Saleha Nisar, Faisal Moeen, Yawar Hayat Khan.
Effect of varying powder liquid ratios and curing conditions on the residual monomer concentration of heat cure acrylic resin.
Pak Oral Dental J Jan ;35(4):713-8.

Objective of the study was to determine the effect of varying powder liquid ratios and curing conditions on the residual monomer concentrations of heat cure acrylic denture resin. Sixty four disc shaped acrylic resin specimens were processed at four powder-liquid ratios (2.22, 2.00, 1.80 and student-ratio) and cured in a heated water bath using 4 different curing regimes. Curing cycles 1A and 1B initiated curing of specimens at room temperature followed by a terminal boil for 60 and 30 minutes respectively. Cycles 2A and 2B initiated curing at 70°C and 100°C respectively, without any terminal boil. The residual monomer concentrations were determined at intervals of 24, 48 and 72 hours using a UV Spectrophotometer. Regression analysis indicated a moderately strong negative correlation (-0.515) between time and residual monomer concentration which suggests residual monomer concentration decrease with storage time. Group 4 (student-ratio) and curing by cycle 2B (placing the assembly in the water bath directly at 100°C) showed the highest overall residual monomer concentrations while group 1 (highest powder-liquid ratio) and curing by cycle 1A showed the least overall residual monomer concentrations. Independent t tests between groups however revealed mean residual monomer concentration of samples cured by cycle 2B (0.32±0.38) to be greater than the 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. It was concluded that students dispensing 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 at least 24-48 hours in water before use will decrease residual monomers being leached into the oral environment.

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