Mini-implants and mini-screws are commonly used in orthodontics to provide extra anchorage. One potential insertion site is between the roots in the alveolar process, which results in a risk of damaging the roots of neighbouring teeth. In an animal-experimental study, 20 mini-screws (bracket screw bone anchors, BSBAs) were inserted into the mandible of five beagle dogs. Each dog received two BSBAs in each lower quadrant, between the roots of the second and third, and third and fourth premolars. Sequential point labelling was performed every 6 weeks with vital stains, and apical X-rays were taken every 6 weeks. Radiographic examination demonstrated damage at three roots because of insertion of the BSBAs. Histological examination at these three roots demonstrated an almost complete repair of the periodontal structure (e.g. cementum, periodontal ligament and bone) in a period of 12 weeks, following removal of the screws.

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The purpose of this study was to evaluate, histologically, root contact, proximity to a root, and proximity to marginal bone level as possible risk factors for the failure of mini-screws when inserted between neighbouring teeth. Twenty mini-screws were inserted into the mandible of five beagle dogs. Each dog received two bracket screw bone anchors in each lower quadrant, between the roots of the second and third, and third and fourth premolars. Every six weeks, apical radiographs were taken and vital stains were administered. Twenty-five weeks after insertion of the screws, the dogs were sacrificed and specimens prepared for histological evaluation. The distance between the screw and the roots and between the screw and the marginal ridge level (MRL) were measured on the histological slides. The presence or absence of root contact was evaluated histologically on serial sections. The number of screws was too small to allow for sound statistical analysis of the factors under investigation. During the evaluation period, 11 screws were lost. Six screws were in contact with a tooth root and five of these were lost. In five sites, the distance between the screw and the tooth was less than 1.0 mm, but only one of these screws was lost. The distance between the screw and the marginal bone level was less than 1.0 mm for nine screws and seven of these were lost. The results of this limited study suggest that root contact and marginal position might be major risk factors for screw failure.

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Mini-implants and miniscrews are commonly used in orthodontics to provide additional temporary intraoral anchorage. Partial osseointegration represents a distinct advantage in orthodontic applications, allowing effective anchorage to be combined with easy insertion and removal. This article reports the histomorphometric findings of the osseointegration of bracket screw bone anchors (BSBAs). In an experimental animal study, four BSBAs were inserted in the alveolar process of the lower jaw in each of five male beagle dogs, aged 6.5 months from the same mother. Eleven screws were lost during the study, nine of them due to lack of primary stability. One screw was removed at the end of the examination period for evaluation of ease of removal. After 6 months, histological evaluation of the eight remaining screws was performed to evaluate the extent of osseointegration. All eight screws showed partial osseointegration (mean 74.48 per cent, standard deviation +/- 15.33 per cent). The amount of osseointegration was independent of loading time and location (anterior or posterior), as tested with an independent samples t-test (P > 0.05). Analysis of the data indicated that small titanium screws were able to function as rigid osseous anchors against an orthodontic load of 200 cN for 6, 12, 18, or 24 weeks after a minimal healing period or no healing period. These findings show that miniscrews, used for temporary anchorage in orthodontics, partially osseointegrate.