Papers by Keyword: Dental Ceramic

Abstract: The purpose of this study was to compare the transmittance of four dental all-ceramic core materials at clinical recommendation thickness.Specimens with 10mm in diameter and 0.50.01mm in thickness,including IPS e.max Press,Zenostar Zirconia,Lava Zirconia and Upcera Zirconia,were fabricated.The transmittance of specimens were measured with PR2650 spectrophotometer and measurements were analysed statistically with SPSS13.0.Experimental results showed that they had significantly different transmittance.There was a decreasing order,IPS e.max Press Lava Zirconia Zenostar Zirconia Upcera Zirconia,which were 6.1136.750 for IPS e.max,1.6042.135 for Lava Zirconia,1.5782.117 for Zenostar Zirconia and 0.9951.265 for Upcera Zirconia.

Abstract: This study aimed to compare the translucency of four veneered dental all-ceramic core materials,including IPS e.max Press,Zenostar,Lava Zirconia and Upcera Zirconia.All specimens were fabricated at 10mm in diameter and 1.00.01mm in thickness.The translucency of specimens were measured with color difference meter and measurements were statistically analysed with SPSS 13.0. Experimental results showed that their translucency had significant difference,the order of relative translucency from high to low was IPS e.max PressLava ZirconiaZenostarUpcera Zirconia.IPS e.max Press which has good optical effect may be preferable for restoring anterior tooth with higher translucent. As for relatively opaque posterior tooth,Upcera Zirconia may be advisable.

Abstract: In this study the subcritical crack growth (SCG) behaviors of five dental bioceramics were evaluated in order to plot the crack growth velocity versus stress intensity factor (v-K) curves. Disc-shaped samples of two sintered porcelains, two glass-ceramics, and a glass-infiltrated ceramic composite were prepared and tested in artificial saliva using a biaxial flexure jig. The SCG parameters were evaluated by the dynamic fatigue test using five constant stress-rates and in an inert condition. Among the tested materials, the lithium disilicate glass-ceramic showed the highest susceptibility to strength degradation by SCG, whereas the glass infiltrated alumina composite showed the lowest susceptibility. The v-K curves showed that the SCG susceptibility significantly affects the crack growth velocity of the different bioceramics.

Abstract: ZrO₂ ceramics are one of the most important materials used in dental prostheses production, due to their excellent mechanical resistance and chemical inertness in the mouth environment. Nevertheless, the combination of low pHs and fluoride presence is able to reduce the chemical stability of these ceramics. In this work, the resistance of commercial blocks of micrometric and nanometric sized Y₂O₃-stabilized ZrO₂ ceramics (ProtMat Materiais Avançados® and Ivoclar®) was evaluated in Fusayama artificial saliva of different pHs with (and without) the presence of fluoride ions. The study was based on the analysis of the amount of Zr⁴⁺ and Y³⁺ ions dissolved in the artificial saliva after different exposure times using ICP OES technique. The XRD technique was also employed to investigate the phase transformations occurring during the degradation process in artificial saliva. The micrometric sized ZrO₂ ceramics presented higher resistance in the artificial saliva than nanometric sized structures.

Abstract: Studies has been reported a significant incidence of chipping of the feldspathic porcelain veneer in zirconia-based restorations. The purpose of this study was to compare the three-point flexural strength (MPa), Weibull parameters, Vickers hardness (VHN) and Vickers indentation fracture toughness (MPa/mm^1/2) in feldspatic porcelains for metal and for zirconia frameworks. Bar specimens were made with the porcelains e.MaxCeram (EM) and VitaVM9 (V9) for zirconia core, and Duceragold (DG) and VitaVMK95 (VK) for metal core (n= 15). Kruskal-Wallis and Dun test were used for statistical analysis. There was no significant difference (p=0.31) among the porcelains in the flexural strength (Median= 73.2; 74.6; 74.5; 74.4). Weibull calculation presented highest reliability for VK (10.8) followed by EM (7.1), V9 (5.7) and DG (5.6). Vickers hardness test showed that EM (536.3), V9 (579.9) and VK (522.1) had no difference and DG (489.6) had the lowest value (p.001). The highest fracture toughness was to VK (1.77), DG (1.58) had an intermediate value while V9 (1.33) and EM (1.18) had the lowest values (p.001). Despite of the suitable flexural strength, reliability and high hardness, the porcelains used to zirconia-based fixed dental prostheses showed lower fracture toughness values.

