The Mophology Observation Of Early Indication In Root Resorption

In orthodontic treatment process, root resorption can often causeirreversible consequences, such as tooth loosing, early loss and so on. Somemeasures, such as using appropriate orthodontic force, reducing the occlusalinterference in the tooth movement and avoiding over-correction, are taken toprevent the resorption. However, there is still unexplained root resorption, whichusually causes the medical disputes. For this problem, we established animalmodel by the way of continuous intrusive heavy force engagement. Continuousintrusive heavy force engagement is one of the most reasons resulting rootresorption in clinic. On the animal model, the periapical radiolucent areas wereusually found before the root resorption was detected on the X-ray film. In orderto investigate whether the periapical radiolucent area was an early indication ofroot resorption, the resorption progress was observed prospectively on theanimal model. By immunohistochemical staining methods, the changes of cellsand molecular expression were studied about this period. It is a preliminarystudy on the role of the periapical radiolucent areas in the mechanism of rootresorption. Ojectives:1. The animal models of root resorption were established by continuousintrusive heavy force engagement. The periapical radiolucent areas should bedetected on the X-ray films. By the dynamic observation of the root resorptionprocessing on the models, it was investigated that whether there was a periapicalradiolucent areas in the stage before the resorption might be detected. And it wasanalyzed that whether the occurrence of periapical radiolucent areas could beregarded as the early indication of root resorption.2. By HE, TRAP and immunohistochemistry staining, the cell and molecularmechanisms were preliminarily analyzed for the periapical radiolucent areasoccurrence.Methods:1. Eight adult hybrid male dogs were divided into three groups randomly.There were three, two and three dogs in group one, two and three, respectively.For the dogs in group one and two, the experimental group teeth and controlgroup teeth were decided. There were24teeth in the experimental group,including maxillary incisors of the dogs in group one and one side maxillaryincisors of the dogs in group two. And there were36teeth in the control group,including the other side maxillary incisors of the dogs in group two and all themandibular incisors of the dogs in group one and two. Continuous heavyintrusive force of350g was imposed to the teeth in experimental group withmini-implant as anchorage, while there was no force imposing to the teeth incontrol group. The teeth in the experimental and control group were observeddynamically by X-ray for a period of8w with1w interval. The differences of theoccurrence of periapical radiolucent areas in the teeth between the two groupswere investigated in order to analyze the relationship between root resorption and periapical radiolucent areas.2. For the teeth of the dogs in group three, the incisors of the zone A weretaken as the experimental group, while the incisors of zone B were taken as thecontrol group. The continuous intrusive heavy force was imposed to the teeth inexperimental group. When the periapical radiolucent areas were detected, thedogs were killed and the paraffin sections were made. By HE staining, thedifferences of morphology and cell composition in the apical areas between theexperimental teeth and control teeth were analyzed. By TRAP staining, thedifferences of the number of osteoclasts in apical regions between theexperimental teeth and control teeth were analyzed. And byimmunohistochemical staining, the differences of the expression of MMP-1、MMP-9、IL-1β were investigated.Results:1. For the24teeth in the experimental group, periapical radiolucent areas weredetected in21teeth. No teeth in the control group was detected to be withperiapical radiolucent areas, which was different significantly with that in theexperimental group(P<0.05). Imposed heavy intrusive force continually,17experimental teeth were detected to be with root resorption in that the rootbecame shortened and the apex became blunt. Among the teeth with rootresorption, periapical radiolucency had been detected early in15teeth, while noperiapical radiolucency had been detected in the other2teeth. For the rootresorption teeth, the teeth with periapical radiolucency detected were more thanthe teeth without periapical radiolucency.2. By HE staining, it was shown that the apical periodontal ligament and theroot apex of the experimental teeth were intact, without significant rootresorption. But the alveolar bone resorption was found in the apical areas with the vacuoles and fatty degeneration. By TRAP staining, it was shown that therewas no significant osteoclasts in the apical region both in the experimental andcontrol teeth. By immunohistochemical study, it was shown that there was highIL-1β expression in the cells surrounding blood vessels in the apical area of theexperimental teeth. And MMP-1and MMP-9were detected in the cytoplasm ofperiodontal ligament fibroblast both in the experimental and control group.Conclusion:It was preliminarily shown that the periapical radiolucency was an earlyindication of root resorption. In the periapical radiolucent areas period, the rootwas still intact, but the alveolar bone resorption had already occurred in theapical area. The results suggested that the root resorption might be prevented ifsome suitable ways be taken during this period.