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Yu Zhang - One of the best experts on this subject based on the ideXlab platform.

  • using glass graded zirconia to increase delamination growth resistance in Porcelain zirconia dental structures
    Dental Materials, 2018
    Co-Authors: Herzl Chai, Adam J Mieleszko, Yu Zhang
    Abstract:

    Abstract Objective Porcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their tendency to delaminate along the P/Z interface remains a practical problem so that assessing and improving the interfacial strength are important design aspects. This work examines the effect of modifying the zirconia Veneering surface with an in-house felspathic glass on the interfacial fracture resistance of fused P/Z. Methods Three material systems are studied: Porcelain fused to zirconia (control) and Porcelain fused to glass-graded zirconia with and without the presence of a glass interlayer. The specimens were loaded in a four-point-bend fixture with the Porcelain Veneer in tension. The evolution of damage is followed with the aid of a video camera. The interfacial fracture energy GC was determined with the aid of a FEA, taking into account the stress shielding effects due to the presence of adjacent channel cracks. Results Similarly to a previous study on PFZ specimens, the fracture sequence consisted of unstable growth of channel cracks in the Veneer followed by stable cracking along the P/Z interface. However, the value of GC for the graded zirconia was approximately 3 times that of the control zirconia, which is due to the good adhesion between Porcelain and the glass network structure on the zirconia surface. Significance Combined with its improved bonding to resin-based cements, increased resistance to surface damage and good esthetic quality, graded zirconia emerges as a viable material concept for dental restorations.

  • a fractographic study of clinically retrieved zirconia ceramic and metal ceramic fixed dental prostheses
    Dental Materials, 2015
    Co-Authors: Zhen Pang, Asima Chughtai, Irena Sailer, Yu Zhang
    Abstract:

    Abstract Objectives A recent 3-year randomized controlled trial (RCT) of tooth supported three- to five-unit zirconia–ceramic and metal–ceramic posterior fixed dental prostheses (FDPs) revealed that Veneer chipping and fracture in zirconia–ceramic systems occurred more frequently than those in metal–ceramic systems [1] . This study seeks to elucidate the underlying mechanisms responsible for the fracture phenomena observed in this RCT using a descriptive fractographic analysis. Methods Vinyl-polysiloxane impressions of 12 zirconia–ceramic and 6 metal–ceramic FDPs with Veneer fractures were taken from the patients at the end of a mean observation of 40.3 ± 2.8 months. Epoxy replicas were produced from these impressions [1] . All replicas were gold coated, and inspected under the optical microscope and scanning electron microscope (SEM) for descriptive fractography. Results Among the 12 zirconia–ceramic FDPs, 2 had small chippings, 9 had large chippings, and 1 exhibited delamination. Out of 6 metal–ceramic FDPs, 5 had small chippings and 1 had large chipping. Descriptive fractographic analysis based on SEM observations revealed that fracture initiated from the wear facet at the occlusal surface in all cases, irrespective of the type of restoration. Significance Zirconia–ceramic and metal–ceramic FDPs all fractured from microcracks that emanated from occlusal wear facets. The relatively low fracture toughness and high residual tensile stress in Porcelain Veneer of zirconia restorations may contribute to the higher chipping rate and larger chip size in zirconia–ceramic FDPs relative to their metal–ceramic counterparts. The low Veneer/core interfacial fracture energy of Porcelain-Veneered zirconia may result in the occurrence of delamination in zirconia–ceramic FDPs.

