Actions of silver diamine fluoride on dentine caries and its caries preventive effect with laser irradiation

Abstract

The effect of silver diamine fluoride (SDF) on the mineral content of carious dentine and the preventive caries effect of erbium-doped yttrium aluminium garnet (Er:YAG) laser irradiation (2,940 nm) combined with SDF application under cariogenic biofilm challenge model was investigated. Firstly, the SDF mechanism of action in the remineralisation of demineralised dentine process observing changes in the mineral content in vitro was investigated. Secondly, we investigated the effect of various laser irradiations at sub-ablative energy levels on the fluoride uptake of 38% SDF treated dentine. Finally, we evaluated the effects of Er:YAG laser irradiation combined with SDF application on the fluoride uptake by dentine under a cariogenic biofilm challenge.

Compared with a 10% sodium fluoride and potassium fluoride solution and a 42% silver nitrate solution with the same content of fluoride and silver respectively, 38% SDF is more effective in promoting remineralisation of demineralised dentine. The dentine samples treated with SDF did not show evident demineralised surface morphology. Although the lesion depth for SDF treated samples was not significantly deeper than for sodium fluoride treated samples, it was demonstrated that SDF has an inhibitory effect on dentine demineralization.

The results of the SDF-laser experiment showed that carbon dioxide (CO2) laser irradiation (10,600 nm) followed by Er:YAG laser irradiation at specific sublablative levels promoted the higher fluoride uptake from SDF application than neodymium-doped yttrium aluminium garnet(Nd:YAG) laser (1,064 nm) and diode laser (810 nm) irradiation. This study provides guidelines for the selection of the appropriate laser irradiation parameters and types to promote an optimal level of fluoride uptake for dentine caries prevention.

Er:YAG laser irradiation was elected among the laser types in the previous experiment for promoting higher levels of fluoride uptake and for its maximal absorption by water and high absorption by hydroxyapatite. The Er:YAG SDF-laser treated dentine was subjected cariogenic bacterial challenge to investigate the caries preventive effect of this treatment. The morphological surface of the treated samples presented many occluded dentinal tubules. There was a major increase in the hardness and elastic moduli values and the fluoride content also increased significantly after the remineralisation process.

To conclude, this study demonstrated that SDF application inhibited dentine demineralization and arrested caries, and that SDF application followed by Er:YAG laser irradiation promoted an increase in fluoride uptake by sound dentine under a cariogenic biofilm challenge.