Charles E. Brukl

Thickness and marking characteristics of occlusal registration strips

T he practice of clinically marking and evaluating occlusal patterns or “high spots” has been empirical to dentistry. Dentists have used ink, silk ribbon with colorants, colored paper, plastic strips with colorants, and wax to visualize occlusal contacts. Little has been reported on the accuracy of the registration materials. Dawson’ suggested that thin silk ribbon was the most efficient method of marking interferences. Halperin et a1.2 studied marking materials to determine thickness, strength, and plastic deformation. They concluded that occlusal registration strips should be less than 21 pm thick and capable of plastic deformation. In addition, they stated that paper was a brittle material and therefore should not be used. Clinical observations revealed that commercially available occlusal registration materials produced a wide range of marks from small, sharply defined areas to broad, ill-defined smudges. 3-5 Information is needed on the variables that affect the size of the mark. Manufacturers’ designations of registration strip thickness presently are not standardized. Descriptions such as microthin, extra thin, extra-extra thin, and thick have only a rough qualititative relationship to the true strip thickness or mark size. Depending on the physical properties of a registration strip, a product may mark the actual contact area or generate a misleading smear or smudge in a noncontacting area. The purpose of this study was to investigate the relationship between registration strip thickness and area of the mark produced under dry laboratory conditions.

Compressive strengths of a new foil and porcelain-fused-to-metal crowns.

This study evaluated the compressive strengths of Renaissance foil and porcelain-fused-to-metal crowns on polycarbonate test dies. Both crown types were veneered with feldspathic porcelain. The compressive strength of the PFM crowns, 1895 +/- 317 N, was statistically higher than that of the Renaissance foil crowns, 1060 +/- 89 N. Comparison of the Renaissance foil crowns compressive strength to published biting forces indicated that the Renaissance crown should function without difficulty.

Marginal distortion of cast restorations induced by cementation

Eleven full veneer crowns were directly constructed on brass stylized dies. Crown marginal openings and vertical heights were measured before and after cementation with zinc phosphate cement. The following results were established. The marginal opening of complete veneer gold crowns increased during cementation. The vertical heights of well fitting crowns also increased significantly after cementation.

Influence of gauging water composition on dental stone expansion and setting time

N umerous studies have disclosed that many substances, when added to the calcium sulfate hemihydrate powder or to the gauging water, alter the setting times and expansions of gypsum products.‘-” Only one study has examined the effects of use of different gauging waters. Deionized water and Oklahoma City tap water yielded approximately equal expansions.” In many locations there is a broad range of gauging waters available for mixing with gypsum: tap, softened, deionized, and distilled. It would be desirable to know whether the choice of water significantly alters the setting times and expansions of gypsum products. When setting time must be reduced, “slurry water” is most commonly used by both dentists and technicians. It would be desirable to know whether the action of the slurry is significantly changed by the water from which it is prepared. A complication arises from the looseness of the definition of slurry water. The term seems to be variously understood to mean either the clear, saturated supernate or the cloudy suspension of particulate gypsum, even though the chemical term slurry unequivocally means a mechanical mixture or suspension. The purpose of this study was to determine the changes in setting times and expansions of gypsum products caused by use of four different gauging waters (distilled, deionized, softened, and naturally hard) and by use of these same waters either saturated with gypsum (supernate) or containing a particulate suspension of gypsum (slurry).

Surface wettability modification of poly(vinyl siloxanes) with nonionic surfactants

Abstract Poly(vinyl siloxanes) are widely used as dental impression materials because of their superior dimensional accuracy and stability in comparison with the other elastomeric impression materials. However, the materials have low surface free energies, making them difficult to wet with the gypsum slurries which are subsequently poured into the impressions. The resultant bubble entrapment discourages their use. In this study, polyy(vinyl siloxane) impression materials were modified by the incorporation of members of a homologous series of nonylphenoxypoly(ethyleneoxy)ethanols and selected surfactants of substantially different chemistries. Contact angles with saturated aqueous gypsum and bubble counts in critical impressions were determined. The resultant contact angles fit a bilinear regression curve when angle is plotted against surfactant HLB number. For members of the homologous series, contact angles for surfactant blends were as predicted by the results for the pure components. Blends of surfactants with markedly different chemistries produced neither a clear minimum contact angle nor a bilinear curve of contact angle versus HLB. For the optimal surfactant, the improved wetting was substantially unaffected by rinsing. The improved wettability for optimally surfactant modified elastomer was reflected by the marked decrease in bubble counts in gypsum pours. The surfactant addition did not significantly degrade either dimensional accuracy or stability.

Film thickness of disclosing wax

lhe fitting of a removable partial denture framework or a metal crown against tooth structure can be facilitated by the aid of disclosing wax.’ This soft wax material is placed on surfaces of restorations that contact the teeth. After insertion and removal of the restorations, interferences will be visible as bright spots (Figs. 1 and 2). When the interferences are removed, the fit of the restoration is improved. Thus, the advantage of disclosing wax is its ability to provide a three-dimensional record of tooth-restoration contacts. The purpose of this investigation was to measure the film thickness of disclosing wax. If this wax has a film thickness greater than that of zinc phosphate cement (25 to 40 pm),2 it seems that its use would be ineffective for fixed restorations. If, however, the film thickness is less than that of zinc phosphate cement, it then would be effective in demonstrating the fit of castings.