The most common fluoride in toothpaste and mouthwash. Among the best-proven ingredients in any personal-care product: it cuts tooth decay by about a quarter.
Fluoride makes enamel harder for acid to dissolve and helps early decay re-harden. Sodium fluoride is the simplest way to deliver it: most toothpastes carry about 1,000-1,450 ppm fluoride (0.22-0.32% sodium fluoride), and daily mouthwashes about 225 ppm (0.05%).
The benefit comes from fluoride sitting on the teeth, not from swallowing it. That is why the advice is to spit out the excess and not rinse straight after brushing.
Decades of randomised trials, pooled in Cochrane reviews, show fluoride toothpaste prevents about 24% of decayed, missing and filled tooth surfaces in children, with a dose-response: 1,450-1,500 ppm does slightly better than 1,000-1,250 ppm. Adults benefit too. Fluoride rinses add protection in children. The main downside, dental fluorosis (white flecks in enamel), comes from young children swallowing toothpaste while their teeth are forming.
96 trials. High-to-moderate certainty that 1,000-1,250 ppm and 1,450-1,500 ppm fluoride toothpastes reduce caries in children and adolescents versus non-fluoride paste, with 1,450-1,500 ppm slightly better; 1,000-1,100 ppm also reduced decay in adults. Side effects were minimal where reported.
Across 70 trials in 42,300 children, fluoride toothpaste prevented about 24% of decayed, missing and filled surfaces compared with non-fluoride paste; the effect was bigger with higher concentration, more frequent and supervised brushing.
Mostly observational and at risk of bias: starting fluoride toothpaste before 12 months of age was weakly associated with more (mostly mild) fluorosis, and higher-fluoride pastes raised fluorosis risk in trials. Where fluorosis is a concern, under-6s may use pastes below 1,000 ppm.
37 trials (15,813 children), mostly supervised school rinsing with sodium fluoride at 230 ppm daily or 900 ppm weekly: about 27% fewer decayed, missing and filled surfaces in permanent teeth (moderate-quality evidence).