Biomechanical and histological evaluation of a new zirconia implant in a canine model
Background: Currently titanium implant fixtures are considered as a gold standard because of their biocompatibility and their clinical success rates have been well documented. The esthetic outcome of restorations supported by titanium implants may be compromised if the dark gray color of the implant shows through a thin peri-implant mucosa or if the implant fixture becomes visible following soft tissue recession. Also titanium might cause allergic reactions. For these reasons, zirconia implants have been considered as alternative materials because of their white color, high material properties and biocompatibilities. Still, further investigations are necessary to confirm the in-vivo performance of these implants. Purpose: The purpose of this study is to determine the histomorphometric and biomechanical properties of zirconia implants manufactured by Shofu Inc. with a sand-blasted and acid-etched surface treatment, compared to that of the titanium implants from the same manufacturer with a sand-blasted and acid-etched surface treatment in a canine model. Material and Methods: Six beagle dogs (1-2 years old) will be used in this split mouth trial. After 8 weeks following extraction of the second to fourth mandibular premolars, zirconia implants (experimental group) and titanium implants (control group) were placed on the each side of mandible. At 8 weeks and 12 weeks after implant placement, the animals were sacrificed, and implants were removed in block sections, and histological and histomorphometric analyses were measured. Specifically, the bone-implant contact (BIC), bone area (BA), removal torque (RTQ), mineral apposition rate (MAR), bone forming area (BFA), and Periotest value (PTV) of the two groups were studied and compared. Results: At 12 weeks post operatively, one Shofu thread type Ti implant were not integrated. Over all failure implant was 0/12 in zirconia group, and 1/12 in titanium group. In 8 weeks samples, only statistical differences were higher BA (p=0.02) in macro threads area and BFA (p=0.02) in zirconia implants group than titanium implants group. In 12 weeks group, zirconia implant group showed higher MAR at 9-10 and 10-11weeks time frame (p=0.02, and 0.04 restectively), and PVT value (p=0.01) than titanium implants group. Removal torque value increased in both titanium and zirconia group with time. Average of removal torque value showed higher in titanium implants than zirconia implants, but the differences were not statistically significant in both 8 weeks (Ti; 64.16±16.93 N-cm, ZrO₂: 42.5±6.01 N-cm : p=0.247) and 12 weeks (Ti; 82.5±9.41 N-cm, ZrO₂: 51.3±19.38 N-cm: p=0.16). In the removal torque analysis, it is observed that the bone-implant interface seems to be of more rigid and brittle in nature as indicated by the lower averaged onset angle, peak angle, area under curve and RTQ. Conclusion: Zirconia implants group showed higher value of BA with macro thread and BFA in 8weeks and MAR at 9-10, 10-11 weeks period, and PVT in 12 weeks post operatively. Within the limited number of samples tested in this study, there is no difference between the BIC and RTQ of zirconia and titanium implants after 8 and 12 weeks of implantation.
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