“…At this temperature it decom poses in a very complex way [Narda et al, 1984], It is evident from the results above that the Sn3P0 4F3 which is generated on the dental surface after topical applications of SnF2 [Wei and Forbes, 1968;Jordan et al, 1971;Krutchkoff et al, 1972] owes its pro tective capacity, at least partially, to its great hydrolytic stability. The stability of this phase is apparently increased at low pH values, and this would be another rea son to explain its protective action.…”