Stability and wear of zirconia crowns with micro-layering

To investigate stability and wear of tooth-supported zirconia single crowns with micro-layering in-vitro.

Molar crowns and specimens were fabricated from 5Y-TZP zirconia (Gen-X, Amann-Girrbach). Three groups were investigated: ML I: 0.1 mm cutback/painted/glazed (MiYO, Jensen); ML II: occlusal 0.3 mm cutback/painted/veneered/glazed (MiYO), and a monolithic control group (polished). After thermal cycling and mechanical loading (TCML), crowns were loaded to failure in a universal testing machine. Two-body wear test was performed. Wear (mean, maximum, antagonist) and roughness (Ra, Rz) were determined with a 3D laser-scanning-microscope.

All crowns survived TCML. In the control (2501.5 N) and ML II group (1775.3 N) significantly lower fracture forces were observed than in ML I (3636.4 N) (p ≤ 0.003). Significant wear differences were found (p ≤ 0.001) but not for antagonist wear (p ≥ 0.202). Lowest wear was observed in the control group 10.2 ± 1.5 µm/28.8 ± 6.4 µm, ML I 112.8 ± 37.3 µm/152.9 ± 42.8 µm, and ML II 192.4 ± 49.1 µm/340.7 ± 54.2 µm. Roughness was characterized by a Ra from 1.6 µm (control) to 3.0 µm (ML II), and a Rz from 11.8 µm (Control) to 24.0 µm (ML II). Roughness significantly differed between control group and ML I (p = 0.002) as well as ML I and ML II (p = 0.020).

Good in-vitro performance and fracture stability without chipping or fracture were found for all systems. Wear and roughness were comparable to conventional ceramic veneering systems.

The micro-layering of zirconia restorations can be recommended, yet the micro-layering could be worn during clinical application.