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See detailBiocompatibility of polymer-infiltrated-ceramicnetwork (PICN) materials with Human Gingival Keratinocytes (HGKs)
GRENADE, Charlotte ULg; Gillet, Marie-Claire ULg; PIRARD, Catherine ULg et al

in Dental Materials (2017), 33

Objective. Biocompatibility of polymer-infiltrated-ceramic-network (PICN) materials, a new class of CAD–CAM composites, is poorly explored in the literature, in particular, no data are available regarding ... [more ▼]

Objective. Biocompatibility of polymer-infiltrated-ceramic-network (PICN) materials, a new class of CAD–CAM composites, is poorly explored in the literature, in particular, no data are available regarding Human Gingival Keratinocytes (HGK). The first objective of this study was to evaluate the in vitro biocompatibility of PICNs with HGKs in comparison with other materials typically used for implant prostheses. The second objective was to correlate results with PICN monomer release and indirect cytotoxicity. Methods. HGK attachment, proliferation and spreading on PICN, grade V titanium (Ti), yttrium zirconia (Zi), lithium disilicate glass-ceramic (eM) and polytetrafluoroethylene (negative control) discs were evaluated using a specific insert-based culture system. For PICN and eM samples, monomer release in the culture medium was quantified by high performance liquid chromatography and indirect cytotoxicity tests were performed. Results. Ti and Zi exhibited the best results regarding HGK viability, number and coverage. eM showed inferior results while PICN showed statistically similar results to eM but also to Ti regarding cell number and to Ti and Zi regarding cell viability. No monomer release from PICN discs was found, nor indirect cytotoxicity, as for eM. Significance. The results confirmed the excellent behavior of Ti and Zi with gingival cells. Even if polymer based, PICN materials exhibited intermediate results between Ti–Zi and eM. These promising results could notably be explained by PICN high temperature–high pressure (HT–HP) innovative polymerization mode, as confirmed by the absence of monomer release and indirect cytotoxicity [less ▲]

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See detailResidual stress profiles in veneering ceramic on Y-TZP, alumina and ZTA frameworks: Measurement by hole-drilling
Fukushima, K. A.; Sadoun, M. J.; Cesar, P. F. et al

in Dental materials (2014), 30(2), 105-111

OBJECTIVES: The residual stress profile developed within the veneering ceramic during the manufacturing process is an important predicting factor in chipping failures, which constitute a well-known ... [more ▼]

OBJECTIVES: The residual stress profile developed within the veneering ceramic during the manufacturing process is an important predicting factor in chipping failures, which constitute a well-known problem with yttria-tetragonal-zirconia polycrystal (Y-TZP) based restorations. The objectives of this study are to measure and to compare the residual stress profile in the veneering ceramic layered on three different polycrystalline ceramic framework materials: Y-TZP, alumina polycrystal (AL) and zirconia toughened alumina (ZTA). METHODS: The stress profile was measured with the hole-drilling method in bilayered disk samples of 19mm diameter with a 0.7mm thick Y-TZP, AL or ZTA framework and a 1.5mm thick layer of the corresponding veneering ceramic. RESULTS: The AL samples exhibited increasing compressive stresses with depth, while compressive stresses switching into interior tensile stresses were measured in Y-TZP samples. ZTA samples exhibited compressive stress at the ceramic surface, decreasing with depth up to 0.6mm from the surface, and then becoming compressive again near the framework. SIGNIFICANCE: Y-TZP samples exhibited a less favorable stress profile than those of AL and ZTA samples. Results support the hypothesis of the occurrence of structural changes within the Y-TZP surface in contact with the veneering ceramic to explain the presence of tensile stresses. Even if the presence of Y-TZP in the alumina matrix seems to negatively affect the residual stress profiles in ZTA samples in comparison with AL samples, the registered profiles remain positive in terms of veneer fracture resistance. [less ▲]

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See detailInfluence of veneer thickness on residual stress profile in veneering ceramic: Measurement by hole-drilling.
MAINJOT, Amélie ULg; Schajer, G. S.; Vanheusden, Alain ULg et al

in Dental Materials (2012), 28(2), 160-167

OBJECTIVES: The veneering process of frameworks induces residual stresses and can initiate cracks when combined with functional stresses. The stress distribution within the veneering ceramic as a function ... [more ▼]

