Types of tooth movement, bodily or tipping, do not affect the displacement of the tooth's center of resistance but do affect the alveolar bone resorption.

OBJECTIVE: To investigate how types of tooth movement, bodily or tipping, influence the displacement of the center of resistance in teeth and alveolar bone resorption. MATERIALS AND METHODS: Ten-week-old female Wistar rats were divided into eight groups of different factors, as follows: type of movement (bodily and tipping) and force magnitude (10, 25, 50, and 100 cN). The maxillary left first molars were moved mesially with nickel-titanium coil springs for 28 days. Micro-computed tomography (micro-CT) images were taken before and after tooth movement. The position of the center of resistance was determined by using finite element models constructed from the micro-CT image. The displacement of the center of resistance and the volume of alveolar bone resorption were measured. RESULTS: The displacement of the center of resistance showed no significant difference between the bodily and tipping groups. The displacements of the center of resistance were increased with force magnitude at 10 and 25 cN, whereas they were not further increased at 50 and 100 cN. On the other hand, cervical alveolar bone resorption was significantly greater in the tipping group than in the bodily group. CONCLUSIONS: Displacement of the center of resistance was not influenced by the types of tooth movement. However, volume of cervical alveolar bone resorption was greater in the tipping movement group than in the bodily movement group.

Increasing the amount of corticotomy does not affect orthodontic tooth movement or root resorption, but accelerates alveolar bone resorption in rats.

Objectives: The purpose of this study was to evaluate the relationships among the volume of bone cut during corticotomy, amount of tooth movement, volume of root resorption, and volume of the resultant alveolar bone resorption after tooth movement. Methods: Ten-week-old female Wistar rats were distributed into the corticotomy groups and a control group that underwent sham corticotomy. Two experiments employing two different orthodontic forces (10 or 25g) and experimental periods (14 or 21 days) were performed. The volumes of the bone cut by corticotomy were 0.1, 1.0, and 1.7mm3 in the 25g groups, and 1.0 and 1.7mm3 in the 10g groups. Nickel-titanium closed-coil springs were set on the maxillary left first molars to induce mesial movement. After orthodontic tooth movement, the amount of tooth movement, volume of root resorption, and volume of alveolar bone resorption were measured. Results: Despite differences in the volume of bone cut among the different corticotomy groups, there were not significant differences in the amount of tooth movement and volume of root resorption between the control group and any of the corticotomy groups. However, higher volume of bone cut during corticotomy was significantly related to the decreased alveolar bone volume-in particular, to the reduced height of the alveolar bone crest after tooth movement. Conclusions: The volume of the alveolar bone cut during corticotomy does not affect tooth movement or root resorption in 10-week-old female Wistar rats; however, it may increase alveolar bone loss after tooth movement.