| Maxilla expansion is usual measure that applied to correct arch constrict, nasal cave constrict, "V" arch shape, provide arch space and active maxillary suture for assisting anterior traction .It has been a century to apply method of maxillary expansion. The methods of maxillary expansion are various. According to the design of appliance, it is divided into bone anchorage, tooth anchorage and mixed anchorage; According to the force and active interim, it is divided into rapid maxillary expansion(RMD), semirapid maxillary expansion(SRMD) and slow maxillary expansion(SMD); According to the effect of expansion, it is divided into orthopedic expansion(palatal suture expansion) and orthodontic effect (abutment tooth moving).Quad helix is a versatile appliance. It has many benefits: convenience operation, fewer alienate feeling. It is used wildly in clinic. Generally speaking, Quad helix expansion belongs to slow expansion, but it can produce orthopedic effect to adolescents. There has been no report about the effect of force change on orthopedic ratio.Some scholars suggest that adult has harder bone structure. The interdigital bone structure prolongs the length of palatal structure. It isdifficult to separate adult's palatal structure. Yet there has been no report about the age increase on orthopedic ratio of Quad-helix.Palatal expansion is ideal target of arch expansion. But during expansion there is also anchorage loss of basal tooth, namely basal tooth tip.Force changing can affect expansion result. The patient who is in different development period has different reaction to the expansion. Conventional studies focus largely on amount of the palatal expansion. But during expansion, abutment teeth can tip, which is side effect. This study focused on the palatal expansion ratio and abutment tooth tipping ratio during Quad helix expansion to different force and different age, and provides evidence of appropriate force for applying Quad helix in clinic.Four components determine the interarch expansion: sutural displacement (Sd-Sd),alveolar process tipping and bending (At+b-At+b), tooth displacement (Td-Td), and tooth tipping (Tt-Tt). (At+b-At+b) were effected by the elastic mechanical property of bone per se. It can recovery to its original state when force is elapsed, and has no contribute to the interarch expansion at last. (Td-Td) is believed to be babutment teeth moving bodily.The abutment teeth is difficulte to move bodily because of Quad-helix functioning on crown. So (Sd-Sd) and (TrTt) can reflect result of expansion and are important signs of expansion.This study simulated the clinical Quad helix expansion style by applying helix to maxillary expansion in rats: To adjust force by the circle loop; Arch wire act on the abutment teeth; The active interim is longer; After original force, the force decrease during expansion.Bone metabolism was labeled by tetracycline. (Sd-Sd) and (Tt-Tt)ratio were measured, by which analysis influence factor of force and age. Mineralization apposition of palatal suture tissues were observed.The purpose of this study is to set up an animal model of helix expansion and explore influence factor of expansion result. Histology evidence was provided and served to clinic. This study consisted of two experiments.The experiment one was to study the effect of force magnitude on expansion ratio and Mineralization apposition rate after helix spring expansion in rats. 50 SD male rats of 6 weeks age were randomly divided into force levels (0, 50, 100, 150, 200 gm) . Each group had 10 rats. Expansion lasted 10 days. The rats of each group were used as making undecalcified tetracycline labeled bone sections and decalcification bone section. The ground sections were observed under ( 6) microscope and ( 100) fluorescence microscope . The images were transmitted into computer , measuring four conformations of expansion : suture displacing (S |
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