The effect of variability in the powder/liquid ratio on the strength of zinc phosphate cement

Abstract

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses ( α = 0.05) were by Students t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturers recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturers instructions. The maximum and minimum powder/liquid ratios, together with the manufacturers recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (P = 0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (P 0.001) and from the mean value obtained from the recommended ratio (P 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material. Copyright © 2011 Jill E. McKenna et al.