Surface changes of mineral trioxide aggregate after the application of bleaching agents: electron microscopy and an energy-dispersive X-ray microanalysis.

INTRODUCTION The aim of this study was to investigate the changes in the surface structure and chemical composition after applying bleaching agents to completely hardened mineral trioxide aggregate. METHODS A total of 12 samples of MTA blocks were divided into three groups, two different bleaching agents, and a control group. The surface structure was observed using a scanning electron microscope. The changes in elemental composition were analyzed by an energy-dispersive x-ray microanalysis (EDX) system. RESULTS The surface of the MTA covered with each bleaching agent changed in terms of both color and structure compared with the control. EDX showed that both bleaching agents affected the elemental distribution. A decrease in Ca and an increase in Si were shown, and this tendency was especially pronounced in the higher hydrogen peroxide concentration group. CONCLUSIONS The acidic conditions induced by bleaching agents brought about the deterioration of the MTA surface. These findings suggest that MTA is an insufficient barrier against tooth bleaching.