Comparison of Regular and Speed Sintering on Low-Temperature Degradation and Fatigue Resistance of Translucent Zirconia Crowns for Implants: An In Vitro Study (original) (raw)
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2018
This <em>in vitro</em> study focused on investigating the fatigue resistance of veneered zirconia molar crowns with different veneering ceramic thicknesses, simulating the relative wear depths under simulated cyclic loading. A mandibular first molar was prepared and then scanned using computer-aided design/computer-aided manufacturing (CAD/CAM) technology to fabricate 32 zirconia copings of uniform 0.5 mm thickness. The manufactured copings then veneered with 1.5 mm, 1.0 mm, 0.5 mm, and 0.0 mm representing 0%, 33%, 66%, and 100% relative wear of a normal ceramic thickness of 1.5 mm. All samples were thermally aged to 6000 thermo-cycles for 2 minutes with distilled water between 5 ˚C and 55 ˚C. The samples subjected to cyclic fatigue and fracture testing using SD Mechatronik chewing simulator. These samples are loaded up to 1.25x10⁶ cycles or until they fail. During fatigue, testing, extensive cracks were observed in samples with 0.5 mm veneering layer thickness. Veneerin...
Clinical Oral Investigations, 2023
Objectives The aim of this study was to evaluate the effect of cyclic mechanical loading on the fracture resistance of 3D-printed zirconia crowns in comparison to milled zirconia crowns. Materials and methods Monolithic zirconia crowns (n = 30) were manufactured using subtractive milling (group M) and 3D additive printing (group P). Nine samples of each group were fractured under one-time loading while the other 6 samples were subjected to cyclic loading for 1.2 million cycles before being subjected to one-time loading until fracture. Scanning electron microscope (SEM) fractographic analysis was carried out on fractured fragments of representative samples. Results The mean for fracture resistance of group M was 1890 N without cyclic loading and 1642 N after being subjected to cyclic loading, and they were significantly higher than that of group P (1658 N and 1224 N respectively). Conclusions The fabrication technique and cyclic loading affect the fracture resistance of zirconia crowns. Although the fracture resistance values for the 3D-printed crowns were lower than those of the milled, still they are higher than the masticatory forces and thus could be considered being clinically acceptable. Clinical relevance Concerning fracture resistance, 3D-printed crowns can withstand the masticatory forces for the long term without any cracks or failure.
Dentistry Journal
(1) Background: This study compared the fracture resistance of additively manufactured monolithic zirconia and bi-layered alumina toughened zirconia crowns on implants. (2) Methods: Maxillary model with a dental implant replacing right second bicuspid was obtained. Custom abutments and full-contour crowns for additively manufactured monolithic zirconia and bi-layered alumina reinforced zirconia crowns (n = 10) were fabricated. The crowns were cemented to implantsupported zirconia abutments and the assembly fixed onto resin blocks. Fracture resistance was measured using a universal testing machine at a crosshead speed of 2 mm/min. A Kruskal-Wallis test was used to analyze the data. (3) Results: Although additively manufactured monolithic zirconia crowns demonstrated a higher mean fracture resistance than bi-layered alumina toughened zirconia crowns, statistical analysis revealed no significant difference in fracture resistance between the two groups. All specimens fractured at the implant-abutment interface. (4) Conclusions: Additively manufactured bi-layered alumina toughened zirconia crowns demonstrated similar fracture resistance to additively manufactured monolithic zirconia crowns when cemented to implant-supported zirconia abutments.
Journal of Advanced Clinical & Research Insights
Purpose: Core materials in metal-ceramic crowns have metal, and all-ceramic crowns may have a zirconia substructure. These core materials are used to reinforce the strength of the prosthesis. The various metal substructures were compared to study the fracture strength and bond failure between the core structure and the layered ceramic. Digital metal laser-sintered (DMLS) substructures can be fabricated to thinner sections of up to 0.3mm. In conditions where there is a need for lesser reduction of tooth structure, the DMLS structures can be a viable alternative to zirconia substructures. The conducted study was intended to evaluate the fracture strength in ceramic crowns with DMLS and zirconia cores. Materials and Methods: A prepared tooth with standardized dimensions was generated using computer-aided design software and milled in metal. Impression of die was made, and 40 epoxy resin dies were prepared. Then, 20 DMLS substructures (Group I) and 20 Zirconia substructures (Group II) were made following in which ceramic veneering was done. Group I is divided into Group I(A) (10 crowns for the load to fracture) and Group I(B) (10 crowns for fatigue test). Group II is divided into Group II(A) (10 crowns for the load to fracture) and Group II(B) (10 crowns for fatigue test). All crowns were cemented to their respective dies using Type I glass ionomer luting cement. All crowns were subjected to thermocycling (5000 cycles) and Group I(A) & Group II(A) crowns were tested for load to fracture , and observational analysis of fracture pattern was carried out. The data were analyzed using SPSS software. Mean and standard deviation were estimated from the samples of each test group. Descriptive statistics was used to find the mean and standard deviation variables. Levene's test was used to test the equality of variances for independent "t" test. Results and Conclusion: The amount of load to fracture for Group I(A) was high with 3163.96 ± 525.27 and that for Group II(A) was 2077.1 ± 388.97. The difference between the mean was found statistically significant (P=0.005). Both DMLS crowns group I(B) and Zirconia crowns group II(B) showed good fatigue resistance on observational examination and there is no evidence of no cracks or fracture at the end of fatigue test. Hence, crowns from both groups expected to resist crack propagation when used clinically. Hence, it may be concluded that mean load to fracture between Groups I(A) and Group II(A) significantly differs.
