Remineralization of softened bovine enamel following treatment of overlying plaque with a mineral-enriching solution.

Pre-softened, gauze-covered bovine enamel blocks were worn in the buccal sulcus of five subjects for seven days. Artificial plaque enmeshed in the gauze was treated four times per day for four days with an enzyme-dependent mineralizing solution, resulting in 20-, 10-, and 200-fold increases in Ca, P, and F, respectively. Enamel beneath this mineral-enriched plaque recovered 37% of the hardness lost from pre-softening, while control enamel beneath untreated plaque recovered only 14%. Test enamel contained from five to 13 times as much F as did control enamel in the outer four layers sampled. Even though direct use of the mineralizing solution without the interposition of plaque caused a hardness recovery and F uptake similar to those in test enamel in vivo, a direct solution effect on enamel is not thought to explain the in vivo effects. Plaque treated with the urea-containing solution rapidly reaches a pH greater than 8, when a precipitate develops, leaving much-reduced ion concentrations in solution. Direct exposure of softened enamel to such a supernatant resulted in reduced hardness recovery and F uptake. It is concluded that the in vivo enamel remineralization was due mainly to the presence of a mineral phase in the overlying plaque. This mineral could have promoted remineralization by creating mildly supersaturated conditions during normal plaque pH cycles.