Influence of Polymers for Use in Saliva Substitutes on De- and Remineralization of Enamel in vitro

Abstract

A number of polymers which have previously been tested for their applicability as thickening agents in saliva substitutes were studied in vitro for their caries-protective properties. These were: polyacrylic acid, carboxymefhylcellulose, xanthan gum, guar gum, hydroxyethylcellulose and porcine gastric mucin. The polymers were tested for their effects on: (1) growth of hydroxyapatite crystals in a supersaturated calcium phosphate solution, (2) dissolution of hydroxyapatite crystals in 50 mM acetic acid, pH 5.2, and (3) demineralization and remineralization of bovine enamel in a pH-cycling model. Growth of hydroxyapatite crystals was strongly inhibited by polyacrylic acid and carboxymefhylcellulose at very low concentrations (0.005% w/v). Other polymers displayed lower inhibition of hydroxyapatite crystal growth. Hydroxyapatite dissolution was inhibited by all polymers except hydroxymethylcellulose and xanthan gum. This occurred both in the presence of the polymers as well as after a 30-min preincubation. In the pH-cycling experiment, bovine enamel specimens with preformed lesions were alternately exposed to a demineralization buffer and a remineralization buffer containing the polymers hydroxyethylcellulose, carboxymethylcellulose, xanthan gum, polyacrylic acid, or porcine gastric mucin. A remineralization buffer containing 1 ppm NaF was used as a positive control. Under the experimental conditions, the control experiment without additives resulted in a net mineral loss (30.6 µmolCa/cm² after 14 days of pH cycling). In the presence of 1 ppm NaF, a small mineral gain was observed (8.6 µmol/cm²). All polymers largely inhibited further demineralization (1.2–12.3 µmol/cm²) except polyacrylic acid which, because of its high calcium-binding capacity, caused demineralization, especially in the remineralization buffer (17.1 µmol/cm²). In conclusion, polymers tested in this study, except the polyacrylic acid, reduced the demineralization of enamel in vitro. The precise mechanism of the protective effect is not clear but it is speculated that formation of an adsorbed polymer layer on the hydroxyapatite or enamel surface may provide protection against acidic attacks.

Effect of thickener agents on dental enamel microhardness submitted to at-home bleaching

“…However, it is an acidic polymer that may cause demineralization, and it has a high calcium-binding capacity that can inhibit hydroxyapatite crystal growth. 24 The carbowax applied in G3 is a polymer of ethylene oxide and water and their ethers (polyethylene glycol), and it is very used as a surfactant in industry, including foods, cosmetics and pharmaceutics. It was used here as an alternative thickener agent based on the formulation of the bleaching agent of G4, whose thickener agent is poloxamer, a co-polymer of polyethylene glycol used as an emulsifying, surfactant, and wetting agent similar to carbowax.…”

Susceptibility of Chlamydia trachomatis to the Excipient Hydroxyethyl Cellulose: pH and Concentration Dependence of Antimicrobial Activity

“…It has been shown that the presence of HEC facilitates the nucleation of calcium phosphate in supersaturated solutions at pH 7.4 (12). Interestingly, when the calciumcarrying capacity of HEC was studied as a function of pH, it was found that HEC promoted the mineralization of calcium phosphate at pH 7 and, consequently, released calcium phosphate at pH 4.8 with no significant hysteresis upon repeated cyclings of pH change, implying that HEC does not undergo chemical degradation at low pH (16). The pH dependence of HEC-promoted mineralization indicates that increased local membrane calcium phosphate would not be expected in the experiments whose results are shown in Fig.…”

Effects of Carboxymethyl Cellulose-Based Saliva Substitutes with Varying Degrees of Saturation with Respect to Calcium Phosphates on Artificial Enamel Lesions

“…Nonetheless, some nonsignificant but distinct differences between C1 and S1 were found in favor of C1 with respect to remineralization properties. An earlier study had shown that growth of hydroxyapatite crystals was inhibited even by low concentrations of CMC (0.005% w/v) in a supersaturated solution at neutral pH [Van der Reijden et al, 1997]. At lower pH (5.2) hydroxyapatite dissolution was inhibited as well.…”