Follow-up Study Of Changes In The Anterior Alveolar Bone In Adult Patients After Retraction Of Anterior Teeth With Cone Beam Computed Tomography

Objective:The aim of this study was to analyze the morphometric changes in the anterior alveolar bone during treatment and retention stage with CBCT,in adult patients with bimaxillary protrusion treated by extraction of four first premolars and retraction of anterior teeth.The correlation between the changes of alveolar bone during treatment period and retention period was analyzed.Methods:Fifteen adult patients with bimaxillary protrusion who had completed orthodontic treatment more than two years,and treated by extraction of four first premolars and retraction of anterior teeth were enrolled,CBCT images of all patients were collected before treatment(T1),after treatment(T2)and retention stage(T3).MPR(multi-planner reformation)of CBCT data is conducted by Dolphin imaging 11.9 software.The labial and palatal vertical bone level and total bone thickness at crest area(TBT1),middle root area(TBT2),and apical area(TBT3)of anterior teeth were assessed.SPSS 25.0 was applied to statistical analysis of all measured data,and pair t-test was used to compare the morphometric changes of alveolar bone before and after treatment and retention stage,and correlation analysis was used to explore the correlation between the changes of alveolar bone during treatment period and retention period.Results:1.The stage of treatment:(1)Changes in the height of anterior alveolar bone: the distance from the lingual CEJ to the alveolar crest increased significantly,that is,the height of lingual alveolar bone decreased significantly,the results were statistically significant;The height of alveolar bone on the labial side of the lower anterior teeth and the maxillary incisors were decreased,and the results showed statistical significance.The height of alveolar bone on the labial side of maxillary central incisors and canines were decreased,but there was no statistical significance.(2)Changes in alveolar bone thickness of anterior teeth: After treatment,alveolar bone thickness at crest,middle root and apical level decreased,and the changes at crest and middle root areas were statistically significant,while the changes in apical area were not statistically significant.2.Retention stage:(1)Changes in alveolar bone height of anterior teeth: in upper anterior teeth,the labial and palatal alveolar bone height both increased with statistical significance except the maxillary central incisor.In lower anterior teeth,the height of labial and lingual alveolar bone increased with statistical significance,and the alveolar bone on the lingual side of the lower anterior teeth and the labial side of the mandibular central incisor increased significantly,indicating that there was significant bone deposition in the retention stage.(2)Changes in alveolar bone thickness of anterior teeth: The alveolar bone thickness of upper anterior teeth increased slightly,and the changes of maxillary central incisor crest,middle root,maxillary lateral incisor crest,maxillary canine root neck and middle root had statistical significance.The alveolar bone thickness of the lower anterior teeth increased slightly,but the increase was small and basically remained stable.Only the alveolar bone thickness at crest area showed statistical significance.(3)The alveolar bone height and thickness in stage T3 is less than that in stage T1,and the alveolar bone height on the palatal side of upper and lower anterior teeth and the thickness of the crest and the middle root level showed statistical significance.3.Correlation analysis: The alveolar bone height of anterior teeth from stage T2 to T3 was negatively correlated with the alveolar bone height from stage T1 to T2,a moderate correlation was observed between the labial side of the upper anterior teeth and the lower anterior teeth.In the maxillary palatal side,the correlation was extremely strong,and there was statistically significant.The change of alveolar bone thickness of upper and lower central incisor crest level from stage T2 to T3 was negatively correlated with the change from stage T1 to T2,with a moderate correlation between |r| of 0.5-0.8,and the results were statistically significant.Conclusions:For adult patients with bimaxillary protrusion,who treated with the removal of the four first premolars and massive retraction of anterior teeth.1.During the treatment stage,the height and thickness of the anterior alveolar bone and the thickness of the alveolar bone would be reduced,in which the height of the palatal alveolar bone and the thickness of the alveolar bone in the crest and the middle root level decreased significantly.2.In the retention stage,the height of the lingual alveolar bone of the anterior teeth increased significantly,while the labial side increased slightly.The thickness of alveolar bone in the crest and middle root level increased,while the alveolar bone at apex area remained stable.3.The amount of alveolar bone apposition in the retention stage is proportional to the amount of alveolar bone resorption in the treatment stage.For the alveolar bone defect caused by massive anterior retraction,the same degree of remodeling will occur in the retention stage,but the amount of alveolar bone is still reduced compared with initial time.