Mesial orthodontic movement of rat molars after extraction of the adjacent first molar and

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The present study aimed to develop a new orthodontic apparatus integrating a removable super-elastic nickel-titanium (NiTi) alloy closed coil springs. Male SD rats (5 weeks old) were used. Maxillary incisors were pinned and utilized as anchorage for a closed-coil appliance. At the same time, upper first molars were extracted. After 5 days interval for wound healing, the activated closed-coil appliance was placed between the fixed incisor and the second molar. Three types of fabricated NiTi closed coil springs were used to generate certain ranges of force 10-40gf. We first assessed the retainability and durability of the apparatus by placing NiTi coil springs at the position for various periods ranging from 4 days to 14 days. The results supported the practical usefulness of the apparatus by showing that most of the NiTi coil springs under investigation remained activated at position throughout the observation periods. Examination of animal specimens in conjunction with microfocus x-ray tomography (μCT) and 3D-reconstruction technology validated that the second and third molars executed mesial drifts, accompanying the force-induced deformation at the incisal-premaxillary bony suture. It is pertinent that alveolar bone modeling in the intraseptal region progressed markedly during tooth displacement, whereas the bodily tooth drift did not accompany any marked compression of periodontal ligament or ankylosis. We also developed experimental models using an Alzet osmotic pump for systemic-infusion of bisphosphonate during tooth movement. Histologic examination revealed the local variation in agent-dependent osteoclastic cell behavior during its systemic delivery period. The present orthodontic tooth movement model will be useful in a wide range of investigation of the kinetics of tooth displacement under magnitude/temporal characteristics, e.g., continuous versus intermittent force application.