Flash tooth whitening: A friendly formulation based on a nanoencapsulated reductant

[Display omitted] •Tooth whitening by oxidation (using peroxides) needs long application times (hours).•Tooth whitening by reduction (using metabilsulfite) reachs impressive results in 3min.•Nanoencapsulation of metabisulfite in liposomes lead to unexpected enhanced results.•Liposomes protect metabisulfite from degradation in the aqueous medium.•Liposomes attach to the tooth surface enhancing the reductant diffusion into enamel. Tooth whitening materials have not undergone relevant advances in the last years. Current materials base their action on the oxidant activity of peroxides, which present the disadvantage of requiring long application times, along with unpleasant side effects of dental hypersensitivity (e.g. sharp pain). In this work, a novel tooth whitening formulation based on the encapsulation of a reducing agent (sodium metabisulfite) in liposomes is developed. An experimental design was applied to optimize the formulation in terms of whitening action and safety, using bovine teeth as in vitro model. Results were obtained by colorimetry, profilometry and nanoindentation techniques. The comparison with standard whitening treatments showed a similar whitening action of the optimized formulation but in remarkable shorter application times. Moreover, teeth roughness values obtained with the presented formulation conformed with ISO 28399. As mechanism of action, results obtained from fluorescent confocal microscopy showed the liposomal formulation to form a layer surrounding the enamel surface, enhancing the treatment efficacy in terms of diffusion of the protected reductant towards the enamel. The better efficiency of this formulation encourages its use as an alternative to current oxidative treatments.