The effect of powder/liquid mixing ratio on the stiffness and impact strength of autopolymerising dental acrylic resins.

The stiffness of representative cured autopolymerising dental acrylic resins was determined by calculation of a secant modulus from measurements in tension of load and extension, and related to the powder/liquid mixing ratio. The impact strengths of autopolymerising, heat-cure and commercial resins were compared. It was found that while the stiffness of autopolymerising resins was unaffected by variations in powder/liquid mixing ratio, extension to failure was greater with lower powder/liquid ratios. The impact strength of autopolymerising resins was found to be greater than that of heat-cure resins, and a tentative explanation is offered. These findings may help to explain the pattern of failure of acrylic resin denture bases.