| The skeletal Class III malocclusion patient with a retruded maxilla often adopts the treatment of facemask for maxillary protraction, but it is still incomplete with regard to the biomechanism of reactions in the circummaxillary sutures to such mechanical stimulation .The aim of this study was to investigate the effects of the changes in the circummaxillary sutures during maxillary protraction in growing rats.Materials And Methods 1, The animal model of Sprague-Dawley rat for maxillary protraction was made in this study, and an appliance based on the principle of protraction headgear was designed and made for maxillary protraction treatment which was hooked over the front of the zygomatic arch ,and a hole was made on the skull in the experimental group rat . and a clasp was placed into the hole for providing orthopaedic anchorage by elasticity traction. 2 . 90 Sprague-Dawley rats were divided into a baseline group, an operated control group and an experimental group at random, and were sacrificed 3,7 ,14,21,28 days after application of the maxillary protraction. The suture sections were stained with routine HE method to observe the general morphological changes and were stained proliferating cell nuclear Antigen using immunohistochemical SP method. The parameters of bone-suture width, the density of cells in the sutures , the density of PCNA positive stained cells were valued by automatic image analysis system to evaluate the changes .Resu I ts At day 3, the bone-suture width was higher in the experimental group than in the two control groups (p < 0.05), and it increased significantly (P < 0.05) at day 7 while there were no significant changes in the controlled groups. Less growth was found in the experimental group in the other time experiments but it was still higher than that in the twocontrols(P < 0.05). 2 The cell density in palatomaxillary sutures rose at day 314 following force application to the maxilla(P < 0.05), but it gradually returned to the regular levels at day 2K 28. And the cell density in the frontomaxillary sutures was higher over the duration of this study (P < 0.05)while there were no statistically significant differences found in the two control groups. 3, Three days after orthopedic treatment, the density of PCNA positive cell gently rose in the experimental groups,while no significant difference was observed between the two controlled groups (P < 0.05) . and the highest amount of cell proliferation expression occurred at the seventh day. Although larger increments in the experimental groups compared with the two control groups, there was a tendency for PCNA positive expression to gradually decrease at the three time points of 14th day 21th day and 28th day.Cone I us i ons 1, We believe this rat model of simulated maxillary protraction presents a feasible way in vivo to study the biomechanism relating to the role of bone sutures in maxillary protraction . 2 Significant changes in new bone formation , blood vessel hyperplasia and cellular proliferation in the treated groups afte maxillary protraction were observed histologically in the sutures ,which suggested that reactions in the sutures might occur as results of rebuilding. 3 There were significantly larger in the bone-suture width in the experimental group than in the two controls seemed to indicate that forward movement of the maxillary complex would be performed with an extraoral anterior-pull appliance. 4 The increases in the cell density in the sutures of the treated groups were higher as compared to the two controlled groups for 3 7 14days indicating that cellular hyperplasia in the expanded sutures were accelerated by the protraction .The cell density in the palatomaxillary sutures and in the frontomaxillary sutures differed in increase ways at the two time points of 21th day and 28th day suggested that the mode of bone formation in the circummaxillary sutures is different from one another..5 The expression of Proliferating Cell Nuclear Antigen(PCNA) were always higher than the controls in the course of this study,which i...
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