Abstract: A method for strengthening and increasing the thickness of the strengthened surface layer of a dental ceramic restorative material where the ceramic material is heat treated with a salt composition containing a lithium ion and a metal ion larger than the lithium ion first at a temperature above the strain temperature followed by a second heat treatment with the salt composition at a temperature below the strain temperature. The treatment is especially effective for all-ceramic, high-leucite feldspathic porcelain restorations.

Abstract: In dental surgery when a tooth is to be crowned, the tooth has to be prepared by cutting a taper. It has been found that for the successful mounting of a crown the taper must be much more exactly prepared than is possible using currently available equipment. The present invention allows the initial position of the axis of a cutter to be related by means of electronic "spirit levels" to a selected axis. Deviation from this axis by more than a predetermined amount is indicated by light sources which can be seen regardless of the position of a handpiece holding the cutter. By means of a code these light sources indicate how the dentist must move the cutter to return to the correct axis.