Research On The Changes Of Root And The Alveolar Bone Before And After The Treatment Of Retracting The Upper Incisors With The Tool Of CBCT

Objective: With the CBCT images measurement on the patients who need extracting bimaxillary premolars because of maxillary protrusion and maximum anchorage to retract upper incisors,the study is trying to find the changes on root and alveolar bone before and after the treatment of retracting the upper incisors.Furthermore,the study will discuss the influence factors of root resorption.All the information will provide clinical reference for reducing orthodontic root resorption.Materials and Methods: The study was conducted on 37 patients who has gotten orthodontic treatment.It is composed by 17 males and 20 female whose average ages are 14.5 years.All the patients were extracted bimaxillary premolars and given maximum anchorage to retract upper incisors.All the patients were scanned by New Tom VGi to obtain CBCT data before and after the treatment of upper incisor retraction.By using the New Tom NNT tool,we get the multiple planar reconstruction,and then adjusting the coronal,axial and sagittal axis.Sagittal slices were evaluated where the maxillary central incisor was longest between incisal edge and root apex in coronal and sagittal view to measure root and alveolar bone changes.The adducent angle and the adducent amount,and the amount of elongation of the upper incisor teeth were measured by cephalograms.Through the statistical analysis tool SPSS 17.0,we take Paired t-test for testing whether there are statistical difference before and after treatment for the crown length,the width of cemento-enamel junction,and root length and height changes of labial and lingual side alveolar bones.By correlation analysis,we also testing whether there are correlation between the adducent angle of central incisor,incisors adducent amount,incisors extension amount,the distance from the upper incisor apex to the labial cortical bone and root absorption amount and the variable quantity of alveolar bone.Result Before and after retracting the upper incisors,the adducent angle of central incisor is 12.92°± 6.43°.Incisors adducent amount is 5.54 ± 2.21 mm.Incisors extension amount is 0.60± 0.95 mm.Root absorption length is 0.81±0.46 mm.Root absorption rate is 6.8%±3.6%.There is statistical difference(P<0.05)for the changes of root length before and after retracting incisor.After retracting the upper incisor,the increasing distance from the labial side alveolar ridge to the cemento-enamel junction is 0.20±0.22 mm and after treatment we find that the height of the labial side alveolar bones is decreased and has statistical difference(P<0.05).The height of Lingual side alveolar bones has no statistical difference.The Pearson correlation coefficient between the adducent amount of the upper incisor and root absorption length is 0.405(P<0.05).The Pearson correlation coefficient between the adducent amount of the upper incisor and root absorption rate is 0.358(P<0.05).And it shows that there is a positive correlation between horizontal displacement of maxillary center incisor and root absorption.The Pearson correlation coefficient between the adducent angle of the upper incisor and root absorption length is 0.251(P>0.05).And the Pearson correlation coefficient between the adducent angle of the upper incisor and root absorption rate is 0.176(P>0.05).It indicates that there is no correlation between the adducent angle of the upper incisor and root absorption.The Pearson correlation coefficient between the horizontal displacement of the upper incisor apex and root absorption length is 0.313(P>0.05),the Pearson correlation coefficient between the horizontal displacement of the upper incisor apex and root absorption rate is 0.280(P>0.05).It shows that there is no correlation between the root absorption of maxillary center incisor and the horizontal displacement of the upper incisor apex.The Pearson correlation coefficient between the distances that is from the upper incisor apex to labial cortical bone and root absorption length is-0.391(P<0.05),the Pearson correlation coefficient between the distances that is from the upper incisor apex to labial cortical bone and root absorption rate is-0.417(P<0.05).It shows that there is negative correlation between the root absorption of maxillary center incisor and the distances that is from the upper incisor apex to labial cortical bone.The Pearson correlation coefficient between the adducent angle of the upper incisor and the variable quantity of the labial side alveolar bones is-0.354(P<0.05)which shows that there is negative correlation between the variable quantity of the labial side alveolar bones and the adducent angle of the upper incisor.Conclusion: 1.The root length of patients with maxillary protrusion is absorbed obviously after treatment.The height of the labial side alveolar bones is reduced.2.There is no correlation between the adducent angle of the upper incisor and root absorption,and there is positive correlation between the adducent amount of the incisor and root absorption.There is negative correlation between the distances that is from the upper incisor apex to labial cortical bone and root absorption,and there is negative correlation between the variable quantity of the labial side alveolar bones and the adducent angle of the upper incisor.