Osteogenic effect of high-frequency acceleration on alveolar bone

Abstract

Mechanical stimulation contributes to the health of alveolar bone, but no therapy using the osteogenic effects of these stimuli to increase alveolar bone formation has been developed. We propose that the application of high-frequency acceleration to teeth in the absence of significant loading is osteogenic. Sprague-Dawley rats were divided among control, sham, and experimental groups. The experimental group underwent localized accelerations at different frequencies for 5 min/day on the occlusal surface of the maxillary right first molar at a very low magnitude of loading (4 µε). Sham rats received a similar load in the absence of acceleration or frequency. The alveolar bone of the maxilla was evaluated by microcomputed tomography (µCT), histology, fluorescence microscopy, scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR imaging), and RT-PCR for osteogenic genes. Results demonstrate that application of high-frequency acceleration significantly increased alveolar bone formation. These effects were not restricted to the area of application, and loading could be replaced by frequency and acceleration. These studies propose a simple mechanical therapy that may play a significant role in alveolar bone formation and maintenance.

Figures

Figure 1.

High-frequency accelerations increase alveolar bone volume. (A) Schematic of vibration application to the occlusal surface of the maxillary right first molar. (B) Average peak strain (mean ± SEM) in buccal and palatal surfaces of the alveolar bone surrounding the upper first molar in response to 0.3 or 0.6 g acceleration with a set frequency of 60 Hz. *Significantly different from 0.3 g. (C) a: Schematic of the area of analysis using μCT. b: Change in BV/TV from µCT analyses of maxillae exposed to different frequencies at peak accelerations of 0.3 g and a peak strain of 4 µε compared with untreated animals after 28 days. *Significantly different from untreated and static animals. **Significantly different from 30 Hz and 200 Hz. (D) Percentage change in BV/TV from µCT analysis of maxillae exposed to different accelerations at a set frequency of 60 Hz compared with untreated animals after 28 days. Each value represents the mean ± SEM of 4 samples. *Significantly different from untreated animals.

Figure 2.

Osteogenic effect of high-frequency acceleration is not limited to the point of application. Sagittal sections from maxillary alveolar bone of the vibration (60 Hz, 0.3 g, 4 με) group and the static group (4 με) 28 days post-treatment. (A) μCT 3D reconstruction of alveolar bone showing changes in trabecular spacing and thickness. (B) Photomicrographs of the entire alveolar bone stained with H&E. (C) Fluorescence microscopy of sections showing calcein labeling. The increased intensity of the label in most of the trabecular surface in the vibration group is indicative of extensive bone modeling. (D) a: Schematic indicating the coronal sections (A, B, C) used in the analysis. b: Bone volume fraction in different zones of alveolar bone in the vibration (60 Hz, 0.3 g, 4 με) and static groups (4 με) at 28 days post-treatment. (E) Average trabecular thickness (F) and trabecular spacing changes in Zone A of the alveolar bone in the vibration and static groups compared with untreated animals after 28 days. Each value represents the mean ± SEM of 4 samples. *Significantly different from untreated and static animals. (G) a: Fluorescence microscopy and b: SEM images of the cortical bone around the mesiobuccal root of the maxillary right first molar reveal the bone modeling activity and changes in the appearance of cortical bone.

Figure 3.

High-frequency acceleration changes the bone mineral content of alveolar bone. Longitudinal sections through the rat right alveolar bone of the vibration (60 Hz, 0.3 g, 4 με) and static groups (4 με) after 28 days of mechanical stimulation. (A) SEM images color-coded for visualization of the differences in mineral density. (B) FTIR images of the static (top row images) and the vibration group (bottom row images) alveolar bone showing in situ changes in the mineral-to-matrix ratio (min/mat), carbonate-to-mineral ratio (carb/min), and collagen crosslinking (crosslinking). The color scale is included for easier visualization of quantitative differences. The mean values ± SD are also included. All FTIR data show significant differences between static and vibration animals.

Figure 4.

High-frequency acceleration induces the expression of bone markers and regulators. Mean “-fold” increases in the expression of osteogenic growth factors (A), growth factor receptors (B), transcription factors (C), extracellular matrix proteins (D), and proteins involved in matrix mineralization (E) are shown for the static group (after 14 days) and the vibration (60 Hz, 0.3 g, 4 με) group at days 3 and 14. Data are shown as a fold-change in gene expression compared with the untreated group. All data from the 14-day vibration group are significantly different from those of the static group at 14 days and the vibration group at 3 days.