| [Objective]:To establish rats’ masseter muscle weak and enhanced animal models through two different methods, and to investigate the effects of the masseter on the growth of the mandible and the condylar.[Methods]:21 SD rats were 48 days old, were randomly divided into three groups, at room temperature 22 ℃, relative humidity of 50% to 60%, lower air velocity ≤0.2,ammonia concentration ≤14mg / m3, noise ≤60dB feeding conditions A week later,the test.Group A(Masseter enhanced group): To enhance the strength of rats’ masseter by chewing chocolate-soaked wood;Group B(Masseter weakened group): To weaken the strength of rat ’s masseter by injecting glucocorticoid triamcinolone acetonide with 0.01 ml / 100 g in the rats’ masseter;Group C(The control group): without any treatment.Eight rats were killed at the 3rd and 6th week in each group, the mandible morphological features were measured and condylar histological characteristics were examined, insulin-like growth factor- examined(IGF-1) expression levels were detected, and to compare the difference in different period in each group.[Results]:In this study, experimental rats’ models were successfully established, include masseter enhanced and masseter weakened.(1)the mandible morphological measurements show that:①: The length evaluation of mandible show: Rats’ mandibular length in group B was significantly lower than group A, group B was lower than group C, group A was longer than the group C; There was a remarkable difference(P<0.05) in thelength evaluation of mandible in three groups.②: ramus height measurement results show: B group of rats ramus height measurement value is less than the height measurements support group A and C group were lower jaw; compared to group A rats ramus height measurements to be significantly greater than the height measurements support group C were lower jaw,the difference was statistically significant.(p<0.05)③: mandibular angle measurement results show: Agroup of rats mandibular angle measurements greater than the measured value of the mandibular angle rat group C, group C rats mandibular angle mandibular angle measurement is greater than the measured value of rats group B, the difference was statistically significant.(p<0.05)④:mandibular height measurement results show: The three group were compared with each other, the difference,however, was not statistically significant.(p>0.05)⑵The measuring results of condylar tissue show:①: Condylar chondrocytes were obviously stratified and tightly packed in group A;②: Condylar chondrocytes were sparse in group B;③: Condylar chondrocytes were sparse in group C, but slightly packed more than group B.⑶ condylar cartilage immunohistochemistry showed, IGF-1 mainly expressed in chondroblast cell layer and hypertrophic cell layer. Quantitive analysis had showed, IGF-1 had higer expression in chondroblast cell layer and hypertrophic cell layer at 3rd week than at 6th week. IGF-1 had higer expression in group A than group C in proliferative cell layer, and express in group C were higer than in group B,no matter at 3rd week or at 6th week.[Conclusion]:1: In the environmental conditions of this study, masseter enhanced favored the growth of mandibular and condyle while reduce the angle of the jaw. The mandibular angle increased with weak masseter muscle.2: In the environmental conditions of this study, the differentiation of thecondylar chondrocyte was positive correlated with the amount of pressure.3: IGF-1 factor as a growth factor expressed in the stages of growth and development, IGF-1 factor expression increased with increasing stress,It means that IGF-1 might be considered as a growth index of the condylar. |
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