Eighteen articles discussed osseous healing, histologic analyses, and BIC of zirconia dental implants. Seven of these articles evaluated zirconia as a coating material, evaluated zirconia dental implants.

Cranin et al investigated the osseointegration of vitallium implants with the addition of ceramic coatings, such as alumina (n  =  9) or zirconia (n  =  9). All alumina-coated vitallium implants and 5 of the zirconia-coated vitallium implants failed after 32 weeks. Investigators concluded that zirconia could be considered a superior ceramic coating to alumina. Nordlund et al studied the tissue integration of 3 types of implant materials in monkeys:

1. alumina with 4% zirconia and 25% magnesia,
2. alumina with 25% silicon carbide,
3. unalloyed titanium implants. No difference in tissue reaction around these 3 types of implant materials was observed after 6–8 months.

Franchi et al evaluated peri-implant tissues of zirconia-coated titanium implants and acid-etched titanium implants by light microscopy. All implants showed new bone trabeculae, vascularized medullary spaces, and close contact with preexisting bone at 2 weeks. Franchi et al also evaluated in an animal study peri-implanted tissues for titanium implants with different surfaces—smooth, titanium plasma sprayed, and zirconia blasted. At 3 months, it was observed that implant surface morphology strongly influenced the rate and the modality of peri-implant osteogenesis. Rough surfaces and in particular zirconia-blasted implants seemed to favor bone deposition on the titanium surface. In another study, the same group24 investigated peri-implant osteogenesis and biologic fixation for various zirconia sandblasted titanium implant surfaces and a machined titanium surface. The highest values for BIC, bone ingrowth, and Vickers hardness were measured in implants sandblasted with zirconia particles, which have higher surface roughness (arithmetical mean roughness [Ra]: 1.52 µm, maximum peak [Rt]: 12.06 µm, and ten-point mean roughness [Rz]: 11.54 µm), followed by zirconia sandblasted implants with lower surface roughness (Ra: 1.32 µm, Rt: 8.76 µm, and Rz: 8.86 µm).

Sollazo et al25 observed titanium implant surfaces coated with zirconia, which can potentially have specific biologic effects. The BIC percentage was 31.8 ± 3.05% for uncoated titanium implants and 43.8 ± 2.05% for titanium implants coated with zirconia at 4 weeks. It was found that zirconia coating would enhance implant osseointegration. Bacchelli et al examined peri-implant osseointegration and found the following: Machined titanium implants had 34.5% BIC, titanium plasma-sprayed titanium implants had 44.7% BIC, alumina-blasted titanium implants had 53.4% BIC, and zirconia-blasted titanium implants had 35.5% BIC at 2 weeks. This was the only study that found zirconia coating was not superior to the other groups; this finding may be attributed to short evaluation time (2 weeks).

Akagawa et al examined the initial implant-bone interface with the 1-stage zirconia screw implant (Goei Industry, Akitsu-Hiroshima, Japan) with different occlusal loading conditions after 3 months in beagle dogs. In the nonloaded group, no superstructure was seen; the loaded group had metal superstructures. At 3 months, no significant difference was noted for BIC between the 2 groups. The BIC was 81.9% for the nonloaded group and 69.8% for the loaded group. The same researchers observed the role of osseointegration around the 1-stage zirconia screw implant (Goei) with various conditions for loading support after 2 years of function in monkeys. Three types of superstructure were provided in each animal to obtain different concepts of support:

1. single freestanding implants,
2. connected freestanding implants,
3. a combination of implant and tooth.

Clinically, all implants were immobile for 24-month loading, and healthy peri-implant mucosa was achieved in the single freestanding, connected freestanding, and implant-tooth support groups, with favorable values for clinical parameters. Histologically, the direct bone-implant interface was generally attained in all observed zirconia implants.

Dubruille et al compared the BIC on 3 types of dental implants: titanium, alumina, and zirconia (Sigma, Lausanne, Switzerland); these were placed into the dog mandible. At 10 months, BIC was found to be 68% for alumina, 64.6% for zirconia, and 54% for titanium. No statistically significant difference was noted between the 3 types of implants. Scarano et al30 demonstrated the bone response to zirconia implants at 4 weeks. A great quantity of newly formed bone was observed with zirconia surfaces, and the percentage of BIC was 68.4%. These studies concluded that zirconia implants are highly biocompatible and osteoconductive.

Mosgau et al evaluated the BIC of zirconia endodontic endosseous cones in apicectomy. The ratio between the total cone/bone contact circumference (ram) and the total cone/fibrous tissue contact circumference (ram) was 0.95 on the titanium surface and 1.47 on the zirconia surface. This indicates that, proportionately speaking, significantly greater bony healing was seen on the zirconia surface than on the titanium surface.

Kohal et al evaluated the soft and hard tissue conditions of sandblasted zirconia implants (ReImplant, Hagen, Germany) and compared them with sandblasted and acid-etched (SLA) titanium implants. The mean mineralized BIC achieved after 9 months of healing and 5 months of loading was 72.9% for titanium implants and 67.4% for zirconia implants.

Hoffmann et al histologically assessed the degree of early bone apposition around zirconia dental implants (Z-system, Konstanz, Germany) at 2 and 4 weeks following insertion. The zirconia implants demonstrated a slightly higher degree of bone apposition (54%–55%) compared with the titanium implants (42%–52%) at the 2-week time point, but bone apposition was higher in titanium (68%–91%) than in zirconia (62%–80%) at 4 weeks.

Langhoff et al compared the BIC of chemically modified (plasma-anodized or coated with calcium phosphate) titanium implants, pharmacologically coated (bisphosphonate or collagen type I with chondroitin sulphate) titanium implants, SLA titanium implants, and SLA zirconia implants. The zirconia implants presented 20% more bone contact than the titanium implants at 2 weeks, improved toward 4 weeks, then were reduced at 8 weeks. Although statistically not significant, a clear tendency was noted for the chemically and pharmacologically modified implants to show better BIC values at 8 weeks compared with the anodic plasma treated-surface of zirconia implants. All titanium implants had similar BIC at 2 weeks (57%–61%); only zirconia was found to be better (77%).

In a study conducted by Deprich et al, 24 screw-type zirconia implants (Konus Dental, Bingen, Germany) with acid-etched surfaces were compared with 24 implants of commercially pure titanium with acid-etched surfaces. At 12 weeks, ultrastructural evidence of successful osseointegration of both implant systems was found. No significant differences in strength and stiffness of attachment between the 2 implant designs were detected at this time point. The same researchers compared osteoblast behavior on structured zirconia (Konus) and titanium surfaces in another study. Attachment kinetics, proliferation rate, and synthesis of bone-associated proteins on both surfaces were examined and compared. At day 1, cell proliferation of zirconia surfaces was similar to that of titanium surfaces. At day 3, cell growth was significantly higher on the zirconia surfaces than on the titanium surfaces. At day 5, cell proliferation continued to be significantly higher on zirconia surfaces than on titanium surfaces. In the last study conducted by this group, the osseous healing of zirconia implants (Konus) was compared with that of acid-etched titanium implants with the same macroscopic design in an animal experiment. At 1, 4, or 12 weeks, BIC was slightly better on titanium than on zirconia surfaces. However, a statistically significant difference between the 2 groups was not observed. Results demonstrated that zirconia implants with modified surfaces resulted in an osseointegration that was comparable with that of titanium implants.