Novel Mouse Orthodontic Tooth Movement Organ Culture Model

Objective: An in vitro mouse tooth orthodontic model will facilitate the further understanding of the cellular and molecular responses of the periodontal ligament and alveolar bone to orthodontic forces. Therefore in this study we have developed an in vitro mandibular tooth movement organ culture model.

Methods: Eight mandibles from four week old wildtype CD-1 mice were dissected and hemisected. A conventional superelastic orthodontic closed coil spring (0.001 x 0.030- inch, GAC, Dentsply) delivering a force of 25 grams was bonded to the incisor and first molar of one hemisected mandible; the other half mandible served as a control. Test and control mandibles were cultured for 2, 6, 12, and 24 hours and processed for routine histologic staining. In addition at 6 hours, PCNA immunostaining (proliferation) was performed on the tension and compression side of the mandibular first molar. Images were captured using a digital camera. A rectangular box of fixed area was constructed and a labeling index (number PCNA positive cells/ total number of cells in the box) was calculated for the tension side compared to the compression side.

Results: Hematoxylin/eosin and crystal violet stained sections showed that the periodontium and surrounding tissues maintained a viable appearance after 2, 6, and 12 hours in culture. Immunohistochemistry using PCNA revealed that there was no significant difference in the PCNA labeling index between the compression and tension side at 6 hours.

Conclusion: A mouse orthodontic tooth movement organ culture model provides a powerful model to delineate initial cellular and molecular events of orthodontic tooth movement. This model may be useful not only for in vitro organ cultures of transgenic mice but also serve as a baseline for further evaluation of the processes involved in an in vivo model.