The Effect Of Controlled Root Movement,Performed With Bone Grafting And Corticotomy-facilitated Orthodontics,on Dental Arch Expansion In Beagle Dogs

BackgroundDental arch expansion is a common treatment method used by orthodontists in clinical work.In the past,rectangular wire was used to control the torque,i.e.root control,when expanding the posterior teeth.However,the initial loading force is relatively large,which can easily cause root resorption,alveolar bone thinning,fenestration,dehiscence and other adverse reactions.At present,corticotomy-facilitated orthodontic treatment is often used in clinic,but the effectiveness of using corticotomy to accelerate tooth movement remains controversial,and the effect of torque control with this technology assisted arch expansion has not been reported.To sum up,it is of great significance to study the effect of torque control on buccal movement of teeth under light force and how orthodontic treatment can be safer and more effective by using corticotomy combined with bone grafting for expansion of posterior teeth.ObjectivesThe purpose of this study is to establish a beagle dog model of light-force expansion of posterior teeth aided by corticotomy-facilitated orthodontics combined with bone grafting.At the same time,this study aims to explore whether the expansion performed with corticotomy-facilitated orthodontics combined with bone grafting can broaden the range of posterior teeth movement in the bucco-lingual direction within the alveolar basal bone,and whether the root control is needed in this situation.A guidance is expected to provided for a safer application of corticotomy-facilitated orthodontics,reduce the incidence of complications in orthodontic treatment,shorten the treatment time effectively,and better restore the physical and even mental health of patients.Materials and MethodsThree male beagle dogs aged 9～12 months old were randomly divided into three groups（Slip-mouth Study）:the non-root-controlled side,the root-controlled side and the non-surgical side.The orthodontic arch expansion was started after application of the appliances.The initial force was 100g.The orthodontic force was re-applied once a week for the next 8 weeks.The teeth were cleaned and gingival crevicular fluid was collected at every time of return visits.The secretion of the gingival crevicular fluid and the residual force of archwire were recorded,and the force of archwire was re-adjusted to 100g at the time of slotting.CBCT was taken before and after orthodontic treatment.The data were imported into Dolphin software to measure the changes of tooth inclination,mid-line distance,the attachment level of alveolar bone,root length,buccal or palatal/lingual bone plate thickness of the second premolars.SPSS 22.0 statistical software was used for statistical analysis and processing,and P<0.05 showed that the difference was statistically significant.Results1、There was no significant difference in the secretion of gingival crevicular fluid and the attenuation of orthodontic force between the non-root-controlled side and the root-controlled side（P>0.05）.2、There was no significant difference in the changes of the long axis of the teeth after corticotomy-facilitated orthodontic expansion combined with bone grafting between the non-root-controlled side and the root-controlled side（P>0.05）.3、In the light-force orthodontic treatment,there was no significant difference in alveolar bone attachment level,root resorption and thickness of alveolar bone between the non-root-controlled side and the root-controlled side（P>0.05）.4、Under the same orthodontic force（100g）,the distance between the tip of tooth crown and the midline in the non-root-controlled side increased significantly（P<0.05）than that in the root-controlled side,but there was no significant difference in the change of the axis tilting between the two sides（P>0.05）,which indicated that the crown and root of the non-root-controlled side could produce more buccal movement in the same time.5、There were significant differences in gingival crevicular fluid secretion,attenuation of orthodontic force,tooth movement distance,alveolar bone attachment level,root resorption and thickness change of buccal alveolar bone between orthodontic expansion with and without buccal corticotomy combined with bone grafting（P<0.05）.ConclusionsWith the application of the light orthodontic force system,in the early stage of corticotomy-facilitated orthodontic expansion combined with bone grafting,there was no significant difference in the changes of dental axis,root and periodontal damage between root-controlled side and non-root-controlled side,suggesting that early use of round wires and light force for buccal movement after corticotomy combined with bone grafting is a safe and effective treatment method.