In vivo performance of zirconia and titanium implants: a histomorphometric study in mini pig maxillae

Objectives: To compare the bone tissue response to surface-modified zirconia (ZrO2) and titanium implants. Methods: Cylindrical low-pressure injection moulded zirconia (ZrO2) implants were produced with an acid-etched surface. Titanium implants with identical shape, sandblasted and acid-etched surface (SLA) served as controls. Eighteen adult miniature pigs received both implant types in the maxilla 6 months after extraction of the canines and incisors. The animals were euthanized after 4, 8 and 12 weeks and 16 zirconia and 18 titanium implants with the surrounding tissue were retrieved, embedded in methylmethacrylate and stained with Giemsa-Eosin. The stained sections were digitized and histomorphometrically analysed with regard to peri-implant bone density (bone volume/total volume) and bone-implant contact (BIC) ratio. Statistical analysis was performed using Mann-Whitney' U-test. Results: Histomorphometrical analysis showed direct osseous integration for both materials. ZrO2 implants revealed mean peri-implant bone density values of 60.4% (SD +/- 9.9) at 4 weeks, 65.4% (SD +/- 13.8) at 8 weeks, and 63.3% (SD +/- 21.5) at 12 weeks after implantation, whereas Ti-SLA implants demonstrated mean values of 61.1% (SD +/- 6.2), 63.6% (SD +/- 6.8) and 68.2% (SD +/- 5.8) at corresponding time intervals. Concerning the BIC ratio, the mean values for ZrO2 ranged between 67.1% (SD +/- 21.1) and 70% (SD +/- 14.5) and for Ti-SLA between 64.7% (SD +/- 9.4) and 83.7% (SD +/- 10.3). For the two parameters investigated, no significant differences between both types of implants could be detected at any time point. Conclusion: The results indicate that there was no difference in osseointegration between ZrO2 implants and Ti-SLA controls regarding peri-implant bone density and BIC ratio.