Effect of Hydrofluoric Acid Etching Duration on Fracture Load and Surface Properties of Three CAD/CAM Glass-Ceramics

Background: The purpose of this study was to investigate the effect of etching time using 9% hydrofluoric acid on Fracture Load (FL) and surface properties, such as Surface Free Energy (SFE) and Surface Roughness (SR) of three CAD/CAM glass-ceramics. Methods: Following glass-ceramics were investigated: EMP (IPS Empress CAD), KLE (KLEMA CAD/CAM glass-ceramic) and EMC (IPS e.max CAD). For FL, standardized crowns for maxillary canines (N=270, n=90) were milled. Each material group was divided into six subgroups (n=15) and etched for 0, 30, 60, 90, 120, and 150s. Crowns were adhesively cemented to metal abutments and subsequently loaded until fracture. For surface property investigations, 55 specimens per material were fabricated, divided into 11 groups (n=5) and etched for: 0, 20, 30, 40, 50, 60, 75, 90, 105, 120, and 150s. SFE using contact angle measurements, SR using profilometer and surface topography with scanning electron microscopy were determined. Data were analyzed using linear covariance analyses/regressions, and two/one-way ANOVA with post-hoc Scheffé test (p<0.05). Results: Unetched EMP crowns showed lower FL than etched for 150s. Unetched and etched for 150s KLE crowns presented lower FL than those etched for 90s. Within EMC, no effect of etching time was observed. The highest SFE was detected for EMC, the lowest for KLE. The highest SR showed KLE, the lowest EMC. KLE and EMP showed no impact of etching time on SFE. EMC increased in SFE with increase of etching time. EMC showed higher SR than KLE and EMP. EMC showed lower SR than KLE. All materials showed an increase of SR dependent on the etching time. Conclusion: General recommendations on etching time cannot be made as etching time showed different effects on fracture load and surface properties.