Apparent bond strength of nonnoble alloy-porcelain combinations.

The apparent bond strengths of four porcelains and five nonnoble alloys were determined. On the basis of the data, the following conclusions can be drawn: The use of Vita, Ceramco, or Will-Ceram porcelains with Rexillium III, Pentillium, or Bak-On-NP alloy gave similar bond strength values. With the exception of Unibond alloy, the bond strength values obtained with Biobond porcelain were lower than those obtained with the other porcelain materials. The ceramometal bond strength values obtained with Unibond alloy were similar with all of the porcelains tested. The continued availability of a bewildering array of new alloys and porcelains suggests the urgent need for research designed to determine the bonding mechanisms and compatibility of various porcelain-alloy combinations. The data from this investigation provide criteria for the rational selection of bond strength-compatible porcelains and alloys for clinical use.

Effect of metal conditioners on porcelain-alloy bond strength.

The effect of three metal conditioners on the apparent bond strength of a single porcelain to four alloys was evaluated. On the basis of the bond strength data the following conclusions can be drawn. The use of metal conditioners provided no improvement in the apparent porcelain-alloy bond strength of Biocast and Biobond alloy. The use of Unibond alloy with its recommended conditioner Uniseal gave lower bond strength values than Unibond without the conditioner. With Rexillium III alloy the use of Uniseal gave the highest bond strength values, but these were statistically equal to those obtained with the recommended coating agent (Jeneric bonding agent). With the exception of Rexillium III alloy, it appears that coating agents may have a function other than bond strength improvement. In light of the continued marketing of new alloys, bonding agents, and porcelains, further research is needed to determine the mechanism of action of bonding agents as well as the porcelain-bonding agent-alloy interaction of various commercial products. Studies designed to address these topics are in progress.

Preliminary observations on clinical use of a base metal casting alloy.

A study was conducted to develop a laboratory technique and to evaluate the clinical efficacy of a base metal casting alloy. Slight modification of recommended investing procedures is required to produce consistently well-fitting castings with the test alloy. After 12 months of clinical service, the test alloy did not differ from the control alloy in tarnish, untoward gingival response, resistance to abrasion, or tooth sensitivity.

The effect of superficial colorant and glaze on the surface texture of vacuum-fired porcelain.

The surface smoothness of dental porcelain after the use of various staining and glazing techniques was examined by scanning electron microscopy. The autogenous glazing technique produced a smooth, slightly pitted surface that has been shown to be biologically acceptable and should be used for restorations where the addition of colorant is unnecessary (Fig. 2). If application of glaze powders is desired, the use of the high temperature-induced glazing technique produces a smooth surface (Fig. 4). The use of colorant as the inducing agent does not produce the same degree of smoothness as do the glaze powders (Fig. 3). For teeth that require minimal shade modification, a thin slurry of glaze followed by the colorant modification should be added too unglazed porcelain and air fired to a high temperature-induced glaze (Fig. 6). For teeth that require major color modifications, colorant fixation at 1,500 degrees F followed by a high temperature induced glaze is warranted. The use of the low temperature (1,500 degrees F)-induced glaze should be restricted to cases where high-temperature firing may be detrimental (Fig. 11).

Soldering nonnoble alloys.

Successful presoldering of nonnoble alloys is variable at best. Under controlled conditions of joint gap distance, investing, and soldering, more than one third of the soldered joints are likely to fail. Furthermore, the recorded strength of successful solder joints was inconsistent. Improved heat application and controlled oxidation are required. Until new materials and/or techniques are developed, the soldering of nonnoble alloys prior to the application of porcelain is unwarranted.

The effect of cooling rate on the apparent bond strength of porcelain-metal couples.

The effects of cooling conditions on the apparent bond strength of a dental porcelain fused to a case substructure were studied. Under the conditions of this investigation slow cooling of the porcelain-metal composite in an oven or rapid cooling in an ice chest from the maturation temperature of the porcelain resulted in the highest values of apparent bond strength. However, additional factors must be considered in the selection of a particular cooling method. From the present data it appears that the most practical procedure for cooling a ceramometal restoration is under a protective cover since it provides the least risk to the integrity of the porcelain-alloy bond and the surface of the porcelain.