Effects of low intensity pulsed ultrasound stimulation on bone regeneration in rat parietal bone defect model

Abstract

Purpose: Low intensity pulsed ultrasound sti-mulation (LIPUS) has been clinically applied to promote bone fracture healing in the orthopedic field. Thus, it is likely that LIPUS also stimulates bone regeneration in bone defects in the cra-nial-maxillofacial area. However, this has not been clearly proved. Furthermore, optimal time point and period of the application after the surgery has not been reported. The purpose of the present study was to evaluate the effect of LIPUS on bone regeneration in the rat parietal bone defects especially focusing on time and period of the application. Materials and Methods: Eighteen Wistar rats (14 weeks old) were divided into 6 groups: 5 experimental groups and a con-trol group. Bone defect of 5 mm diameter was prepared on each side of the parietal bone and customized gelatin membranes were placed over the bone defects. LIPUS (160 mW/cm 2 , 15 min/day) was applied to the defect area with an active transducer externally in the experimental groups according to the schedules of the appli-cations: Group 1 (day 6 -12), group 2 (day 13 -19), group 3 (day 20 -26), group 4 (day 6 -19) and group 5 (day 6 -26). All the animals were sacrificed at 28 days. The defects were analyzed with micro CT and then histologically. Results: In Group 1, new bone formation was signifi-cantly promoted and the newly-formed bone was thick and matured compared to the one of the control group. In other experimental groups there were tendencies of stimulation of new bone formation; however, they were not statis-tically significant. Discussion and Conclusion: The present study demonstrated that amount of new bone formation in the bone defect de-pended on the time and period of LIPUS appli-cation. It has been suggested that application of LIPUS at an early healing period, the second week after the surgery, effectively accelerated new bone formation.