Understanding the Chemistry of Dental Erosion

Abstract

Dental erosion is caused by repeated short episodes of exposure to acids. Dental minerals are calcium-deficient, carbonated hydroxyapatites containing impurity ions such as Na(+), Mg(2+) and Cl(-). The rate of dissolution, which is crucial to the progression of erosion, is influenced by solubility and also by other factors. After outlining principles of solubility and acid dissolution, this chapter describes the factors related to the dental tissues on the one hand and to the erosive solution on the other. The impurities in the dental mineral introduce crystal strain and increase solubility, so dentine mineral is more soluble than enamel mineral and both are more soluble than hydroxyapatite. The considerable differences in structure and porosity between dentine and enamel influence interactions of the tissues with acid solutions, so the relative rates of dissolution do not necessarily reflect the respective solubilities. The rate of dissolution is further influenced strongly by physical factors (temperature, flow rate) and chemical factors (degree of saturation, presence of inhibitors, buffering, pH, fluoride). Temperature and flow rate, as determined by the method of consumption of a product, strongly influence erosion in vivo. The net effect of the solution factors determines the overall erosive potential of different products. Prospects for remineralization of erosive lesions are evaluated.

Chelating effect of citric acid is negligible for development of enamel erosions

“…The solutions were prepared immediately before being used in the respective experiment (1)(2)(3)(4), in which enamel samples were superfused with the acidic solution.…”

“…Among other acids, citric acid (Cit) is very common in beverages and known for its erosive effect and its ability to form complexes with calcium dissolved from the dental crystals. Different complexes with different dissociation constants (pK Ca ) may be formed, such as (Ca 2+ + H 3 Cit -<-> CaH 3 Cit + , pK: 1.10), (Ca 2+ + H 2 Cit 2-<-> CaH 2 Cit, pK: 3.09), (Ca 2+ + HCit 3-<-> CaHCit -, pK: 4.68), (Ca 2+ + 2H 2 Cit 2-<-> Ca(H 2 Cit) 2 2-, pK: 6.79), (Ca 2+ + 2HCit 3-<-> Ca(HCit) 2 4-, pK: 8.02) [3,4]. Larger pK-values indicate stronger binding of the ligand to calcium [3].…”

“…Different complexes with different dissociation constants (pK Ca ) may be formed, such as (Ca 2+ + H 3 Cit -<-> CaH 3 Cit + , pK: 1.10), (Ca 2+ + H 2 Cit 2-<-> CaH 2 Cit, pK: 3.09), (Ca 2+ + HCit 3-<-> CaHCit -, pK: 4.68), (Ca 2+ + 2H 2 Cit 2-<-> Ca(H 2 Cit) 2 2-, pK: 6.79), (Ca 2+ + 2HCit 3-<-> Ca(HCit) 2 4-, pK: 8.02) [3,4]. Larger pK-values indicate stronger binding of the ligand to calcium [3]. This formation of calcium complexes by citrate molecules is indicated as an additional relevant factor for the loss of dental hard during erosion.…”

“…According to a recent publication by Shellis et al [3], the extent to which this phenomenon enhances the erosive effect of organic acids has yet to be quantified. It is obvious that citric acid is a very complex and specific chemical compound rendering it difficult to predict the erosive potential of differently concentrated citric acid solutions.…”

Does dentifrice provide the necessary saturation of ions in oral fluids to favour remineralisation?

“…The significance of the changes in the molecular composition of mixed saliva has been previously shown in diabetes, oncology and pathologies of the oral cavity [4][5][6][7][8][9]. Considerable deviation of the molecular composition in the oral fluid can have an influence on the content of mineral complexes in plaque fluid and thus, impact on the process of enamel remineralisation [1,[10][11][12][13]. Remineralisation is the recognised process of dental enamel recovery promoted by the plaque fluid and mixed saliva being oversaturated with ions (Са 2+ , HPO 4 2-, Na + , Mg…”