Biomechanical Analysis Of Alveolar Bone Remodeling After Corticotomy

Corticotomy-facilitated orthodontic treatment, as important part of surgical-assisted orthodontic tooth movement, has become popular gradually due to the great facilitation on clinic orthodontics, which has numerous advantages of more traditional orthodontics, including faster, complex tooth movement with greater envelop. Recent research on the mechanism of this process has mainly focus on two aspects. One is Regional accerleration Phenomenon (RAP); the regional stimulation can speed up the rate of bone turnover through acceleration of demineralization-remineralizaion process. The remodeling rate of alveolar bone and periodontal ligament (PDL) can be accerlerated if the corticision gets close to the tooth to be moved, thus facilitate orthodontic tooth movement. The other is en-block movement of bone segment; corticotomy can lead to a bone-bending effect through reduction of the alveolar bone resistance to orthodontic tooth movement by breaking the continuity of the bone layer. The second explanation proposed mechanical factor might be mechanism of corticotomy, but this viewpoint is just the result of clinical observation and lack of the related research on the regulation of mechanical distribution after corticotomy and relationship between mechanical distribution and remodeling of periodontal tissue.In this research, the dynamic remodeling information of alveolar bone was get through animal study and in-vivo Micro-CT scan, as well as the quantification of partitioned alveolar bone reconstructed from CT image. On the other hand, a 3-D finite element model of corticotomy-facilitated tooth movement of rat was developed to calculate the mechanical distribution in dento-alveolar structures. Then, corresponding relationship between mechanical distribution and remodeling of periodontal tissue can be established and evaluated. These results contribute to explorer the biomechanical mechanism of corticotomy-facilitated orthodontics. Three parts involved in this research are as following:I Establishment of animal model of corticotomy-facilitated orthodontic tooth movement and in-vivo Micro-CT scan18 male Sprague Dawley (SD) rats were divided into group A and group B randomly. For group A, the maxillary first molars were served as orthodontic side and control side seperately. For group B, the maxillary first molars were served as corticotomy-facilitated orthodontic tooth movement side and corticotomy side separately. The corticotomy approach was designed as the circumscribing removal of partial cortical bone around the first molar. The orthodontic design was mesial movement of the first molar pulled with Ni-Ti spring to incisor. The in-vivo Micro-CT scan was performed before orthodontic load and at days 3,7,14,28 after load. The movement distance of the first molar, alveolar bone density and bone volume fraction around the mesial root of the first molar were calculated.The results showed that:the rate of tooth movement on corticotomy-facilitated orthodontic side was significant higher than orthodontic side, but the gross distance of tooth movement within 4 weeks showed no statistical difference. Corticotomy induced drastic bone turnover more early than orthodontic load and the influence of corticotomy and orthodontic load can overlapped partly. These indicated that orthodontic tooth movement has a close relationship with alveolar bone density; corticotomy can accerlerate bone turnover to speed up tooth movement.â…¡ 3-D FEA of corticotomy-facilitated orthodontic tooth movement of rat3-D FE model of corticotomy-facilitated orthodontic of rat was established with converse modeling method on the base of Micro-CT image of SD rat. The PDL and alveolar bone around the mesial root was partitioned according to the direction of orthodontic load and corresponding part of root. The initial displacement of the first molar and the stress/strain in PDL and alveolar bone were calculated.The result of FEA showed that:the first molar presented a tipping movement under orthodontic load and the cortical bone segment showed a remarkable movement relative to the left alveolar bone. Corticotomy can change the distribution and magnitude of the max and min principal strain in PDL and Von Mises stress in alveolar bone. Analysis of these mechanical results combined with bone density demonstrated that alveolar bone density can be affected by the stimulation of corticotomy and orthodontic load; and there is a close relationship between bone dentisy and the min principal strain in PDL and Von Mises stress in alveolar bone after exclusion the factor of corticotomy stimulation.â…¢ 3-D FEA of corticotomy-facilitated orthodontic tooth movement of clinical caseIn this section, the spiral CT images of a typical maxillary protrusion patient were collected, on the base of which a 3-D FE model of corticotomy-facilitated retraction of anterior teeth was built to calculate and compare the biomechanical influences of two corticotomy approaches on dento-alveolar structures. Another 3-D FE model of canine distalization was built. Diverse corticotomy approaches were designed and modeled to select an optimal one after calculation of initial displacement of canine, the stress/strain in PDL and alveolar bone.The results showed that corticotmy can affect the mechanical distribution and magnitude in dento-alveolar structures during retraction of anterior teeth and canine. The affection correlates to the position and scope of corticotomy surgery. A distal corticotomy closer to canine may be a better option for rapid canine retraction taking account of its biomechanical effects and surgical injure.