Root Resorption Induced By Tooth Movement: The Basic And Clinical Study

External apical root resorption is a common iatrogenic problem associated with orthodontic treatment and it has received considerable attention.(Robert 1998).The orthodontic force cause the tooth movement as well as periodontal tissue remodeling. It has been shown repeatedly that root resorption is an inevitable consequence of tooth movement. Many previous radiological and histological studies revealed that apical root resorption is an important side effect of tooth movement with which the orthodontic specialty should be concerned. Therefore, More systematical studies on apical root resorption are urgently required. The aim of the present project was to develop a animal model for root resorption induced by tooth movement to study the expression of biological markers related to tooth movement. A further aim was to study root resorption caused by treatment-related factors in orthodontic patients.Chapter I The expression of proteolytic enzymes and the cytokine IL-6 in root-resorbing tissues. Section I: The aim of this experiment was to investigate the expression of Cathepsin K and MMP-9 to identify their roles in root resorption. A model for tooth movement was developed. A closed coil spring was used to mesialise the upper first molar on one side of the upper jaw of the rats. The upper first molar on the other side was used as a control tooth. The spring delivered a force of 50 cN for 7 days. Thirty histological sections from each sample were selected randomly for in situ hybridization and immunohistochemical staining. Digoxin-labeled DNA probes for Cathepsin K and MMP-9 were prepared and used for in situ hybridization. Antibodies for Cathepsin K and MMP-9 were used to detect the protein expression of Cathepsin K and MMP-9. It was found that both Cathepsin K and MMP-9mRNA and proteins were specifically expressed in odontoclasts and osteoclasts. Either Cathepsin K or MMP-9 were significantly more strongly expressed in experimental samples than in control samples. In most of the root resorption samples, nearly all the odontoclasts and osteoclasts were MMP-9 or Cathepsin K positive cells .The results indicate that both MMP-9 and Cathepsin K may play an important role in root resorption during tooth movement in a model similar to bone resorption. Section II: The aim of this experiment was to detect the expression of IL-6 in root resorption tissue. The same animal model was used as in the previous section. A digoxin-labeled DNA probe for IL-6 was prepared and and used for in situ hybridization. An antibody for IL-6 was used to detect the expressions of IL-6 protein. It was showed both by in situ hybridization and by immunohistchemical staining that IL-6 is highly expressed in osteoblasts, PDL fibroblasts, osteocytes, odontoblasts and some of the mononuclear cells in the bone marrow. The expression of both IL-6 mRNA and proteins in the experimental group was significantly higher than in control group. This study was the first to observe the expression of IL-6 in root resorption area. The results suggest that IL-6 may regulate root resorption and bone resorption by stimulating the formation of odontoclasts or osteoclasts.Chapter II This clinical study was performed to study root resorption induced by tooth movement. The specific aim of this investigation was to compare root resorption after the application of continuous intrusive and extrusive forces in the same individual. In 9 patients (mean age 15.3 years), the maxillary first premolars were randomly intruded or extruded with a continuous force of 100 cN for eight weeks. Ten maxillary first premolars from six randomly selected orthodontic patients served as controls. The extent of root resorption was determined by scanning electron microscopy. A quantitative assessment of the percentage of resorbed area of the total root surface was performed on composite micrographs. The severity of root resorption was also assessed by visual scoring of the root. Root resorption mainly occurred at the apical part of the roots in both experimental groups. Intruded teeth 5.78 +3.86% of...