You'll never forget to replace your toothbrush again with this handy four pack of replacement bristles for slim and pocket sonic toothbrushes! Fading blue bristles let you know when it's time for a new head.about every three months. The bristles are medium weight, which dentist recommended for optimal sonic cleaning! Please note that these heads are not for violife sonic+uv countertop toothbrush, which are sold separately (model number vio901). Great style coupled with smart function is a key part of everything made at violife. From the original countertop sanitizer to uv sanitizing travel toothbrush holders, denture cleaners, mouth guard cleaners, cell phone sanitizers and portable electric toothbrushes, violife continues to marry great style.even a hint of fashion.to otherwise mundane items. People who buy violife care about their health, their home, their family, and their personal sense of style.