Isabelle Denry

Our purpose was to investigate the effect of heat treatment on the reversibility of the tetragonal to monoclinic transformation in 3Y‐TZP, and associated surface roughness. The goals were to determine the onset temperature of the reverse transformation, and characterize surface roughness after accelerated aging, and after aging followed by heat treatment. 3Y‐TZP disc‐shaped specimens were sintered at temperatures from 1300 to 1550°C. The reversibility of the transformation was investigated by X‐ray diffraction (XRD) after accelerated aging, followed by heat treatment at temperatures from 350°C up to 850°C. The surface roughness (R_rms) was measured by atomic force microscopy after polishing, after accelerated aging for 1 or 10 h, and after aging followed by heat treatment. XRD showed that the fraction ofm‐phase increased linearly with grain size after aging for 10 h (1.0–29.8%). The transformation was reversed for all groups after heat treatment at 850°C/min., with only trace amounts ofm‐phase remaining for the group sintered at 1550°C. A significant increase in mean surface roughness was observed after accelerated aging (1.59–7.45 nm), compared to polished groups (0.83–1.0 nm). However, the mean surface roughness after accelerated aging for either 1 or 10 h, followed by heat treatment at 850°C/min. (1.18–2.1 nm), was not significantly different from that of the polished groups. This was attributed to the reverse transformation. XRD revealed that the monoclinic to tetragonal transformation, was complete after heat treatment at 500°C for 1 min, for specimens sintered at 1550°C and aged 10 h. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010

Over the past forty years, the technological evolution of ceramics for dental applications has been remarkable, as new materials and processing techniques are steadily being introduced. The improvement in both strength and toughness has made it possible to expand the range of indications to long-span fixed partial prostheses, implant abutments and implants. The present review provides a state of the art of ceramics for dental applications.

The purpose of this study was to investigate the effect of cerium and bismuth coloring salts solutions on the microstructure, color, flexural strength, and aging resistance of tetragonal zirconia for dental applications (3Y‐TZP). Cylindrical blanks were sectioned into disks (2‐mm thick, 25‐mm in diameter) and colored by immersion in cerium acetate (CA), cerium chloride (CC), or bismuth chloride (BC) solutions at 1, 5, or 10 wt %. The density, elastic constants, and biaxial flexural strength were determined after sintering at 1350°C. The crystalline phases were analyzed by X‐ray diffraction before and after aging in autoclave for 10 h. The results showed that the mean density of the colored groups was comparable with that of the control group (6.072 ± 0.008 g/cm³). XRD confirmed the presence of tetragonal zirconia with a slight increase in lattice parameters for the colored groups. A perceptible color difference was obtained for all groups (ΔE* = 2.57 ± 0.48 to 14.22 ± 0.98), compared with the control. The mean grain size increased significantly for the groups colored with CC or CA at 10 wt %, compared with the control group (0.318 ± 0.029 mm). The mean biaxial strength of CA1%, CA5%, and BC1% groups was not significantly different from that of the control group (1087.5 ± 173.3 MPa). The flexural strength of all other groups decreased linearly with increasing concentration for both cerium salts (860.7 ± 172 to 274.4 ± 67.3 MPa). The resistance to low temperature degradation was not affected by the coloring process. Coloring with cerium or bismuth salts produced perceptible color differences even at the lowest concentrations. A decrease in flexural strength at the higher concentrations was attributed to an increase in open porosity. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008

The evolution of dental ceramics over the past four decades has been remarkable in light of the increase in the diversity of materials and fabrication techniques that have become available. As a consequence, the applications and indications for all-ceramic materials continue to expand. The purpose of the present article is to review the evolution of dental ceramics from the various aspects of crystalline phases, glassy matrix, flaws andin vivoperformance.

The purpose of this study was to evaluate microstructural and crystallographic phase changes after grinding 3Y‐TZP dental ceramics. Ceramic blanks were sintered according to manufacturer's recommendations and divided into four groups: (A) as‐sintered control, (B) diamond‐ground manually under water, (C) ground and polished, and (D) ground and annealed at 1000°C for 1 h. Bulk specimens were analyzed by X‐ray diffraction to characterize the crystalline phases. The microstructure was investigated by SEM. XRD analyses showed that the control group and the group that was ground and annealed contained only tetragonal zirconia. However, after grinding or after grinding followed by polishing, rhombohedral zirconia and strained tetragonal zirconia were present, without any detectable amount of monoclinic zirconia. Annealing led to the disappearance of both residual lattice strain and the rhombohedral phase. The microstructure of the ground and polished specimens was characterized by significant residual surface damage associated with grain pullout to a depth of about 20 μm. This type of damage could have an impact on the long‐term fatigue behavior of 3Y‐TZP. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006

Niobium oxide has been shown to improve biocompatibility and promote bioactivity. The purpose of this study was to evaluate the effect of niobium oxide additions on the microstructure and thermal properties of fluorapatite glass‐ceramics for biomedical applications. Four glass‐ceramic compositions with increasing amounts of niobium oxide from 0 to 5 wt % were prepared. The glass compositions were melted at 1525°C for 3 h, quenched, ground, melted again at 1525°C for 3 h and furnace cooled. The coefficient of thermal expansion was measured by dilatometry. The crystallization behavior was evaluated by differential thermal analysis. The nature of the crystalline phases was investigated by X‐ray diffraction. The microstructure was studied by SEM. In addition, the cytotoxicity of the ceramics was evaluated according to the ASTM standard F895‐84. The results from X‐ray diffraction analyses showed that fluorapatite was the major crystalline phase in all glass‐ceramics. Differential thermal analyses revealed that fluorapatite crystallization occurred between 800 and 934°C depending on the composition. The coefficient of thermal expansion varied from 7.6 to 9.4 × 10⁻⁶/°C. The microstructure after heat treatment at 975°C for 30 min consisted of submicroscopic fluorapatite crystals (200–300 nm) for all niobium‐containing glass‐ceramics, whereas the niobium‐free glass‐ceramic contained needle‐shaped fluorapatite crystals, 2 μm in length. None of the glass‐ceramics tested exhibited any cytotoxic activity as tested by ASTM standard F895‐84. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005

Previous work has shown that heat pressing of mica‐based glass‐ceramics can lead to crystal alignment along the direction of pressing. The purpose of this study was to evaluate the effect of heat pressing on the fracture toughness of mica‐based glass‐ceramics. Glass rods (12 × 60 mm) were prepared by melting the glass composition at 1400 °C for 2 h. Ingots (12 × 12 mm; n = 5) and discs (12 × 1.5 mm; n = 10) were cut from the rods. The discs were heat treated to simulate heat pressing and served as controls. A machinable mica‐based glass‐ ceramic (Dicor MGC) also served as control. Bar‐shaped wax patterns (2 × 4 × 22mm) were invested and heat pressed at 875 °C. The elastic constants were determined with the use of the pulsed ultrasonic velocity method. The fracture toughness was measured by the indentation strength technique. The degree of texture was assessed qualitatively by X‐ray diffraction and quantitatively on digital SEM micrographs. The results showed that the mean fracture toughness of the heat‐pressed specimens (1.96 ± 0.19 MPa · m^0.5) was significantly higher than that of the heat‐treated controls (1.51 ± 0.21 MPa · m^0.5) or the proprietary mica glass‐ceramic (Dicor MGC; 1.66 ± 0.04 MPa · m^0.5) (p < .001). It was concluded that heat pressing led to a significant increase in fracture toughness in mica glass‐ceramics because of crystal alignment along the direction of pressing. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 70B: 37–42, 2004