Influence of thermal expansion mismatch on residual stress profile in veneering ceramic layered on zirconia: Measurement by hole-drilling.
Mainjot, Amélie ; ; et al
in Dental materials : official publication of the Academy of Dental Materials (2015)
OBJECTIVES: Mismatch in thermal expansion coefficient between core and veneering ceramic (Deltaalpha=alphacore-alphaveneer, ppm/ degrees C) is reported as a crucial parameter influencing veneer fractures ... [more ▼]
OBJECTIVES: Mismatch in thermal expansion coefficient between core and veneering ceramic (Deltaalpha=alphacore-alphaveneer, ppm/ degrees C) is reported as a crucial parameter influencing veneer fractures with Yttria-tetragonal-zirconia-polycrystal (Y-TZP) prostheses, which still constitutes a misunderstood problem. However, the common positive Deltaalpha concept remains empirical. The objective of this study is to investigate the Deltaalpha dependence of residual stress profiles in veneering ceramic layered on Y-TZP frameworks. METHODS: The stress profile was measured with the hole-drilling method in bilayered disc samples of 20mm diameter with a 0.7mm thick Y-TZP framework and a 1.5mm thick veneer layer. 3 commercial and 4 experimental veneering ceramics (n=3 per group) were used to obtain different Deltaalpha varying from -1.3ppm/ degrees C to +3.2ppm/ degrees C, which were determined by dilatometric analyses. RESULTS: Veneer fractures were observed in samples with Deltaalpha>/=+2.3 or </=-0.3ppm/ degrees C. Residual stress profiles measured in other groups showed compressive stresses in the surface, these stresses decreasing with depth and then becoming more compressive again near the interface. Small Deltaalpha variations were shown to induce significant changes in residual stress profiles. Compressive stress near the framework was found to decrease inversely to Deltaalpha. SIGNIFICANCE: Veneer CTE close to Y-TZP (+0.2ppm/ degrees C Deltaalpha) gived the most favorable stress profile. Yet, near the framework, Deltaalpha-induced residual stress varied inversely to predictions. This could be explained by the hypothesis of structural changes occurrence within the Y-TZP surface. Consequently, the optimum Deltaalpha value cannot be determined before understanding Y-TZP's particular behavior when veneered. [less ▲]Detailed reference viewed: 36 (5 ULg)
Influence of firing time and framework thickness on veneered Y-TZP discs curvature.
; ; et al
in Dental materials : official publication of the Academy of Dental Materials (2014), 30(2), 242-248
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 ▲]Detailed reference viewed: 22 (1 ULg)
3D-Characterization of the veneer-zirconia interface using FIB nano-tomography.
MAINJOT, Amélie ; ; 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 ▲]Detailed reference viewed: 38 (1 ULg)
Influence of cooling rate on residual stress profile in veneering ceramic: Measurement by hole-drilling.
MAINJOT, Amélie ; ; Vanheusden, Alain 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 ▲]Detailed reference viewed: 67 (5 ULg)