Abstract: 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 about 0.5 to 5. After the treatment the composition is removed from the tooth surface. In various embodiments of the invention the pH of the composition can range between about 0.5 and 3, a narrower range being between 1 and 1.75. After treatment, the enamel may be restored chemically or by means of a porous layer. If the enamel is restored chemically, then an aqueous solutions of one or more edible acids with particles selected from the group of Ca, Cr, Ba, Cd, Mg, P, As, Si, F, or Na is used.