Effects of Intermittent Vibrational Forces on Maxillary Expansion in Rats

Objectives: The aim of this study was to investigate the effects of superimposed intermittent vibrational forces (VF) on maxillary expansion in rats.
Methods: Fourty-six 7-week-old rats were randomly assigned into four groups and received rapid maxillary expansion only (RME-only), RME and vibrational force (REM+VF), VF-only, and no treatment (control). RME was achieved using stainless steel springs bonded on the maxillary molars calibrated to deliver 22g of expansion. VF was applied locally over the hard palate at 60 Hz and 20±5 cN load for 8 minutes/day, 3 times/week. After 14 days, the animals were euthanized and the maxillae were scanned using micro-CT to measure palatal width, suture width, bone volume fraction (BV/TV), and mean grayscale values. The mineral opposition rate (MAR) and osteoclast surface ratio (Oc.S/BS) were quantified from histologic sections using Bioquant Osteo software. Two-way ANOVA with Bonferroni’s post-hoc tests were used for all comparisons at the 5% level of statistical significance.
Results: Both RME groups had significantly higher palate widths, suture widths, Oc.S/BS, MAR and significantly lower BV/TV than groups without RME (p<0.001). RME+VF had significantly lower palatal width, lower MAR and higher BV/TV when compared to RME-only. VF had no effects on BV/TV or MAR in the VF-only or control groups (p<0.001). VF had no effects on Oc.S/BS or suture width in all groups. Neither RME nor vibration had a significant effect on the mean grayscale values.
Conclusions: Intermittent VF prevents excessive maxillary expansion with less immature new bone deposition at the suture margins. Although intermittent VF enhances trabecular bone with a higher bone volume fraction, it does not affect relative mean bone density with or without RME.