The Oral-B iO Gentle Care replacement brush heads are designed specifically for those with sensitive teeth and gums who use the iO series handles. Each pack contains four white heads featuring a round shape and up to 4,000 soft bristles that work together to remove up to 100% more plaque than a manual toothbrush. To ensure your comfort during brushing, these heads include a cushioning outer ring that protects the gums from irritation. You will know exactly when it is time for a fresh head because the bristles change color, typically every three months, helping you maintain optimal oral hygiene without having to track the date manually.