THE APPLICATION OF RESONANCE FREQUENCY MEASUREMENTS TO STUDY THE STABILITY OF TITANIUM IMPLANTS DURING HEALING IN THE RABBIT TIBIA

The aim of this investigation was to measure the resonance frequency o f a number of implants placed in the rabbit tibia at insertion and at predetermined periods thereafter and to correlate the results with his tomorphometric measurements made when the animals were sacrificed. Ten mature New Zealand White rabbits were used in the study. Two c.p. thr eaded titanium implants were placed in the right tibia of each animal. Resonance frequency measurements were made by screwing a small transd ucer onto a standard abutment mounted on each fixture. Measurements we re repeated with the transducer oriented perpendicular and parallel to the long axis of the tibia for all proximal implants 14 and 28 days a fter placement and in 6 implants additionally at 42, 56, 93, 122 and 1 68 days after which all animals were sacrificed. Histomorphometric ana lysis comprised 2 parts; measurement of bone-implant contact area and height. A significant increase in resonance frequency was observed aft er 14 (405 Hz, +/-234 Hz) and 28 (658 Hz, +/-332 Hz) days. The increas e in resonance frequency levelled after approximately 40 days and litt le further change was observed. The variation in bone-implant contact area was relatively small (1.8-4.9 mm(2)) and the range of bone-implan t contact heights was also narrow (-1.5-+1.5 mm). Values for resonance frequencies plotted against contact area and height were grouped arou nd 10 kHz. In conclusion, it was shown that resonance frequency measur ements can be made at placement and during healing in vivo and changes may be related to the increase in stiffness of an implant in the surr ounding tissues.