Differential healing states of the surgical alveolar defect have been assumed to affect the timing of post-operative orthodontic intervention. The in vivo studies were designed to: 1) elucidate the effect of timing of force application on the rates of tooth movement and defect regeneration; and 2) investigate differential gene expression pattern in the tissue regenerated in the defect overtime with or without orthodontic tooth movement.The beagle model used involved a critical-sized defect including the extracted socket of a maxillary first premolar and protraction of the second premolar into the defect. The animals were allocated into a control group, a defect-only group, a bone-grafted defect group and a laser-irradiated grafted group. Force application time points were established at immediate, two weeks and twelve weeks after surgery. For the intergroup comparison, the weekly rate of tooth movement, micro-CT quantitative analysis, triple-fluorochrome staining and microarray gene screening were performed.The findings suggest that tooth movement into the surgical gap in this animal model can be favorably undertaken at the two-week time period. We also show that immediate traction could be permissible following bone grafting; however, a longer duration of effective tooth movement was observed even with delayed force initiation after surgery. In contrast, low-level laser therapy (LLLT), inhibited tooth movement possibly due to accelerated defect healing. Based on the differential gene expression pattern between the natural and tooth movement-accompanied healing, we concluded that optimal timing of post-surgical force application is dependent on sustaining the woven bone period. This study provides a basis to elucidate biological modulators controlling the formation of woven bone state to achieve optimal tooth movement.
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