The toothbrush is an oral hygiene instrument used to clean the teeth and gums that consists of a head of tightly clustered bristles mounted on a handle, which facilitates the cleansing of hard-to-reach areas of the mouth. Toothpaste, which often contains fluoride, is commonly used in conjunction with a toothbrush to increase the effectiveness of tooth brushing. Toothbrushes are available with different bristle textures, sizes and forms. Most dentists recommend using a toothbrush labelled "soft", since hard bristled toothbrushes can damage tooth enamel and irritate the gums. Toothbrushes have usually been made from synthetic fibers since they were originally developed, although animal bristles are still sometimes used.