An alumina toughened zirconia composite for dental implant application: in vivo animal results

Abstract

Ceramic materials are widely used for biomedical applications because of their remarkable biological and mechanical properties. Composites made of alumina and zirconia are particularly interesting owing to their higher toughness with respect to the monolithic materials. On this basis, the present study is focused on the in vivo behavior of alumina toughened zirconia (ATZ) dental implants treated with a hydrothermal process. A minipig model was implemented to assess the bone healing through histology and mRNA expression at different time points (8, 14, 28, and 56 days). The novel ATZ implant was compared to a titanium clinical standard. The implants were analyzed in terms of microstructure and surface roughness before in vivo tests. The most interesting result deals with a statistically significant higher digital histology index for ATZ implants with respect to titanium standard at 56 days, which is an unprecedented finding, to the authors' knowledge. Even if further investigations are needed before proposing the clinical use in humans, the tested material proved to be a promising candidate among the possible ceramic dental implants.

Figure 1

Implant geometry. Note: SEM images were acquired at low magnification to depict the shape of the titanium implant (a) and the alumina toughened zirconia implant (b).

Figure 2

Implant surface morphology. Note: SEM images were acquired at high magnification to depict the surface morphology of the titanium implant (a) and the alumina toughened zirconia implant (b).

Figure 3

Implant topography. Note: Surface roughness of titanium (a) and alumina toughened zirconia (b) implants was determined and graphically portrayed.

Figure 4

Expression of the osteogenic differentiation markers. Quantitative real-time polymerase chain reaction (RT-PCR) analysis of BMP-2 (a), osteonectin (b), collagen type I (c), and osteocalcin (d) transcript level (n = 3 for each condition for each time point). One-way analysis of variance (ANOVA) with post hoc Dunnett's test was used to assess statistical significance.

Figure 5

Representative histological images of cortical bone at 8 days. Note: E&E stain showing sporadic necrotic lacunae within cortical bone in proximity to the implant surface at 8 days (a) and healthy bone (b). This phenomenon occurred only at the earliest time point in a few cases for both alumina toughened zirconia and titanium implants and may be due the preparation of the implant site by drilling.

Figure 6

Representative histological images of DHI calculation. Representative samples of the virtual histological slides used to calculate DHI at day 56 are reported for titanium (a, b) and alumina toughened zirconia (c, d) implants, respectively, at lower (a, c) and higher (b, d) magnification.

Figure 7

Digital Histology Index (DHI). Note: The DHI values differed in a statistically significant way (Student's t-test P < 0.001) between the alumina toughened zirconia (ATZ) and the titanium samples at day 56 (ATZ = 53.3% ± 6.5, Ti = 35.3% ± 1.9). At 28 days no significant difference could be found (ATZ = 45.4% ± 4.5, Ti = 32.1% ± 6.4).