Papers by Author: Seiji Ban

Abstract: The aim of the study was to investigate the reaction of phosphate bonded investment to zirconia during for the heat-pressing technique. Two kinds of dental zirconia were used in this study (inCoris ZI and P-NANOZR). Zirconia was invested into the three kinds of phosphate-bonded investment (Ceravety, PC-15 and Norivest). The investments were fired at several different temperatures. The X-ray diffraction peaks due to monoclinic ZrO₂ were not detected on the waxed-up side of zirconia discs. It demonstrates that no low temperature degradation occurred during the heating of the investment. X-ray diffractometry revealed that the peak assigned to ZrP₂O₇ was detected on the contact side of zirconia discs fired with phosphate-bonded investment at 850 and 950°C. It also revealed that diffraction peak assigned to YPO₄ and the monoclinic ZrO₂ were detected in the same side of zirconia discs contacted with phosphate-bonded investment fired at 1100 °C. It can be concluded that the reduction of Y caused the transformation from tetragonal to monoclinic phase and the reduction of strength.

Abstract: The bond strengths between two kinds of zirconia and three kinds of feldspathic veneering porcelains were measured. The specimens were prepared at four firing temperatures for three holding periods, respective opaque porcelain was painted and vacuum-fired. Then, each dentin porcelain was condensed in an acrylic resin mold and vacuum-fired under the conditions mentioned above. Cross sections of the interface between zirconia and porcelain were observed with a scanning electron microscope. The specimens were fixed to specimen holder on a universal testing machine. Data of the bonding test were statistically analyzed. The results showed that all the four factors statistically affected the bonding strength (p<0.01). The contribution of the firing temperature was highest and that of the porcelain type was lowest (p<0.01).

Abstract: Three kinds of dental zirconia (Cercon, NANOZR, and P-NANOZR) were ground and polished with seven kinds of clinical device and materials. After these grinding and polishing, the surface roughness and the glossiness were analyzed. The crystal phases of the surface were analyzed with a micro X-ray diffractometer. The results demonstrated that all three zirconia showed the smallest roughness and the highest glossiness when they were polished with diamond-containing polishing pastes. Tetragonal to rhombohedral transformation was observed on the ground and polished surfaces of Cercon and ZENOSTAR, whereas monoclinic phase was also detected on the ground and polished surface of P-NANOZR. The polishing with diamond-containing pastes showed the smallest transformation amount of rhombohedral and monoclinic phases. It is concluded that dental zirconia can be well polished with diamond-containing pastes, and the phase transformation are also reduced.

Abstract: The aim of this study was to investigate the response of osteoblast-like cells (MC3T3-E1) to the surface of hydroxyapatite-containing glass coating on zirconia (HA-G-Zr) in comparison to yttria stabilized zirconia (Y-TZP). The MC3T3-E1 cells were cultured on HA-G-Zr and Y-TZP specimens in 24-well tissue culture plates. Surface properties were evaluated by X-ray diffractometry, Fourier tranfer infrared microscopy (FT-IR) and scanning electron microscopy (SEM). Cell proliferation in each well was measured by MTT assay. Cell morphology was observed by SEM. Cell differentiation was evaluated by alkaline phosphatase (ALP) activity and osteocalcin levels. After the glass coating on Y-TZP, X-ray diffraction peaks due to hydroxyapatite (HA) were observed clearly. HA-G-Zr appeared on surface of uneven and roughened state, wherein microcracks on the microns in width and many voids of several microns in size were present. Time-dependent proliferation and differentiation of MC3T3-E1 cells were found in all the specimens. MC3T3-E1 cells on HA-G-Zr plates showed higher differentiation than Y-TZP. These results demonstrated that HA-G-Zr showed better cellular biocompatibility than Y-TZP.

Abstract: 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).

Abstract: The aim of this study was to determine the biaxial flexure strength of a commercially available dental pulp capping or cavity liner material, mineral trioxide aggregate (MTA). MTA and a conventional pulp capping material, calcium hydroxide, were used in this study. Each material was prepared into a disk-shaped specimen. Those specimens were stored in 100% humidity atmosphere at 23 or 37°C for 3 or 24 h. Six specimens in each condition were used for the biaxial flexure test using a piston-on-three-ball according to ISO-6872. Surface pH values were determined. The biaxial flexure strengths of MTA after setting in 24h were larger than those of Dycal (p <0.01). pH value of MTA was higher than that of Dycal. These results indicated that MTA was clinically usage material.

Abstract: 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).

Abstract: 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.

Abstract: 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.

Abstract: 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.