2021
Background Short-time sintering may offer advantages including saving time and energy but there is limited evidence on the effect that altering sintering time has on the accuracy of monolithic zirconia crowns. The purpose of this in vitro study was to investigate the effect of shortened sintering time on the marginal and internal t of 3Y-TZP (three mol% yttria-stabilized tetragonal zirconia polycrystal) and 4Y-TZP (four mol% yttriastabilized tetragonal zirconia polycrystal) monolithic crowns. Methods Sixty monolithic zirconia crowns were fabricated for the maxillary rst molar tooth on the prefabricated implant abutment. Groups were created according to the material composition: 3Y-TZP Generation 1 (alumina wt; ≤0.5%, < 15% cubic phase), 3Y-TZP Generation 2 (alumina wt; ≤0.05%, < 15% cubic phase) and 4Y-TZP (alumina wt; ≤0.05%, > 25% cubic phase). Two different sintering protocols were performed: same nal sintering temperature (1500°C) and various rates of heating (10°C/min and 40°C/min), cooling down speed (-10°C/min and − 40°C/min), holding time (45 and 120 minutes), and total sintering time (approximately 2 and 7 hours, respectively). The marginal and internal t of the crowns were determined using the silicone replica technique. Comparisons between groups and sintering times were analyzed using two-way ANOVA. Pairwise multiple comparisons were performed using the t-test (p < 0.05). Results The mean marginal gap values of 4Y-TZP zirconia revealed statistically signi cant increase for the speed sintering protocol (p < 0.0001), while no difference was observed between the sintering protocols for the mean marginal gap values of 3Y-TZP groups. Conclusions Although all groups showed clinically acceptable gap values (<120 µm), altering the sintering time had an effect on the marginal t of the crowns manufactured from 4Y-TZP zirconia. Shortening the sintering time may lead to differences within clinically acceptable limits. The manufacturer's recommendations according to material composition should be implemented with care.
Coatings
This study evaluated the effects of the sintering temperature on Vickers microhardness and three-point flexural strength values of two multi-layered zirconia materials. Multi-layered zirconia systems with four distinct layers were selected: DD cube ONE ML (4Y-TZP) and DD cubeX2 ML (5Y-TZP). In total, 96 plate-shaped A2-shade specimens were obtained using individual layers of these two zirconia materials. The individual layers were then divided equally into batches with three different sintering temperatures (1300, 1450, and 1600 °C), and the Vickers microhardness was assessed. Another group of 72 bar-shaped specimens was prepared from the same materials. These were similarly divided into three different sintering temperatures, and the flexural strength was assessed. SEM was used to conduct fractographic analyses. The data were analyzed using SPSS 24.0 software with a p-value < 0.05. The microhardness and flexural strength of 4Y-TZP were higher than those of the 5Y-TZP at all the ...
Sintering Strategies for Dental Zirconia Ceramics: Slow Versus Rapid.
Purpose of Review Advances in zirconia ceramics have expanded their application in dentistry, necessitating faster delivery of zirconia-based restorations. With the introduction of high translucency grades of zirconia ceramics, the rapid sintering strategies that aim to reduce processing times can have a central impact on clinically relevant properties. The present review has surveyed the available literature evaluating the properties of rapidly sintered dental zirconia ceramics. Recent Findings Recent studies emphasize the evolution of sintering protocols for zirconia ceramics, especially highlighting differences between conventional sintering (CS) and rapid methods like speed (SS) and high-speed sintering (HSS). These modern rapid sintering techniques transform the microstructure of zirconia ceramics, impacting its translucency, flexural strength, and aging resistance. These properties exhibit variability based on zirconia type and chosen sintering process, with HSS showing particular promise. Summary Rapid sintering protocols offer efficient alternatives to traditional zirconia ceramic processing, with benefits in cost and time. Despite the recent findings, discrepancies persist within zirconia generations, calling for further standardization and investigation.
In vitro performance of full-contour zirconia single crowns
Dental Materials, 2012
d e n t a l m a t e r i a l s 2 8 ( 2 0 1 2 ) 449-456 Zirconia CAD/CAM Veneering porcelain Full-contour Single crown a b s t r a c t Objectives. Zirconia based restorations exhibited high failure rates due to veneering-porcelain fractures. Milling to full-contour might be an alternative approach for zirconia restorations. The aim of this study was to evaluate full-contour zirconia crowns in terms of light-transmission, contact wear (restoration and antagonist) and load-bearing capacity. Powder build-up veneered zirconia substructures and CAD/CAM-veneered zirconia substructures served as controls.
The Eurasia Proceedings of Health Environment and Life Sciences, 2023
An ex-vivo study aimed to investigate the fracture resistance of monolith-single layer zirconia of 1.5 mm thickness for dental molar crowns concerning simulating failure behavior under simulated cyclic loading with an extended lifetime of up to 5 million cycles. Sixteen molar crowns were scanned after preparation through computer-aided manufacturing (CAD/CAM) technology to recreate the zirconia crowns, which have a uniform occlusal surface thickness of 1.5 mm. All the samples went through thermal aging by putting them through 6000 thermo-cycles for 3 minutes with the use of distilled water at a temperature range between 5 ˚C and 55 ˚C. All samples were placed under cyclic fatigue loading using the SD Mechatronik chewing simulator and afterward subjected to two-dimensional movements for almost five million cycles. Tests were carried out in distilled water at room temperature. The sample was observed, tested, and photographed every five hundred thousand cycles. The surface cracks were observed within the vicinity of the contact area only and extended with increasing cycles. Minor wear depth was observed in the crowns relative to the damage observed in the Ni-Cr alloy steel flat indenter. No chipping or complete failure was observed in all tested samples which suggested that full-contour zirconia crowns are good for extending the long life service of dental restorations.