Histological analysis is considered to be the gold standard method of evaluating osseointegration around a bone-implant. However, this method requires invasive specimen preparation and is capable of representing only one plane. By comparison, micro-computed tomography (μCT) is a fast and convenient method that offers three-dimensional information but is hampered by problems related to resolution and artifacts, making it a supplementary method for osseointegration analysis. To verify the reliability of μCT for osseointegration evaluation, this animal model study compared bone-to-implant contact (BIC) ratios obtained by the gold standard histomorphometric method with those obtained by the μCT method, using a rabbit tibia implant model. A sandblasted, large-grit, acid-etched (SLA) implant and a machined surface implant were inserted into each tibia of two rabbits (giving eight implants in total). Bone-implant specimens were analyzed using μCT with a spiral scan technique (SkyScan 1275) and histological sections were prepared thereafter. Three-dimensional (3D) reconstructed μCT data and four two-dimensional (2D) μCT sections, including one section corresponding to the histologic section and three additional sections rotated 45°, 90°, and 135°, were used to calculate the BIC ratio. The Pearson’s test was used for correlation analysis at a significance level of 0.05. The histomorphometric BIC and the 2D-μCT BIC showed strong correlation (r = 0.762, P = 0.046), whereas the histomorphometric BIC and 3D-μCT BIC did not (r = -0.375, P = 0.385). However, the mean BIC value of three or four 2D-μCT sections showed a strong correlation with the 3D-μCT BIC (three sections: r = 0.781, P = 0.038; four sections: r = 0.804, P = 0.029). The results of this animal model study indicate that μCT can be used to complement the histomorphometric method in bone-implant interface analyses. With the limitations of this study, 3D-μCT analysis may even have a superior aspect in that it eliminates random variables that arise as a consequence of the selected cutting direction.

Purpose Osseointegration consists of bidirectional bone formation around modified implant surfaces by contact osteogenesis and distance osteogenesis. This study tested whether contact osteogenesis on the surface of a modified titanium (Ti) implant is stimulated by cytokines in the blood. Methods In the first two types of experiments, sandblasted, large-grit, acid-etched Ti implants and turned Ti tubes were inserted into rabbit tibiae. To exclude the influence of distance osteogenesis, the tubes were inserted into the tibiae, and implants were placed inside the tubes. In a third type of experiment, the implants and tubes were inserted into the rabbit tibiae, and platelet-rich plasma (PRP) or recombinant human bone morphogenetic protein-2 (rhBMP-2) was applied topically. Four weeks after implantation, undecalcified specimens were prepared for histomorphometry. Bone-to-implant contact (BIC) and bone area per tissue (BA) were measured, and the data were analysed using one-way ANOVA at a significance level of 0.05. Results When the response of bone to Ti tubes with implants was compared to that without implants (first experiment), little bone formation was found inside the tubes. The mean BIC of implant specimens inside the tubes was 21.41 ± 13.81% in a second experiment that evaluated bone responses to implants with or without Ti tubes. This mean BIC value was significantly lower than that in the implant-only group (without tubes) (47.32 ± 12.09%, P = 0.030). The third experiment showed that rhBMP-2 significantly increased contact osteogenesis on the implant surface, whereas PRP had no effect (mean BIC: 66.53 ± 14.06% vs. 16.34 ± 15.98%, P = 0.004). Conclusions Platelet-rich plasma alone is unable to trigger contact osteogenesis on the modified titanium implant surface.

The dental implant relies on osseointegration and the response of bone to the implant surface. This process comprises bidirectional bone formation, including bone deposition on the implant surface toward the existing bone (contact osteogenesis) and vice versa (distance osteogenesis). It is unclear whether these processes are independent or whether contact osteogenesis is initiated by other factors. Therefore, this study aimed to identify the initiator of contact osteogenesis. We hypothesized that contact osteogenesis does not occur when it is physically isolated from distance osteogenesis, which would imply that some factors from the wounded bone normally promote contact osteogenesis. Using a rabbit tibial implant model, we tested the effects of human recombinant bone morphogenetic protein-2 (BMP-2) and plasma-rich plasma, which are possible initiators from bone and blood, respectively. Titanium implants with BMP-2 showed a better bone-to-implant contact (BIC) ratio. We concluded that BMP-2 initiated contact osteogenesis on the surface of titanium implants.