Artificial carious lesions were produced in human enamel using a diphosphonate/organíc acid system over periods up to 30 days, and progress assessed by depth measurement. Acids studied were lactic, acetic, propionic, isobutyric, succinic, tartaric, hydrochloric and hydrofluoric. The rate of lesion progress was found to be a function of calculated unionized acid concentration, and acid dissociation constant. Acetic acid made a major contribution to the rate of lesion formation, even at pH 5.0 or higher and is likely to be as important as lactic acid in the in vivo caries situation. Mixtures of acetic and lactic acid had additive demineralizing properties. This emphasizes the importance of acid type and concentration rather than pH alone.

A mouthrinse formulated to fulfill physicochemical requirements for rapid remineralization of early carious lesions was investigated in vivo using intraoral appliances in adults. Human enamel slabs with artificially induced early lesions were embedded in the appliances. Complete rehardening of the inner 40–50 μm and twofold rehardening of the remaining body of the lesion occurred in 160-μm deep lesions with a 1-min mouthrinse on each of 14 consecutive days. Saliva alone rehardened the inner 20 μm only. At least the inner half of lesions 65 μm deep rehardened completely and the remaining body of the lesion rehardened fourfold over 14 days. Monofluorophosphate toothpastes, tested similarly remineralized to the same extent as saliva alone and increased the surface layer hardness. The remineralizing solution shows potential value as a daily mouthrinse for the prevention or reversal of early carious lesions.

Physicochemical data related to remineralization of carious lesions were determined. Diffusion properties of calcium ions, fluoride ions, calcium-anion complexes, and cation-fluoride complexes were studied using protein-impregnated and protein-apatite-impregnated membranes. Stability constants of metal-fluoride and amine-fluoride complexes were determined by titration. Artificial carious lesions were produced in human enamel and immersed in remineralizing solutions containing calcium, zinc, strontium, phosphate, acid anions, fluoride and organic cations at various pH levels. Selected samples were reimmersed in demineralizing solution. Sodium fluoride, acidulated phosphate-fluoride and calcium-phosphate fluoride solutions were tested similarly. Calcium-anion complexes diffused rapidly through protein gels. Metal-fluoride complexes were generally too weak to affect diffusion rates but some cations enhanced fluoride transport. Partial remineralization of lesions occurred with the new test solutions more rapidly than with traditional fluoride preparations, and further demineralization was markedly reduced. Remineralizing solutions based on this new hypothesis show promise as an improved caries preventive measure.