Toothbrush abrasion of surface softened enamel studied with tapping mode AFM and AFM nanoindentation

The aim of the present in vitro study was to investigate the toothbrush abrasion of surface softened enamel using tapping mode atomic force microscopy (TM-AFM) and AFM nanoindentation. TM-AFM investigations showed that the typical prismatic pattern as observed after demineralisation was retained after toothbrushing. The exposure to artificial saliva resulted in the deposition of a 'sausage-shape' material with random orientation. Brushing of these samples did not lead to a complete removal of this deposited material. Enamel mineral loss increased with increasing demineralisation time and increased further, although only to a small extent, due to subsequent toothbrushing. Exposure to artificial saliva did not alter the amount of enamel mineral lost due to the brushing treatment. AFM nanoindentation investigations showed that the three different demineralisation treatments caused three statistically different reductions in both surface hardness and reduced elastic modulus values, with the shortest exposure time having the least effect on the nanomechanical properties of the enamel samples. Toothbrushing did result only in a small increase in hardness and reduced elastic modulus. The present study has shown that toothbrushing of surface softened enamel leads to minor changes in the surface morphology and nanomechanical properties. The amount of enamel lost due to toothbrushing was independent of the demineralisation time and was lower compared to the mineral loss caused by the demineralisation treatments. Furthermore, the exposure to artificial saliva offers minimal protective effect to the softened enamel surface against toothbrushing.