| [Objective] Using CT to observe three-dimensional changes of rhesus monkeys' maxilla and upper dental arch of retractive forces with zygomatic implant anchorage, and to evaluate the effects of backward traction to the maxilla and upper dental arch with the anchorage.[Materials and Methods] 1. To establish the animal model: Five male rhesus monkeys with fixed dentition were randomly divided into test groups,which include 1.5 months ( test group 1) and 3 months ( test group 2) and control group. Two monkeys for test group 1,another two for test group 2 and the rest one served as control (did not wear appliance). Two titanium miniplates were surgically fixed on the left and right zygomatic bones as the anchorage for backward traction of maxilla for each test monkey. A NiTi closure coil was attached to the miniplate and maxillary dental splint on each side. A backward force of 150g was exerted on each side of the maxilla (totally 300g) for test groupes. The direction of force was parallel to the occlusal plane. 2.To observe the morphologic effects: To observe and analysis the experiment results simplely by comparing photographs,models and skulls of pretreatment and posttreatment. 3. To investigate the three dimensional changes: Three dimensional reconstructions were set up after CT sanning in pretreatment and posttreatment with the same scanning conditions and scopes. To analysis the three dimensional changes by measuring some typical and clear points in both maxilla and upper dental arch.[Results] 1. The implants anchorage: The zygomatic implants kept stable without any loose or deformity during the whole experiment. 2.The morphologic effects :Compared with photographs,models and skulls of test groups and control group showed that the molar relationship of both sides changed from Class I into Class III and the edge-to-edge anterior dental relationship replaced by crossbite,the distance was 3mm and 5mm in 1.5 months and 3 months respetively. 3.CT images : The upper dentition and the maxillary position of test groups were markedly backward changed and the maxillary length decreased. There was no significant difference of maxilla and upper dentition between pretreatment and posttreatment of control group (p>0.05). However,obvious backward movement can be observed in test groups. Points UI,U6B,ANS,PNS,Zm moved distally about 3.18mm,1.7mm,1.69mm,0.12mm,1.45mm respectively in 1.5 months test group,while more significant changes presented in 3 months test group, points UI,U6B,ANS,PNS,Zm moved distally about 4.67mm,3.38mm,4.13mm,1.49mm,2.27mm respectively. There were more distinct changes in the foreside of maxilla than the backside. Maxillary central incisors moved lingually and the palatal plane (ANS-PNS/SN) rotated counterclockwise slightly,0.98°in 1.5 months test group and 1.4°in 3 months test group. Statistic analyses showed that ,in 1.5 months test group ,there was significant difference in sagital backward movement of upper dentition (p<0.05) ,but no significant difference in vertical and horizontal changes of upper dentition between control group and 1.5 months test group,also between pretreatment and posttreatment of itself. The maxilla seemed to be maintained in the same positions(p>0.05)in 1.5 months test group. However,the results of 3 months test group was not as the same as 1.5 months test group,there were more significant difference in sagital backward movement of the upper dentition (p<0.01) and the maxilla (p<0.05),the vertical and horizontal positions has not changed obviously in both upper dentition and the maxilla.[Conclusion] 1. The results indicate that the zygomatic minimplant anchorage can tract the maxilla and the upper dentition backward and restrain their growth effectively. 2. Zygomatic bones can be selected as implant sides and zygomatic miniplate implants can be utilized as the stable and effective anchorage in maxillary orthopedic treatment. 3.Three-dimensional changes were observed after treatment, spiral CT was useful in the three-dimensional evaluation of maxilla. |
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