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A type III gold alloy and six different ceramic surfaces were secured in an abrasion machine opposing extracted teeth to determine their relative abrasiveness and resistance to wear. The rankings of restorative materials from least abrasive to most abrasive were: gold alloy, polished; cast ceramic, polished; porcelain, polished; cast ceramic, polished and shaded; porcelain, polished and glazed; cast ceramic, cerammed skin shaded; and cast ceramic, cerammed skin unshaded. The ranking of materials from most wear-resistant to least wear-resistant was: gold alloy, cast ceramic cerammed, cast ceramic cerammed and shaded, porcelain polished, porcelain glazed, cast ceramic polished and shaded, and cast ceramic polished.

Fixed partial dentures cemented to dies of adjustable mobility were subjected to repeated impacts at three different sites. Immobile abutments retained their prostheses longer than mobile abutments. Impacts that fell between the centers of rotation of the abutments were withstood longer than impacts that fell nearer the ends of the prostheses. This study failed to show a significant difference between the effect of impacts perpendicular to the occlusal plane and impacts angled 45 degrees toward the lingual plane. The results of this study suggest that (1) crowns that anchor rigid prostheses to mobile teeth require greater retentive ability than crowns on relatively immobile abutments and (2) occlusal impacts are best withstood when they fall on the areas of the fixed partial denture over and between the centers of rotation of the abutment teeth. If a fixed partial denture must withstand loading outside these areas, as is the case with cantilevered pontics and some tilted abutments, the retainer furthermost from the anticipated eccentric load must have exceptionally good retention.

A method for fabricating a “safety ring” on cast crowns to which a ligature can be tied to prevent swallowing or aspiration of cast restorations has been described. A report of a fixed partial denture swallowed during try-in was presented.

S i n c e the advent of the cast gold restoration in dentistry, many uses have been made of this method for restoring posterior teeth with proximal lesions. The restorations have ranged (rom simple intracoronal inlays to gold veneer crowns of various types. Of the designs that have been used, some have been based on scientific principles, while others have been rooted in empiricism and tradition. One of the more enduring of the cast restorations has been the Class II inlay? This restoration has been used extensively for 50 years, with many dentists attributing to it advantages which may, in fact, not exist. Cast gold has certain properties which make it superior to silver amalgam,, another material commonly used for Class II restorations. However, many clinicians and researchers have come to realize that, while gold may be stronger and harder, these assets alone do not assure a superior means of restoring Class II lesions. The material itself does not strengthen the remaining tooth structure in a Glass II restoration, that type of restoration being purely intracoronal. Modifications must be made in the design of the preparation to take advantage of the desirable physical properties of the material and to protect the tooth from further breakdown. °-, :~ The purpose of this investigation was to determine the stresses induced at certain critical areas of the tooth by various designs of cast gold restorations when subjected

The relationship between the surface finish on cast gold restorations and the amount of plaque deposited on that surface was examined. Six different finishes were tested. The rouge finish was found to accumulate significantly less plaque than the other finishes. Every finish exhibited some plaque accumulation, even after the first 24 hours. Each finish accumulated progressively more plaque at each successive time interval.

Four variations of an MOD onlay preparation were studied for retention and resistance. Boxes were more effective than an isthmus in increasing retention value. The combination of boxes and isthmus showed the highest retention. The combination of boxes and isthmus also exhibited the highest resistance. There was no difference in resistance between boxes and the isthmus.

Five preparation designs were tested for retention and resistance. Retention values for all partial veneer crowns were significantly lower than those for the complete veneer crown. Resistance values increased significantly with the addition of grooves and/or extension of axial surface coverage. Addition of grooves and/or extension of axial surface coverage produced small increases in retention values but marked increases in resistance values.

There are many types of articulators that can be used for making fixed restorations. While unquestionably the most accurate, the fully adjustable instrument is not feasible or necessary for many forms of simple occlusal treatment. The effects of tooth-hinge axis radius, intercondylar distance, and condylar inclination on occlusal morphology have been discussed. Guidelines have been proposed for matching the type of articulator with the extent of treatment anticipated. The use of small, nonadjustable hinge articulators is not recommended.

The relationship between preparation finish line configurations and marginal stability of porcelain-fused-to-metal restorations during the firing cycle was studied. Four labial finish lines presently in use were examined. The shoulder finish lines, with and without a bevel, were found to produce significantly less distortion in labial margins of porcelain-fused-to-metal restorations than do chamfer finish lines with and without a bevel.

A brief history of the development of the currently popular porcelain-fused-to-metal restoration has been presented. A tooth preparation design has been described with labial reduction of 1.2 mm. done in two planes to allow a bulk of porcelain for esthetic appeal while protecting the integrity of the pulp. A beveled shoulder finish line is advocated on the labial to aid in minimizing distortions which can occur during the fabrication of the restoration. Occlusal contact on metal is recommended, especially for posterior teeth. A bridge design has also been presented, with an exposed metal strip on the lingual and a small pontic tissue contact in porcelain.

A comprehensive scheme has been presented for the restoration of endodontically treated teeth. A technique for making cast gold dowel-cores from direct acrylic resin patterns has been described. The method can be used for mutilated teeth with favorable root forms. An alternate method, the pin-retained amalgam core, can be used for teeth needing extensive restorations but which lack favorable root size and shape.