The effect of added particles on the properties of Ag3 Sn-additive amalgams.

Physical and chemical properties of amalgam alloys containing varying amounts of copper were evaluated. Evidence presented refutes the theory of physical strengthening due to the addition of silver-copper by its eutectic. Results suggest that reactive copper could be more advantageously added to the system by using fewer copper additive particles; these particles may need to have a greater copper content that those used in Dispersalloy.

Selection of a resin system for anterior fracture treatment.

The tensile strength of the bond formed between etched bovine enamel and selected resin systems was evaluated; also, the need for a resin pulpal barrier was examined. Results indicate that the BIS-GMA unfilled primer is unnecessary for strength or as a pulpal protectant. The large scatter of results substantiates the clinical hypothesis that the effectiveness of the acid etch is highly variable.

Laser fusion of selected dental casting alloys.

Laser-fused precious, nonprecious, and mixed metal welds were investigated for optimum weld energy requirement as determined by tensile strength tests. These strengths were compared to soldered unions. Laser fusion is as good as, or better than, unions created by conventional dental joining methods.

Loading rate and temperature as variables in amalgam bending.

Three commercial dental amalgams of known dissimilar clinical properties were evaluated in pure blending at widely different loading rates and temperatures. Comparative data of fracture stress at 140 F rank these alloys according to their clinical fracture resistance; the phenomenon of creep may account for early marginal fracture prior to corrosion-induced fracture.

Adherence of ceramic coatings on chromium-cobalt structures.

A method has been developed for the consistent adherence of flame-sprayed ceramic coatings to Vitallium. The critical step involves etching the metal by the anodic polarization technique. This procedure allows complex geometrics to be corroded evenly, and, by suitable choice of etching solution and conditions, enables any metal to be substituted. The bond is capable of sustaining more severe deflections than are experienced during intraoral function. Despite the number of cracks generated during testing, the ceramic layer remains intact. The ceramic-metal bond is mechanical. The corroded surface provides greater surface area, thus permitting a number of retention sites. Analysis of the ceramic microstructure finds it to be suitable for tissue ingrowth.

Amalgam containing nickel or tungsten dispersions. I.

Wetting tests were conducted to determine compatability between select dispersion powders and Ag3Sn. Subsequently, a method was perfected for incorporating nickel or tungsten powder into the Ag3 Sn ingot. Initial studies reveal good distributions of the dispersed phase in the ingots and the comminuted alloys, after amalgamation, appear to retain their normal working characteristics.

Amalgam containing nickel or tungsten dispersions. II.

The technique of injecting dispersed phase particles into an Ag-Sn melt followed by rapid quenching was utilized. Results of this investigation show that a marked improvement of the brittle amalgam alloy occurs.

Improving the fracture resistance of dental ceramic.

A time-temperature sequence for optimally strengthening dental ceramic by ion exchange was investigated. Stress relaxation occurs at higher temperatures and/or longer times. Improved strenghts are obtained in a reasonable period of time that could be used for clinical application.

A flexural method for evaluation of metal-ceramic bond strengths.

A test technique is presented for evaluating metal-ceramic bond strengths. The test piece consists of a four-point loaded metal beam with porcelain bonded to the central tension side of the beam. The test produced failures at predictable locations and was able to differentiate between metal surface treatments.

Color and translucency changes during and after curing of esthetic restorative materials.

OBJECTIVES: This study was conducted to evaluate various types of contemporary resin composites and glass ionomer restorative materials for color differences that occur during light curing and after submersion in water. Additionally, translucency was evaluated through the use of a translucency parameter for each of these materials at these times. METHODS: A translucency parameter was calculated from observed colors of 2 mm thick layers of light, medium and dark shades of popular restorative materials on black and white backings. The colors of these materials were also calculated, based on Kubelka-Munk theory, for layers on a B2 shade backing. Repeated measures analyses of variance were used to identify statistically significant factors for color differences and translucency parameters. RESULTS: A statistically significant interaction was found between the products, shades and time intervals or times studied for both color difference and translucency parameter. There is relatively high variability in both lightness and translucency changes among these popular products, with some products increasing and others decreasing in these parameters with curing and subsequent water submersion. SIGNIFICANCE: Kubelka-Munk theory can be used to calculate the color of a layer of material on a backing other than those used to determine the Kubelka-Munk coefficients, thereby increasing the efficiency of research into the optical properties of esthetic restorative materials. The relatively large optical changes which occur as popular esthetic restorative materials are cured and subsequently submersed in water indicate that these changes should be taken into account during any initial clinical appearance match at placement of the unset material.