Effect of mixing methods on the compressive strength of glass ionomer cements

Objective: The purpose of the study was to evaluate the effect of the mixing method on the compressive strength and porosity of dental glass ionomer cements. Method: Five glass ionomer cements were chosen for use in the study. Two were hand mixed and three were encapsulated. The latter were mixed either by shaking or rotating. Following mixing by rotation some samples were centrifuged before use. The 24 h compressive strength was determined for each cement/mixing regime combination and fracture surfaces were examined using SEM. Results: The mixing method had a significant effect on compressive strength (P < 0.05). For the luting/lining cement, hand mixing produced a significantly greater compressive strength (P < 0.05). For the restorative cement, there were only small differences between specimens mixed by different methods and hand mixing gave a significantly lower compressive strength than mixing by rotation followed by centrifuging (P < 0.05). Porosity was incorporated in all samples and low values of compressive strength were associated with larger pores. Significance: The strength of glass ionomer cements is affected by incorporated porosity and this is dependent on the method of mixing. For some cements hand mixing is favoured in order to reduce porosity and increase strength brit this is not generally applicable to all cements. (C) 2001 Elsevier Science Ltd. All rights reserved.