Partially stabilized zirconia: Mechanical and optical properties and effect of chairside adjustments and fatiguing

Abstract

Monolithic partially stabilized zirconia (PSZ) is commonly used in restorative dentistry for its strength, wear resistance, esthetics, and biocompatibility. However, the effects of thermo-mechanical fatiguing and chairside adjustments on its mechanical and optical properties are still not fully understood.

This in vitro study evaluated how yttria content, material thickness, simulated mastication, and chairside adjustments affect strength, phase transformation, surface roughness, and optical properties of 3Y-PSZ, 4Y-PSZ, and 5Y-PSZ. Disc specimens (0.7 mm and 1.2 mm thick) underwent biaxial fracture testing before and after mastication simulation (1.2 million cycles, 110 N, 5°C–55°C thermal cycling). Adjustments were performed using either coarse diamond burs or a dedicated zirconia adjustment kit. Flexural strength performed according to ISO 6872 standards; X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) assessed phase transformation and fracture pattern. Atomic Force Microscopy (AFM) and spectrophotometry were utilized to evaluate surface roughness, surface gloss, translucency, and contrast ratio.

Lower yttria content and greater material thickness significantly improved fracture resistance. 3Y-PSZ had the highest strength; 5Y-PSZ, the lowest. Thinner specimens (especially 4Y and 5Y) were more prone to fracture under fatiguing. Coarse diamond adjustments reduced flexural strength and increased monoclinic phase content, particularly in 3Y and 4Y groups. Adjustment with coarse bur only led to significant increase in surface roughness. Utilizing the dedicated zirconia adjustment kit caused less surface damage and phase transformation while preserving optical properties In conclusion, yttria content and adjustment protocols significantly influence zirconia properties. Higher yttria improves translucency but reduces strength. Chairside polishing preserves properties better than coarse grinding. Clinically, proper adjustment techniques are essential to maintain zirconia’s properties.