Source: {"pile_set_name": "USPTO Backgrounds"}

Multiple-unit dental restorations (i.e., bridges or pontics) have for many years been made by preparing a metal base or coping and then adding several layers of dental porcelain over the metal to simulate, as closely as possible, the appearance of natural teeth. The metal base for the bridge is usually assembled on a master cast and the individual units (teeth) are fastened together with wax containing rosin, known in the dental profession as "sticky wax". The assembly of individual units bonded together with wax is then carefully removed from the master cast and is embedded in a unitary mass of refractory cement ("soldering investment"), with only the portions of the units that are to be joined to the adjacent units exposed. After the cement has hardened, the wax is removed, as by flushing with boiling water. Next, the units are soldered together. After the soldering operation, the assembly is removed from the investment and is ready for the addition of the porcelain layers.
Recently, all-ceramic dental restorations have become commercially available. Because no metal is used in their fabrication, all-ceramic restorations can be made to more closely resemble natural dentition. Such all-ceramic dental restorations are disclosed, for instance, by Starling et al. in U.S. Pat. No. 4,265,669. Naturally, the techniques for producing an all-ceramic dental restoration must differ in some respects from those used to produce a metal-based restoration. For instance, in the preparation of an all-ceramic multiple unit restoration, the individual units cannot be soldered together as they are in a metal-based restoration. This invention is directed to a procedure that is particularly applicable for joining the individual units to each other in the production of an all-ceramic multiple unit dental restoration, although the invention is more widely applicable to the joining of all types of ceramic components that must be joined in precise spatial relationship.