Investigation of the removal torque of miniscrews after giving different direction of moment—an animal study
Date Issued
2009
Date
2009
Author(s)
Wu, Kuan-Yi
Abstract
Miniscrews, which are different from traditional dental implants, can be loaded immediately or quite early after primary stability established. New design of its head structure , with a bracket slot , tube, or hole, can be connected to a sectional wire in order to achieve three dimenisional control of tooth movement during orthodontic treatment. However, this mechanical design would give a moment, which may endanger the stability of the miniscrews. Therefore, we used animal experiments to simulate this type of loading on miniscrews to test its effect on the miniscrew stability. Eighty miniscrews (2.0mm diamter, 11mm length) were surgically placed in maxillary and mandibular alveolar bone between canine and first molar in 3 adult mongrel dogs. At each quardrant, we bonded the brackets on the posterior miniscrews. At left side, we gave a clockwise moment to the posterior miniscrew by cantilever arm devices. At right side, we gave a counter-clockwise moment to the posterior miniscrew. The total experimental time was six months in dogs A and B, and seven months in dog C. Each dog was given metabolic bone labeling at three-week intervals. Clinically, we recorded the insertion torque, the removal torque and loading time of each miniscrews before animals sacrificed. In order to observe the tissue changes at interface of bone and miniscrews, samples were embedded with resin and sectioned with microtomes, and the results were evaluated under a microscope By multivariate logistic regression method, parameters from clinical data and histological results were analysed for their influences on removal torque. Clinical data showed: 1) In some areas, the brackets on miniscrews were rotated gradually by the given moment. 2) There was a significant positive correlation between the loading time of miniscrews and the removal torque, but not the other variables. 3) There was no significant difference in the removal torque between the clockwise- and counter-clockwise groups. 4) The values of insertion torque were significantly higher in the mandible than those in the maxilla. Histological finding showed:1) Higher bone to implant contact (BIC) ratio was found towards the tip of the miniscrews. 2) In experimental loading group, there seems to be more flurorence labeled bone tissue surrounding the miniscrews.
Subjects
primary stability
miniscrews
animal study
giving moment
removal torque
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