Abstract
Aim: To evaluate the influence of cobalt-chromium (Co-Cr) coping fabrication methods and ceramic application on the marginal and internal fit of metal-ceramic crowns. Methods: Co-Cr copings for metal-ceramic crowns were prepared by lost wax casting or CAD-CAM machining of sintered blocks. The fit was analyzed using the silicone replica technique at four assessment points: marginal gap (MG), axial wall (AW), axio-occlusal (AO) angle, and central occlusal (CO) wall. After the initial analysis, the copings were ceramic-veneered with the layering technique, and the fit was again determined. Data were statistically analyzed by paired and unpaired Student’s-t test (α=0.05). Results: Marginal and internal fit before ceramic application according to the coping manufacturing method showed significant differences only at CO (p < 0.001), with milled copings (137.98±16.71 μm) showing higher gap values than cast copings (112.86±8.57 μm). For cast copings, there were significant differences at MG (before 109.13±8.79 μm; after 102.78±7.18 μm) and CO (before 112.86±8.57 μm; after 104.07±10.63 μm) when comparing the fit before and after ceramic firing. For milled copings, there was significant difference only at AO (before 116.39±9.64 μm; after 108.54±9.26 μm). Conclusion: This study demonstrated that the coping fabrication method influenced the internal fit. Ceramic firing maintained or improved the fit of the metal-ceramic crowns. The marginal discrepancy of all restorations, before and after ceramic firing, can be considered clinically acceptable.
Highlights
Metal-ceramic crowns are still commonly used for indirect single-unit restorations and fixed partial dentures[1,2], because they combine the strength of the metal infrastructure and the esthetics provided by the veneering ceramic[3]
Ten copings were obtained by lost wax casting fabricated with a Co-Cr alloy (Fit Cast Cobalt, Talmax, Curitiba, Brazil) with the following composition: 61% cobalt, 30% chromium, 5.9% molybdenum,
Sample size was determined based on previous studies that evaluated the marginal fit of metal-ceramic restorations before and after ceramic firing[17,18,19]
Summary
Metal-ceramic crowns are still commonly used for indirect single-unit restorations and fixed partial dentures[1,2], because they combine the strength of the metal infrastructure and the esthetics provided by the veneering ceramic[3]. Even with the increase in the clinical indications of all-ceramic restorations, metal-ceramic crowns are the treatment of choice for patients with parafunctional oral habits, mainly for the posterior region[2]. It happens because of their high mechanical properties and predictability of long-term clinical outcomes[4]. Indirect restorations with good marginal fit may reduce gingival inflammation and cement dissolution, which are among the most common causes for prosthetic failures, in addiction, excellent internal fit promotes proper seating of the crown, compromising neither the margins nor the preparation[9]
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