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See detailLe point sur l'émaillage de la zircone: aspects cliniques et scientifiques
MAINJOT, Amélie ULg

Conference (2013, January 25)

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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 (2013)

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 firing time and framework thickness on veneered Y-TZP discs curvature.
Jakubowicz-Kohen, Boris D.; Sadoun, Michael J.; Douillard, Thierry et al

in Dental materials : official publication of the Academy of Dental Materials (2013)

OBJECTIVES: The objective of the present work was to study the curvature of very thinly, veneered Y-TZP discs of different framework thicknesses submitted to different firing times. METHODS: Fifteen 20-mm ... [more ▼]

OBJECTIVES: The objective of the present work was to study the curvature of very thinly, veneered Y-TZP discs of different framework thicknesses submitted to different firing times. METHODS: Fifteen 20-mm-wide Y-TZP discs were produced in three different thicknesses: 0.75, 1, 1.5mm. One disc from each group was left unveneered while the others were layered with a 0.1mm veneering ceramic layer. All discs underwent five firing cycles for a total cumulative firing time of 30min, 1, 2, 5 and 10h at 900 degrees C. The curvature profile was measured using a profilometer after the veneering process and after each firing cycle respectively. A fitted curve was then used to estimate the, curvature radius. The coefficient of thermal expansion (CTE) measurements were taken on veneering, ceramic and Y-TZP beam samples that underwent the same firing schedule. Those data were used to calculate the curvature generated by CTE variations over firing time. RESULTS: All bilayered samples exhibited a curvature that increased over firing time inversely to framework thickness. However non-veneered samples did not exhibit any curvature modification. SIGNIFICANCE: The results of the present study reveal that even a very thin veneer layer (0.1mm) can induce a significant curvature of Y-TZP discs. The dilatometric results showed that Tg and CTE, variations are not sufficient to explain this curvature. A chemical-induced zirconia volume, augmentation located at the framework sub-surface near the interface could explain the sample, curvature and its increase with firing time. [less ▲]

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See detailClinical risk factors related to failures with zirconia-based restorations: An up to 9-year retrospective study.
Koenig, Vinciane; Vanheusden, Alain ULg; Le Goff, Stephane O. et al

in Journal of dentistry (2013), 41(12), 1164-74

OBJECTIVES: The first objective of this study was to retrospectively evaluate zirconia-based restorations (ZBR). The second was to correlate failures with clinical parameters and to identify and to ... [more ▼]

OBJECTIVES: The first objective of this study was to retrospectively evaluate zirconia-based restorations (ZBR). The second was to correlate failures with clinical parameters and to identify and to analyse chipping failures using fractographic analysis. METHODS: 147 ZBR (tooth- and implant-supported crowns and fixed partial dentures (FPDs)) were evaluated after a mean observation period of 41.5+/-31.8 months. Accessorily, zirconia implant abutments (n=46) were also observed. The technical (USPHS criteria) and the biological outcomes of the ZBR were evaluated. Occlusal risk factors were examined: occlusal relationships, parafunctional habits, and the presence of occlusal nightguard. SEM fractographic analysis was performed using the intra-oral replica technique. RESULTS: The survival rate of crowns and FPDs was 93.2%, the success rate was 81.63% and the 9-year Kaplan-Meier estimated success rate was 52.66%. The chipping rate was 15% and the framework fracture rate was 2.7%. Most fractographic analyses revealed that veneer fractures originated from occlusal surface roughness. Several parameters were shown to significantly influence veneer fracture: the absence of occlusal nightguard (p=0.0048), the presence of a ceramic restoration as an antagonist (p=0.013), the presence of parafunctional activity (p=0.018), and the presence of implants as support (p=0.026). The implant abutments success rate was 100%. CONCLUSIONS: The results of the present study confirm that chipping is the first cause of ZBR failure. They also underline the importance of clinical parameters in regards to the explanation of this complex problem. This issue should be considered in future prospective clinical studies. CLINICAL SIGNIFICANCE: Practitioners can reduce chipping failures by taking into account several risk parameters, such as the presence of a ceramic restoration as an antagonist, the presence of parafunctional activity and the presence of implants as support. The use of an occlusal nightguard can also decrease failure rate. [less ▲]

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See detail3D-Characterization of the veneer-zirconia interface using FIB nano-tomography.
MAINJOT, Amélie ULg; Douillard, Thierry; Gremillard, Laurent et al

in Dental materials : official publication of the Academy of Dental Materials (2013), 29(2), 157-65

