Seiji Ban

Biaxial flexure strength and low temperature degradation of Ce‐TZP/Al2O3 nanocomposite and Y‐TZP as dental restoratives

The purpose of the present study was to evaluate the mechanical durability of a zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al(2)O(3) nanocomposite) in comparison to yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) and discuss its application on ceramic dental restorations. The disk-shaped specimens of both materials were stored in physiological saline solution at 80 degrees C for 30 days, in 4% acetic acid at 80 degrees C for 30 days, and in an autoclave at 121 degrees C for 10 days. Before and after storage, specimens were subjected to the biaxial flexure test and to the determination of the monoclinic zirconia content. After autoclaving, Y-TZP showed remarkable increasing of the content of monoclinic zirconia: 0.3 vol % before and 49.9 vol % after, and slight decreasing of biaxial flexure strength: 1046 MPa before and 892 MPa after; whereas Ce-TZP/Al(2)O(3) nanocomposite showed no significant difference in the monoclinic content (4.8-5.5 vol %) and the biaxial flexure strength (1371-1422 MPa) after storage in any conditions. It is concluded that, compared to Y-TZP, the Ce-TZP/Al(2)O(3) nanocomposite has a high biaxial flexure strength along with a satisfactory durability in terms of low-temperature aging degradation in above conditions. This study indicates that the Ce-TZP/Al(2)O(3) nanocomposite demonstrates excellent mechanical durability for dental restorations such as all-ceramic bridges.

Effect of loading conditions on bi-axial flexure strength of dental cements

A ball-on-three-ball bi-axial flexure test was used to evaluate the flexure strengths of five kinds of dental cements (zinc phosphate, polycarboxylate, glass ionomer, silicate, and zinc oxide-eugenol cements). The bi-axial flexure strengths of zinc phosphate cement discs of variable dimensions were also measured to determine the size effects of test specimens. Finite element stress analyses were performed on disc specimens which were subjected to both a concentrated load and a uniformly distributed load. The observed values were compared with the theoretical value calculated by the finite element method. A ball-on-three-ball bi-axial flexure test could not be used for thicker specimens, since the fracture origin of these specimens is more likely to occur on the loaded side.

Effect of Sandblasting and Heat Treatment on Biaxial Flexure Strength of the Zirconia/Alumina Nanocomposite

The effect of sandblasting and heat treatment on biaxial flexure strengths of the zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) was evaluated in comparison to that of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The disc-shaped specimens of the nanocomposite and Y-TZP were sandblasted with 70)m alumina powder. After sandblasting, half of the specimens were heated at 1000°C for 5 min. The biaxial flexure strengths of Y-TZP were independent on the sandblasting, but decreased with the heat treatment. On the other hand, the biaxial flexure strength of the nanocomposite increased with the sandblasting and significantly decreased with the heat treatment. The content of monoclinic ZrO2 of Y-TZP and the nanocomposite increased with the sandblasting pressure and dramatically decreased with the heat treatment. These results suggest that the stress-induced transformation from tetragonal to monoclinic of the nanocomposite occurs more easily than Y-TZP.

Effect of Grinding, Sandblasting and Heat Treatment on the Phase Transformation of Zirconia Surface

This study was aimed to investigate the effect of grinding, sandblasting by alumina and SiC, and heat treatment on the phase transformation from tetragonal to monoclinic zirconia on the surface of yttria stabilized tetragonal zirconia (Y-TZP) and zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite). The monoclinic phase content of both materials increased with the grinding and the sandblasting, while it decreased with the heat treatment. The monoclinic content sequentially increased with the sandblasting and decreased with the heat treatment to each specific value. The SiC-sandblasting produced the larger monoclinic content than alumina-sandblasting. Furthermore, the content changes of the nanocomposite were larger than Y-TZP.

Effect of Sintering Condition, Sandblasting and Heat Treatment on Biaxial Flexure Strength of Zirconia

The effect of sintering condition, sandblasting and heat treatment on biaxial flexure strengths of the zirconia/ alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite, referred to NANOZR) was evaluated in comparison to that of yttria stabilized tetragonal zirconia polycrystals (Y-TZP). The disc-shaped specimens of NANOZR and Y-TZP were cut from the full-sintered or middle-sintered ones. The discs cut from the middle-sintered ones were finally sintered at the same temperature for the full-sintered one. These four kinds of disc were treated in various conditions combined with the sandblasting, the heat treatment, and the storage. The biaxial flexure strength of both middle- and full-sintered Y-TZP decreased with the autoclaving, whereas those of both NANOZR did not change with it. The monoclinic content of both the materials increased with the sandblasting and decreased with the heat treatment. Regardless of the sintering condition, the monoclinic content of the Y-TZP dramatically increased with the autoclaving and those of NANOZR remarkably increased with the sandblasting. Regardless of the different surface roughness, the biaxial flexure strengths of both materials strongly depended on the content of monoclinic ZrO2 on the surface.

Effect of Surface Treatments on Bonding Strength of Dental Ceramics to Resin Cements

The aim of this study was to investigate the effect of surface treatments on bonding strength of two kinds of zirconia to three kinds of resin cements. After thermal cycling, the shear bonding strength of both zirconia decreased in all the resin cements. The bonding strengths of two resin cements in which primer contains silane dramatically decreased after the thermal-cycling (p<0.01). Although the surface roughness of both zirconia sandblasted by 125-%m SiC was quite larger than that by 70-%m alumina (p<0.05), there were no significant differences in the bonding strength of the resin cement to both zirconia sandblasted by 70-%m Al2O3 and 125-%m SiC (p>0.05).

Proliferation of Osteoblast-Like Cells on Zirconia/Alumina Nanocomposite

The aim of this study was to evaluate the biocompatibility with the proliferation of osteoblast-like cell (MC3T3-E1) on zirconia/alumina nanocomposite (NANOZR) in comparison to yttria stabilized zirconia (3Y-TZP) and titanium (Ti). Cellular proliferations after 1-, 3-, 6-, and 9-day incubation were calculated from the measurement of the MTT activities of the proliferated cell and were analyzed by two-way ANOVA. Time-dependent proliferation of MC3T3-E1 in all the sample was observed in all three materials with culture days. However, these were no significant differences in the proliferation between three kinds of material, indicating all the materials have a similar-good biocompatibility.

Effect of Surface Treatments on Bonding Strength of Zirconia to Dental Cements

The aim of this study was to investigate the effect of surface treatments on bonding strength of two kinds of zirconia to two kinds of dental cements. After thermal cycling, the shear bonding strength of both zirconia with alumina coating increased in both cements. The shear bonding strength of both zirconia with sandblasting decrease in Fuji plus after thermal cycling (p<0.05). There was no significant difference between NANOZR and Y-TZP (p>0.05). The bonding strengths of NANOZR with the alumina coating were higher than those with sandblasting after thermal-cycling (p<0.05).