Papers by Author: K.S. Oh

Abstract: In Vitro Bond strength of base-coated (Y, Fe)-TZPs (yttria and iron co-doped tetragonal zirconia polycrystals) were investigated to evaluate the feasibility for the ceramic bracket applications. Pre-sintered (Y,Fe)-TZP brackets were machined, abraded and spray-coated with granule slurries containing 10~50 wt% of flux. Better adhesion to the base surface of the brackets was observed by raising the amount of flux in the slurries. It may be because of the fusion and the collapse of the granules as a result of the high amount of flux. The one-way analysis of variance indicated that there were significant differences in bond strength measurements between the experimental groups except 30% and 50% flux content groups. The Weibull distribution revealed that 50% flux content group is the best with a high characteristic strength value. Mean ARI values exhibited large differences and ranged from 1.6 for 50% flux content group to 3.0 for non-coated group. Adhesive remnant of adhesive resin was decreased by increasing the flux up to 50%. Reduction in adhesive remnant is likely due to the higher bonding of adhesive resin to granules. No teeth and bracket damages were found in any teeth de-bonded by shear force. The base-coated brackets with higher strength (11.5 MPa) and no adhesive remnant were newly proposed for the orthodontics applications.

Abstract: In this study, we attempted preparation and assessments of composite pastes of demineralized bone matrix (DBM) and calcium phosphate cement (CPC). While the composite pastes presented self-setting behavior up to a certain DBM content without significant differences in setting time, temperature increase and phase transformation, compressive strength and injection capability decreased in general with the DBM content. The DBM particulates were observed to uniformly disperse in the composite cross-sections, suggesting a new model of bioactive paste with tissue regenerative function.

Abstract: Yttria and iron co-doped tetragonal zirconia polycrystals ((Y, Fe)-TZPs) were investigated to evaluate the feasibility for the ceramic bracket application. Presintered the (Y,Fe)-TZPs brackets were machined, abraded and coated with granule spray containing 10~50 wt% of flux. Finally, the base-coated brackets were sintered. Roughness of the coated surface was decreased to 13 um and 10 um when the flux content was 30 wt% and 50 wt%, respectively. It may be due to the fusion and the collapse of the granules as a result of the high amount of flux. Better adhesion to the base surface of the brackets and irregular shape were observed by raising the amount of flux in the slurries. Wetting angle of ethylene glycol droplet on the (Y,Fe)-TZP bare surface was determined to be 41.85°, however, the angle became 0° after the granule spraying treatments. The (Y,Fe)-TZP brackets exhibited uniform embossed base and good wetting. The newly developed base-coated bracket could be highly applicable to enhance retention and to reduce adhesive resin remnant during the bracket debonding.

Abstract: Two tetragonal (t) zirconia-alumina composites were prepared by adding Al2O3 (20 vol%) into t-ZrO2 solid solutions doped with 3.0 mol% Y2O3, 1.6 mol% Nb2O5, 3.6 mol% CeO2 (Al20Ce) and 5.3 mol% Y2O3, 4.6 mol% Nb2O5 (Al20) as the femoral heads for the total hip replacements. The effect of machining and annealing on the hydrothermal stability and surface roughness of the composites was evaluated by comparing with the commercial 3 mol% Y2O3 stabilized t-ZrO2 (3Y-TZP). Machining was conducted by using the high-precision machine, where the spindle speeds (rpm 9000~18000) and the electroplated wheels (#400, 800) can be easily adjusted. The machined specimens were annealed at temperatures from 900 to 1300 oC and subsequently autoclaved for 5 days at 120oC under 0.3 MPa water vapor pressure. Although the phase stability and surface roughness of the machined composites were found to be inferior, the hydrothermal stability of the annealed and subsequently autoclaved composites was determined to be excellent as compared with that of the commercial 3Y-TZP. The lower phase stability of the machined composites was likely to be due to numerous machining damages (surface defects) of the composites than those of 3Y-TZP.