A CBCT Study On The Changes Of Tooth Root And Alveolar Structure Around Maxillary Anterier Teeth In Adults With ClassⅡ~1 After Retraction

Objective :To analysis the changes of tooth root and alveolar structure about anterier teeth in adult class II Division 1 cases after retraction by using non-invasive cone beam CT(cone beam computed tomography)technology.In order to provide a theoretical basis for design of clinical diagnosis and treatment.Methods:20 adult patients with class II Division 1 were selected,with an average age of 24.8years.All patients were treated by extraction treatment of 2 maxillary first premolars and2 mandibular second premolar,selection of self ligating brackets(0.022 inches by 0.028inches)for aligning and leveling teeth.When the 0.018 x 0.025 inch stainless steel wire were replaced,intend to use the intermaxillary traction method and sliding adduction to complete anterior teeth retraction.In the treatment process of the T0 phase(anterior): A tooth is fully aligned,upper and lower have to replace the closing gap required for main arch wire and wire placement time more than 1 months;T1(adduction): The gap was closed completely,1 month later,CBCT was taken as well as T0,all taken by the same technician.Measurements taken on CBCT image T0 and T1 phase,were observed on the incisor retraction,root length,labial and lingual alveolar bone thickness and height of alveolar bone about anterior teeth.The time of treatment from stage T0 to stage T1 was also recorded.All measurements were performed by the same person and measured again after the first 2 weeks of measurement.Results:1.The adductive distance of maxillary central incisor: during the process of adduction,the crown of maxillary central incisor moved more in tongue direction,and the amount of adduction in crown was(4.581 ±1.374 mm)and the root was(3.414 ±1.260 mm).2.Root resorption: after adduction,the root length of the anterior teeth decreased in different degrees,the central incisor was(0.685 ± 0.260 mm),the lateral incisior was(0.515 ± 0.190 mm)and the canine was(0.465 ± 0.292mm)respectively,and the difference was statistically significant(P < 0.05).3.Alveolar bone thickness: the thickness of labial alveolar bone increased after adduction,but there was no statistical difference(P > 0.05),and the thickness of alveolar bone in palatine side decreased(P < 0.05).The alveolar bone thickness of the labial apical region decreased,and the difference was statistically significant(P < 0.05),while the alveolar bone thickness of the palatine apical region increased,but there was no statistical difference(P > 0.05).4.The height of alveolar bone: after adduction,the height of alveolar bone in labial and palatal side of anterior teeth decreased,and the difference of palatal side was statistically significant(P < 0.05).5.Treatment time: the average treatment time was(8.45±1.25)months for all patients in stage T0 to T1.Conclusion:1.There are different degrees of root resorption in adult class II division 1 cases after retraction.2.The alveolar bone can not follow the tooth movement for 1:1 physiological remodeling.The alveolar bone remodeling shows that the bone resorption is larger than the bone hyperplasia,and there are risks of bone cracking and bone fenestration.