pro·phy·lax·is. , pl. prophylaxes ( prō'fi-lak'sis, -sēz) 1. Prevention of disease or of a process that can lead to disease. 2. In dentistry, extrinsic stain removal and sealing procedures done to maintain or improve oral health. [Mod. L. fr. G. pro-phylassō, to guard before, take precaution]