Hydroxyapatite is used in toothpaste to prevent cavities and reduce dentin sensitivity.[1] There’s not enough research to say how it measures up to fluoride.
As a dietary supplement, it has been used as a source of calcium to slow osteoporosis and for reducing osteoporosis-related pain. The forms found in dietary supplements include ossein-hydroxyapatite complex (OHC) and microcrystalline hydroxyapatite compound, both of which are sourced from powdered bone and contain bone proteins in addition to hydroxyapatite.[2][3][4]
Hydroxyapatite has also been formulated as an injectable skin filler that is FDA-approved to cosmetically treat wrinkles and facial fat loss in people with human immunodeficiency virus (HIV).[5]