Oral-B iO Series Gentle Care Replacement Electric Toothbrush Heads 4 Pack - Black. This toothbrush head is especially designed for a gentle and effective clean on sensitive areas and gums. It features up to 4000 soft bristles and a cushioning outer ring to precisely adapt to the curvature of teeth and protect gums. The iO Technology combines Oral-B's iconic round brush heads with the gentle micro-vibrations of iO toothbrush for Oral-B's best cleaning performance. Oral-B iO brush heads are exclusively designed to fit Oral-B iO toothbrushes. Dentists recommend changing brush heads every 3 months for optimal cleaning efficacy. Oral-B is the #1 brand most used by dentists worldwide with clinically proven results.