Method for molding dental restorations and related apparatus

#The present invention relates to a process for the molding of metal free dental restorations such as crowns, bridges, inlays, onlays, etc., from glass-ceramic materials. The invention is also concerned with apparatus which permits dental restorations to be easily molded from glass-ceramic materials and, lastly, the invention relates to the resulting dental restorations.

#In the prior art, various methods have been used to form metal free dental restorations from glass-ceramic materials. Glass ceramic materials because of their strength, translucency, non-toxicity and other physical properties are ideal materials for use in forming dental restorations. Because of their suitability, glass-ceramic materials have been used to form dental restorations for at least eighty years. In the prior art, the most widely used means for forming dental restorations from mixtures of glass and ceramic materials is a process which utilized a slurry of glass and ceramic particles. In this process, a die is formed which is an exact replica of the remaining portion of the tooth to which the restoration is to be secured. It is understood by one skilled in the art that the remaining portion of the tooth has been prepared by the dentist in such a manner that the attachment of the restoration is facilitated. To start the process, the dentist takes an impression of the prepared tooth to create a negative impression of the prepared tooth or teeth. This negative impression is then packed with a material to form a positive impression of the prepared tooth or teeth. This positive impression is called a die. Platinum foil is then pressed over the die to form a matrix which is essentially a foundation on which the dental restoration is built. In order to form up the dental restoration, many layers of a slurry of a particulate glass-ceramic material are applied to the platinum foil matrix. As multiple layers of the slurry are built-up and dried, a semi-solid structure is formed which can be carved into shape of the desired dental restoration. Once the desired shape is achieved, the structure is then removed from the die. At this stage, the structure is referred to as a green structure. The structure is then fired. During the firing process, the particulate glass-ceramic material fuses into a solid mass. Because the green structure is formed from multiple layers of the dried glass-ceramic material, uneven fusing may result. As a result of this uneven fusing, the physical properties of the finished restoration may be detrimentally affected, thereby creating an inferior dental restoration. Further, as can be seen from the above description, the overall process is very labor intensive.

#Other methods for forming the green restoration have been considered in the prior art, for example, in U.S. Pat. No. 2,196,258, a mixture of particulate glass and ceramic materials which incorporates a binder is packed into a flexible mold to form a green structure which is then fired to form a finished structure. Again, because the process entails the fusing of particulate material, uneven fusing may result and, hence, a weakened and inferior dental restoration may result.

#FIG. 1 is a flow chart showing the steps of the preferred embodiment of the process of this invention;

#FIG. 2 shows a sectioned lost wax mold for use in the invention;

#FIG. 3 shows a sectioned structure illustrating the heating step of this invention;

#It should be noted that FIGS. 2 through 10 are schematic representations of apparatus which may be useful in this invention.

#FIG. 1 generally described the overall process of the subject invention, wherein the dental restorations are formed by the molding of a glass-ceramic material. As can be seen in FIG. 1, the first step is the formation of a mold having a suitable mold cavity therein. To start the process whereby the mold cavity is formed, the tooth or teeth in the human mouth are prepared by the dentist by procedures which are commonly known in the prior art. By using impressions which are provided by the dentist, a positive wax form is then formed and positioned in a mold usually called a ring. A semi-liquid investment material is then poured around the positive wax form. Once the investment material sets up and cures, the resulting mold is placed in a furnace and heated, thereby causing the wax to melt and run out of a sprue hole which is integral with the mold. The finished mold is then complete. This constitutes the formation of a mold by the lost wax process.

#In the second step of FIG. 1, a button of a glass-ceramic material is placed in deformable crucible 8, as is illustrated in FIG. 3. The button of a glass-ceramic material constitutes a small cylinder of the glass-ceramic material which usually weighs about six grams, and has a diameter of about two cm, and a thickness of about one cm. These buttons of glass-ceramic materials are a convenient shape, whereby these materials may be manufactured, sold and used. It is understood by one skilled in the art that a sufficient amount of the glass-ceramic material must be used in order to form the desired dental restoration.