An evaluation of the mechanical properties of ‘hydrothermal’ dental glass after water immersion and surface polishing

Abstract

Objectives. To investigate claims that Duceram low-fusing ceramic (Duceram-LFC), a ‘hydrothermal’ dental veneer will increase in strength after hydrolytic testing and surface polishing. Methods. Using pre-determined powder/liquid slurry constituents, nominally identical Duceram-LFC disc-shaped specimens were fabricated to obtain mean bi-axial flexure strengths, standard deviations, Weibull modulus ( m) and Vickers hardness. Thirty specimens were tested ‘dry’ (control), after 24 and 48 h immersion in a water bath maintained at 37±1 °C and a further 30 samples polished to a 6 μm nap finish. Results. Mean bi-axial flexure strengths of specimens tested dry were found to be 67.04±13.87 MPa ( m=7.23±1.32) compared with 61.01±15.23 MPa ( m=4.29±0.78) and 68.42±23.36 MPa ( m=3.29±0.60) for 24 and 48 h immersion, respectively. Following surface polishing, the bi-axial flexure strength was 95.91±22.4 MPa ( m=4.37±0.8). Vickers hardness numbers showed no significant difference between the dry control group and after 24 and 48 h immersion ( P>0.05). Significance. Results obtained do not support claims for surface flaw and/or defect healing through the formation of an SiOH layer at the surface of Duceram-LFC specimens over time. However, the polishing regime interrupted the defect population associated with flaws present in dry (control) samples of Duceram-LFC which can be attributed to an associated reduction of initial surface flaws and/or defects.