Objectives : The purpose of this study was to histomorphometrically compare a noncoated threaded zirconia implant vs. a noncoated threaded titanium implant in a rabbit model. The study tested the hypothesis that the bone-tissue response to noncoated zirconia implants was qualitatively and quantitatively similar to noncoated titanium implants.

Materials and methods : Six healthy male New Zealand White Rabbits and a total of 24 implants were used. Two screw-shaped threaded commercially pure titanium implants and two screw-shaped threaded zirconia implants of 7.0 mm in length and 3.3 mm in diameter were randomly inserted into the right and left mid-tibial diaphysis. In order to label the amount of mineralized bone, a 10 mg/kg dose of calcein green solution was administered at both 26 days and 27 days post-implantation. Six weeks after implantation, animals were euthanized and specimens were obtained. Half of the specimens were subjected to biomechanical testing (removal torque analysis; RT) while the other half was embedded in polymethylmethacrylate (PMMA) un-decalcified and sectioned to approximately 80 μm. Only histomorphometry data were reported here. The degree of bone contact with the implant surface (BIC), amount of bone in between the threads (BA), and the intensity and extent of bone labeling (BL) were measured at the four-most coronal threads. In addition, the amount of mineralized surface (MS) was assessed by measuring the intensity and the extent of circumferential bone labeling of the periosteum. A paired t -test was used. The level of significance was set to p < 0.05.

Results : No statistically significant difference was detected between the zirconia and titanium groups in terms of BIC values. For the zirconia and titanium groups, the BIC was 26.0% ± 17.2% and 35.8% ± 21.8%, respectively. On the other hand, statistically significant differences were demonstrated in (a) the BA levels (zirconia = 72.0% ± 11.1%; titanium = 81.0% ± 8.9%) and the MS levels (zirconia = 22.7% ± 14.5%; titanium = 40.4% ± 18.2%), favouring the titanium group, and (b) the amount of bone label in between the threads (zirconia = 40.4% ± 20.7%; titanium 15.4% ± 5.6%), favouring the zirconia group. The higher amount of MS in titanium group may be related to the difference in the modulus of the implants, while the BA and calcein labelled BA may due to both modulus and material surface chemistry differences.

Conclusions : Within the limitations related to using a small sample size, we conclude that titanium implants and zirconia implants share a similar degree of BIC, though titanium implants have a higher BA compared to zirconia.