  • on the interfacial fracture of Porcelain zirconia and graded zirconia dental structures
    Acta Biomaterialia, 2014
    Co-Authors: Herzl Chai, Adam J Mieleszko, Yu Zhang
    Abstract:

    Porcelain fused to zirconia (PFZ) restorations are widely used in prosthetic dentistry. However, their susceptibility to fracture remains a practical problem. The failure of PFZ prostheses often involves crack initiation and growth in the Porcelain, which may be followed by fracture along the Porcelain/zirconia (P/Z) interface. In this work, we characterized the process of fracture in two PFZ systems, as well as a newly developed graded glass-zirconia structure with emphases placed on resistance to interfacial cracking. Thin Porcelain layers were fused onto Y-TZP plates with or without the presence of a glass binder. The specimens were loaded in a four-point-bending fixture with the thin Porcelain Veneer in tension, simulating the lower portion of the connectors and marginal areas of a fixed dental prosthesis (FDP) during occlusal loading. The evolution of damage was observed by a video camera. The fracture was characterized by unstable growth of cracks perpendicular to the P/Z interface (channel cracks) in the Porcelain layer, which was followed by stable cracking along the P/Z interface. The interfacial fracture energy GC was determined by a finite-element analysis taking into account stress-shielding effects due to the presence of adjacent channel cracks. The resulting GC was considerably less than commonly reported values for similar systems. Fracture in the graded Y-TZP samples occurred via a single channel crack at a much greater stress than for PFZ. No delamination between the residual glass layer and graded zirconia occurred in any of the tests. Combined with its enhanced resistance to edge chipping and good esthetic quality, graded Y-TZP emerges as a viable material concept for dental restorations.

Paulo G Coelho - One of the best experts on this subject based on the ideXlab platform.

  • residual stress of Porcelain fused to zirconia 3 unit fixed dental prostheses measured by nanoindentation
    Dental Materials, 2017
    Co-Authors: Vinicius P Fardin, Estevam A Bonfante, Paulo G Coelho, Malvin N Janal, Nick Tovar, Lukasz Witek, Dimorvan Bordin, Gerson Bonfante
    Abstract:

    Abstract Objective To evaluate the residual stress (nanoindentation based on hardness) of fatigued Porcelain-fused to zirconia 3-unit fixed dental prostheses (FDP) with different framework designs. Methods Twenty maxillary 3-unit FDP replacing second-premolar (pontic) were fabricated with conventional framework-design (even-thickness of 0.5 mm and 9 mm2 connector area) and modified framework-design (thickness of 0.5 mm presenting lingual collar connected to proximal struts and 12 mm2 connector area). Connector marginal ridges were loaded and the fractured and suspended FDPs were divided (n = 3/each) into: (1) Fractured zirconia even-thickness (ZrEvenF); (2) Suspended zirconia even-thickness (ZrEvenS); (3) Fractured zirconia with modified framework (ZrModF); (4) Suspended zirconia with modified framework (ZrModS); (5) Non-fatigued FDP with conventional framework design (Control). The FDPs were nanoindented at 0.03 mm (Region of Interest (ROI) 1), 0.35 mm (ROI 2) and 1.05 mm (ROI 3) distances from Porcelain Veneer outer surface with peak load 4000 μN. The Linear Mixed Analysis of Variance (ANOVA) Model on ranks and Least Significant Difference Test on ranks (95%) were used. Results Highest rank hardness values were found for Control group and ZrModS, whereas the lowest values were found in ZrModF. Statistical differences (p = 0.000) were found among all groups except for comparison between ZrModS and Control group (p = 0.371). Hardness between ROIs were statistically significant different (p  Significance Framework-design modification did not influence the residual stress of Porcelain-fused to zirconia fatigued 3-unit FDP. Whereas fractured FDPs showed the highest residual stress compared to suspended and control FDPs. Residual stress increased as nanoindented away from framework.

  • probability of survival of implant supported metal ceramic and cad cam resin nanoceramic crowns
    Dental Materials, 2015
    Co-Authors: Estevam A Bonfante, Paulo G Coelho, Marcelo Suzuki, Fabio Cesar Lorenzoni, Lidia A Sena, Ronaldo Hirata, Gerson Bonfante
    Abstract:

