EcoDent - TerrADent Replaceable Heads. These nylon bristles have exceptionally consistent and superior quality. The heads lock into place and do not dislodge with use. Replacement heads come in a handy 3-pack; you essentially get 3 toothbrushes for the price of 1, with less waste and a much lower bacterial load. These factors are key when it's time for a new brush due to use, illness or a recommendation to switch bristle firmness.