| Lateral functional shift of the mandible was one of the most frequent malocclusions, usually accompanied with unilateral posterior crossbite. Because of the existing of abnormal functional environment , lateral functional shift of the mandible was characterized by transverse rotation of the entire mandible around a vertical axis toward one side of the head during closing .It would cause pathological changes of occlusion, temporomandibular joint , jaw bone and muscles et al. In other words, severe facial asymmetry could create esthetic concerns and functional abnormality and affect physical and mental health of these patients.Unless treated in time during growing period, functional mandibular shift could not heal by itself. With growing up, pathological remodeling of the temporomandibular joint would occur and the facial asymmetry and the shift of the mandible would aggravate gradually .The effect of the mandibular functional shift on the mandiblar growth remain controversary especially whether the functional shift would cause structural bone asymmetry of mandible.It was still unclear that what kind of adaptive change would occur to the growing pattern of functional shift patient by early treatment.The objects of this study were to evaluate the effect of the mandibular functional shift on the growth and development of the mandible after constructing the mandibular functional animal model of 4-week-old male SD rats. Basing on above animal model, the adaptive remodeling of condylar cartilage were investigated in this study. The main purpose of the study was to provide an objective basis for the early intervention and follow-up treatment of the lateral functional shift through this research. This research was divided into three parts:1. The study of lateral functional shift of the mandible---building of animal model upon rats.Sixty 28-day-old male Sprague-Dawley rats were randomly divided into three groups: shift(24), recovery(12), and control(24). At 4 weeks of age, each animal in the shift and recovery groups received an appliance designed to produce a lateral functional shift of the mandible to the left side about 2mm, the animal model upon rats mimicking the lateral functional shift of human being has been set up. And, the movement trajectory of inferior incisor were observed and recorded within some periods. The results were as follows: The mandible movement of experimental group after 1 week with the appliance shows displace towards left side ;that of recovery group after 1 week without the appliance shows the almost same frequency bilateral like the control group. The results showed that we had successfully set up the feasible model of a lateral functional shift.2. The morphological responses of a lateral functional shift and a shift release of the rat mandible during the growth period.Basing on the animal model, the digital dental film and Dimaxis Pro 3.1.1image analysis system was used to analyze the morphological changes of a lateral functional shift and a shift release of the rat mandible during the growth period on the animal model. In the shift group from 2 to 4 weeks, the Cd-Me,Co-Me,Go-Me were greater on the right side compared with the left side ( P<0.05),but CdH,CoH,MeH of the right side were smaller than left side( P<0.05). However, in the recovery group, 1 week after appliance removal, the changes of Cd-Me,CdH,Co-Me,CoH,Go-Me and MeH like the shift group. 2 weeks after appliance removal, Cd-Me,CdH,Co-Me,CoH,Go-Me and MeH of the left and right were almost equa(lP>0.05). From 2 weeks, Cd-Me,CdH,Co-Me,CoH,Go-Me and MeH in the shift and recovery group were all smaller than the control group( P<0.05). The results were as follows: A lateral functional shift led to the adaptive changes of the mandibular body and rames of the SD rats, and morphological asymmetry of the mandible. The early treatment could improve the asymmetry, but the development of the mandible still showed off the hysteresis.3. The histological changes of a lateral functional shift and a shift release of the rat condylar cartilage during the growth period.The purpose of this study was to evaluate the histological changes of a lateral functional shift and a shift release of the rat condylar cartilage by the routine microscopic examination, including routine and special staining method. The routine staining method was adopted to differentiate the different structure and their changes of condylar cartilage. AB/PAS displayed variation of the cartilage cell and matrix. The analysis was as follows: The thickness in the central and posterior regions on the left side decreased at 1 week, and it decreased obviously in the lateral region at 2 weeks. AB positive reaction in the cartilage cells from the germinal zone to the transformation zone weakened gradually, and PAS positive reaction in the cartilage matrix enhanced. In the shift group at 2 weeks, the cartilage thickness increased in the central and posterior regions on the right side, AB positive reaction in the cartilage matrix from the germinal zone to the matural zone enhanced than the control group. From 3 weeks, the thickness in the anterior region became thinner obviously than the control. However, in the recovery group, at 1 week after appliance removal (3 weeks), PAS positive reaction in the germinal zone cells on both sides are weaker than control group, AB positive reaction in transitional zone and the matural zone cells enhanced; and AB positive reaction in the cartilage matrix from the germinal zone to the transformation zone enhanced comparing the control group. At 2 weeks after appliance removal (4 weeks), the cartilage thickness in the anterior region on the right side became thicker than the control group, and that in the posterior region decreased. Only the cartilage thickness in the posterior region on the left side increased slightly. The results displayed as follows: A functional shift of rat mandible during the growth period caused changes of the thickness and cell proliferation in the corresponding areas of the condylar cartilage. Following early treatments, the thickness and cell proliferation in the corresponding areas would retrieve gradually approaching to normal levels. |
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