Yukimichi Tamaki

Effects of investment type and casting system on permeability and castability of CP titanium

STATEMENT OF PROBLEM Several factors, such as casting systems and investment properties, are important to obtain a sound titanium casting. Although various casting systems and investments for titanium are commercially available, their effects on CP titanium castability are not clear. PURPOSE The purpose of this study was to determine permeability of investments and to evaluate the effects of investment type and casting system on titanium castability. MATERIAL AND METHODS Three investments for titanium (experimental gypsum-bonded investment, Selevest CB, and Speed Titan) and 4 titanium casting systems (Cyclarc, Ti-Cascom, Vulcan T, and Ticast Super R) were used. Permeability was measured using a flow meter and argon gas at 0.1, 0.2, and 0.3 MPa. Castability was calculated as the percentage of reproduced holes compared to a perforated wax pattern. Data for castability and permeability were analyzed separately with 2-way ANOVA and the Tukey HSD test (alpha=.05). RESULTS The ANOVA for permeability and castability showed significant interaction (P<.001 and P=.004, respectively). Differences in permeability among the 3 investments increased with a higher gas pressure. Permeability of the experimental investment at each pressure level was significantly greater than that of the other investments, except for Speed Titan at 0.1 MPa (P<.05). The permeability of Selevest CB at each pressure level was significantly less than that of the other investments (P<.05). Cyclarc and Ti-Cascom specimens were not significantly different, in terms of castability, using the investments evaluated, but castability of Vulcan T and Ticast specimens varied significantly by the investment used (P<.05). CONCLUSIONS Within the limitations of this study, investment type, pressure level, and their combinations influenced permeability. Castability of titanium was influenced by investment type, casting system, and their combinations. The investment with the highest permeability did not demonstrate the best result for castability.

EFFECTS OF SURFACE ROUGHNESS AND DIMORPHISM ON THE ADHESION OF CANDIDA ALBICANS TO THE SURFACE OF RESINS: SCANNING ELECTRON MICROSCOPE ANALYSES OF MODE AND NUMBER OF ADHESIONS

AIM Candida albicans is a common oral fungus but can cause serious conditions such as Candida stomatitis. We investigated C. albicans adhesion to the surface of denture-base resins at two growth phases. METHODS Fungal suspensions of logarithmic (9 h) and stationary phase (24 h) C. albicans (JCM2085) were used. Scanning electron microscopy (SEM) confirmed that yeast and mycelial forms were predominant in 9-h and 24-h cultures, respectively. Resin strips were polished to three surface roughness levels (Ra 3.2 μm, Ra 0.48 μm and Ra 0.06 μm) and were then immersed in C. albicans suspensions for both phases. The SEM images were taken at five sites on each strip. RESULTS Adhesion of mycelial-form C. albicans on rough surfaces (Ra = 3.2) was 2.2 times higher than on smooth surfaces (Ra = 0.06; 7030 vs 3580 adhesions/mm(2), P < 0.01). The hyphae of these mycelial forms fully penetrated the surface cracks. Fewer adhesions occurred for yeast-form C. albicans, regardless of surface type (440-620 adhesions/mm(2), P = n.s.). CONCLUSION Adhesion of yeast-form C. albicans was indifferent to surface roughness. In contrast, mycelial adhesion increased with surface roughness of the resin because mycelia infiltrated the minute protuberances on rough surfaces.

Synergistic responses of superficial chemistry and micro topography of titanium created by wire-type electric discharge machining

Wire-type electric discharge machining has been applied to the manufacture of endosseous titanium implants as this computer associated technique allows extremely accurate complex sample shaping with an optimal micro textured surface during the processing. Since the titanium oxide layer is sensitively altered by each processing, the authors hypothesized that this technique also up-regulates biological responses through the synergistic effects of the superficial chemistry and micro topography. To evaluate the respective in vitro cellular responses on the superficial chemistry and micro topography of titanium surface processed by wire-type electric discharge, we used titanium-coated epoxy resin replica of the surface. An oxide layer on the titanium surface processed by wire-type electric discharge activated the initial responses of osteoblastic cells through an integrin-mediated mechanism. Since the mRNA expression of ALP on those replicas was up-regulated compared to smooth titanium samples, the micro topography of a titanium surface processed by wire-type electric discharge promotes the osteogenic potential of cells. The synergistic response of the superficial chemistry and micro topography of titanium processed by wire-type electric discharge was demonstrated in this study.

Bone Regenerative Potential of Mesenchymal Stem Cells on a Micro- Structured Titanium Processed by Wire-Type Electric Discharge Machining

A new strategy with bone tissue engineering by mesenchymal stem cell transplantation on titanium implant has been dawn attention. The surface scaffold properties of titanium surface play an important role in bone regenerative potential of cells. The surface topography and chemistry are postulated to be two major factors increasing the scaffold properties of titanium implants. This study aimed to evaluate the osteogenic gene expression of mesenchymal stem cells on titanium processed by wire-type electric discharge machining. Some amount of roughness and distinctive irregular features were observed on titanium processed by wire-type electric discharge machining. The thickness of suboxide layer was concomitantly grown during the processing. Since the thickness of oxide film and micro-topography allowed an improvement of mRNA expression of cells, titanium processed by wire-type electric discharge machining is a promising candidate for mesenchymal stem cell based functional restoration of implants.

A modified porous titanium sheet prepared by plasma-activated sintering for biomedical applications.

This study aimed to develop a contamination-free porous titanium scaffold by a plasma-activated sintering within an originally developed TiN-coated graphite mold. The surface of porous titanium sheet with or without a coated graphite mold was characterized. The cell adhesion property of porous titanium sheet was also evaluated in this study. The peak of TiC was detected on the titanium sheet processed with the graphite mold without a TiN coating. Since the titanium fiber elements were directly in contact with the carbon graphite mold during processing, surface contamination was unavoidable event in this condition. The TiC peak was not detectable on the titanium sheet processed within the TiN-coated carbon graphite mold. This modified plasma-activated sintering with the TiN-coated graphite mold would be useful to fabricate a contamination-free titanium sheet. The number of adherent cells on the modified titanium sheet was greater than that of the bare titanium plate. Stress fiber formation and the extension of the cells were observed on the titanium sheets. This modified titanium sheet is expected to be a new tissue engineering material in orthopedic bone repair.