    Abstract Objectives To evaluate the probability of survival and failure modes of implant-supported resin nanoceramic relative to metal-ceramic crowns. Methods Resin nanoceramic molar crowns (LU) (Lava Ultimate, 3M ESPE, USA) were milled and metal-ceramic (MC) (Co–Cr alloy, Wirobond C+, Bego, USA) with identical anatomy were fabricated ( n  = 21). The metal coping and a burnout-resin Veneer were created by CAD/CAM, using an abutment (Stealth-abutment, Bicon LLC, USA) and a milled crown from the LU group as models for Porcelain hot-pressing (GC-Initial IQ-Press, GC, USA). Crowns were cemented, the implants ( n  = 42, Bicon) embedded in acrylic-resin for mechanical testing, and subjected to single-load to fracture (SLF, n  = 3 each) for determination of step-stress profiles for accelerated-life testing in water ( n  = 18 each). Weibull curves (50,000 cycles at 200N, 90% CI) were plotted. Weibull modulus ( m ) and characteristic strength ( η ) were calculated and a contour plot used ( m versus η ) for determining differences between groups. Fractography was performed in SEM and polarized-light microscopy. Results SLF mean values were 1871N (±54.03) for MC and 1748N (±50.71) for LU. Beta values were 0.11 for MC and 0.49 for LU. Weibull modulus was 9.56 and η  = 1038.8N for LU, and m  = 4.57 and η  = 945.42N for MC ( p  > 0.10). Probability of survival (50,000 and 100,000 cycles at 200 and 300N) was 100% for LU and 99% for MC. Failures were cohesive within LU. In MC crowns, Porcelain Veneer fractures frequently extended to the supporting metal coping. Conclusion Probability of survival was not different between crown materials, but failure modes differed. Significance In load bearing regions, similar reliability should be expected for metal ceramics, known as the gold standard, and resin nanoceramic crowns over implants. Failure modes involving Porcelain Veneer fracture and delamination in MC crowns are less likely to be successfully repaired compared to cohesive failures in resin nanoceramic material.

  • residual thermal stress simulation in three dimensional molar crown systems a finite element analysis
    Journal of Prosthodontics, 2012
    Co-Authors: Estevam A Bonfante, Brian T Rafferty, Nelson R F A Silva, Jay C Hanan, E D Rekow, Van P Thompson, Paulo G Coelho
    Abstract:

    Purpose: To simulate coefficient of thermal expansion (CTE)-generated stress fields in monolithic metal and ceramic crowns, and CTE mismatch stresses between metal, alumina, or zirconia cores and Veneer layered crowns when cooled from high temperature processing. Materials and Methods: A 3D computer-aided design model of a mandibular first molar crown was generated. Tooth preparation comprised reduction of proximal walls by 1.5 mm and of occlusal surfaces by 2.0 mm. Crown systems were monolithic (all-Porcelain, alumina, metal, or zirconia) or subdivided into a core (metallic, zirconia, or alumina) and a Porcelain Veneer layer. The model was thermally loaded from 900°C to 25°C. A finite element mesh of three nodes per edge and a first/last node interval ratio of 1 was used, resulting in approximately 60,000 elements for both solids. Regions and values of maximum principal stress at the core and Veneer layers were determined through 3D graphs and software output. Results: The metal-Porcelain and zirconia-Porcelain systems showed compressive fields within the Veneer cusp bulk, whereas alumina-Porcelain presented tensile fields. At the core/Veneer interface, compressive fields were observed for the metal-Porcelain system, slightly tensile for the zirconia-Porcelain, and higher tensile stress magnitudes for the alumina-Porcelain. Increasingly compressive stresses were observed for the metal, alumina, zirconia, and all-Porcelain monolithic systems. Conclusions: Variations in residual thermal stress levels were observed between bilayered and single-material systems due to the interaction between crown configuration and material properties.

Joel D. Bumgardner - One of the best experts on this subject based on the ideXlab platform.

