Before you brush your teeth, your mouth is a cesspool of bacteria. When you stick a toothbrush in your mouth, it's likely loaded with fecal coliform bacteria so you need to keep it clean, too.
Ultraviolet (UV) sanitizers are one of the best and most convenient to use. They produce ultraviolet light which kills the bacteria on your toothbrush. They destroy the nucleic acids in the bacteria disrupting their DNA. This leaves pathogens unable to reproduce or function properly so they die out.
Clean and sanitized aren't the same thing. Clean means you can't see dirt with your eye. Sanitized means germ free. Most people give their toothbrush a quick rinse and put it away. But a rinse doesn't remove all traces of bacteria and a damp toothbrush is a verdant breeding ground for bacteria to spend the night multiplying. By morning, your toothbrush still looks clean, but it's grossly unsanitary.
Studies have shown that UV sanitizers effectively kill bacteria and microorganisms, but not 100 percent of them. In fact, other forms of sanitizing were found to be equally or more successful at eliminating microorganisms from toothbrushes.
Soaking toothbrushes in anti-microbial rinses, such as mouthwash, for up to twenty minutes was considered very effective. Though inconvenient microwaving for one minute completely eradicated life found on toothbrushes. Equally effective were tests where sticking a toothbrush in the dishwasher and running it through a cleaning cycle eliminated the majority of bacteria present...even more inconvenient that a microwave!
For a review of sanitizers see HERE.