Fig. 1: Piezo-catalysis effect and working principle for tooth whitening.

a Illustration of mechanical vibration between toothbrush and teeth during daily toothbrushing. b The traditional abrasive-based toothpaste method, where tooth whitening is realized by the mechanical friction between teeth and abrasive. c The proposed piezo-catalysis effect-based tooth whitening method wherein piezoelectric particles replace traditional abrasive in the toothpaste, to generate reactive oxygen species via piezo-catalysis to bleach tooth stains. The detailed mechanism of piezo-catalysis effect, i.e., d the original electrostatic balance state of a poled piezoelectric material; e the release of screening charges under compressive stress, which combine with water molecules and then produce reactive species; f the modified electrostatic balance state under maximum compressive stress; g the adsorption of charges from the surrounding electrolyte under reduced compressive stress. The charges in the electrolyte with opposite polarity to the adsorbed charges will participate in the redox reaction to produce reactive species.