An evaluation of the mechanical properties of 'hydrothermal' dental glass after water immersion and surface polishing.

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 48h immersion in a water bath maintained at 37+/-1 degrees C and a further 30 samples polished to a 6 micrometer nap finish. RESULTS: Mean bi-axial flexure strengths of specimens tested dry were found to be 67.04+/-13.87MPa (m=7.23+/-1.32) compared with 61.01+/-15.23MPa (m=4.29+/-0.78) and 68.42+/-23.36MPa (m=3.29+/-0.60) for 24 and 48h immersion, respectively. Following surface polishing, the bi-axial flexure strength was 95.91+/-22.4MPa (m=4.37+/-0.8). Vickers hardness numbers showed no significant difference between the dry control group and after 24 and 48h 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.