}} Stannous fluoride, also known as tin(II) fluoride, is the chemical compound with the formula SnF₂. This colourless solid is a common ingredient in toothpaste. In the enamel, it converts apatite into fluoroapatite, which is more resistant to attack by acids generated by bacteria. Sodium fluoride and sodium fluorophosphate perform similarly. Stannous fluoride can be mixed with calcium abrasives while the more common sodium fluoride gradually becomes biologically inactive combined with calcium. It has also been shown to be more effective than sodium fluoride in controlling gingivitis.

Stannous fluoride was used (under the trade name Fluoristan) in the original formulation of the toothpaste Crest., though it was later replaced with sodium monofluorophosphate. However it is the active ingredient in Crest Pro Health brand toothpaste according to the label on the box and the tube. Crest Pro Health also issues a warning on the tube that stannous fluoride may cause staining; and that by proper brushing this can be avoided; and that their particular formulation is resistant to staining.

Used in combination with abrasives that contain calcium, sodium fluoride is ineffective; stannous fluoride remains effective when used with such abrasives. Stannous fluoride can cause surface staining of teeth, but these stains are not permanent.

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