Extra soft standard size bristles fit all Philips Sonicare models. The extra soft bristles are great for sensitive mouths or just starting to brush with a Sonicare toothbrush. In the set: 2 standard size Sensitive S2 brush heads S Sensitive brush head is designed for sensitive teeth and gums. The ultra-soft bristles ensure effective cleaning and a gentle brushing experience. . The reminder bristles turn white when it's time to replace the brush head.