  • metallurgical surface and corrosion analysis of ni cr dental casting alloys before and after Porcelain firing
    Dental Materials, 2008
    Co-Authors: Hsinyi Lin, Bonnie Bowers, John T Wolan, Zhuo Cai, Joel D. Bumgardner
    Abstract:

    Abstract Objectives A Porcelain Veneer is often fired on nickel–chromium casting alloys used in dental restorations for aesthetic purposes. The Porcelain-fused-to-metal (PFM) process brings the temperature to over 950 °C and may change the alloy's corrosion properties. In this study, the metallurgical, surface, and corrosion properties of two Ni–Cr alloys were examined, before and after PFM firing. Methods Two types of alloy were tested—a high Cr, Mo alloy without Be and a low Cr, Mo alloy with Be. Before the PFM firing, specimens from both alloys were examined for their microstructures, hardness, electrochemical corrosion properties, surface composition, and metal ion release. After the PFM firing, the same specimens were again examined for the same properties. Results Neither of the alloys showed any differences in their electrochemical corrosion properties after the PFM firing. However, both alloys exhibited new phases in their microstructure and significant changes in hardness after firing. In addition, there was a slight increase in CrOx on the surface of the Be-free alloy and increased Mo–Ni was observed on the surface of both alloys via X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). This might be one of the reasons why both alloys had increased Ni and Mo ion release after firing. Significance The PFM firing process changed the alloys’ hardness, microstructure, and surface composition. No significant changes in the alloys’ corrosion behavior were observed, however, the significant increase in metal ion release over a month may need to be further investigated for its clinical effects.

  • metallurgical surface and corrosion analysis of ni cr dental casting alloys before and after Porcelain firing
    Dental Materials, 2008
    Co-Authors: Bonnie Bowers, John T Wolan, Joel D. Bumgardner
    Abstract:

    OBJECTIVES: A Porcelain Veneer is often fired on nickel-chromium casting alloys used in dental restorations for aesthetic purposes. The Porcelain-fused-to-metal (PFM) process brings the temperature to over 950 degrees C and may change the alloy's corrosion properties. In this study, the metallurgical, surface, and corrosion properties of two Ni-Cr alloys were examined, before and after PFM firing. METHODS: Two types of alloy were tested-a high Cr, Mo alloy without Be and a low Cr, Mo alloy with Be. Before the PFM firing, specimens from both alloys were examined for their microstructures, hardness, electrochemical corrosion properties, surface composition, and metal ion release. After the PFM firing, the same specimens were again examined for the same properties. RESULTS: Neither of the alloys showed any differences in their electrochemical corrosion properties after the PFM firing. However, both alloys exhibited new phases in their microstructure and significant changes in hardness after firing. In addition, there was a slight increase in CrO(x) on the surface of the Be-free alloy and increased Mo-Ni was observed on the surface of both alloys via X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). This might be one of the reasons why both alloys had increased Ni and Mo ion release after firing. SIGNIFICANCE: The PFM firing process changed the alloys' hardness, microstructure, and surface composition. No significant changes in the alloys' corrosion behavior were observed, however, the significant increase in metal ion release over a month may need to be further investigated for its clinical effects.

Panos Papaspyridakos - One of the best experts on this subject based on the ideXlab platform.

  • computer assisted design computer assisted manufacturing zirconia implant fixed complete prostheses clinical results and technical complications up to 4 years of function
    Clinical Oral Implants Research, 2013
    Co-Authors: Panos Papaspyridakos
    Abstract:

    Objective To report the clinical results and technical complications with computer-assisted design/computer-assisted manufacturing (CAD/CAM) zirconia, implant fixed complete dental prostheses (IFCDPs) after 2–4 years in function. Materials and methods Fourteen consecutive edentulous patients (16 edentulous arches) were included in this study. Ten of the patients were women and four were men, with an average age of 58 years (range: 35–71). Ten mandibular and six maxillary arches were restored with Porcelain fused to zirconia (PFZ) IFCDPs. Of the 16 arches, 14 received one-piece and 2 received segmented two-piece IFCDPs, respectively. The mean clinical follow-up period was 3 years (range: 2–4). At the last recall appointment, biological and technical parameters of dental implant treatment were evaluated. Results The implant and prosthesis survival rate following prosthesis insertion was 100% up to 4-year follow-up. The prostheses in 11 of the 16 restored arches were structurally sound, exhibited favorable soft tissue response, esthetics, and patient satisfaction. Five IFCDPs (31.25%) in four patients exhibited Porcelain Veneer chipping. Chipping was minor in three prostheses (three patients) and was addressed intraorally with polishing (one prosthesis) or composite resin (two prostheses). One patient with maxillary and mandibular zirconia IFCDP exhibited major Porcelain chipping fractures which had to be repaired in the laboratory. Function, esthetics, and patient satisfaction were not affected in three of the four fracture incidents. Median crestal bone loss was 0.1 mm (0.01–0.2 mm). The presence of parafunctional activity, the IFCDP as opposing dentition, and the absence of occlusal night guard were associated with all the incidents of ceramic chipping. Conclusion CAD/CAM zirconia IFCDPs are viable prosthetic treatment after 2–4 years in function, but not without complications. The Porcelain chipping/fracture was the most frequent technical complication, with a 31.25% chipping rate at the prosthesis level. Despite the technical complications, increased patient satisfaction was noted.

