To begin, take off the plastic protective cap (if your toothbrush has one), and proceed to examine your toothbrush for any metal. If the toothbrush contains a large amount of metal, it is best to look into other tactics for sterilizing it, as opposed to using a microwave. However, if it contains a small amount of metal, it is fairly safe to sterilize it using your microwave, provided that the toothbrush remains submerged in water at all times when it is in the microwave.
Now, take a microwave-safe cup, and place your toothbrush in this with the bristled side pointing down. Pour water into the cup, until the bristled head of the toothbrush is entirely submerged. Make sure there is enough water to keep the bristles submerged at all times when it is in the microwave – add in a little extra water, to compensate for any that might evaporate.
Then, place this cup in the microwave, and run it on high until the water begins to boil – how long it takes for the water to boil depends on your microwave and its temperature settings. Once the water reaches a boil, maintain it for around two to three minutes.
After this time period has elapsed, turn the microwave off, and slip on a pair of oven mitts. Then, take the cup out of the microwave, let the toothbrush cool down, and proceed to tap it hard against the side of the cup a couple of times – this will dislodge any additional debris that might have gathered on the bristles.
Finally, pour the water out of the cup, rinse the toothbrush under running water, and then repeat the procedure one more time, for good measure.