Comparing four different methods of measuring fracture toughness and its relationship with fractal dimension in a polycrystalline (3Y-TZP) dental ceramic.

Abstract

Objectives: Previous studies reported various methods of measuring fracture toughness of dental ceramics. The objectives of this study were to compare different methods and to validate fractal analysis to estimate fracture toughness for a polycrystalline dental ceramic.

Methods: Bar-shaped specimens were prepared from 3 mol% yttria-stabilized tetragonal polycrystalline (3Y-TZP) ceramic. Each specimen was prepared with a series of indentations using a Vickers diamond at 150 N followed by loading in 4-point flexure until failure. Fracture toughness (K_c) was calculated using modified indentation (MI), quantitative fractography (QF), and surface crack in flexure with residual stresses (SCF-RS) techniques. We estimated fracture toughness using fractal analysis. Epoxy replicas of fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine fractal dimensional increment (D*) by the Minkowski cover algorithm. Fracture toughness was estimated using the relationship between K_c and square-root of D* for polycrystalline ceramics.

Results: Mean fracture toughness by MI, QF, and SCF-RS techniques were 4.56 ± 0.44 MPa·m^1/2, 4.14 ± 0.82 MPa·m^1/2, and 4.09 ± 0.93 MPa·m^1/2, respectively. Mean fracture toughness estimated from D* values was 2.80 ± 0.13 MPa·m^1/2.

Significance: The fracture toughness of 3Y-TZP ceramic was calculated using different methods. Fractal dimension can be used to estimate the baseline fracture toughness for this material and can be paired with other methods to estimate the amount of transformation toughening.