INFLUENCE OF IMPLANT DIAMETERS ON THE INTEGRATION OF SCREW IMPLANTS -AN EXPERIMENTAL-STUDY IN RABBITS

The influence of diameter on the integration of titanium screw-shaped implants was studied in the rabbit tibia by means of removal torque me asurements and histomorphometry. Implants 3.0, 3.75, 5.0, and 6.0 mm i n diameter and 6.0 mm long were inserted through one cortical layer in the tibial metaphyses of nine rabbits and allowed to heal for 12 week s. The implants were then unscrewed with a torque gauge, and the peak torque required to shear off the implants was recorded. The histologic analysis in undemineralized ground sections comprised (1) a gross des cription of the implant sites and assessments of (2) the total implant length in bone and (3) in the cortical passage, as well as (4) the th ickness of the cortical bone adjacent to the implants. From the remova l torque values obtained and morphometric measurements, a mean shear s tress value was calculated for each implant type. The biomechanical te sts showed a statistically significant increase of removal torque with increasing implant diameter. The resistance to shear seemed to be det ermined by the implant surface in supportive cortical bone, whereas th e newly formed bone at the periosteal and endosteal surfaces did not s eem to have any supportive properties after 12 weeks. It is suggested that wide diameter implants may be used clinically to increase implant stability.