B ench-curing heat-processed acrylic resins before processing is suggested for the purpose of equalizing pressure in the mold, releasing internal stress, dispersing monomer uniformly, and exposing resin teeth to the monomer.‘*2*+ Opinion varies on the exact amount of time a packed flask should bench-cure before being placed in a processing unit. Two hours is the most commonly quoted length of time.3 A text on dental materials refers to bench-curing only to state that manufacturer’s directions should be followed.’ Two manufacturers suggest bench-curing for 30 minutes.5~6 One states that their resin can be placed directly into water at processing temperature (163” F) immediately after bench-curing. 6 Another manufacturer suggests bench-curing for 20 minutes, but only when their material is to be placed directly into boiling water.’ The latter manufacturer cautioned against the procedures when processing “thick” sections of resin. Shari-y’ suggests a period of 1 to 4 hours without citing references, and Heartwell and Rahn* do not mention bench-curing. Boucher et al.9 suggest 30 to 60 minutes, and Hudis’O suggests bench-curing for 1 hour but adds that longer periods would not be detrimental. In a review of the literature for the Council on Dental Research on processing heat-cured denture base resins, Stanford and Paffenbarger” did not mention benchcuring. The intent of allowing the monomer to penetrate the polymer during bench-curing is to enhance the physical properties of the resin. In addition, residual islands of monomer can result in porosity within the cured resin. Usually, when a packed flask is placed in a curing unit, the water is assumed to be at room temperature (70” F) or at least well below processing temperature (160” to 163” F).3 Rapid polymerization of heat-cured acrylic resin does not begin until it reaches a temperature of