Date of Award
Master of Science (MS)
Introduction: Low-magnitude, high-frequency (LMHF) mechanical vibration is proven to be anabolic and can increase alveolar bone mass. The objectives of this study were to generate an orthodontic retention cell culture model and investigate the effects of LMHF mechanical vibration on human periodontal ligament fibroblast (HPLF) cells after orthodontic loading (retention) in vitro. Materials and Methods: HPLF cells were seeded at a density of 4x105/well in 6-well Flexcell culture plates (Day 0). On day 3, the cells were mechanically stretched (15% surface extension) for 1 hour to mimic orthodontic loading/tension in vitro. On day 5, the cells were randomly assigned to 5 groups: a sham control group (0 Hz) and 4 vibration groups (30, 60, 90, and 120 Hz). Cell culture media were changed to fresh growth media (wells #1-3) and differentiation media (wells #4-6), and subsequently refreshed every 5 days until the end of the experiment. Mechanical vibration was applied for 20 minutes per day for 28 consecutive days, while static cells (0 Hz) were used as control. The cells were then stained for collagen type I and bone nodules, photographed, and quantified using a customized computer program. The experiment was repeated four times (n=4). Statistically, one-way ANOVA was used to test for significant differences in collagen type I production and bone nodule formation with Tukey post hoc comparison to find differences between the groups. P value less than 0.05 was considered statistically significant. Results: After 28 days of retention in culture, with or without mechanical vibration, HPLF cells produced collagen type I and bone nodules in all groups. All vibrated groups (30, 60, 90 and 120 Hz) showed increased production of collagen type I compared to sham control (0 Hz). However, 120 Hz produced the highest amount of collagen type I, which was significantly higher than all other groups (p=0.028). Changes in bone nodule formation were like that of collagen type I, but with no statistically significant difference (p=0.056). Conclusion: LMHF mechanical vibration increases the production of collagen type I and bone nodules by HPLF cells in vitro, suggesting its possibility of enhancing tooth stability during orthodontic retention.