The Inhibitory Effect of Fe(II) on enamel dissolution

Previous research has shown that both Cu(II) and Fe(II) are anticariogenic in rats. This effect was attributed to the bactericidal properties of both ions. However, recent work in our laboratories demonstrated that Cu(II) directly inhibited acid dissolution of human enamel in an in vitro abiotic system, raising the possibility of an alternative cariostatic mechanism. Objectives: The aim of this study was to investigate any effect for Fe(II) on the acid dissolution of human enamel. Methods: Six sound permanent premolars were bisected mesio-distally along the midline. Roots and cut surfaces were covered with nail varnish. Tooth halves were sequentially exposed for 1 minute to each of a series of 7 vials containing 10 mmol/L acetic acid (pH =3.2). Samples were rinsed in distilled water between exposures. The 4th vial also contained 10 mmol/L iron sulphate. Contralateral tooth halves were exposed to a similar series of vials but with no Fe(II) present. Enamel dissolution was determined by measuring the phosphate content of each vial spectrophotometrically. Results: The results showed that the presence of Fe(II) in vial 4 reduced the amount of enamel dissolved by 40% (p < 0.05). The protective effect was still evident in vials 5 and 6 (which did not contain Fe(II)) but this was not statistically significant. Conclusions: The results indicate that in addition to its bactericidial properties, Fe(II) can directly inhibit the acid dissolution of enamel. The mechanism responsible for the protective effect is unknown but it might involve stabilisation of the mineral surface by heteroionic substitution or the surface precipitation of an acid resistant iron complex. The possibility that Fe(II) may have a useful therapeutic role in combating caries and enamel erosion should be investigated further.