DISSOLUTION OF POWDERED HUMAN ENAMEL SUSPENDED IN ACID-SOLUTIONS AT AHIGH SOLID SOLUTION RATIO UNDER A 5-PERCENT CO2 ATMOSPHERE AT 20-DEGREES-C/

The aim was to examine the nature of enamel dissolution in aqueous sus pensions with a high solid/solution ratio and in a CO2-rich atmosphere . Before experimentation, a water-saturated mixture of 95% N-2-5% CO2 was passed through the acid solutions for 24 hr. Samples of 2 g of pow dered enamel were suspended in 7 ml of either 5 or 10 mmol/l HClO4, wi th or without 2 parts/10(6) fluoride and kept gently agitated for 24 h r in the above atmosphere. The same enamel samples were repeatedly exp osed to fresh acid for 26 runs. All experiments were duplicated. The a queous phase was analysed after 20 min and 24 hr for calcium, phosphat e, fluoride, chloride, sodium and magnesium. It was found that after 2 0 min the fluoride was invariably taken up in the enamel and the solut ion was supersaturated with respect to hydroxyapatite with pH ranging 6.7-5.6. During the following 24 hr pH increased further, the supersat uration remained unchanged and the concentrations of calcium and phosp hate in solution decreased. In contrast, sodium, magnesium and chlorid e were released from enamel during the entire period. In the later run s, the supersaturation with respect to hydroxyapatite was only modest and the decrease of calcium and phosphate concentrations limited, as w ere the release of sodium, magnesium and chloride. It is concluded tha t despite a CO2-rich atmosphere, calcium, phosphate and carbonate were released from enamel and quickly established a supersaturation with r espect to hydroxyapatite with a secondary reprecipitation of mineral. It indicates that within the dental caries lesion in vivo, lesion flui d cannot exist undersaturated with respect to enamel apatite. (C) 1997 Elsevier Science Ltd.