Abstract: The purpose of this study was to study effects of the mechanical properties of veneering porcelain on stress distribution of dental zirconia layered structure by three-dimensional finite element analysis. A 3-D geometric model of the first maxillary molar was established, a tooth preparation was simulated by the Imageware software. A crown was designed and divided into three layers: core, middle layer and outer veneer layer. The elasticity modulus of the middle layer was 70GPa for the control model up to 175GPa for the tested models. Loads of 200N were applied over a 1 mm diameter area beneath the tip of the mesial-distal cusp, simulating typical occlusal contact areas, the stress distribution of the crown systems were analyzed. Results show that within the geometry of the crown configuration, one concentration district of maximum principal stress occurred on the occlusal surface closely proximal to the loading position, several sub-maximum principal stress area were observed, such as margin regions of the mesial face, lingual face, distal faces, buccal face and occlusal fossa. Middle layer with higher modulus can effectively disperse the stress concentration in the layered zirconia all-ceramic crown system.

Abstract: To study the influence of background color to 3 all-ceramic system core materials.The chromaticity value of all samples that were put on noble metal, Ni-Cr alloy, Hg-Ag alloy and resign background were measured with chromatism instrument, and chromatic aberration among groups were calculated. The chromatic aberration of Empress II samples on different background color could be distinguished by human eyes, but those of Alumina and Zirconium were unable to being distinguished. In conclusion, the influence of background color to Empress II and In-Ceram Alumina of AL1 were lager. When chosen as core material, noble metals should be covered to keep prosthesis from clinical color-transform. As background to In-Ceram Alumina of AL2, it was unnecessary for resin to be covered. In-Ceram Alumina of AL3, AL4 and In-Ceram Zirconium weren’t affected by background color.

Abstract: The present paper probes into the effect of background color of different post-core materials on the core materials of In-Ceram AL2 Electroformed Alumina, Z21 Electroformed Zirconia, Cercon base color Zirconia, and Cercon base Zirconia. The spectrocolorimeter was used to measure colorimetric values of all groups of samples against the background of noble metal, nickel-chromium alloy, silver amalgam and resin, and to calculate the color difference among the groups. The result showed that the color difference of Cercon base color Zirconia viewed against different backgrounds was identifiable by human eyes (ΔE > 1.5). In contrast, the color differences of In-Ceram AL2 Electroformed Alumina, Z21 Electroformed Zirconia and Cercon base Zirconia viewed against different backgrounds were unidentifiable by human eyes (ΔE < 1.5). Based on this, it can be stated that Cercon base color Zirconia is significantly affected by background color. Thus, proper method to shelter the background color should be adopted. In addition, AL2 Electroformed Alumina, Z21 Electroformed Zirconia, and Cercon base color Zirconia are less influenced by the background color, thus it is not necessary to cover the background color.

Abstract: The aim of this study was to functionalize the surface of Ce-TZP/Al₂O₃ dental ceramic with a nano-structured alumina coating to improve resin bonding. A total of 40 densely sintered disc-shaped specimens (15.5 + 0.03 mm in diameter and 2.6 + 0.03 mm thick) were produced from commercially available NANOZIR blocks and randomly divided into 2 groups of 20. Half of the discs in each group received an alumina coating that was fabricated by exploiting the hydrolysis of aluminum nitride (AlN) powder. The coating was characterized using scanning electron microscopy (SEM). The shear bond strength of the self-adhesive luting cement G-cem was then studied for the coated and uncoated surfaces before and after thermocycling (TC). The SEM analysis revealed that the application of an alumina coating to Ce-TZP/Al₂O₃ ceramics created a highly retentive surface for resin penetration. The resin bond strength to the coated groups was significantly higher than to the uncoated groups, both before and after TC (p ≤ 0,05).

Abstract: The purpose of this study was to investigate the influence of in vitro low-temperature degradation (LTD) treatments on the structural stability and mechanical properties of two commercial Y-TZP ceramics candidate for dental application. TZ-3YS and TZ-3YS-E powder were chosen because of there minor differences of chemical composition. The two powders were compacted at 200MPa using cold isostatic pressure, and densely sintered at 1500°C and 1450°C for 2hr respectively. Two methods of in vitro LTD treatments were performed, the first is to autoclave specimens in steam at 134°C, 2bar, for 1 to 5hr; the second is to immerse specimens into 4% acetic acid at 80°C for 168 hr. XRD was used to identify the crystal phases, flexural strength were tested according to ISO 6872 standard, surface microstructure was evaluated by Atomic Force Microscopy (AFM). Results show that the relative content of monoclinic phase was increasing with the prolonged aging time, the TZ-3YS was more sensitive to LTD compared with TZ-3YS-E. LTD tests did not necessary reduce the flexural strength of Y-TZP ceramics, the nucleation and growth of monoclinic phase were detected by AFM, and the surface microstructure induced by LTD was not identical between the two Y-TZP ceramics. AFM was a sensitive method to evaluate the transformation of Y-TZP ceramics. To choose appropriate Y-TZP powder for dental application, it is mandatory to examine the microstructure before and after LTD.