The iO 4 electric toothbrush features Oral-B's best technology combining a dentist-inspired round brush head with micro-vibrating bristles for a professional purifying clean feel at home. The Smart Pressure Sensor helps prevent you from brushing either too hard or too softly to better protect your gums. Gum Guard alerts you to time spent brushing with too much pressure. Replace your Oral-B iO toothbrush head every 3 months for the best results.