Effect of varying powder liquid ratios and curing conditions on the residual monomer concentration of heat cure acrylic resin: An inviro analysis.

Objectives: To determine the effect of varying powder liquid ratio and curing conditions on residual monomer concentration of heat cure acrylic resin.
Methods: Sixty four disc shaped acrylic resin specimens processed at four powder liquid ratios(2.22,2.00,1.80, student ratio) and cured in a heated water bath using 4 different curing regimes. Curing cycle 1A and 1B initiated curing at room temperature followed by a terminal boil for 60 and 30 minutes respectively. Cycle 2A and 2B initiated curing at 70″C and 100″C respectively, without terminal boil.
The residual monomer concentration was determined at an interval of 24,48 and 72 hours using a UV Spectrophotometer.
Results: Regression analysis indicated moderately strong negative correlation(-0.0515) between time and residual monomer concentration which suggests decrease in residual monomer concentration with storage time.
Group 4 (student-ratio) and curing cycle 2B (placing the assembly in the water bath directly at 100″C) showed the highest ovarall residual monomer concentrations while group 1 (highest powder-liquid ratio) and curing cycle 1A showed the least overall residual monomer concentrations.
Independent sample t tests between groups revealed that mean residual monomer concentration of samples cured by cycle 2B (0.32+-0.38) to be greater than mean (0.06+- 0.07) of samples cured by cycle 1A (p value=0.02) suggesting that cycle 1A will produce less residual monomers irrespective of the powder-liquid ratio.
Conclusions: Students dispencing acrylic powder and liquid monomer without calculations would lead to higher residual monomers if a proper curing regime is not followed.
Using a 60 minute terminal boil in the polymerization process is strongly recommended.
Storing the acrylic denture bases for atleat 24-48 hours in water before use will decrease residual monomer being leached into the oral environment.