Biomechanical Study On Orthodontic Tooth Movement Before And After Increasing Alveolar Bone Mass With PAOO

Objective: Periodontally accelerated osteogenic orthodontics(PAOO)can increase the thickness of the alveolar bone,providing a new treatment idea for the orthodontic clinic cases in which orthodontic treatment is difficult due to the thin alveolar bone.Although there are some reports of successful clinical treatment,there are fewer reports of biomechanical studies of orthodontic tooth movement in cases with thin alveolar bone using PAOO surgery to guide bone regeneration and increase the thickness of the alveolar bone.In this study,three-dimensional finite element analysis was used to compare and analyse the changes in the stress distribution of teeth,alveolar bone and periodontal ligament(PDL)during the movement of orthodontic teeth before and after PAOO surgery,as well as the changes in the displacement trend of orthodontic teeth,in order to provide a theoretical basis for orthodontic clinical treatment.Methods: One patient who attended the orthodontic department of Lanzhou University Dental Hospital from December 2020 to March 2021 and required periodontally assisted accelerated osteogenic orthodontics(PAOO)surgical treatment to increase the bone volume in the labial side of the mandibular anterior region was selected,and a three-dimensional finite element analysis model was constructed based on the patient’s preoperative and 6-month postoperative cone-beam CT(CBCT)data of PAOO,which were recorded as model A(preoperative model)and model B(postoperative model).The orthodontic tooth movement process was combined with the patient’s actual clinical orthodontic treatment performed,and the three-dimensional finite element analysis models of both cases simulated the left mandibular cuspid(33 teeth)in experimental group I: distal movement of 0.25 mm,experimental group II: lingual movement of 0.25 mm,and experimental group III:intrusion movement of 0.1 mm.To investigate the stress distribution of the left mandibular cuspid,PDL,surrounding alveolar bone and the initial displacement trend of the left mandibular cuspid before and after PAOO surgery under the action of the clear aligner.Results: In the three experimental groups:(1)Dental stress analysis: The maximum Von-Mises stresses values in 33 teeth were all model A>B,and the total stresses were also model A>B;in the same group of experiments,the maximum equivalent stresses was distributed in similar areas and the trend of the total stress distribution was similar.(2)PDL stress analysis: The maximum Von-Mises stress values in the PDL of 33 teeth were all model A>B,and the overall stress values were also model A>B;in the same group of experiments,the maximum equivalent stresses was distributed in similar areas and the trend of the total stress distribution was similar.(3)Alveolar bone stress analysis: The maximum Von-Mises stress values of the alveolar bone around 33 teeth were all model A>B,meanwhile the equivalent stress distribution of both showed a gradual decrease from the top of the alveolar ridge to the root.(4)Initial displacement analysis: The initial displacements in the main displacement direction for all six observation points of 33 teeth showed model B>A,which were larger compared to the respective two axial directions,all showing a gradual decrease trend in displacement from the tip of the tooth to the apical point.Conclusion: The biomechanical characteristics on orthodontic tooth movement before and after increasing alveolar bone mass with PAOO surgery were different.With the clear aligner,the postoperative equivalent forces on the dentition,PDL,and surrounding alveolar bone were smaller than before the surgery,and the initial displacements of the orthodontic teeth after the surgery were larger than before;this suggests that PAOO can release the restriction of thin alveolar bone on the movement of orthodontic tooth by increasing the thickness of alveolar bone,effectively reducing the force on the roots,PDL,and alveolar bone,avoiding the stress concentration on orthodontic tooth in the thin alveolar bone area that can cause complications when moving,and improving the efficiency of tooth movement.