A Study On The Effect Of Altered Masticatory Force On The Condylar Cartilage And Subchondral Bone In Growing Rabbit

Objective to establish the animal model of altered masticatory force, to explore the effect of masticatory force on development of condylar cartilage and ultrastructural changes of the condylar subchondral bone in growing rabbit and to study on the BrdU labeling in both structures.Method In the first experiment, thirty-two,10-day-old New Zealand white rabbits with normal hard food were divided into two groups randomly. In group one before sacrificing1week ago, every rabbit every day was injected intraeritoneally with bromodeoxyuridine(BrdU)50mg/kg. In group two every rabbit was injected intraperitoneally with BrdU50mg/kg for2consecutive weeks and then each group of four rabbits was sacrificed at2,4,6,8weeks after the beginning of the experiment. In the second third and forth experiments, thirty-two,10-day-old New Zealand white rabbits were divided into two groups randomly. One group was received the normal hard diet and the other group received a powder soft diet. Both groups were injected intraperitoneally with bromodeoxyuridine(BrdU)50mg/kg for2consecutive weeks and then sacrificed at2,4,6,8weeks after the first BrdU injection. Presences of BrdU, PTHrP and Ihh were detected using immunohistochemistry and morphological change was examined by HE staining. The architecture properties of the subchondral bone was analysed by micro-CT and the presence of BrdU was detected using immunohistochemistry.Result:1、An stable model of altered masticatory force can be established successfully by changing the hardness of food.2、The method for labeling the proliferation that rabbits were injected intraperitoneally with BrdU50mg/kg for1consecutive weeks before sacrificing is effective. The presence of BrdU can’t stay a long time in this study when using for labeling the condylar cartilage progenitor cells3、Altered masticatory force can cause the change of thickness of condylar cartilage. Compared with the soft-diet group, the thickness of anterior part of condylar cartilage in the hard-diet group was increased significantly. There was no significant change in the thickness of intermediate part of condylar cartilage. The thickness of posterior part of condylar cartilage was thicker in the soft-diet group.4、Altered masticatory force cause the difference of rate of BrdU labeling. Immunohistochemical analysis revealed staining of BrdU localized in the all cartilage zones and subchondral bone. BrdU-positive cells were abundantly detected in the proliferative zone. The BrdU labeling rate of hard-diet group in anterior intermediate and posterior part of condylar cartilage was higher than the soft-diet group significantly in the2nd week. The BrdU labeling rate of soft-diet group in intermediate and posterior part of condylar cartilage was higher than the hard-diet group significantly in the6th week. In8th week both groups can’t detect the BrdU-positive cells.5、Ihh/PTHrP signals exert important modulation function in endochondral ossification of condylar cartilage. In the model of reducing masticatory force, there exists a time sequence. In2week, Ihh was expressed higher in the hard diet group. And in4week, PTHrP was expressed higher in the hard diet group.6、In4week Tb.Th, BV and Tb.N were reduced in the soft diet group, while Tb.Sp increased in the hard diet group. BrdU-positive cells were abundantly detected in the hard diet group. In8week there were no significant differences between two groups of micro-CT microarchitecture parameters while the BrdU-positive cells were more in soft diet group than hard diet groupConclusion The growing rabbit with low masticatory force has a slow proliferation initiation. It suggests that the proper masticatory force can promote the proliferation of cell in cartilage and have an effect on ultrastructural changes of condylar subchondral bone in growing rabbit. The development of two structures is still affected by the internal factor such as gene.