Effect of pigmentation on the strength of dental Y-TZP/porcelain bilayered structure / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the effect of two methods of pigmentation on the flexural strength of dental Y-TZP/porcelain layered structure.</p><p><b>METHODS</b>KaVo zirconia substructures were pigmented by dipping presintered blocks in the coloring solution VITA LL1 and LL5, and colored TZ-3YS zirconia substructures were fabricated by adding pigments before isostatic pressing. The colors No.1 and No.5 were used for the test. The specimens were made in monolithic or bilayered forms, and the flexural strength was tested. XRD and SEM with EDX were used to analyze the characteristics of the surface structure.</p><p><b>RESULTS</b>In KaVo group, no significant differences were found in the flexural strength between white and LL1 and LL5 colored monoclinic materials, nor in bilayered structures. While in TZ-3YS group, significant differences were noted in the flexural strength between color No.5 white and color No.1 monoclinic materials, but not between the latter two subgroups. The flexural strength was significantly lowered by veneering with porcelain in both zirconia groups, and similar findings were observed with the monoclinic materials. Only the tetragonal phase was detected in both of the zirconia groups.</p><p><b>CONCLUSION</b>Pigmentation has no apparent effects on the bonding strength between the veneering porcelain and zirconia. Both coloring methods are appropriate when the concentration of the pigments is under deliberate control.</p>

Effects of three types of veneering porcelain on bending strength of KAVO(TM) Y-TZP/porcelain bilayered structure / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the effect of three types of veneering porcelain on the bending strength of KAVO Y-TZP/porcelain layered structure.</p><p><b>METHODS</b>KAVO zirconia ceramics were used as the substructure. To form Y-TZP/porcelain bilayered structure, a leucite-based veneering porcelain was fired on the zirconia substructures by slip-casting technique with dentin washbake, and two nano-fluorapatite-based veneering porcelains were fired on the zirconia substructures by either slip-casting or pressed-on technique with or without liner coverage. The bending strength was tested according to ISO 6872 standard, and the veneered surfaces of the fracture samples were analyzed by scanning electron microscopy (SEM).</p><p><b>RESULTS</b>For covering KAVO zirconia core material, the conventional veneering slurry-porcelain combined with liner or wash firing had significant higher bending strength than pressed-on porcelain. SEM showed that the main failure type at the interface was adhesive failure.</p><p><b>CONCLUSION</b>Thin layer sintering using washbake program or liner on KAVO zirconia surface increases the surface wettability, and this procedure may be indispensable when veneering on the surface of dental zirconia.</p>

Structure and properties of colored dental tetragonal zirconia stabilized by yttrium ceramics / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the structure, mechanical and low temperature aging properties of colored dental zirconia ceramics.</p><p><b>METHODS</b>5 graded colored dental zirconia ceramics were made by adding colorants and their combinations into a 3Y-TZP (tetragonal zirconia stabilized by 3mol% yttrium) powder, the green body were compacted at 200 MPa, pre-sinter at 1,050 degrees C and maintained for 2 h, then densely sintered at 1,500 degrees C for 2 h. Specimens were cut from each of the 5 graded colored blocks. Physical, mechanical properties as well as chemical stability were tested, microstructure were observed, crystalline phase were identified by X-ray diffraction (XRD), aging properties were assessed by measurement of the relative content of monoclinic phase and bending strength testing.</p><p><b>RESULTS</b>The overall density of colored zirconia ceramics was over 99.7%, linear shrinkage was about 20%, while thermal expansion coefficient was about 11 x 10(-6) x degrees C(-1), the crystalline phase was tetragonal, bending strength was over 900 MPa which was slightly lowered than that of the uncolored zirconia, fracture toughness was slightly higher. Good chemical stability in acetic acid was observed. After aging treatment, tetragonal-to-monoclinic phase transformation was detected up to 40%, while bending strength was not significantly degraded.</p><p><b>CONCLUSION</b>The results showed that colored 3Y-TZP ceramics presented good mechanical properties even after aging treatments, and was suitable for dental clinical use.</p>

