Pectin, alginate and gum arabic polymers reduce citric acid erosion effects on human enamel

Consumption of acidic soft drinks may lead to the dissolution and softening of human enamel, known as erosion. The first aim of this in vitro study was to test the hypothesis that food-approved polymers added to citric acid solutions (CAS) decrease the erosion of human dental enamel compared to citric acid solutions without these polymers. The second aim was to test the hypothesis that these polymers added to CAS form a polymer layer directly on the eroded enamel surface.

Enamel samples were obtained by embedding pieces of non-erupted human third molars in resin, grinding, and polishing them. CAS with pH values (pH: 2.3, 3.3 and 4.0) of typical soft drinks were prepared and modified by adding one of the following food-approved polymers (1%, w/w): highly esterified pectin (HP), propylene glycol alginate (PGA) and gum arabic (GA). The enamel samples were exposed to these polymer-modified citric acid solutions (PMCAS) or CAS not containing polymers, respectively, for different time periods (30, 60 and 120s). Atomic force microscopy (AFM)-based nanoindentation was used to analyze the nanomechanical properties of the treated enamel samples and the control samples. The enamel nanohardness and the reduced elastic modulus of the samples treated with PMCAS were statistically analyzed (ANOVA, t-test) and compared to the mechanical properties of the samples treated with unmodified CAS. Thus treated enamel samples were imaged by scanning electron microscopy (SEM) to investigate the surface morphology of the different enamel samples.

Enamel samples treated with PMCAS containing GA or PGA showed statistically significantly higher nanohardness (p<0.05) compared to samples treated with CAS. PMCAS containing HP did not reduce the enamel nanohardness loss significantly compared to the CAS treated enamel samples. The enamel samples eroded with PMCAS show generally a smoother surface compared to the enamel surfaces of samples treated only with CAS as detected by SEM. Therefore, it is hypothesized that the polymers possibly adsorb on the eroded enamel surface.

The present in vitro erosion study shows that some of the polymers used in this study may possibly adsorb like a protective layer directly onto the human enamel surface. For GA and PGA this possibly formed polymer layer reduces the erosive effects of citric acid solutions as shown by nanoindentation measurements.