Histomorphometric evaluation of the bone surrounding orthodontic miniscrews according to their adjacent root proximity / 대한치과교정학회지

OBJECTIVE: This study was conducted to perform histomorphometric evaluations of the bone surrounding orthodontic miniscrews according to their proximity to the adjacent tooth roots in the posterior mandible of beagle dogs. METHODS: Four male beagle dogs were used for this study. Six orthodontic miniscrews were placed in the interradicular spaces in the posterior mandible of each dog (n = 24). The implanted miniscrews were classified into no loading, immediate loading, and delayed loading groups according to the loading time. At 6 weeks after screw placement, the animals were sacrificed, and tissue blocks including the miniscrews were harvested for histological examinations. After analysis of the histological sections, the miniscrews were categorized into three additional groups according to the root proximity: high root proximity, low root proximity, and safe distance groups. Differences in the bone–implant contact (BIC, %) among the root proximity groups and loading time groups were determined using statistical analyses. RESULTS: No BIC was observed within the bundle bone invaded by the miniscrew threads. Narrowing of the periodontal ligament space was observed in cases where the miniscrew threads touched the bundle bone. BIC (%) was significantly lower in the high root proximity group than in the low root proximity and safe distance groups. However, BIC (%) showed no significant differences among the loading time groups. CONCLUSIONS: Regardless of the loading time, the stability of an orthodontic miniscrew is decreased if it is in contact with the bundle bone as well as the adjacent tooth root.

Cortical bone thickness and root proximity at mandibular interradicular sites: implications for orthodontic mini-implant placement / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to provide clinical guidelines to indicate the best location for mini-implants as it relates to the cortical bone thickness and root proximity. METHODS: CT images from 14 men and 14 women were used to evaluate the buccal interradicular cortical bone thickness and root proximity from mesial to the central incisor to the 2nd molar. Cortical bone thickness was measured at 4 different angles including 0degrees, 15degrees, 30degrees, and 45degrees. RESULTS: There was a statistically significant difference in cortical bone thickness between the second premolar/ first permanent molar site, central incisor/central incisor site, between the first/second permanent molar site and in the anterior region. A statistically significant difference in cortical bone thickness was also found when the angulation of placement was increased except for the 2 mm level from the alveolar crest. Interradicular spaces at the 1st/2nd premolar, 2nd premolar/1st permanent molar and 1st/2nd permanent molar sites are considered to be wide enough for mini-implant placement without root damage. CONCLUSIONS: Given the limits of this study, mini-implants for orthodontic anchorage may be well placed at the 4 and 6 mm level from the alveolar crest in the posterior region with a 30degrees and 45degrees angulation upon placement.