The aim of this study was to determine if the bactericidal effect of microwaving gypsum casts is maintained at maximum capacity of the oven (16 casts). Batches of 8 and 16 gypsum casts made from in vivo impressions were divided in half. One half of each cast was microwaved at 900 W for 5 minutes. The remaining halves were left untreated. When assessed for bacteriological growth, the median cfu/mL of the untreated casts was between 105 and 106, while the microwaved casts showed a cfu/mL of 0, indicating that microwaving as described will disinfect gypsum casts even at maximum capacity of the oven.