Key Engineering Materials Vols. 512-515

Abstract: The matching properties of ceramics and veneering porcelain play an important role for the overall color and mechanical properties of dental crowns. The Vita VM9 veneering porcelain was coated on the surfaces of two zirconia, three-point flexural strength, heat shock resistance and the overall color after veneered with porcelain were tested. The results showed that the interlayer cracks, radial cracks or porcelain body cracks were not appeared in all samples during thermal shock experiments at 60~220°C. Their flexural strength was all above 700MPa and the overall color covered the common color of VITA-3D Master shade guide. There is good thermal compatibility between the two dental shaded zirconia ceramics and Vita VM9 veneering porcelain. The mechanical properties are suitable for clinical posterior teeth area restorative, and the overall color is also suitable for the requirements on the color and brightness of clinical dental restoration.

Abstract: Low temperature aging (LTD) is an important factor of Y-TZP ceramic as artificial joint femoral head and dental restorative materials in vivo for long-term application. In this paper, the accelerated aging experiments on Y-TZP ceramics were conducted. The t-m phase transition is occurring from the surface to the inside during low temperature aging of Y-TZP ceramics. As content of phase transformation increases, thickness of phase transformation layer increases. While the content of surface monoclinic phase is less, the volume expansion and surface stress caused by phase transformation can make cracks and holes shrink or even close, then the flexural strength increase. As a large number of surface monoclinic phase was generated, due to there are a lot of microscopic defects in the phase transition layer, crystals loose, strength of grain boundary lower than that of not aging area and phase transformation layers fracture in the intergranular mode, that damages the flexural strength. Therefore, the flexural strength increase firstly and then decrease with the increase of surface monoclinic content.

Abstract: Abstract. The purpose of the study was to evaluate the affection of post-core materials on the resultant color of lithium disilicate ceramic restorations. Twenty disk-shaped core-veneer specimens were prepared with IPS e.max Press and IPS e.max Ceram. Twenty-five substructure specimens were also prepared. Color measurements were performed for all specimens with each substructure by a calibrated spectrophotometer. Lab chromatic values were obtained. The chromatic aberration (△E) compared with dentine substructure was 1.33 for ziconia based combinations , 1.40 for resin based combinations, 4.37 for cobalt chromium alloy based combinations and 3.05 for gold metal alloy based combinations. The zirconia and resin post-core materials are recommended to form substructures for the lithium disilicate ceramic restorations. Cobalt chromium alloy and Gold metal alloy post-core materials are not recommended.

Abstract: Despite the expanded application for zirconia in restoration dentistry, there is less clear recommendation in the literature regarding the relation between zirconia surface roughness and its shear bond strength to resin cements. The aim of this study was to assess the effect of surface roughness of Cercon zirconia on its shear bond strength to resin cements. 66 Zirconia rectangular specimens (10 mm×10 mm×3 mm) were prepared from Cercon zirconia blocks, finished using a diamond rotary cutting instrument, sintered, and then assigned into 6 groups. The specimens in the first group without polishing were used as control. Other groups were polished against 120#, 240#, 360#, 500# and 600# sand paper after sintered, respectively. Ceramic surface were analyzed by scanning electron microscopy (SEM) and Surface profilometer. 10 samples of each group were bonded with Variolink N resin cements respectively and submitted to shear bond strength test. Shear bond strength was measured and statistically analyzed. The results showed that the population means of 6 groups of samples were not equal. There was no significant difference between control group and 600# sand paper treated group, 500#, 360# and 240# sand paper treated groups (P>0.05), but a significant difference among the other groups (P<0.05). Findings of this study revealed that the shear bond strength might be raised by increasing the surface roughness of Cercon zirconia. Therefore, the surface roughness of Cercon zirconia has an effect on the shear bond strength, but is not the determining factor in clinical use.

Abstract: To investigate the influence of alveolar bone loss and post design on stress distribution of a severely damaged canine. The residual canal dentin wall in the cervical region was standardized at 0.5mm in thickness. Twelve two-dimensional finite element models were created. The models were varied in their alveolar bone loss. The post systems include computer-aided design/computer-aided manufacturing zirconium post, prefabricated glass fiber post, cast stainless steel post, and cast gold post. The numerical models were considered to be restored with an all-ceramic crown. A load of 100N was applied to the crown at an angle of 45 degree on the lingual surface, and Mises stresses were calculated. Finite element analysis revealed that cast stainless steel post system showed the lowest maximum Mises stress in the dentine at 86.46 MPa, while, glass fiber post resulted in the highest stress concentration in the dentin at 174.3 MPa. Stresses were reduced by increasing alveolar height. Loss of alveolar bone loss may lead to an increased risk of failure.

