Fixation of an orthodontic anchor screw using beta-tricalcium phosphate in a screw-loosening model in rats.

Objectives: To create an orthodontic anchor screw (OAS)-loosening model and to investigate whether filling the bone hole with beta-tricalcium phosphate (β-TCP) can fix the OAS against orthodontic force.

Materials and methods: Bone holes with different diameters (1.6, 2.1, or 2.5 mm) were drilled in the tibias of 11-week-old male Wistar rats, and an OAS (3.0 mm in length and 1.2 mm in diameter) was inserted. After a healing period of 2 or 4 weeks, orthodontic force was applied, and the diameter of the bone hole appropriate for the loosening model was determined. Subsequently, under the loosening model, the bone hole was filled with β-TCP, orthodontic force was applied, and movement of the OAS and surrounding tissue changes were evaluated by micro-computed tomography images and histological specimen analysis.

Results: The bone hole of 1.6 mm in diameter was employed as the OAS-loosening model. When β-TCP was inserted into the bone hole, the linear distance and mesial tipping angle of the OAS movement decreased markedly. Furthermore, the values of bone morphometry significantly increased with β-TCP filling.

Conclusions: An OAS-loosening model was established in rats and demonstrated that the loosening OAS was stabilized by β-TCP filling through bone formation. β-TCP may be useful for fixation of a loosening OAS.