Objectives. To investigate the chipping resistance of veneered zirconia specimens and compare it to the chipping resistance of porcelain fused to metal (PFM) specimens.Methods. Veneered zirconia and PFM bar specimens were prepared in clinically relevant thicknesses. The specimen edges were chipped with different magnitude forces, producing chips of various sizes. The range of sizes included small chips that did not penetrate all the way through the veneers to the substrates, and also chips that were very large and reached the zirconia or metal substrates. The relationship between force magnitude and chip size (edge distance) was graphed. The resulting curves were compared for the veneered zirconia and PFM specimens. Knoop hardness vs. force graphs for the veneers and substrates were also obtained.Results. The zirconia and PFM veneer chipping data followed a power law (coefficient of determination, R-2 > 0.93) as expected from the literature. The curves overlapped within the combined data scatter, indicating similar resistance to chipping. The chips made in both types of specimens detached and did not penetrate into the substrate when they reached the veneer/substrate intersections. The hardness-load curves for the veneers and substrates all exhibited an indentation size effect (ISE) at low loads. The Knoop hardness values with uncertainties of +/- one standard deviation at 4N loads for the metal, zirconia, and the metal and zirconia veneers are: (2.02 +/- 0.08, 12.01 +/- 0.39, 4.24 +/- 0.16 and 4.36 +/- 0.02 GPa), respectively, with no statistically significant difference between the veneers (Tukey pairwise comparison at 0.95 family confidence).Significance. This work indicates that a similar resistance to chipping might be expected for veneered zirconia and PFM restorations, in spite of the large difference in substrate hardness. Differences in susceptibility to chip spalling were not detected, but the chips in both specimen types detached off the sides in a similar manner instead of extending into the substrates. (C) 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

The factors influencing the success of dental porcelain-metal restorations were investigated according to the broad categories of porcelain-metal bonding and porcelainmetal thermal compatibility. The bonding of porcelain to dental alloys (Ni-Cr or Co-Cr based) was found to be closely related to those alloys' respective oxide adherence strengths. One class of alloys (Pd-Ag based) tended to form an internal oxide. For this latter class of alloys, porcelain adherence seemed to result from mechanical interlocking between the porcelain and palladium-silver nodules formed on the alloy surface by a Nabarro-Herring creep mechanism. In order to ensure thermal compatibility in new porcelain-metal system, the role of thermal properties of the porcelain cooled at high rates in the dental fabrication process must be understood. The glass transition temperature and thermal expansion characteristics at high cooling rates were the properties needed in order to utilize the generalized Timoshenko equation in evaluating interface bending stress in porcelain-fused-to-metal restorations. Glass transition temperature measurements have been made for a limited number of porcelains demonstrating the feasibility of using the modified bending beam viscometer for rapid heating and cooling rate measurements. For the production of a successful porcelain-metal restoration, both a strong interface bond and thermal compatibility between the porcelain and metal are required. Because of inadequacies in current bond tests for use in evaluating dental porcelain-metal systems, a new bond test was developed as a part of this research program. In addition, the adherence of the oxides formed at high temperatures to their respective alloys was measured by means of a high-strength cyanoacrylate cement. The adherence strengths of the various oxides were found to vary widely and to be correlated closely to the porcelain adherence. Contact angle measurements were found to be an unreliable indicator of porcelain adherence, with the lowest contact angle (highest work of adhesion) being exhibited on an alloy with a non-adherent oxide, and hence poor porcelain bonding. Oxide adherence appears to be the common thread running among the different types of alloys which determines their ability to bond well with porcelain. Some palladium-silver alloys were found not to produce an external oxide, but rather an internal one. The stress produced by the internal oxidation of tin and indium was found to drive a Nabarro-Herring creep process and produce nodules of pure palladium-silver on the alloy surface. Adherence of porcelain in such systems may be primarily mechanical. A method for measuring porcelain properties at rapid heating and cooling rates has been developed. The measurement of the glass transition temperature at rates up to 500°C on a dental porcelain has been accomplished. A laser dilatometer capable of measuring the thermal expansion coefficient at similar rates is under construction.

Dental materials are those materials used to provide therapy for the hard and soft oral tissues. This therapy includes the replacement of oral tissues lost through disease with inert materials, ie, metallic, ceramic, and organic, or with composites employing combinations of these three broad classes. The operative restorations and prostheses are made of amalgam, precious and nonprecious alloys, special cements, synthetic polymers, porcelain, and glass‐ceramics, all of which must withstand the rigors of the oral environment (see also Prosthetic and Biomedical Devices). The accessory materials needed in the fabrication procedures include synthetic polymers, synthetic and natural gums and waxes, hydrocolloids, gypsums, and refractories. These materials are used by ca 170,000 practicing dentists in the United States (1992) and more than 8,500 commercial U.S. dental laboratories employing ca 40,000–50,000 technicians.