Fatigue behavior of dental ceramics for occlusal veneers: Impact of the material thickness.

Abstract

This study evaluated the effect of the material thickness on the fatigue behavior of a polycrystalline and a glass-ceramic used for occlusal veneers. Disc-shaped specimens of 4 mol% yttria-stabilized zirconia (4YSZ, IPS e.max ZirCAD MT) and lithium disilicate (LD, IPS e.max CAD) were fabricated in three thicknesses (0.5, 1.0 and 1.5 mm; n = 15) and adhesively cemented to fiberglass-reinforced epoxy resin discs to reach a total height of 3.5 mm. Cyclic fatigue testing was performed at 20 Hz with an initial load of 300 N, increasing by 50 N every 10,000 cycles up to 600 N, and then by 100 N every 10,000 cycles until failure, detected by transillumination (defined as the presence of cracks or structural discontinuities identified by light transmission). Fatigue failure load (FFL) and cycles for fatigue failure (CFF) were recorded. Fractographic and degree of conversion analyses were performed. Data was analyzed with Kaplan-Meier and analysis of variance tests. The results showed that 4YSZ exhibited superior FFL and CFF compared to LD, except for the 1 mm thick specimens. For LD, increasing thickness from 0.5 mm to 1.0 mm and 1.5 mm improved fatigue resistance, though no difference occurred between 1.0 mm and 1.5 mm. For 4YSZ, no difference was found between 0.5 mm and 1.0 mm, but 1.5 mm showed superior performance. All fractures originated from the cementation surface, and resin cement degree of conversion was unaffected by ceramic type or thickness. These findings support the clinical feasibility of minimally invasive zirconia occlusal veneers (≥0.5 mm), whereas lithium disilicate requires at least 1.0 mm thickness for reliable mechanical performance.