A method for treating hard tissue infection in a site-specific manner, comprising preparing a negative mold of the hard tissue using an impression material which contains a diagnostic additive which generates an identifiable signal on contact with infected tissue; applying a treatment agent to the negative mold at one or more of infected sites; and re-applying the negative mold on the originally molded hard tissue for a suitable period of time. Also disclosed are methods for making the negative mold, a mouthpiece corresponding to the negative mold, and a treatment device, as well as the treatment device and mouse piece so produced.