| It is well know that the biological basis of Orthodontics is the plasticity of jaw, the strength-proof of cementum and the stability of periodontal ligament internal environment. As the most active part in human bone metabolism, alveolar bone is one of the most important subjects in Orthodontics.Much research has been done on tooth movement and remodeling of the periodontal tissues when a mesial tipping movement force is carried on rats and as a result, the theory of "three-part cumulative tooth movement kinetics" is summarized. In almost of their investigations, emphasis was put on how the tooth were moved and its relationship with time, there is still no report on changes of elements such as phosphorum and calcium during tooth movement in alveolar bone, which is in close relation with bone remodeling.In this study, a 50g-force was carried on rats' maxillary first molars, Ca/P ratios were detected with X-ray energy dispersive system (EDS) and histologic changes of periodontal tissues in 28 days after tooth loading were observed. Through morphology and Ca/P ratio changes, we want to investigate the biological laws of tooth movement and supply experiment foundation for clinical treatment.35 male adult SD rats were divided into 7 groups in which 6 were experimental and 1 was control. For experimental groups, each rat was loaded a 50g-force on its maxillary first molar. 1, 3, 7, 14, 21, 28 days after the operation, rats were killed by overdose anesthesia. Some Samples were drawn and fixed in glutaraldehyde. After being frozen in liquid nitrogen, alveolar bones were split into two parts and the observing surface was exposed. After cleaning, dehydrate, dessication and carbon plating, the elements concentration was detected andanalyzed by x-ray energy dispersive system(EDS). Other samples were drawn and fixed in formalin solution. With decalcification and dehydration, samples were embedded in paraffin and cut into 5-um sections. After stained with hematoxylin and eosin, sections were observed through light microscopy.X-ray energy dispersive system(EDS) can directly and accurately investigate concentrations of some elements in alveolar bone during orthodontic treatment of SD rats' maxillary first molars, at the same time,it provides a good method for the study of orthodontic biology.In the tension side,at the initial time,Ca/P ratio decreased because new bone was formed by osteoblasts.Then new bone was calcified graduately,and with the improving of calicification of alveolar bone, Ca/P ratio increased to the normal level.In the pressure side, Ca/P ratio also decreased at the initial time ,but the reason is different from that of the tension side.Lots of osteoclasts were found in this phase.Then, Ca/P ratio was kept in a lower level and many osteoblasts and osteoclasts were observed beginning from the 7th day to the 14th day.As the recalcification of alveolar bone, Ca/P ratio came back to the initial level.In conclusion, remodeling of alveolar bone presented a dynamic process after operation of the maxillary first molar in rats.It is found that there are complicated osteoblastic and osteoclastic activities both in the tention and pressure sides, accompanied by changes of Ca/P ratio,which tends to the new balance in the end. |
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