The International Journal of Prosthodontics, 03/1993

Castings simulating a maxillary central incisor coping were fabricated from five representative high-palladium alloys, using burnout temperatures of 1,400 degrees F and 1,500 degrees F, with a carbon-free phosphate-bonded investment. Three castings of each alloy were individually prepared at each burnout temperature. Each casting was sectioned into two specimens, and one specimen was subjected to simulated porcelain firing heat treatment. Polished and etched specimens in as-cast and heat-treated conditions were examined with optical and scanning electron microscopes. Mean values of Vickers hardness (1-kg load) were determined for each alloy and condition. It was observed that the simulated porcelain firing cycles caused major changes in as-cast bulk microstructures for the three first-generation alloys, while only subtle alterations were observed for the two second-generation alloys. In addition, complex regions associated with oxidation processes were found near the surfaces of all the heat-treated alloys. While the as-cast microstructure and the hardness of each alloy did not vary appreciably for the two burnout temperatures, the incidence of hot tearing in one first-generation alloy was substantially reduced at the lower burnout temperature. Statistically significant decreases in hardness generally occurred in the high-palladium alloys after the simulated porcelain firing cycles, but the relatively small changes (usually 10% or less) should not have any clinical significance. Other clinically relevant applications are also discussed.

Porcelain laminate veneers are affected by the color of prepared abutment teeth, so that if these teeth are discolored they may cause problems in a restoration. This paper describes how complementary color theory is applied to resolve this situation and provide a more esthetic restoration. Tooth discoloration is classified into four base colors: orange, brown, blue-purple, and reddish gray, and a shade selection technique and a veneer fabrication technique are presented.

This study investigated the three-dimensional nature of crown fit and the effects of adjustment and luting. Standardized preparations were made on extracted premolars and impressions and dies made. Complete-coverage castings were fabricated using base metal alloy. The castings were placed on their respective teeth and measurements made. The castings were then adjusted using a silicone disclosing medium and remeasured. They were then assigned to one of five luting agent groups and cemented. A relative term describing tilting was defined. Casting adjustment decreased tilting and cementation increased tilting. Resin cements tilted castings significantly more than did zinc phosphate, glass-ionomer, or polycarboxylate cements.

This study investigated the effects of hue and value of mold materials on the polymerization of resin composite inlays fabricated by an indirect process. Three colors of molds were used, and 10 specimens each of three resin composite materials were light polymerized on each of the die materials for each test. The specimens were postirradiation heat polymerized. Compressive strength, flexural strength, Knoop hardness, and bond strength to enamel and dentin were measured. Although differences in properties between specimens polymerized on different die materials were not always significant, the values obtained from the white mold were highest in all tests followed by those obtained on the gray and then the black molds. Correlations (r2) between lightness or value and compressive and flexural strength, hardness, and bond to enamel and dentin values were greater than 0.90. Die color and value appear to be important factors influencing the properties of indirect resin composite inlays even though they are heat polymerized after light activation.

This paper reports on 76 consecutively placed In-Ceram restorations (61 complete-coverage crowns and 15 fixed partial dentures). Their survival rates were determined using the Kaplan-Meier method. During the 35-month observation period no crown failures occurred, a five-unit fixed partial denture fractured, and another fixed partial denture was removed because of periodontal complications. Thus, In-Ceram complete-coverage ceramic crowns are apparently indicated for anterior and posterior teeth. A larger number of subjects must be studied to assess the indication for all-ceramic fixed partial dentures.

Eighty-five resin bonded prostheses were evaluated in a retrospective study over a 15-year period. All had been in function for at least 4.5 years. Multifactorial variables were studied to ascertain their effect on debonding and the health of the oral tissues. The results showed: (1) the caries rate of the retainer teeth was 6%, (2) the mean gingival indices for the prostheses were significantly higher (P > .0001) than those of the remaining dentition, (3) 61% of the restorations had not debonded (if failure resulting from trauma was not included, the incidence of debonding dropped to 19%), and (4) all patients liked their prostheses.

The various clinical and laboratory procedures for use of auxiliary prefabricated metal screw retention, castable plastic telescopic, and custom laboratory-fabricated systems are presented as adjuncts to implant-supported restorative procedures. These devices aid in the fabrication of predictable and retrievable screw-retained, fixed-detachable implant-supported prostheses for various conditions and combinations of support. Ancillary screw systems are also useful in solving cosmetic problems when implant placement compromises this goal.

Patients receiving artificial crowns and fixed partial dentures at a prosthodontic clinic were examined 18 to 23 years after treatment. The long-term results were good, especially for the metal ceramic restorations: 79% remained unchanged and only 3% had been removed. The success rate for the gold-resin restorations was less favorable: 43% remained unchanged and 33% had been removed. The use of one cantilever extension unit had not negatively influenced the results for the fixed partial dentures. Generally, those abutment teeth that had been removed during the observation period had received previous endodontic treatment before restorations had been placed. Endodontic complications on abutment teeth were more frequent in the mandible than in the maxillae.

Molar teeth were prepared to a standardized cylindric form using a lathe. Dicor crowns were luted on these preparations using zinc phosphate, glass-ionomer, and resin cements. The crowns were thermocycled and subjected to fracture loading to compare the effect of the different luting agents on fracture strength. Five finishing lines were used to determine if resin cement and associated bonding procedures could counteract the negative effect certain finish lines produce on all-ceramic crowns. When resin cement was used in conjunction with restoration and tooth precementation bonding treatments, the crowns were significantly stronger than when glass-ionomer or zinc phosphate cements were used. No difference in strength was found between the five finish lines when the crowns were cemented with resin and associated bonding procedures.

This work compared the tensile strength of two glass compositions with published values of currently available dental porcelains. The influence of several variables, such as air and vacuum firing, firing temperature, surface roughness, immersion in water, and the inclusion of filler particles, on the inherent strength of the glass compositions is also discussed. The authors developed a glass frit having a tensile strength of 102.4 MPa as determined by the biaxial flexure technique. This value compares favorably with the reported strength of commercial brands of feldspathic porcelains. The strength of this glass was not significantly reduced as a result of surface abrasion or immersion in distilled water.

This study attempted to bond glass-ionomer and zinc phosphate cements to a dental ceramic with the aid of a coupling agent and appropriate surface preparation. Four luting agents were shear tested after thermocycling: a glass-ionomer cement with three titanate coupling agents, three zircoaluminate coupling agents, and a silane coupling agent; a light-activated glass-ionomer cement with a silane coupling agent; a zinc phosphate with a titanate coupling agent; and the manufacturer's resin/silane as control. The light-activated glass-ionomer cement/silane coupling agent had the highest mean strength (3.8 MPa) followed by the control (3.7 MPa) and glass-ionomer/carboxy zircoaluminate (2.4 MPa). These measures were significantly (P .05) higher than those of glass-ionomer/silane, zinc phosphate, and other lower ranking groups. Light-activated glass-ionomer cement was successfully bonded to dental ceramics. Carboxy zircoaluminate showed good results for bonding conventional glass-ionomer cement.

The purpose of this investigation was to evaluate the tensile bond strength of one type of impression material adhesive to three different custom tray materials: one autopolymerizing (Fastray) and two light-polymerizing (Triad and Extoral). The effect of different surface treatments was evaluated for each of the materials. No significant difference in impression material adhesive mean tensile bond strengths was exhibited for any of the materials as the result of variations in the surface treatment. It was observed that the Triad tray material groups, with different surface treatments, exhibited significantly higher impression material adhesive mean tensile bond strengths than the autopolymerizing tray resin and the Extoral light-polymerizing material.