In vitro evaluation of low-temperature aging effects of Y2O3 stabilized tetragonal zirconia polycrystals dental ceramics / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the influence of in vitro low-temperature degradation (LTD) treatment on the structural stability of 5 kinds of Y2O3 stabilized tetragonal zirconia polycrystals (Y-TZP) dental ceramics.</p><p><b>METHODS</b>TZ-3YS powder was compacted at 200 MPa using cold isostatic pressure and pre-sintered at 1050 degrees C for 2 h forming presintered blocks. Specimens were sectioned into 15 mm x 15 mm x 1.5 mm slices from blocks of TZ-3YS, Vita In-Ceram YZ, Ivoclar, Cercon Smart, and Kavo Y-TZP presintered blocks, 18 slices for each brand, and then densely sintered. Specimens were divided into 6 groups and subjected to an accelerated aging test carried out in an autoclave in steam at 134 degrees C, 0.2 MPa, for 0, 1, 2, 3, 4, and 5 h. X-ray diffraction (XRD) was used to identify crystal phases and relative content of monoclinic phase was calculated. Specimens for three-point bending test were fabricated using TZ-3YS ceramics according to the ISO 6872 standard and bending strength was tested before and after aging. The polished and aging specimens of TZ-3YS and Cercon Smart zirconia ceramics were observed by atomic force microscopy (AFM) to evaluate surface microstructure.</p><p><b>RESULTS</b>Tetragonal-to-monoclinic phase transformation was detected for specimens of TZ-3YS, Vita In-Ceram YZ, Ivoclar, and Kavo zirconia ceramics except for Cercon Smart ceramics after aging, and the relative content of monoclinic phase was increasing with the prolonged aging time. TZ-3YS was the most affected material, Kavo took the second, and Vita and Ivoclar were similar. Aging had no significant negative effects on flexural strength of TZ-3YS with average bending strength being over 1100 MPa. The nucleation and growth of monoclinic phase were detected by AFM in surface of Cercon Smart zirconia in which monoclinic phase was not detected by XRD.</p><p><b>CONCLUSIONS</b>The results suggest that LTD of dental Y-TZP is time dependent, but the aging test does not reduce the flexural strength of TZ-3YS. The long-term clinical serviceability of dental Y-TZP needs further observation.</p>

Preparation and chromaticity properties of colored dental 3Y-TZP ceramics / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To obtain and investigate the chromaticity properties of colored dental 3Y-TZP ceramics with different colorant combinations.</p><p><b>METHODS</b>Colorant combinations were mixed with TZ-3Y-S powder, then the mixtures were compacted at 200 MPa using cold isostatic pressure, densely sintered at 1500 degrees C for 2 h forming 5 graded colored dental zirconia ceramics. Specimen were sectioned into 10 mm x 10 mm x 0.5 mm and 10 mm x l0 mmx 1 mm slices from the sintered blocks. Color measurement was performed under black background using spectrophotometer. The chromaticity properties were compared with that of the VITA In-Ceram YZ shade guide.</p><p><b>RESULTS</b>Five colored dental zirconia ceramics were obtained. The lightness decreased gradually, and the chroma value increased gradually. The color differences of the two thickness specimens were little. The parameters of the color space were L*: 67.76-77.78; a*: -2.19-3.80; b*: 12.13-25.01, which was similar with that of the VITA In-Ceram YZ shade guide, while the lowest value of lightness was relatively higher than that of the VITA In-Ceram YZ shade guide.</p><p><b>CONCLUSION</b>Colored 3Y-TZP dental ceramics are suitable for clinical use. There is a need to develop more darkness shaded zirconia dental ceramics.</p>

The preparation, structure evaluation and preliminary application of biomimetic biphasic calcium phosphate scaffold / 中华外科杂志

<p><b>OBJECTIVE</b>To fabricate biomimetic biphasic calcium phosphate BCP ceramic scaffolds using three-dimensional (3D) gel-lamination technology and evaluated their structure with 3D parameters and related method.</p><p><b>METHODS</b>Series two-dimensional images of femoral head's specimen of dogs were obtained by micro-computed tomography (Micro-CT). According to these images, porous biomimetic biphasic calcium phosphate (BCP) ceramic scaffolds with oriented trabecular structure were fabricated by three-dimensional (3D) gel-lamination technology. And then, the three-dimensional structure of the scaffolds were reconstructed by computer according to Micro-CT images of these scaffolds and evaluated by three-dimensional parameters. These parameters included bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular spacing (Tb.Sp) and structure model index (SMI). The biomechanical properties and biocompatibility of these scaffolds were also evaluated in the study. Six scaffolds, which were combined with BMCs (bone mesenchymal cells, BMCs), were planted into the bone defect of six dogs' femoral head respectively.</p><p><b>RESULTS</b>There was no significant difference between trabecular samples and BCP scaffolds in BV/TV, Tb.Th, Tb.N, and Tb.Pf (P > 0.05). The trabecular system of the scaffold, which had some orientation, represented plate-like model. With a micro-porous porosity of 62%, the average compressive modulus and ultimate strength along the axis of the scaffolds reached (464.0 +/- 36.0) MPa and (5.6 +/- 0.8) MPa respectively. The results of animal test indicated that the trabeculae of these scaffolds were covered by a layer of new bone after 10 weeks of operation.</p><p><b>CONCLUSION</b>Porous BCP scaffolds have been produced with oriented microarchitectural features designed to facilitate vascular invasion and cellular attachment and with initial mechanical properties comparable to those of trabecular bone.</p>