C. Sforza - One of the best experts on this subject based on the ideXlab platform.

  • Seven-year prospective clinical study on zirconia-based single crowns and fixed dental prostheses
    Clinical Oral Investigations, 2015
    Co-Authors: G.m. Tartaglia, Ernesto Sidoti, C. Sforza
    Abstract:

    Objectives Zirconia-based prostheses are used for esthetic crown and fixed restorations, but follow-ups are still limited. The authors evaluated the 7-year clinical results of 303 zirconia core restorations, performed in a general dental private practice. Materials and methods Clinical events (fracture and loss of retention, gingivitis, tenderness, excess cement, and temporary pain) were recorded in 303 zirconia core restorations positioned in 88 patients. Kaplan-Meier survival probability estimates were computed for failures (needed the replacement or removal of the prosthesis) and complications (resolved without replacing the prosthesis). Results One hundred and fifty single crowns (130 tooth-supported, 20 implant-supported) and 153 multiple units up to 6 elements (49 tooth-supported, 104 implant-supported) were followed-up for 7 years in 88 patients (40 men, 48 women), aged 35–89 years (mean 57). During the follow-up period, there were no complications for 287 (95 %) of the restorations. Sixteen restorations/abutment teeth (5 %) had some complication: extraction of abutment tooth (7, 2 %); caries (2, 1 %), Porcelain Veneer fracture (3, 1 %), loss of retention (4, 1 %). Nine (3 %) restorations were recorded as failures. The overall 7-year survival probability estimate for failures was 0.966 (95 % confidence limits, 0.932 and 0.983), for complications was 0.976 (95 % confidence limits 0.947 and 0.989), with a cumulative survival rate of 94.7 %. Conclusions Within the analyzed follow-up, zirconia core restorations appear a good clinical solution, with favorable functional properties. Clinical relevance All ceramic restorations can be successfully used for both single-and multiple-unit prostheses, either teeth or implants supported.

  • Full-mouth zirconia-based implant-supported fixed dental prostheses : five year - results of a clinical pilot study
    2014
    Co-Authors: G.m. Tartaglia, C. Sforza
    Abstract:

    Introduction: Full-mouth reconstruction using dental implants and CAD-CAM prosthodontic procedure is a new option model in oral rehabilitation. One of the most consolidated promising material is yttria-stabilized tetragonal zirconia polycrystals, usually called \u201czirconia\u201d. It is chemically derived from zirconium sand, partially stabilized with yttrium, and then mechanically pressed into zirconia blocks that are used for CAD-CAM technology. In this paper we provide the 5-year results from a pilot study on full-mouth implant-supported zirconia-based \ufb01xed dental prostheses (FMIZBRs). Methodology: Five women aged 55-75 years had received FMIZBRs from the same private practice. At the 5-year follow up visit, restorations remained in situ and were still in use. Results: There were no failures and no biological complications during the follow-up period (100% survival rate). Eight FMIZBRs experienced some minor Porcelain Veneer fractures that were easily polished. None of the fractures impaired function or aesthetics. The patients were fully satis\ufb01ed with the treatment. Conclusion: Results from this pilot study suggest that FMIZBRs can be a treatment option that is rapidly shaping the coming dental rehabilitation area on implants