OBJECTIVES: The phenomena occurring during zirconia frameworks veneering process are not yet fully understood. In particular the study of zirconia behavior at the interface with the veneer remains a ... [more ▼]

OBJECTIVES: The phenomena occurring during zirconia frameworks veneering process are not yet fully understood. In particular the study of zirconia behavior at the interface with the veneer remains a challenge. However this interface has been reported to act on residual stress in the veneering ceramic, which plays a significant role in clinical failures such as chipping. The objective of this study was thus to investigate the veneer-zirconia interface using a recent 3D-analysis tool and to confront these observations to residual stress measurements in the veneering ceramic. METHODS: Two cross-sectioned bilayered disc samples (veneer on zirconia), exhibiting different residual stress profiles in the veneering ceramic, were investigated using 2D and 3D imaging (respectively Scanning Electron Microscopy (SEM) and Focused Ion Beam nanotomography (FIB-nt), associated with chemical analysis by Energy Dispersive X-ray Spectroscopy (EDS). RESULTS: The observations did not reveal any structural change in the bulk of zirconia layer of both samples. However the presence of structural alterations and sub-surface microcracks were highlighted in the first micrometer of zirconia surface, exclusively for the sample exhibiting interior tensile stress in the veneering ceramic. No interdiffusion phenomena were observed. SIGNIFICANCE: FIB nanotomography was proven to be a powerful technique to study the veneer-zirconia interface. The determination of the origin and the nature of zirconia alterations need to be further studied. The results of the present study support the hypothesis that zirconia surface property changes could be involved in the development of tensile stress in the veneering ceramic, increasing the risk of chipping. [less ▲]

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See detailResidual Stress in Veneering Ceramic
MAINJOT, Amélie ULg

Conference (2012, April 04)

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See detailLimites et futur des procédés CFAO pour les prothèses tout céramique
MAINJOT, Amélie ULg

in Entretiens de Bichat. Médecine (2012)

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See detailResidual Stress in Veneering Ceramic
MAINJOT, Amélie ULg

Doctoral thesis (2011)

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See detailInfluence de la vitesse de refroidissement sur le profil de contraintes résiduelles dans la céramique d’émaillage : mesures avec la méthode du trou incrémental
MAINJOT, Amélie ULg; Schajer, Gary; VAN HEUSDEN, Alain ULg et al

Conference (2011, June 23)

INTRODUCTION : La fabrication des couronnes et des bridges génère des contraintes résiduelles dans la céramique d’émaillage et dans l’infrastructure lors du procédé de refroidissement. Les contraintes ... [more ▼]

INTRODUCTION : La fabrication des couronnes et des bridges génère des contraintes résiduelles dans la céramique d’émaillage et dans l’infrastructure lors du procédé de refroidissement. Les contraintes résiduelles sont un facteur important qui contrôle le comportement mécanique des restaurations. La connaissance de la distribution des contraintes en fonction de la profondeur peut aider à comprendre les échecs, particulièrement le chipping, qui est une problématique répandue avec les prothèses à infrastructure en zircone yttrium. L’objectif de cette étude est d’analyser la variation du profil de contraintes dans la céramique d’émaillage sur infrastructure métal ou zircone, en fonction de la vitesse de refroidissement. METHODES : La méthode du trou incrémental, souvent utilisée en ingénierie industrielle, a été adaptée à pour être utilisée au niveau de la céramique d’émaillage 1. Le profil de contraintes a été mesuré dans des des disques de 20 mm de diamètre, comprenant une infrastructure de 0.7 mm d’épaisseur en métal ou en zircone yttrium, et une couche de céramique d’émaillage de 1.5 mm d’épaisseur. Trois procédures de refroidissement différentes ont été étudiées. RESULTATS: Il a été observé que l’amplitude des contraintes mesurées en surface de la céramique d’émaillage augmente avec la vitesse de refroidissement, alors que l’amplitude des contraintes en profondeur diminue. Des contraintes en compression ont été mesurées à la surface de tous les échantillons. En profondeur, des contraintes en compression ont été mesurées au niveau des échantillons à infrastructure métal et des contraintes en traction au niveau des échantillons à infrastructure zircone. DISCUSSION ET CONCLUSIONS : La vitesse de refroidissement influence l’amplitude des contraintes résiduelles. Celles-ci peuvent influencer le comportement mécanique des bicouches à infrastructure métal et zircone. La nature du matériau d’infrastructure influence la nature des contraintes en profondeur, les échantillons zircone montrant un profil de contraintes beaucoup plus défavorable que les échantillons métal. L’hypothèse de la transformation de phase de la zircone est mise en avant pour expliquer ce comportement. REFERENCES : ¬¬¬¬¬¬¬1 Mainjot, A., et al. (2011) Dental Materials 27 : 437-444. Fig 1 Profil de contraintes dans l’émaillage des échantillons zircone. CC= Classic Cooling, MC= Modified Cooling, SC= Slow Cooling. [less ▲]

