PubMed · 13266288
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H VAN THIEL. 1955. [Removable bridge construction].. https://pubmed.ncbi.nlm.nih.gov/13266288/
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STATEMENT OF PROBLEM: Dual-arch trays are often used by the dentists to make crown impressions of opposing quadrants simultaneously. Metal and plastic trays are available, but little is known about the accuracy of the impressions and resultant working dies. PURPOSE: The purpose of this study was to conduct a clinical trial to compare the accuracy of gypsum working dies made from impressions with metal dual-arch, plastic dual-arch, and complete-arch custom trays. MATERIAL AND METHODS: Eight patients requiring a posterior single tooth implant restoration were selected on the basis of inclusion and exclusion criteria. A customized abutment was measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) by use of a measuring microscope. Three polyvinyl siloxane impressions were made of the abutment with a complete-arch custom tray, a plastic, and a metal dual-arch tray. Each impression was poured with type IV improved dental die stone. The diameter (buccolingual and mesiodistal), from gingivoaxial to gingivoaxial point angle, and height (occlusogingival), gingivoaxial to occlusoaxial point angle of the abutment standard was determined by measuring each dimension several times to obtain a mean. These 3 mean values served as the controls and were compared with the same measurements of the gypsum dies generated by the 3 different impression techniques. The patient was asked to rank the 3 impressions in order of overall comfort. A multivariate repeated measures single factor ANOVA was used in the statistical analysis (alpha=.05). When main effects were significant, a pairwise comparison of mean values was conducted with Bonferonni adjustment for multiple comparisons. RESULTS: There were no significant differences in die accuracy among the 3 trays for the mesiodistal (3.507 mm) and occlusogingival (3.584 mm) dimensions of the implant abutment. Dies were smaller than the standard for these 2 dimensions and larger in the buccolingual dimension. There was a significant difference in accuracy between the metal and plastic dual-arch trays. The dies produced from the metal dual-arch tray were 20 microm larger than the abutment standard compared with 3 microm larger for the plastic tray. The occlusogingival dimension of the working dies was 30 to 40 microm shorter than the implant abutment. Seven of the 8 patients ranked the plastic dual-arch impression as the most comfortable and the complete-arch custom tray as the least comfortable. CONCLUSIONS: Within the limitations of this study, the dimensions of working dies from a custom tray impression did not differ significantly from those created with dual arch trays. However, working dies from a plastic dual-arch tray were more accurate buccolingually than those from metal dual-arch trays.
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STATEMENT OF PROBLEM: The application of solder material to metal frameworks could affect the porcelain-to-metal failure load and possibly compromise the longevity of porcelain-fused-to-metal crowns. PURPOSE: This in vitro study assessed the influence of solder on the porcelain failure load between metal and porcelain, using crown-shaped specimens. MATERIAL AND METHODS: Forty standardized crown patterns were fabricated on a metal die and cast with noble alloy (Protocol). The specimens were divided into test (soldered, n=20) and control (nonsoldered, n=20) groups. A 2-mm-diameter perforation was produced on the buccal surface of the test specimens, 1.5 mm apical to the junction between occlusal and buccal surfaces. The perforation was repaired with high-fusing white ceramic solder material. All castings were finished with aluminum oxide stones and airborne-particle abraded with 50-microm aluminum oxide at 75 psi of pressure. Two layers each of opaque and dentin porcelain were applied on all specimens. All crowns were subjected to a vertical compressive load with a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The loading apparatus of the device contacted the buccal cusp only. In both control and test groups, 10 crowns were loaded with a stainless steel pin (phase I) whereas the remaining 10 in each group were loaded with a carbon steel pin (phase II). Means of loads at failure were recorded in each group for each pin type and compared (soldered vs nonsoldered) by use of a t test (alpha=.05). RESULTS: Mean failure load for nonsoldered crowns was 349 +/- 63 kgf in phase I and 228 +/- 49 kgf in phase II. Soldered crowns showed a significantly lower failure load (265 +/- 82 kgf [phase I; P<.02] and 154 +/- 108 kgf [phase II; P<.04]) and a greater standard deviation. CONCLUSION: Soldered metal-porcelain crown specimens demonstrated a significantly lower load at failure. Within the limits of this study, it was concluded that solder material might negatively affect porcelain-metal crowns.