Dental floss is a cord of thin filaments used to remove food and dental plaque from between teeth in areas a toothbrush is unable to reach. As the build-up of plaque in interproximal areas is the primary cause of dental disease, such as gingivitis and dental caries, the use of floss is commonly recommended in order to prevent these conditions from developing. Despite the availability of a number of interdental cleaning aids, dental floss has received the most attention, although it can be challenging to use as it requires a high level of dexterity, resulting in less use. It has been widely accepted that the use of floss has a favourable effect on plaque removal and disease prevention and the American Dental Association reports that up to 80% of plaque can be eliminated with this method] Several reviews, however, have failed to find any clear benefit over toothbrushing alone.

Dental professionals recommend that a person floss once per day before or after brushing to allow the fluoride from the toothpaste to reach between the teeth. Floss is commonly supplied in plastic dispensers that contain 10 to 100 meters of floss. After pulling out approximately 40 cm of floss, the user pulls it against a blade in the dispenser to cut it off. The user then strings the piece of floss on a fork-like instrument or holds it between their fingers using both hands with about 1–2 cm of floss exposed. The user guides the floss between each pair of teeth and gently curves it against the side of the tooth in a 'C' shape and guides it under the gumline. This removes particles of food stuck between teeth and dental plaque that adhere to dental surfaces below the gumline.

The American Dental Association has stated that flossing in combination with tooth brushing can help prevent gum disease and halitosis. A 2012 review of trials concluded that flossing in addition to tooth brushing reduces gingivitis compared to tooth brushing alone. In this review, researchers found "some evidence from twelve studies that flossing in addition to tooth brushing reduces gingivitis compared to tooth brushing alone" but only discovered "weak, very unreliable evidence from 10 studies that flossing plus tooth brushing may be associated with a small reduction in plaque at 1 and 3 months."