| Background and objective:Class II malocclusion is one of the most common orthodontic problems. Mandibular retrognathia is the major aetiology of class Ⅱ malocclusion. A variety of functional appliances have been used to stimulate mandibular growth in adolescence with mandibular retrognathia.Type1diabetes mellitus, which is characterized by a lack of insulin production, has a peak incidence at10to14years of age, which is the most optimal time for stimulating mandibular growth in adolescence with mandibular retrognathia. It is inevitable that orthodontists will confront adolescent patients with type1diabetes mellitus who seek for orthodontic treatment to correct mandibular retrognathia. But whether there exists difference between these patients and normal patients in correcting mandibular retrognathia with functional appliances is still unclear. Since patients and orthodontists think more highly of delicate and individual orthodontic treatments, it is necessary to make clear it.Mandibular growth includes the growth of mandible ramus, mandibular body and condyle. The mandibular condylar cartilage is a major growth site of the mandible, thus it plays an important role in regulagting the mandiublar growth. Mandibular advancement achieved by functional appliance may promote the condylar remodeling and subsequently accelerate the mandibular growth. Besides the remodeling of hard tissue, functional orthopedic therapy may stimulate the maxillofacial skeletal muscle to remodel adaptively. Previous studies have proven that ectopterygoid is closely involved in the movement of condyle, while its functional status also has effect on the growth remolding of the condylar cartilage. Investigating the responses of the condylar cartilage and ectopterygoid during the period of experimental mandibular advancement in diabetic rats may help us better understand the adaptive remodeling of condyle and ectopterygoid in adolescence with type1diabetes mellitus and mandibular retrognathia during the period of functional appliances treatment.Method:Seventy-five-three-week-old male Sprague-Dawley rats were divided into3groups:"normal ","diabetes" and "diabetes with insulin-treatment". Bite-jumping appliances were applied to the rats in the experimental groups. At0,1,2,3and4weeks after placement, animals were killed, and the condyle and the lateral pterygoid muscles were excised. The condyle processed using routine histologic techniques; The features of condylar morphology were investigate using HE staining; MMP-8, MMP-9and TIMP1were detected using immunohistochemistry technology; The lateral pterygoid muscles of each rats were collected for Na+-K+-ATPase activity analysis, Na+-K+-ATPase al and a2subunits mRNA analysis by quantitative real-time PCR and protein analysis for al and a2subunits by Western blot.Results:1.Histological analyses in samples revealed a difference in central section of condylar cartilage layer thickness among the normal^diabetes and diabetes with insulin-treatment after mandibular forward positioning. Total layer thickness of the cartilage in three groups was increased except at the first week. There was no significant difference in the total layer thickness among the three groups at the first week. Total layer thickness of the cartilage in diabetes was thinner than that of normal groups at2W, which was largely determined by decreased thickness of the proliferative layer and chondrogenic layer. But it was thicker than that of normal groups at3W and4W, which was largely determined by increased thickness of the hypertrophic layer notwithstanding the proliferative layer and chondrogenic layer was thinner than that of normal groups. There was no significant difference in histological morphous between the normal group and diabetes with insulin treatment group.2. Mandibular advancement in rats caused a gradual increase in the expression of MMP-8, MMP-9, TIMP-1, MMP-8/TIMP-1and MMP-9/TIMP-1when compared with the control group. Diabetes decreased the expression of MMP-8and MMP-9induced by mandibular advancement while increased the expression of TIMP-1when compared with the normal group. The ratio of MMP-8/TIMP-1and MMP-9/TIMP-1showed a significant decrease in diabetic animals as compared with the normal group. A recovery of these parameters could be observed in the group with experimental diabetes treated with insulin.3. Mandibular advancement in rats increased Na+-K+-ATPase enzyme activity in lateral pterygoid muscle among the three groups. Diabetes decreased the Na+-K+-ATPase enzyme activity when compared with normal group.4. Mandibular advancement in rats also stimulated the mRNA and protein expression of Na+-K+-ATPase al and a2subunit. Compared with normal group, a significant decrease in the mRNA and protein expression of al and a2subunit was observed in diabetes at1、2、3and4W, whereas an increase in the mRNA and protein expression of α2subunit at OW. A recovery of these parameters could be observed in the group with experimental diabetes treated with insulin.Conclusion:During mandibular forward positioning induced by functional appliance, diabetes decreased the renovation of cartilage and new bone formation, meanwhile, diabetes also reduced the Na+-K+-ATPase enzyme activity in lateral pterygoid muscle. However, condylar cartilage and lateral pterygoid muscle response to mandibular forward positioning in insulin-treated diabetic rats does not differ significantly from that observed in healthy subjects. Therefore, people with diabetes should not receive functional orthopedic treatment until their metabolic status normalizes and their poor remodeling capacity of condylar and lateral pterygoid muscle be corrected. |
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