The Experiment Reserch Of Corticotomy Facilitated Molars Intrusion

The application and popularization of micro screws implant anchorage have solved the problem of teeth intrusion with large scope. Because the current studies cannot provide individualized optimal force , so large-scale intrusion of teeth always accompany with some adverse reactions,such as root absorption,pulp reaction and hyaline degeneration of periodontal membranes. Corticotomy made teeth and alveolar bone as a whole by cutting off the bone cortex,to reduce the bone resistance and to accelerate teeth move in movement process. However, there has not systemic basic study in domestic and foreign research reports.This study constructing"tooth - upper jaw - Straight Wire"finite element model through the FEA method to research the biomechanical effects of corticotomy facilitated molars intrusion. And then constructed the animal experiment model of corticotomy facilitated molars intrusion to explore that whether the method could reduce root resorption and pulp reaction,and accelerate reconstruction of PDL and alveolar bone. To provide theory basis for the clinical application of corticotomy facilitated molars intrusion. 1 The 3-D finite element analysis maxillary molars intrusionThe DICOM format geometrical information of the maxilla bone and the teeth were obtained through the 64 row helical CT scanning. The MIMICS software were used to construct the 3-D model of bone.And then teeth and 3-D brackets and arch wires were gained from Solidworks CAD software.And the ANSYA software was used to investigate the biomechanical effects. 6 working condition be assumed in this study:①Without CF, simulate molars intrusion by buccal loading.②Without CF, simulate molars intrusion by bilateral loading.③With unilateral CF, simulate molars intrusion by bilateral loading.④With unilateral CF, simulate molars intrusion by buccal loading.⑤With bilateral CF, simulate molars intrusion by buccal loading.⑥With bilateral CF, simulate molars intrusion by bilateral loading.Four kinds of intruded force be designed:50g,100g,150g,200g. The corticotomy incision design as: 2 vertical and 1 horizontal corticotomy cuts were made mesially, distally,and apically.Horizontal incision is about 4-5mm to root apical,while vertical incisions were about 2-3mm from alveolar crest and intersect with horizontal incision. Incision width is 2mm. Ansys12.0 finite element software is used to complete the analysis.The results show:①With the same force and incision design: The maximum stress of root in these load patterns were detected in the furcation.The maximum initial displacement of teeth be gained by bilateral loading,however,stress concentration of root bifurcate and PDL would be increased obviously at the same time. Teeth movement appeared bodily intrusion by bilateral loading,while inclining movement appeared by unilateral loading which maximum initial displacement is detected in the root apex of distal-buccal.And bodily intrusion with unilateral loading can be achieved by adding torque.There is no excessive stress concentration phenomenon appeared in PDL.②With the same force and load pattern: There is no significant effect on initial displacement of teeth and the stress distribution of root and PDL with different incision design.All of them presented a trend of bodily intrusion,and the maximum stress concentrated on root bifurcate and PDL of distal buccal root apex.It's needed to note that the stress is more concentrated in incisions with bilateral incision design than that with unilateral incision design.③With the same incision design and load pattern:Both the initial displacement of teeth and the stress of root,PDL and bone cortex were increased with loading force rised.2 The preliminary biology research of corticotomy facilitated molars intrusionThe bilateral mandibular 3rd and 4th premolars of 2 male Beagle dogs were selected as experimental teeth in our study.One side of mandibular was randomly selected as experimental side,the other as control side,and 2~nd premolar was served as blank control. Miniscrews were placed bilaterally between the roots of the mandibular 3~rd and 4~th premolar. On the experimental side of the mandibular,the corticotomy was performed as:the vertical corticotomy cuts were made about 2 mm to the alveolar crest and extended to intersect with horizontal incision which was about 3mm below the root apices. The 3~rd and 4~th premolars were intruded against the miniscrews with nickel- titanium coil springs on both sides.The intrusion force was setted as 100g. Both dogs were killed 4 weeks after orthodontic force application.We use HE dyeing methods to observe the histology.Results:①We can see root absorption in both experimental side and control side which mainly distributed in root apical region,but that in control side is more serious.②The hyalinization of PDL in the experimental side is less than that in control side.③In pulp tissue,control side showed higher vacuolization of the odontoblast layer than that in experimental side, and which hyperemia edema was more serious.④In controlled side,the number of capillary blood vessels in the periodontal ligament below the apical foramen presented significantly decrease,while it is not significant in experimental side.⑤More absorbed lacunes and osteoclast can be seen in alveolar bone of experimental side than the control side.Conclusions: The design of the bone cortex incision was no significant influence to the stress and strain distribution of root and PDL periodontal in the initial stage. But it appeared obvious stress concentration phenomenon. A series of adverse reactions appeared in teeth movement processs. However,compared with the traditional method, The CF would reduce root absorption, pulp reaction and hyaline degeneration of PDL, and accelerate the reconstruction of the alveolar tissue. Which was good for rapid and widespread movement of tooth , and improve orthodontic treatment effect.