Aim: To assess and compare the impact and flexural strength of heat cure acrylic resin polymerized by microwave and conventional methods after immersion in artificial saliva for 2 days, 60 days, 90 days and 120 days.

Materials and methods: The present study was carried out on 160 specimens. They were categorized into two groups. Each group consisted of 80 specimens, polymerized either by conventional or microwave methods. All the specimens were immersed in artificial saliva, for varying periods of 2 days, 60 days, 90 days and 120 days. Flexural strength was measured by a universal testing machine and impact strength by Izod impact test. Analysis of the results was done by Statistical Package for the Social Services version 20 (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, SPSS version 20.0. Armonk, NY: USA, IBM Corp) for Windows software.

Results: Conventionally cured resin had the highest flexural and impact strength values after 2 days of immersion in artificial saliva. There was a significant decrease in strength as the number of days of immersion increased (p < 0.001).

Conclusion: Conventional acrylic resin polymerized in a water bath exhibited better flexural, and impact strength values than microwave cured the resin. All the samples cured by both methods showed a significant reduction in strength when immersed for a period of 60–90 days and thereafter became static over 120 days.

Clinical significance: As dentures are exposed to moist environment constantly and with time, their strength gets reduced. Prosthodontists should have adequate knowledge regarding the physical properties of materials used for denture preparation and also the pros and cons of different polymerization methods. In our study, conventional acrylic resin polymerized in a microwave method exhibited lesser strength values, but they were clinically acceptable; so, this method can be used for curing dentures.