Final answer:
The form of professionally applied topical fluoride with the highest PPM fluoride concentration is fluoride varnish, which can contain up to 22,600 ppm.
Step-by-step explanation:
The form of professionally applied topical fluoride with the highest parts per million (PPM) of fluoride concentration is fluoride varnish. Fluoride varnish can contain fluoride concentrations as high as 22,600 ppm, which is considerably higher than other forms such as foam, gel, or rinse.
Fluoride varnish is often preferred for professional applications because of its higher concentration, which may reduce the amount of plaque accumulated, decrease the number of mutans streptococci and lactobacilli, and possibly promote calcium fluoride deposits more than lower concentration alternatives. This heightened effectiveness must be balanced with caution due to the increased risk of harm at higher concentrations.