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The Use of Gold Alloys in Dental Applications
Man’s attempt to replace lost teeth dates to the seventh century BC, when the Etruscans tried animal teeth bound with gold alloy bands. Historically, a number of materials have been used to carve replacement teeth, including ivory and wood. Despite these efforts the inability to replicate the environment of the mouth and the poor fit of the restorations resulted in loss of masticatory function.
The fabrication of dental prosthetic devices was revolutionized in the early 1900s with the adaptation of the lost-wax method of casting to the fabrication of dental inlays, crowns, and bridges. This invested pattern methodology developed by H. William Taggert solved the ill-fitting problem. The excellent fit provided by the method allowed the restorations to be cemented in place and function like natural teeth. (The cementation process defines the classification of these prosthetic devices as “fixed” prosthetics as opposed to “removable” prosthetics such as dentures or partial dentures.)
1. Evolution of the Prosthetic Fabrication Process
In the fabrication of a single crown, the lost-wax method involves several steps:
Step 1. The dentist prepares the natural tooth by grinding away the diseased portion leaving a “stump.” The unique outer surface of the remaining tooth structure will mate to the inner surface of the prostheses.
Step 2. An impression of the “stump” and adjacent gingival regions is taken using a nonaqueous elastomer material and sent to a dental laboratory. The impression material now has a negative image of the area of interest in the patients’ mouth.
Step 3. The dental lab pours a stone model into the impression. The stone hardens creating a positive replica of the area of interest in the patient’s mouth.
Step 4. Wax is built up on the model by hand for the portion of the tooth that will be replaced by alloy. A sprue is attached to the wax pattern.
Step 5. The wax pattern and sprue are invested in a refractory material that hardens and is placed in a furnace. The wax is melted and vaporized leaving a void.
Step 6. The dental alloy is cast into the void thus duplicating the wax pattern.
The inside contours of the cast alloy from Step 6 matches the outer surface of the prepared “stump” in Step 1. This allows the restoration to “fit” and restores masticatory function. The prostheses feels and functions like the natural tooth. A more detailed description of the lost-wax process can be found in Anusavice (2003).
The alloys first used in the early 1900s were high-gold alloys (75%+) containing silver and copper. These materials were easy to cast by torch, worked well with available gypsum-based investments, and exhibited excellent biocompatibility and corrosion resistance in the mouth. At first the entire restoration was made of the gold alloy. Later acrylic facings were mechanically attached to the outer surfaces of the gold teeth in order to make the restorations appear more life-like when the patient smiled. The esthetics of fixed prosthetics was advanced further in the 1960s with the introduction of a porcelain-fused-to-metal (PFM) system developed by Weinstein et al. (1962). The left-hand side of Fig. 1 shows a cross-sectioned PFM crown, the alloy portion is a thin-wall casting fabricated using the same lost-wax method as before but the bulk of the restoration is made by firing successive layers of porcelain onto the alloy. The alloy provides the fit and imparts resiliency and strength to the restoration while the porcelain imparts life-like esthetics. This type of restoration quickly became the restoration of choice and remains so today. In order to accommodate the firing of porcelain the traditional gold–silver–copper alloys could not be used for the PFM processing technique.
To learn more, take a look at the article Gold Casting Alloy, New, for Dental Applications from the Major Reference Work Encyclopedia of Materials: Science and Technology. This article will also be part of our innovative Reference Module in Materials Science and Materials Engineering. Now live on ScienceDirect, this visionary resource combines thousands of encyclopedic and comprehensive articles into one interdisciplinary product. It will save you time and energy by displaying the multidisciplinary links across topics in the broad and complicated field of Materials Science and Materials Engineering in one authoritative platform.
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