How often should I replace electric toothbrush heads?

Every three months, or sooner if the bristles are visibly frayed or splayed. Worn bristles lose their stiffness and cannot clean effectively. Most electric toothbrush brands sell replacement heads in multi packs to bring down the per head cost. Some premium models like the Sonicare ProtectiveClean have BrushSync technology that tracks head usage and reminds you when it is time to swap.