Octacalcium phosphate (OCP) is proving to be an important intermediary in the formation of tooth and bone mineral and various pathological calcifications. Before this mineral can form, its solubility product must be exceeded. Thus, a knowledge of its precise values under various conditions is required for a basic understanding of calcification processes. The methodology suitable for measuring the solubility of metastable phases was developed and used to determine the negative logarithms of the solubility products of OCP, p K sp (OCP), at 4, 4.8, 6, 18, 23.5, and 37 °C. This methodology includes (1) the use of high solid-to-liquid ratio, 10 mg/mL, to minimize the effects of hydrolysis, (2) frequent sampling during equilibration to detect possible effects of hydrolysis, (3) equilibration from supersaturation and from undersaturation, and (4) equilibration in the absence and presence of a CO 2 -containing atmosphere. The resulting p K sp (OCP) values are 48.3±0.2, 48.3±0.2, 48.2, 48.3, 48.4±0.1 and 48.7±0.2 at 4, 4.8, 6, 18, 23.5, and 37 °C. A 5.5% CO 2 atmosphere did not change the apparent p K sp (OCP) value significantly. The value of p K sp (OCP) obtained by approaching equilibrium from supersaturation was essentially the same as that from undersaturation. The effects of (1) the use of different ionic models, (2) OCP hydrolysis, and (3) differences in equilibrium constants on the apparent p K sp (OCP) values are described; the latter two contribute significantly to the differences in p K sp (OCP).

Results from previous studies show that a two-solution fluoride (F) rinse is significantly more effective than a NaF rinse of the same F content of 250 microg/g (ppm) in remineralizing enamel and root lesions in an in vitro cyclic de- and remineralization model. In the present study, the two-solution rinse and two NaF rinses with F contents of 250 ppm and 1000 ppm were evaluated in an intra-oral remineralization model. Caries-like lesions were formed in the enamel of extracted human molars with the use of a pH 4 demineralizing solution. Thin sections of the enamel (approximately 120 microm) containing lesions were prepared, and the mineral contents of the lesions were assessed by quantitative microradiography. With the cut surfaces protected by nail varnish, 3 enamel specimens were mounted with wax in the lingual areas of a removable mandibular appliance. The study used a randomized, crossover design with seven subjects. In each of the 3 legs of the study, subjects wore the appliances continuously except when eating, drinking, and brushing their teeth. Twice daily (after breakfast and before bedtime), the subjects received a one-minute rinse with 20 mL of (1) 250-ppm-F NaF rinse, (2) 1000-ppm-F NaF rinse, or (3) 228-ppm-F two-solution F rinse. At the end of the 14-day experimental period, the sections were retrieved, and the mineral contents of the lesions were again assessed quantitatively. The results show that both the 1000-ppm-F NaF and 228-ppm-F two-solution rinses produced a greater (p < 0.05) remineralization than did the 250-ppm-F NaF rinse. The remineralization produced by the two-solution rinse was not statistically different (p > 0.05) from that produced by the NaF rinse with 4x the F content (1000 ppm F).

The amounts of loosely-bound fluoride (F) deposited on human enamel by two topical F treatments were measured with use of a constant-composition F washing method. Enamel biopsies conducted before treatment and after the washing were used for determination of the firmly-bound F uptake. The results showed that (1) the washing system did not remove F from untreated enamel surface, (2) a four-minute application of an acidulated phosphate fluoride (APF) gel deposited 27.2 (2.4) (mean, S.E.) micrograms of loosely-bound F per cm2 of enamel surface and 186 (111) ppm of firmly-bound F in the outer 10 microns of enamel, and (3) a four-minute application of a pH-2.1 dicalcium phosphate dihydrate (DCPD)-forming solution followed by APF produced 44.9 (3.1) micrograms/cm2 of loosely-bound F and 1280 (354) ppm of firmly-bound F in the outer 10 microns of enamel. The results showed that the DCPD pre-treatment effectively enhanced the enamel reactivity with F, so that the DCPD-APF treated enamel acquired greater amounts of both loosely-bound F and firmly-bound F than did samples treated with APF alone.