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Effect of stretch frequency on osteogenesis of periodontium during periodontal ligament distraction.

OBJECTIVES
Periodontal ligament distraction (PDLD) can accelerate orthodontic tooth movement (OTM). However, the effect of stretch frequency on osseous formation during PDLD remains unclear. Here, we sought to identify the effect of PDLD frequency on the osteogenic remodeling of the periodontium.


MATERIALS AND METHODS
(1) In vitro, five human periodontal ligament stem cell (PDLSC) cultures were randomized to either static conditions or exposure to a cyclic stretch force involving 12% deformation at frequencies of 0.3, 0.5, 0.7 or 1.0 Hz for 12 h, and the osteogenic differentiation of PDLSCs was assessed using Western blotting. (2) In vivo, 18 beagle dogs underwent orthodontic distalization of bilateral maxillary first premolars. In the test groups, PDLD was performed at a frequency of two or six times/day, while Ni-Ti coil springs were applied to mimic traditional OTM in the control group. The amount of OTM and histological staining were estimated after force loading for 5, 10, and 15 days.


RESULTS
(1) In vitro, the expression of osteogenic specific markers (runt-related transcription factor 2 [Runx2], type I collagen [COL-I], and osteocalcin [OCN]) increased with the frequency of tensile force, to a peak at 0.7 Hz. (2) In vivo, both PDLD groups displayed a greater rate of OTM and a higher bone metabolism than the control group. The expression of COL-I and OCN was significantly reinforced in the six times/day-PDLD group in comparison to the two times/day-PDLD group.


CONCLUSIONS
The cyclic stretch force enhances osteogenesis of the periodontium in a frequency-dependent manner.