Oral B Kids Frozen II Refills x4 are refills for the electric toothbrush, specifically for children. The heads have  special, shorter filaments that provide a delicate, extra-soft brushing, making them ideal for little ones' teeth and mouths. The heads have  Indicator bristles that fade in color to help remind you to replace them at least every 3 months. They are compatible with all Oral-B electric toothbrush handles, except Oral-B Sonic.