Abstract
Aim: To evaluate the retention of Y-TZP crowns cemented in aged composite cores ground with burs of different grit sizes. Methods: Sixty composite resin simplified full-crown preparations were scanned, while 60 Y-TZP crowns with occlusal retentions were milled. The composite preparations were stored for 120 days (wet environment-37°C) and randomly distributed into three groups (n=20) according to the type of composite core surface treatment. The groups were defined as: CTRL (control: No treatment), EFB (extra-fine diamond bur [25μm]), and CB (coarse diamond bur [107μm]). The grinding was performed with an adapted surveyor standardizing the speed and pressure of the grinding. The intaglio surfaces on the crowns were air-abraded with silica-coated alumina particles (30 μm) and then a silane was applied. The crowns were cemented with self-adhesive resin cement, thermocycled (12,000 cycles; 5/55°C), stored (120 days) and submitted to aretention test (0.5mm/min). The retentive strength data (MPa) were analyzed using one-way analysis of variance and Tukey test, as well as Weibull analysis. Failures were classified as 50C (above 50% of cement in the crown), 50S (above 50% of cement in the substrate) and COE (composite core cohesive failure). Results: No statistical difference was observed among the retention values (p=0.975). However, a higher Weibull modulus was observed in the CTRL group. The predominant type of failure was 50S (above 50% of cement in the substrate composite). Conclusion: The retention of zirconia crowns was not affected by grinding using diamond burs with different grit sizes (coarse/extra-fine) or when no grinding was performed.
Highlights
Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics have been increasingly used over the years because of their superior flexural strength, flexural toughness, and phase-transformation toughening mechanism compared with traditional materials[1]
Amaral et al.[4] showed that the retention of Y-TZP crowns is higher when cemented to dentin in comparison with composite resin
The most common type of failure was 50S (Figure 3)
Summary
Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics have been increasingly used over the years because of their superior flexural strength, flexural toughness, and phase-transformation toughening mechanism compared with traditional materials[1]. To improve the bond strength of zirconia to resin cements, tribochemical air-abrasion is commonly employed This technique uses alumina particles coated with silica to generate micromechanical retention and a reactive surface for silanization[1]. Significant loss of coronal tissue is commonly observed in endodontically treated teeth, resulting in the need for post-retained restorations for both aesthetic and functional rehabilitation[3] These restorations can be performed with prefabricated fiber-post cementation followed by a core build-up with composite resin[3]. During the clinical treatment with prosthetics, dentists will often use provisional restorations in patients before permanent restoration can be performed During this period, the composite core build-up can be exposed to moisture, variances in pH and temperature[6] and temporary luting cements[7]. Surface alterations of the composite core could be required to improve their adhesion to resin cements and for optimal crown retention[6]
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