| Objective:Anchorage is one of the key factors that affect the implant success rate in orthodontic treatment. The traditional anchorage methods are uncomfortable, and usually they can not provide adequate anchorage because of the anatomical factors of the jaw. The emergence of micro-implant anchorage retrieves the deficiencies of traditional anchorage methods and expands the scope of orthodontic treatment. However, the stability of the implant should have been paid more attention among orthodontics scholars. Lundgrens pointed out that the success or failure of dental implants directly were related to jaw bone density, cortical thickness, the width of the jaw, as well as the blood supply in the planting bed. Miyawaki found that micro-implants implanted in high-angle patients appeared a high expulsion rate, he suggested that high-angle patients should have been chosen a bigger diameter mini-implants to increase the implant-bone contact area so that increase its stability. Holmes et al also investigated that the stress distribution in implant-bone interface influenced the stability of implant by the finite element method. It was found out that the thicker the cortical bone thickness and the higher the density, the more stable the implant. At present, there is little anatomical research in implanting position, and the factors affect the cortical bone density and cortical bone thickness were not yet clear.In this study, spiral CT three-dimensional reconstruction techniques were applied to measure the cortical bone thickness and density. This study aims at researching the cortical bone CT value and thickness and its variation of usually implanting location and studying the difference between face types. We hope it provide a theoretical basis for clinical research and practical operation.Materials and methods: 1 The subjects were 23 patients. Healthy malocclusion clinical patients were selected, including 13 adults (7 males and 6 females), teenagers (5 males and 5 females). Spiral CT was used to scan the upper and lower jaws of the 23 patients. After three-dimensional reconstruction, the cortical bone thickness and CT value were measured from 2mm up to 14mm away from the alveolar ridge top at the intervals of 2mm.7 group data was measured in the same place of the patients.2 The subjects were divided into high-angle, low-angle, average-angle three groups which according to the mandibular plane angle (FH-MP) of cephalometric measurement.3 SPSS13.0 software and two-sample T tests were used to analyze CBT and CBCT of the jaw in different gender and age, and to find that whether there are significant differences between genders and age. Single-factor analysis of variance test was used to research CBT and CBCT of the jaw and to analyze if there are significant differences in different face types.Results: The greater the height, the thicker the cortical bone tended to be and the greater cortical bone CT value tended to be.1 CBT: The average CBT ranged from 0.97mm to 1.77mm in the maxilla and 1.03mm to 2.97mm in the mandible. The mandibular cortical bone was significantly thicker than that of the maxilla. U56 and U67 had no difference in CBT, but both of them were significantly thicker than U23 in CBT. The CBT among L67, L56 and L23, L67 was the thickest, L56 was the second, L23 was the thinnest.2 CBCT: The CBCT of mandibular in L56 and L67 was significantly thicker than that of the maxilla in U56 and U67. There were no significant differences in different tooth positions in maxilla. There was no significant difference in CBCT between L56 and L67, both of them were larger than L23. There was no significant difference in CBCT between U23 and L23.3 CBT and CBCT in gender and ageThe CBCT in adolescent was smaller than in adult (P<0.05).There was no significant difference in CBT between different age groups. CBT and CBCT in gender were no significant differences.4 CBT and CBCT in different face typeCBT in U23 of three group face type patients and in L23 of average-angle, high-angle face type patients was thinner than other position. Especially in U23 of high-angle face type patients, the CBT was probably less than 1 mm.5 The CBCT in L23,U23,U56,U67 within 5mm from alveolar ridge crest for high-angle patients was significant lower than other position.6 The CBT in U56,U67 of average-angle and high-angle patients was obviously lower than that of low-angle patients. The CBT in L56 and L67 among three face type patients was no significant difference.7 The CBT in maxilla of high-angle patients was the smallest, average-angle patients was the second and low-angle patients was the largest. The CBT in mandible of three face types was no significant difference.8 The CBCT in maxilla and mandible of high-angle patients was obviously lower than that of average-angle and low-angle patients.Conclusion:1 The cortical bone thickness was the thinnest between lateral incisor and canine, and was the thickest between first molar and second molar. We should pay more attention when mini-implants are inserted in the thin position.2 The cortical bone CT value in posterior area of mandible was the highest, and the sclerotin in this area was the most hardest.3 The cortical bone thickness in high-angle patients was the thinnest and the cortical bone CT value was the lowest.4 There are no significant differences in cortical bone thickness between youth and adult, while the cortical bone CT value in adult was significantly greater than that of younger people.5 The cortical bone thickness and the cortical bone CT value were not significantly different between men and women.6 The cortical bone thickness were thinner in anterior area of the jaw for average-angle, high-angle patients and the anterior area of maxilla for low-angle patients. Especially we should pay more attention when mini-implant was inserted in high-angle patients, because the cortical bone thickness was possible less than 1mm.7 Cortical bone CT value within 5mm from alveolar ridge crest were obviously low in anterior area of jaw and posterior area of maxilla for high-angle patients. We should be careful when carrying out embedding operation.
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