Coloration of mica glass ceramic for use in dental CAD/CAM system / 中华口腔医学杂志

<p><b>OBJECTIVE</b>An intrinsically colored machinable glass-ceramic containing tetrasilicic fluormica as the predominant crystal phase was studied, which was used in molar crown in dental CAD/CAM system.</p><p><b>METHODS</b>Orthogonal design analysis was used to select appropriate base formula, coloration and heat treatment process.</p><p><b>RESULTS</b>Factors influencing the color appearance of mica glass ceramic were nucleation agent and the ratio of Mg(2+) to K(+) in base formula; Cerium oxide (CeO(2)) was used as the main coloration; The preferred heat treatment was 650 degrees C for 1 h and 1,000 degrees C or 1,050 degrees C for 3 h - 4 h.</p><p><b>CONCLUSIONS</b>This mica glass-ceramic could provide 4 to 5 color appearance for dental use, it showed excellent machinability which was eminently suitable for use in dental CAD/CAM system.</p>

The bonding characteristic of titanium and RG experiment porcelain / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To study the bonding characteristic of Titanium and RG experiment porcelain.</p><p><b>METHODS</b>5 specimens with a size of 10 mm x 5 mm x 1.4 mm were cast from pure titanium. Then 1 mm of RG experiment opaque and body porcelain were fused on the surface of the titanium specimens. The interface of titanium and porcelain was analyzed with a scanning electron microscope with energy-despersive spectrometry; 6 metal specimens with the size of 25 mm x 3 mm x 0.5 mm were cast from Ni-Cr alloy and a uniform thickness of 1 mm of VMK 99 porcelain was veneered on the central area of 8 mm x 3 mm 18 metal specimens as the same size were cast from pure titanium. The uniform thickness of 1 mm of VITA TITANKERAMIK porcelain, of Noritake super porcelain Ti-22 and of RG experiment porcelain were veneered on every 6 specimens respectively in the central area of 8 mm x 3 mm. The specimens were subjected to a three-point bending test on a load-test machine with a span of 20 mm, then the failure loads were recorded and statistically analysised. The RG porcelain/titanium crown was fabricated by fusing RG opaque porcelain and body porcelain to cast titanium substrate crown.</p><p><b>RESULTS</b>The SEM results show no porosity and crackle were found in the interface. The energy-dispersive spectrometry show that there are Si, Ti and O in the 1 micro m layer between porcelain and titanium, which suggesting titanium and experiment porcelain bonding well. The three point test showed the fracture force for the combinations of titanium/VITA TITANKERAMIK porcelain, titanium/Noritake super porcelain Ti-22 and titanium/RG experiment porcelain were (7.233 +/- 2.539) N, (5.533 +/- 1.199) N and (6.316 +/- 1.433) N respectively. There were not statistically significant differences among them (t test, P < 0.01). The fracture force for the Ni-Cr alloy/VMK99 porcelain combination (12.733 +/- 3.297) N was significantly greater than those of the cast titanium/porcelain (t test, P > 0.05). The crown was translucent with no crack.</p><p><b>CONCLUSION</b>RG porcelain is well compatible with titanium.</p>

Strength and fracture toughness of MgO-modified glass infiltrated alumina for CAD/CAM.

OBJECTIVE: This study was conducted to investigate the effect of MgO additive to Al2O3 on the flexural strength, fracture toughness of glass infiltrated alumina for CAD/CAM application. METHODS: Alumina blanks with additive of 0.5 wt% MgO were prepared via isostatic pressing and sintering at 1400 degrees C for 2h, and then alumina-glass composites were fabricated by infiltrating the molten glass into the partially sintered alumina compact. Flexural strength and fracture toughness were determined using three point bending methods and a single edge notched beam method. The mechanism of crack propagation was observed under a field emission scanning electron microscope. RESULTS: The three-point flexural strength and fracture toughness of partially sintered alumina and alumina-glass composite were 210 MPa, 1.86 MPam(1/2), and 432.2 MPa, 5.12 MPam(1/2), respectively, and they were free of shrinkage during the processing of glass infiltration. The field emission SEM micrograph indicated that indentation caused a non-planar crack propagation including crack deflection and crack bowing. SIGNIFICANCE: MgO was used as an additive to alumina to improve the strength and fracture toughness of partially sintered alumina and alumina-glass composite. The high strength and toughness are related to toughening by the distribution of alumina with uniform particle sizes, crack bowing, crack deflection and the beneficial wetting properties of the particle surface.