| Malocclusion, which is one of the most frequently encountered diseases in stomatology, has a very high incidence.Nowadays more and more people pay attention to the disease. The insufficient maxillae, one of common malocclusions, can affect chewing, language, and other functions, and affects beauty and the physical and mental health. Stenosis or crowding, which was resulted fromthe insufficient maxilla, can be corrected by maxillary expansion in the clinical treatment. However, it needs a long time fornew boneformation and mineralization after rapid maxillary expansion (RME). Or it will be quite easy to relapse. In most cases, the new bone formation will be affected by many factors and absorbed again. Thus the maxilla and dental arch become narrow again. The incidence of relapse is very high. So acceleratingbone remodeling in the mid-palatal suture will be helpful to shorten the retention period afterRME.Purpose:By the RME animal model, this researchaimed to study the effects of strontium ranelate (SR) on the midpalatal suture remodeling and bone morphogenic protein-2 (BMP-2) expression in the suture after expansion. Wewould find some certain theoretical basis and experimental evidenc efor the appliance of SR on clinical orthodontic treatment to promote the suture reconstruction, prevente relapse and shorten the retention period.Methods:We divided thirty-six Wistar rats into three groups according to the random number table:A, B, and C groups. There was nothing done in the group A. The two-loop spring expander was inserted into the rats’molars in the groups B and C. After activated, the expander would genetate the force (0.98N). Besides, rats in the group C would be perfused 600 mg/kg SR.The rats were euthanized on the 4th,7th, and 10th days. The morphological structure and BMP-2 expression in the mid-palatal suture were observed in the three groups.Results:1. Overall observation:On the 2th and 3th day after the expansion, the weight went down in the two expansion groups. And they rose on the 4th day. The weights in the two expansion groups were less than that in the group A on the whole period (P＜0.05). With the macroscopic observation, the maxillary width in groups B and C was wider than the group A.2. Measurement in microCT:The suture width in the groups B and Cbecame wider than that in the group A in the study (P<0.05). On the seventh and tenth days, the transverse width was smaller in the group C than that in the group B (P>0.05). Besides, bone volumein the midpalatal suture of the two groups B and C decreased significantly (P>0.05) versus A.On the seventh and tenth days, in comparision with the bone volume of the group B, that in the group C was larger (P>0.05).3. HE results:In the group A, the structure of the maxilla remained almost the same. There were few chondrocytes and osteoblast, which became mature. The fibrous tissue in the midpalatal suture of the groups B and C were streched wider and cartilaginous components grew into the fibrous tissue.Some osteoblasts proliferated and became activein the suture margine. On the7th and lOthdays, compared with that in the group B, new boneand cells were much morein the group C.4. Immunohistological results:Only on the 4th day, the MOD value of BMP-2 in the group B was higher (P＜0.05) than the MOD value in the group A. MOD value of BMP-2in the group C was more (P＜0.05) than that of the groups A and Bonthewhole expeiment.Conclusions:1. The large, mechanical and expansive force of 0.98 N could expand the midpalatalsuture, the dental arch and maxillaof the growing rats.2. With expanding force, SR can increase the bone volume and the expression of BMP-2 in the mid-palatal suture.3. SR can accelerate the differentiation of osteoblast and new bone formationand calcification, which will be helpful to maintain the expansion effects, and decrease relapse after RME. |
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