OBJECTIVES: The veneering process of frameworks induces residual stresses and can initiate cracks when combined with functional stresses. The stress distribution within the veneering ceramic as a function of depth is a key factor influencing failure by chipping. This is a well-known problem with Yttria-tetragonal-zirconia-polycrystal based fixed partial dentures. The objective of this study is to investigate the influence of veneer thickness on the stress profile in zirconia- and metal-based structures. METHODS: The hole-drilling method, often used for engineering measurements, was adapted for use with veneering ceramic. The stress profile was measured in bilayered disc samples of 20mm diameter, with a 1mm thick zirconia or metal framework. Different veneering ceramic thicknesses were performed: 1mm, 1.5mm, 2mm, 2.5mm and 3mm. RESULTS: All samples exhibited the same type of stress vs. depth profile, starting with compressive at the ceramic surface, decreasing with depth up to 0.5-1.0mm from the surface, and then becoming compressive again near the framework, except for the 1.5mm-veneered zirconia samples which exhibited interior tensile stresses. Stresses in the surface of metal samples were not influenced by veneer thickness. Variation of interior stresses at 1.2mm from the surface in function of veneer thickness was inverted for metal and zirconia samples. SIGNIFICANCE: Veneer thickness influences in an opposite way the residual stress profile in metal- and in zirconia-based structures. A three-step approach and the hypothesis of the crystalline transformation are discussed to explain the less favorable residual stress development in zirconia samples. [less ▲]

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See detailInfluence of zirconia framework thickness on residual stress profile in veneering ceramic: Measurement by hole-drilling.
MAINJOT, Amélie ULg; Schajer, G. S.; Vanheusden, Alain ULg et al

in Dental Materials (2012), 28(4), 378-384

OBJECTIVES: Framework design is reported to influence chipping in zirconia-based restorations, which is an important cause of failure of such restorations. Residual stress profile in the veneering ceramic ... [more ▼]

OBJECTIVES: Framework design is reported to influence chipping in zirconia-based restorations, which is an important cause of failure of such restorations. Residual stress profile in the veneering ceramic after the manufacturing process is an important predictive factor of the mechanical behavior of the material. The objective of this study is to investigate the influence of framework thickness on the stress profile measured in zirconia-based structures. METHODS: The stress profile was measured with the hole-drilling method in bilayered disc samples of 20mm diameter with a 1.5mm thick veneering ceramic layer. Six different framework thicknesses from 0.5mm to 3mm were studied. Two different cooling procedures were also investigated. RESULTS: Compressive stresses were observed in the surface, and tensile stresses in the depth of most of the samples. The slow cooling procedure was found to promote the development of interior tensile stresses, except for the sample with a 3mm thick framework. With the tempering procedure, samples with a 1.5mm thick framework exhibited the most favorable stress profile, while thicker and thinner frameworks exhibited respectively in surface or interior tensile stresses. Significance: The measurements performed highlight the importance of framework thickness, which determine the nature of stresses and can explain clinical failures encountered, especially with thin frameworks. The adequate ratio between veneering ceramic and zirconia is hard to define, restricting the range of indications of zirconia-based restorations until a better understanding of such a delicate veneering process is achieved. [less ▲]

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See detailResidual stress measurement in veneering ceramic by hole-drilling
Mainjot, Amélie ULg; Schajer, Gary; Vanheusden, Alain ULg et al

in Dental Materials (2011), 27(5), 439-444

Residual stresses can substantially affect veneering ceramic performance. The hole drilling method is an industrial method to measure these stresses, and it has been adapted here for dental use. The ... [more ▼]

Residual stresses can substantially affect veneering ceramic performance. The hole drilling method is an industrial method to measure these stresses, and it has been adapted here for dental use. The method was successfully applied on bilayer disc samples of veneering ceramic sintered either on Co–Cr alloy or on Y-TZP framework characteristic of dental prostheses. The method allows stress depth profile measurement in a range of 1.2 mm of depth from surface. Because of the small stresses present in dental prostheses, sensitive and stable measurement equipment is required. The residual stress measurements confirm the expectation from the previous literature of compressive residual stresses in the veneering ceramic surface on VM and VZr prostheses. The results showed a gradual shift to tensile residual stresses at 0.5–1 mm depth from the surface. The measured stress profiles in the VZr samples showed residual stresses of larger magnitude and concentration of tensile stresses in a smaller area, which could be a potential source of the problems encountered in clinical practice. Future studies on the mechanical behavior of Y-TZP restorations need to focus on the influence of each independent parameter, such as veneering ceramic thickness, expansion coefficient mismatch, heat treatment parameters and cooling rate, on residual stress profile. The hole-drilling residual stress measurement method described here provides an effective method for studying these parameters. It would then be possible to compare the experimental measurements with the results of finite element analyses of crowns and bridges. [less ▲]

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