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See detailFit of single tooth zirconia copings: comparison between various manufacturing processes.
Grenade, Charlotte ULg; MAINJOT, Amélie ULg; Vanheusden, Alain ULg

in Journal of Prosthetic Dentistry (2011), 105(4), 249-55

STATEMENT OF PROBLEM: Various CAD/CAM processes are commercially available to manufacture zirconia copings. Comparative data on their performance in terms of fit are needed. PURPOSE: The purpose of this ... [more ▼]

STATEMENT OF PROBLEM: Various CAD/CAM processes are commercially available to manufacture zirconia copings. Comparative data on their performance in terms of fit are needed. PURPOSE: The purpose of this in vitro study was to compare the internal and marginal fit of single tooth zirconia copings manufactured with a CAD/CAM process (Procera; Nobel Biocare) and a mechanized manufacturing process (Ceramill; Amann Girrbach). MATERIAL AND METHODS: Abutments (n=20) prepared in vivo for ceramic crowns served as a template for manufacturing both Procera and Ceramill zirconia copings. Copings were manufactured and cemented (Clearfil Esthetic Cement; Kuraray) on epoxy replicas of stone cast abutments. Specimens were sectioned. Nine measurements were performed for each coping. Over- and under-extended margins were evaluated. Comparisons between the 2 processes were performed with a generalized linear mixed model (alpha=.05). RESULTS: Internal gap values between Procera and Ceramill groups were not significantly different (P=.13). The mean marginal gap (SD) for Procera copings (51(50) mum) was significantly smaller than for Ceramill (81(66) mum) (P<.005). The percentages of over- and under-extended margins were 43% and 57% for Procera respectively, and 71% and 29% for Ceramill. CONCLUSIONS: Within the limitations of this in vitro study, the marginal fit of Procera copings was significantly better than that of Ceramill copings. Furthermore, Procera copings showed a smaller percentage of over-extended margins than did Ceramill copings. [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 (2011)

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 (2011)

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)

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See detailInfluence of cooling rate 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 : official publication of the Academy of Dental Materials (2011)

OBJECTIVES: The manufacture of dental crowns and bridges generates residual stresses within the veneering ceramic and framework during the cooling process. Residual stress is an important factor that ... [more ▼]

OBJECTIVES: The manufacture of dental crowns and bridges generates residual stresses within the veneering ceramic and framework during the cooling process. Residual stress is an important factor that control the mechanical behavior of restorations. Knowing the stress distribution within the veneering ceramic as a function of depth can help the understanding of failures, particularly chipping, a well-known problem with Yttria-tetragonal-zirconia-polycrystal based fixed partial dentures. The objective of this study is to investigate the cooling rate dependence of the stress profile in veneering ceramic layered on metal and zirconia frameworks. 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 20mm in diameter, with a 0.7mm thick metal or Yttria-tetragonal-zirconia-polycrystal framework and a 1.5mm thick veneering ceramic. Three different cooling procedures were investigated. RESULTS: The magnitude of the stresses in the surface of the veneering ceramic was found to increase with cooling rate, while the interior stresses decreased. At the surface, compressive stresses were observed in all samples. In the interior, compressive stresses were observed in metal samples and tensile in zirconia samples. SIGNIFICANCE: Cooling rate influences the magnitude of residual stresses. These can significantly influence the mechanical behavior of metal-and zirconia-based bilayered systems. The framework material influenced the nature of the interior stresses, with zirconia samples showing a less favorable stress profile than metal. [less ▲]

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See detailA new method to measure residual stresses in veneering ceramic
Mainjot, Amélie ULg; Van Heusden, Alain ULg; Sadoun, Michael

Conference (2010, July 16)

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See detailInfluence of veneer thickness on residual stresses in zirconia prostheses.
Mainjot, Amélie ULg; Schajer, Gary; Vanheusden, Alain ULg et al

in Dental Materials (2010)

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

Poster (2010)

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See detailZircone: analyse des causes d'échec
Mainjot, Amélie ULg

in Entretiens de Bichat. Médecine. Entretiens de Bichat (Les) (2010)

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