Effect of Therapeutic Ultrasound on In-vitro model of Orthodontic Force

OBJECTIVES: To investigate the effect of low intensity pulsed ultrasound (LIPUS) on the dentoalveolar structure while undergoing orthodontic force in mandible slice organ culture.

METHODS: Mandibles were dissected from eight 28-day-old male Wistar rats; the mandibles were sectioned into 1.5mm with a 0.006” diamond wafer saw then cultured in six well plates at 37°C in an atmosphere of 5% CO2, in a humidified incubator. After 24 hours a 0.019×0.025" stainless steel wire loop was applied to each slice with a calibrated force of 50 grams. The slices were divided into three groups including control (n=7), 5 minute US application (n=10), and 10 minute US application (n=10). The LIPUS were applied using a 2.5 transducer that produces incident intensity of 30 mW/cm2 of the transducer's surface area. After five days the slices were fixed and evaluated histologically for the predentin and cementum thicknesses, odontoblast, preodontoblast and periodontal ligament PDL cell count. In addition, the extent of osteoclastic and odontoclastic cells were analyzed using tartrate resistance acid phosphate (TRAP) staining. Statistical comparison between groups was performed using ANOVA test.

RESULTS: The thickness of the cementum and predentine layers were significantly increased in the ultrasound groups however the difference between the 5 and 10 minute ultrasound groups were not significant. The odontoblast, PDL cell count in the compression and tension sides were increased in the ultrasound groups but not statistically significant. Pre-odontoblastic cell layer were increased in the 10 min LIPUS group. More frontal resorption lacunae were found in the compression side of the ultrasound groups.

CONCLUSION: The application of LIPUS has resulted in an increased number of cells in the periodontal ligament and has induced tooth material apposition presented by the increased thickness of the non-mineralized predentine layer. The potential of bone remodeling has been increased by the application of LIPUS.