Abstract: Abstract. This study investigated the relative translucency of IPS E.max core-veneer combinations of different colors at a clinically appropriate thickness. Core specimens (n=5) of IPS E.max were produced and veneered with IPS E.max veneering porcelain to a final dimension (13 mm in diameter, 1.5mm in thickness). Luminous reflectance was measured three times each specimen with a calibrated spectrophotomete. Contrast ratios were measured from the luminous reflectance(Y) of the tested specimens with a black (Yb) and a white background (Yw). Contrast ratios ranged from 0.798-0.818 for LT core-veneer combinations, 0.831-0.845 for MO core-veneer combinations, 0.929-0.941 for HO core-veneer combinations. There were no significant difference in contrast ratios of core-veneer combinations of the same series (P>0.05). Contrast ratios of LT, HO, MO core-veneer specimens were significantly different (P<0.05). Luminosity and chroma are not related to the relative translucency of core-veneer specimens. LT core-veneer combinations exhibited highest relative translucency, followed by MO and HO core-veneer combinations.

Abstract: To compare thickness of veneering ceramics dependence of the stress profile in veneering ceramic layered on zirconia and metal frameworks. Cylindrical core materials dentine ceramic specimens whose diameter is 20.0mm, thickness is 0.5mm were made with customized method, and then Upcera zirconia and metal plate were veneered, the thickness of the veneering ceramics respectively were 1.25mm, 1.50mm and 1.75mm, a total of six groups (n=10). An CAD-CAM machine was used for the drilling procedure and residual stress profile of all-ceramic crowns and metal-ceramic crowns was calculated. The mean residual stress of zirconia all-ceramic restorations were: respecitively, 60.15±5.54MPa for 1.25mm thickness of veneering; 53.37±5.12MPa for 1.50mm thickness of veneering; 45.64±4.53MPa for 1.75mm thickness of veneering. The mean residual stress of glass infiltrated alumina all-ceramic restorations were: respectively, 61.32± 5.76MPa for 1.25mm thickness of veneering; 52.45±5.35MPa for 1.50mm thickness of veneering; 45.89±4.26MPa for 1.75mm thickness of veneering. Residual stress profile of all-ceramic restorations was significantly different among specimen groups of Y-TZP and Metal plate (P>0.05). There was also significantly different among specimen groups which had same thickness of the veneering ceramics but not belonged to same frameworks (P<0.01). As the depth increases, the stress gradually increases, reaching the maximum at the interface of MV or CV. The residual stress of frameworks was tensile stress, but the residual stress of veneering porcelain interior was compress. With the veneer porcelain thickness, the residual stress of the interface gradually reduce.

Abstract: To evaluate the masking ability of IPS e.max all-ceramics system of HO series. IPS e.max Press HO ingots were fabricated into twenty cylindrical specimens (n=5) with the diameter of 13mm and four different thinknesses (0.4mm, 0.6mm, 0.8mm, 1.0mm). All specimens after veneered, gazed and cemented to metal substrate disks (thickness 3mm, diameter 13mm) were measured on both the white background and metal substrate disks background using a spectrophotometer and values of L, a and b were calculated to compare color differences among four groups. Meanwhile ΔE with the preselected required color (A2 color) were calculated. ΔE<1.5 was considered a clinically acceptable color match. In the 0.4mm thickness specimens group, the values of L, a and b significantly increased (-1.36±0.05, -0.15±0.06, -1.46±0.02, respectively) between the white background and abutment background. But there were no significant color differences in the other three groups (P<0.05). In the 0.6mm and 0.8mm thicknesses specimens groups, the color difference values (0.71±0.04, 1.14±0.06, respectively) with A2 color were less than the defined value. Thus the cylindrical specimens with the thickness of 0.6mm, 0.8mm and 1.0mm could mask the metal substrate disks background sufficiently and the thickness of 0.6mm and 0.8mm had an acceptable color match compared with the target color. IPS e.max all-ceramics system of HO series can produce clinically acceptable color match and have the capacity to mask a dark background such as a dark tooth or core buildup material.

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: This experiment was to study the transmittance of 3 all-Ceramic system core materials, including 4 colors of Vita In-ceram Alumina,4 colors of Vita In-Ceram Zirconium and 3 colors of Empress II,and to provide basis for clinical choice of core materials.With Vita alpha veneer porcelain as control,the transmittance of all samples was determined with spectrophotometer under D65 standard source.The transmittance of materials was 1.434%~3.843% for Vita In-Ceram Alumina,0~0.587% for Vita In-Ceram Zirconium,5.620%~6.665% for Empress II.As a whole,the transmittance of Empress IIwas the best of 3 core materials,that of In-Ceram Alumina was the worse,that of Vita In-Ceram Zirconium was the worst.