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Biomaterials in TMJ replacement933water. LTD results in surface roughening and micro-cracking, which in articulating joint bearings leads to increased wear and debris release into the surrounding tissue and eventual implant failure.(97,98) In an attempt to overcome the issues associated with ZrO2, ceramic composites fabricated of mixtures of Al2O3 and ZrO2 have recently been developed, combining the advantageous properties of both components. Composites with Al2O3 as the primary or continuous phase (70% to 95%) and ZrO2 as the secondary phase (30% to 5%) are called zirconia-toughened alumina (ZTA). While the excellent wear characteristics and aging resistance of the Al2O3 matrix are maintained, ZrO2 reinforcement increases the strength and fracture toughness.(96) Mixtures composed mainly of ZrO2 (80%) with additions of Al2O3 (20%) are referred to as alumina-toughened zirconia (ATZ).(96) ATZ composites maintain the high flexural strength and fracture toughness of the ZrO2 matrix, while the presence of Al2O3 significantly improves resistance to aging compared with pure ZrO2, although aging resistance remains less than that seen with ZTA materials.(99)Currently, two ZTA grades and one ATZ grade are commercially available: Biolox Delta (76.1 wt % Al2O3, 22.5 wt % ZrO2, and 1.4 wt % other), Bioceram (79 wt % Al2O3, 19 wt % ZrO2, and 2 wt % others), and Ceramys (80 wt % ZrO2 and 20 wt % Al2O3).(96) To prevent a loss in hardness and to prevent crack propagation, Cr2O3 and SrO, respectively, were added in very low quantities to Biolox delta, composing about 1 wt % of the composition.(100) Several in vitro hip simulator wear studies have reported significantly reduced wear rates for ZTA-on-ZTA and ATZ-onATZ compared to Al2O3-on-Al2O3.(101) Furthermore, Chevalier et al. have shown that newly developed ZTA materials with carefully controlled nanosized microstructure exhibit very limited wear damage in a hip simulator, while having a crack resistance well beyond that of all existing biomedicalgrade ceramics.(98) Overall, these data corroborate the hypothesis that the mechanical performance and durability of ZTAs are suitable for application as an articulating bearing surface, such as in TMJ TJR. However, it should be noted that in vivo research and clinical data for ZTA are currently limited, and longer implantation studies are required.(96)Nikolas de Meurechy NW.indd 93 05-06-2024 10:14