Laboratory strength of glass ionomer and zinc phosphate cements

Purpose The present in vitro study examined 3 mechanical properties, namely compressive, flexural, and diametral tensile strength, of various commercially available cements and core materials as a function of time after mixing. Materials and Methods The examined materials were 2 cermet cements (Ketac Silver [ESPE, Seefeld, Germany] and Chelon Silver [ESPE]), 1 metal‐reinforced glass ionomer cement (Miracle Mix [GC Dental Industrial Corp, Tokyo, Japan]), 2 conventional glass ionomer cements (Ketac Bond [ESPE] and Ketac Cem [ESPE]), 1 standard cure zinc phosphate cement (Harvard Cement [Richter and Hoffmann, Berlin, Germany]), and 1 zinc phosphate cement with the addition of 30% silver amalgam alloy powder (Harvard Cement 70% with Dispersalloy 30% [Richter and Hoffmann/Johnson and Johnson, East Windsor, NJ]). Properties were measured using a universal testing machine at 15 minutes, 1 hour, and 24 hours after first mixing. Results Compressive strengths varied widely between the 3 times of measurement from 5.8 ± 6.6 MPa for Ketac Cem to 144.3 ± 10.2 MPa for Ketac Silver. Twenty‐four hours after mixing, the Bonferroni test showed significant (p≤ .01) differences between Ketac Silver and all other materials tested. Diametral tensile strengths ranged widely from 4.4 ± 0.9 MPa for Ketac Cem to 11.5 ± 2.2 MPa for Chelon Silver. At 15 minutes, 1 hour, and 24 hours after first mixing, the analysis of variance did not show any significant differences between Ketac Silver, Chelon Silver, and Miracle Mix. The 3‐point flexural strength of Ketac Silver showed, at 15 minutes with 13.5 ± 3.9 MPa and at 24 hours with 27.2 ± 7.4 MPa, the highest values. Conclusions Setting time influences the mechanical properties of the materials tested in this study. Ketac Silver, a glass ionomer cement reinforced with sintered glass‐silver particles, showed the highest mechanical properties of the examined materials.