Increase of Periodontal Ligament Elasticity during Development

Objective: Changes of mechanical properties including elasticity of periodontal ligament (PDL) in a course of development are not fully understood. The elasticity of the tissue is strongly correlates with sound speed conducting in the tissue. Recently a new-concept scanning acoustic microscopy (SAM) using a single pulsed wave was developed, which enables us to assess the tissue elasticity, based on the conduction speed. This study aimed to elucidate the changes of the elasticity of rat PDL in a course of development by using the SAM.

Materials and Methods: Male Wistar rats (3, 4, 5 and 7 weeks postnatally) were used in this study. The mandibles were resected after euthanasia. The tissues were decalcified and embedded in paraffin. The embedded tissue was cut into 5-µm thick sagittal serial sections. The deparaffinized sections were processed for SAM analysis and the sound speed of PDL was measured.

The thickness and sound speed were calculated by analyzing the interference between two reflections at the surface and the interface between the tissue and the glass. Gradation color and gray scale images were produced for clear visualization and calculation of the sound speed, respectively. The sound speed of PDL was measured and compared with the corresponding light microscopic images.

All data were evaluated by One-way Factorial ANOVA and posthoc Bonferroni-Dunn test. A P value less than 0.05 was considered statistically significant.

Results: SAM clearly visualized the sound speed of interradicular fibers in the rat PDL. The sound speed of interradicular fibers increased significantly in the course of the experimental period (3w: 1523±7.9 m/s, 4w: 1538±3.1 m/s, 5w: 1551±2.3 m/s and 7w: 1559± 17.5m/s).

Conclusions: SAM is a powerful tool for evaluating the elasticity of targeted tissues. The results suggest that the increased elasticity of PDL is one of developmental processes of the periodontal tissues.