Abstract: An appliance which is entirely, or includes components, formed of a thermoplastics material, e.g., conventional nylon-bristle toothbrushes, may be sterilized by first bringing water contained in a reservoir of an uncovered sterilization tray to, or near, its boiling point by initial exposure to microwave energy. Thereafter, the appliance is placed in the sterilization tray in proximity to the microwave-preheated water. The sterilization tray may then be covered and subjected to an additional (shorter) cycle of microwave energy. During this subsequent microwave cycle, the water in the reservoir boils so that steam fills the covered container and is pressurized to less then about 10 psig (e.g., due to the fluid-tight seal formed by the container's cover). The steam and the microwave energy are sufficient to sterilize the toothbrush bristles.