Dynamic fatigue behavior of dental porcelain modified by surface deposition of a YSZ thin film

Purpose: The objective of this study was to evaluate the basic fatigue parameters of a dental porcelain modified by deposition of a yttria-stabilized zirconia (YSZ) thin film and to compare the data to that of an unmodified control. Methods: Two hundred bars (2 × 2 × 15 mm³) were cut from ProCAD blocks. Specimens were wet-polished with 1200-grit SiC abrasive. One surface of each bar was sandblasted with 50 μm Al₂O ₃ abrasive (50 psi). Half the specimens were further modified through deposition of a 3-μm YSZ thin film on the sandblasted surface. Depositions were performed using an radio frequency magnetron sputter system (working pressure of 15 mT, 150°C, 30:1 Ar:O₂ gas ratio). Specimens were tested at different stressing rates: 5.0, 0.1, and 0.01 MPa/s (n = 25/group) in deionized water (37°C), and inert strength was determined in air (25°C, 70 MPa/s). All strength measurements were carried out by three-point bending (span = 10 mm) in a servo-electric test system. Results: The mean flexural strength values (MPa) and standard deviation for the uncoated sandblasted group were: 98.6 (5.5), 90.7 (5.9), and 84.2 (8.5), and for the sandblasted + YSZ thin film group: 125 (9.4), 119.3 (7.8), and 102.8 (7.0), for the highest to the lowest stressing rates, respectively. The fatigue parameters n and lnB were calculated by linear regression of dynamic fatigue data. For the uncoated group, n = 38 and lnB = 4.7 MPa²/s, and for the coated group, n = 33 and lnB = 10.8 MPa²/s. Weibull analysis was also performed showing that the characteristic parameter (σ_o) was 113.3 and 125.7 MPa for the uncoated and coated group, respectively. Conclusions: There was an increase in strength for specimens modified by application of a YSZ thin film. It is hypothesized that thin-film application modifies flaws or residual surface stress states.