Marginal Fit of Metal-Ceramic Copings: Effect of Luting Cements and Tooth Preparation Design.

PURPOSE: To evaluate the effect of the triad finish line design, axial wall convergence angle, and luting cement on the marginal fit of metal copings used in metal-ceramic crowns. MATERIALS AND METHODS: Schematic dies and their respective copings were cast in NiCr alloy. The dies exhibited the following finish line/convergence angle combinations: sloping shoulder/6°, sloping shoulder/20°, shoulder/6°, shoulder/20°. Marginal fit was evaluated under a stereomicroscope, before and after cementation. Copings were air-abraded with 50 µm Al2 O3 particles and cemented with Cimento de Zinco, RelyX U100, or Panavia F cements (n = 10/group). Data were square-root transformed and analyzed by 3-way factorial random effect model and Tukey's post hoc test (α = 0.05). RESULTS: Statistical analysis showed significance for the interactions finish line and convergence angle (p < 0.05), convergence angle and time (p < 0.001), and luting cement and time (p < 0.001). Sloping shoulder/20° provided the highest marginal discrepancy when compared to the other finish line/convergence angle combinations, which were statistically similar among each other. For both convergence angles and for all luting cements, the marginal discrepancy was significantly higher after cementation. Before and after cementation, 6° provided better marginal fit than 20°. After cementation, Panavia F provided higher marginal discrepancy than Cimento de Zinco. CONCLUSION: Lower convergence angle combined with shoulder and a low-consistency luting cement is preferable to cement metal copings.

Shear bond strength of metal-ceramic repair systems.

This study evaluated the shear bond strength of different repair systems to nickel-chromium (NiCr) alloy after storage in water for either 24 hours or six months. One hundred cylindrical specimens (3 mm thick x 9 mm diameter) were fabricated using an NiCr alloy and embedded in a PVC ring, where they received one of five bonding and resin composite repair treatments (n = 20): Clearfil SE Bond/Clearfil AP-X (Group 1), Bistite II DC/Palfique (Group 2), CoJet/Z100 (Group 3), Scotchbond Multi-Purpose Plus/Z100 (Group 4; reference group), and CoJet Sand plus Scotchbond Multi-Purpose Plus/Z100 (Group 5). The specimens were stored in distilled water for 24 hours at 37 degrees C, thermocycled for 1,000 cycles in two baths (at 5 degrees C and 55 degrees C) with a dwell time of 30 seconds for each bath, and stored in distilled water at 37 degrees C for either 24 hours or six months. At 24 hours, Group 3 presented the highest mean values (P < 0.001); at six months, Group 5 demonstrated the highest mean values (P < 0.001). At six months, Group 5 presented a significant increase in shear bond strength (P < 0.001), while Groups 1 and 3 showed a significant reduction (P < 0.001). There were no significant differences between the storage times for Group 2 (P = 0.064) or Group 4 (P = 0.490).

Effect of metal primers on bond strength of resin cements to base metals.

STATEMENT OF PROBLEM: A strong and durable bond between a metal framework and a resin-based luting agent is desired. Metal primers have been shown to be very effective on noble alloys. However, there is insufficient information about their effect on base metals. PURPOSE: The purpose of this study was to evaluate the effect of metal primers on the shear bond strength of resin cements to base metals. MATERIAL AND METHODS: A total of 160 cast commercially pure titanium (CP Ti) and NiCr alloy (VeraBond II) disks were embedded in a polyvinyl chloride ring, and their surfaces were smoothed with silicon carbide papers (320, 400, and 600 grit) and airborne-particle abraded with 50-mum aluminum oxide. Specimens of each metal were divided into 4 groups (n=20), which received one of the following luting techniques: (1) Panavia F, (2) Alloy Primer plus Panavia F, (3) Bistite II DC, or (4) Metaltite plus Bistite II DC. Forty minutes after preparation, all specimens were stored in distilled water at 37 degrees C for 24 hours and then thermal cycled (1000 cycles, 5-55 degrees C). After thermal cycling, the specimens were stored in 37 degrees C distilled water for an additional 24 hours or 6 months before being tested in shear mode. Data (MPa) were analyzed using 3-way ANOVA and the post hoc Tukey test (alpha=.05). Each specimen was examined under an optical microscope (x30), and the failure mode was classified as adhesive, cohesive, or a combination of these. RESULTS: The only significant difference between the Panavia F and Alloy Primer plus Panavia F groups occurred in the NiCr alloy at 24 hours, at which point Panavia F demonstrated superior bond strength compared to Alloy Primer plus Panavia F (P<.001). The Bistite II DC and Metaltite plus Bistite II DC groups were not significantly different. The Bistite II DC and Metaltite plus Bistite II DC groups demonstrated significantly lower bond strength to CP Ti (P<.001) than the Panavia F and Alloy Primer plus Panavia F groups, and significantly lower bond strength to NiCr alloy (P<.001) than Panavia F. The Panavia F (P<.01) and Alloy Primer plus Panavia F groups' bond strength to titanium presented a significant increase (P<.001) in shear bond strength at 6 months. In general, the groups exhibited higher shear bond strength to CP Ti than to NiCr alloy (P<.01). The failure mode was 100% adhesive for all groups. CONCLUSIONS: The metal primers did not promote an increase in adhesive bonding of resin cements to NiCr alloy and to CP Ti. Water storage had no adverse effect on the shear bond strength of the groups. The shear bond strengths to titanium were significantly higher than those to the NiCr alloy.