlations between root resorption and labially tilted angle.Kappa consistency test was used to compare the consistence between the two observers.Results1.The volumes of post-treatment is statistically smaller than pre-treatment,the result of paired-samples t-test is P<0.05.2.There is no statistically significant difference between male and female,the result of independent samples t-test is P>0.05.3.There is no statistically significant difference among different incisors,the result of One-Way ANOVA is P>0.05.4.The difference of root volumes between pre-treatment and post-treatment is statistically significant when labially tilted angle changes for 7°or more;there is fixed quantity relationship between them.The result of Pearson coefficient is P<0.01.5.The type of root resorption can be classified as flat form,cone-shaped form and slope form.In the upper incisors the apical root resorption is in the labio-lingual direction;In the lower incisors the apical root resorption is in the lingual-labial direction.The result of Kappa consistency test is moderate,that is 0.452 for maxillary and 0.422 for mandibular.Conclusions1.Root resorption occurs in adults of skeletal class Ⅲ after orthodontic treatment before orthognathic surgery.2.There is no difference between male and female,also no difference among eight incisors.3.There is positive correlation relationship between labially tilted angle and root resorption when labially tilted angle changes for 7°or more:as labially tilted angle increases incisor root volumes will decrease.4.Root resorption occurs mainly in apical one third and usually becomes shorter and thinner than before;The type of root resorption can be classified as flat form,cone-shaped form and slope form,and most of the apical root resorption represents as cone-shaped form and slope form.