3D-Characterization of the veneer-zirconia interface using FIB nano-tomography.

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 ▲]

Limites et futur des procédés CFAO pour les prothèses tout céramique

in Entretiens de Bichat. Médecine. Entretiens de Bichat (Les) (2012)

Influence de la vitesse de refroidissement sur le profil de contraintes résiduelles dans la céramique d’émaillage : mesures avec la méthode du trou incrémental

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 ▲]

Fit of single tooth zirconia copings: comparison between various manufacturing processes.

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 ▲]

Influence of zirconia framework thickness on residual stress profile in veneering ceramic: Measurement by hole-drilling.

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 ▲]

Influence of cooling rate on residual stress profile in veneering ceramic: Measurement by hole-drilling.

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 ▲]

Influence of veneer thickness on residual stresses in zirconia prostheses.

in Dental Materials (2010)

Zircone: analyse des causes d'échec

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

Adaptation des infrastructures unitaires en zircone sur piliers dentaires : comparaison d'un procédé CFAO avec un procédé de fabrication mécanisée

Conference (2009, June)

Antibiotic prescribing in dental practice in Belgium.

in International Endodontic Journal (2009), 42(12), 1112-7

AIM: To assess the types and frequency of antibiotic prescriptions by Belgian dentists, the indications for antibiotic prescription, and dentists' knowledge about recommended practice in antibiotic use ... [more ▼]

AIM: To assess the types and frequency of antibiotic prescriptions by Belgian dentists, the indications for antibiotic prescription, and dentists' knowledge about recommended practice in antibiotic use. METHODOLOGY: In this cross-sectional survey, dental practitioners were asked to record information about all antibiotics prescribed to their patients during a 2-week period. The dental practitioners were also asked to complete a self-administered questionnaire regarding demographic data, prescribing practices, and knowledge about antibiotic use. A random sample of 268 Belgian dentists participated in the survey. RESULTS: During the 2-week period, 24 421 patient encounters were recorded; 1033 patients were prescribed an antibiotic (4.2%). The median number of prescriptions per dentist for the 2 weeks was 3. Broad spectrum antibiotics were most commonly prescribed: 82% of all prescriptions were for amoxycillin, amoxycillin-clavulanic acid and clindamycin. Antibiotics were often prescribed in the absence of fever (92.2%) and without any local treatment (54.2%). The most frequent diagnosis for which antibiotics were prescribed was periapical abscess (51.9%). Antibiotics were prescribed to 63.3% of patients with periapical abscess and 4.3% of patients with pulpitis. Patterns of prescriptions were confirmed by the data from the self-reported practice. CONCLUSIONS: Discrepancies between observed and recommended practice support the need for educational initiatives to promote rational use of antibiotics in dentistry in Belgium. [less ▲]