Notes on the Dissolution of Human Dental Enamel in Dilute Acid Solutions at High Solid/Solution Ratio

Abstract

The aim of the present study was to elucidate the nature of the relationship between enamel apatite and lesion fluid during demineralization. Powdered enamel in samples of 1.0 g was suspended in 3 ml of 10 30 50, or 70 mmol/l HCl under gentle agitation for up to 24 h at 20°C. After 20 min and 24 h pH and the concentrations of calcium and phosphate were determined and the degree of saturation with respect to various calcium phosphates calculated. The experiments were replicated 15 times using the same enamel samples. Twenty minutes after the start of dissolution, both pH and concentrations of calcium and phosphate had increased, and the solution became supersaturated with respect to hydroxyapatite and in some runs also with respect to brushite. During the subsequent 23 h and 40 min, pH continued to increase, despite the super-saturation with respect to apatite, whilst the concentrations of calcium and phosphate decreased due to formation of apatite and, occasionally, brushite mineral. The data indicated that release of carbonate from enamel and its conversion to H₂CO₃ caused the increase in pH and thus, played a major role in the dissolution-reprecipitation process.

Enamel Erosion by Some Soft Drinks and Orange Juices Relative to Their pH, Buffering Effect and Contents of Calcium Phosphate

“…In comparison, the entire permanent dentition weighs less than 50 g [Bolk, 1925]. However, this does not mean that a dentition can be dissolved in 1 liter of a pH 3 juice because during the dissolution of dental apatite, pH shifts to higher values as a result of the dissolution of the apatite [Larsen et al, 1993]. Further, the above calculation is based on equilibrium conditions which do never occur in the oral cavity: most of the drinks wash quickly through the mouth without even being in contact with the teeth.…”

Studies on the Influence of Fluoride on the Equilibrating Calcium Phosphate Phase at a High Enamel/Acid Ratio

“…3D) F tended to shift the points closer to the HAp line so that the slopes of the regres- In each graph points from equilibrations in 10 mmol/1 HCI fall at the bottom right of the series, and those from equilibrations in 70 mmol/I HCI at the top left. Points from runs in the absence of F are unpublished data from a previous study [Larsen et al" 1993], sion lines were 1.66 with F and 1.58 without F (difference not significant). However, the slope of all points in the 15th equilibration was significantly different from the slope formed by all points in the 1st, 3rd and 5th equilibrations combined (p<0.005), and was not significantly different from the theoretical slope for HAp, 1.67.…”

“…1939], washed twice in acetone and dried. Such enamel is known to contain 'junction' panicles and some residual dentine, but in a previous study [Larsen et al, 1993] enamel so isolated did not behave differently in acid solubility experiments from enamel separated using pure bromo form. and therefore containing less dentine contaminant.…”

“…1986;Pearce et al, 1984], using the extended Dcbye-Hiickel equation [Carrels and Christ.1965], Details of the calcula tion o f theoretical values for ion activities in HCI solutions equilibrat ed with HAp have been given previously [Larsen et al. 1993]; log (Ca2 ) (OH )2 and log (H )'( P O /) values were then calculated and potential plots [Brown, 1973] constructed.…”

“…In a recent study o f the solubility of powdered human dental enamel at high solid/solution ratio [Larsen et al, 1993], falling calcium (Ca) and phosphate (P) solution val ues during early equilibrations provided direct evidence for the formation of a second calcium phosphate phase. A ris ing Ca/P ratio in solution was consistent with brushite for mation, but this mineral could not always be confirmed by ion activity product calculations or by X-ray diffraction.…”