Which is correct, 1 minute or 4 minutes, for an in-office fluoride treatment?

The only clinically documented treatment time is 4 minutes for both APF and NSF, Nearly 20 years ago, lab studies showed that APF’s low pH (3.5) has fast fluoride uptake in the first minute. Since young patients struggled with the gag reflex during a 4 minute treatment, dental professionals often removed the tray at 1 minute. Since NSFs are known to work slower, they were less prone to remove the tray at 1 minute. Today, many offices use both the APF and NSF at one minute feeling that the Rx dose is still beneficial.