The present invention is a number of methods and devices for tooth rejuvenation and hard tissue modification comprising applying a layer of a peroxide-free composition to a tooth surface. The applied composition comprises an aqueous solution of one or more edible acids. The composition has a pH selected from the range of 0.5 to 1.75. After the treatment the composition is removed from the tooth surface. Hard tissue rejuvenation comprises forming a post-treatment layer having a composition which is different from that of the hard tissue of the hard tissue by selectively heating a porous layer on the hard tissue.
