The ISSA Hybrid Brush Head is engineered for vigorous brushing while remaining gentle on the gums. It features inner PBT polymer bristles that provide an invigorating cleaning routine and outer silicone bristles that provide a gentle gum massage. The combination of PBT and silicone make it suitable for individuals seeking a stronger cleaning experience or experiencing increased plaque buildup. The inner soft, silicone bristles minimize bacteria buildup, so it's more hygienic than your traditional nylon-bristle toothbrush. Designed to be used with the revolutionary ISSA Toothbrush, the Hybrid Brush head comes in all four vibrant hues: Mint, Lavender, Cobalt Blue, and Cool Black. Replace the brush head once every 6 months.