Effects of near-field ultrasound stimulation on new bone formation and osseointegration of dental titanium implants in vitro and in vivo.

A near-field ultrasound stimulation system was designed for use in in vitro and in vivo trials. The intensity of ultrasound was studied to optimize the osseointegration of the dental titanium implant into the adjacent bone. MG63 osteoblast-like cells were seeded on commercial purity titanium (CP-Ti) plate, and then sonicated for 3 min/day at a frequency of 1 MHz and intensities of 0.05, 0.15 and 0.30 W/cm(2), using either pulsed or continuous ultrasound. Cells were analyzed to determine viability (inhibition of (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction) and alkaline phosphatase (ALP). Tissue culture was performed in vitro by placing a CP-Ti plate in a cultured rat neonatal calvarial defect in response to ultrasound stimulation. In the in vivo trial, screw-shaped CP-Ti implants were inserted into the metaphysis of rabbit tibia, and then stimulated by ultrasound for 10 min daily for 30 d. All samples were processed for histomorphometric evaluation and analyzed by image system. Color Doppler ultrasonography was inspected to evaluate the supply of blood flow. Pulsed ultrasound groups had higher MTT and ALP than control. Tissue culture indicated that pulsed ultrasound groups promoted cell migration and new bone regeneration more effectively than in the control. In animal study, blood flow and mature type I collagen fibers were more prevalent around titanium implants, and bone formation was accelerated in pulsed ultrasound groups. In conclusion, low-intensity pulsed ultrasound at 0.05-0.3 W/cm(2) may accelerate cell proliferation and promote the maturation of collagen fibers and support osteointegration.