Biomedical subjects

Naohiko Iwasaki

Publications and source records attributed to Naohiko Iwasaki.

6 recordsLinked to original sources

PubMed2005

Radiopacity of experimental composite resins containing radiopaque materials.

This study aimed to investigate the relationship between the radiopacity of an experimental light-cured composite resin and the amount and type of its radiopaque material: Ti, SrCO3, ZrO2, BaSO4, or Bi2O3. Radiopacity of each material was evaluated in terms of aluminum equivalent thickness using an aluminum step wedge. Then, the half-value layer thickness of the experimental composite resin, which had an aluminium equivalent thickness of 1 mm, was evaluated. It was found that the effects of elemental composition were not identical when evaluated in terms of aluminum equivalent thickness and by half-value layer. Nevertheless, both measurement methods indicated that radiopacity increased with increase in radiopaque material content as well as increase in atomic number of the element.

Absorptiometry, Photon↗

PubMed2005

Basic evaluation of cast joining for electroformed coping using multi-purpose alloys.

The purpose of this study was to evaluate the bonding interface and bonding strength of electroformed coping when cast joining was used with a multi-purpose alloy. The multi-purpose alloy was cast at a mold temperature of 700, 750 or 800 degrees C. A high noble alloy tab was also soldered onto an electroformed coping as a control. Sectioned surfaces of cast joining and soldered specimens were observed using a scanning electron microscope and analyzed using an electron probe micro analyzer. Shear bonding strength of specimens cast at 750 degrees C and that of soldered specimens were determined. The edge of the cast joining alloy was round, but this improved as temperature increased. Diffusion of elements from the cast joining alloy and electroformed coping was detected at the interface, which contributed to a significantly higher bonding strength in the cast joining specimen than in the soldered specimen. These results suggested that the cast joining could be potentially employed for electroformed copings.

Dental Abutments↗

PubMed2005

Effective factors including periodontal ligament on vertical root fractures.

The purpose of the present study was to analyze effective factors including periodontal ligament on vertical root fractures (VRFs). Eighty maxillary central incisors were assigned to eight groups, depending on master apical file (MAF) size, loading point and existence of a simulated periodontal ligament (PDL). The gutta-percha in the root canal was vertically pressed with a Co-Cr rod using a universal testing machine. An ordinal logistic analysis was employed to determine significant factors. VRFs were observed in 88.8% of the specimens but no horizontal fractures were found. There were three types of VRFs: partial fracture not involving the apex (PF, 41.3%), partial fracture involving the apex (AF, 40.0%), and complete fracture (CF, 7.5%). MAF size significantly affected VRFs (p < 0.05); large MAF size exhibited more partial fractures involving the apex. Loading point and existence of PDL did not affect VRFs.

Dental Instruments↗

PubMed2004

Effect of test method on flexural strength of recent dental ceramics.

The purpose of the present study was to evaluate the relationships among three flexural strengths of recent dental ceramics using 3-point and 4-point bending tests and biaxial flexural test. Three brands of porcelain for veneering (d.SIGN, Supper porcelain AAA, Vintage Hallo), two injectable ceramics (Empress 2, OPC 3G), and one castable ceramic (Crys-Cera) were used. Twenty bar-shaped and 10 disc-shaped specimens of each ceramic type were prepared according to manufacturers' instructions, polished, and subjected to 3-point and 4-point bending tests and biaxial flexural test, respectively. Three flexural strengths for each ceramics were compared using one-way analysis of variance and Tukey comparison, and also investigated by Weibull analysis. The biaxial flexural strength and 3-point bending strength of all ceramics, except OPC 3G and Crys-Cera, were significantly greater than the corresponding 4-point bending strength. As for OPC 3G and Crys-Cera, their biaxial flexural strengths were significantly greater than their 3-point bending strengths, which is contrary to the other ceramics. The Weibull moduli ranged from 6.6 to 20.8. The Weibull moduli of examined ceramics, except Crys-cera, were statistically insignificant regardless of test methods.

Analysis of Variance↗

PubMed2003

[Fit of electroformed porcelain-fused-to-metal crown on implant abutment].

This study compared the adaptation of a conventional and an electroformed porcelain-fused-to-metal crown. A master model was selected from an ITI implant with a solid abutment (height: 4 mm). Conventional cast metal frameworks of 0.7 mm thickness were prepared with a high noble metal alloy (Degudent U, Degussa) for porcelain fusing (n = 5). Electroformed frameworks of 0.2 mm thickness were determined using pure gold deposition on the abutment using the Auro-Galva-Crown system (AGC, Wieland) (n = 5). Subsequently, a porcelain (Super Porcelain AAA, Noritake) was fused to each framework. Internal gaps between the framework and its abutment were determined using the thickness of a silicone fit checking material. The gaps were measured both before and after porcelain fusing. The thicknesses of the silicone layer of the electroformed and the conventional porcelain-fused-to-metal crown were 34.6 and 38.5 microns at the margin, 33.2 and 39.6 microns at the internal slope, 22.0 and 33.0 microns at the axial, 58.6 and 65.1 microns at the occlusal, respectively. Three-way analysis of variance revealed that the mean gaps in the electroformed porcelain-fused-to-metal crown were significantly thinner than those in the conventional porcelain-fused-to-metal crown (p < 0.05). The electroformed porcelain-fused-to-metal crown showed better adaptability than the conventional porcelain-fused-to-metal crown regardless of porcelain fusing.

Crowns↗

PubMed2002

Temporal relationship between cytosolic free Ca(2+) and membrane potential during hypotonic turgor regulation in a brackish water Charophyte Lamprothamnium succinctum.

Internodal cells of a brackish water charophyte, Lamprothamnium succinctum, regulate turgor pressure in response to changes in external osmotic pressure by modifying vacuolar concentrations of KCl. An increase in cytosolic concentration of free Ca(2+) ([Ca(2+)](c)) is necessary for the progress of turgor regulation induced by hypotonic treatment. Initial changes in membrane potential and [Ca(2+)](c) upon hypotonic treatment were measured to examine the temporal relationship between the two parameters. Fura-dextran (potassium salt, M(r) 10,000, anionic) that had been injected into the cytosol was used to measure [Ca(2+)](c). Membrane potential and membrane conductance under a current-clamp condition were also measured. Decrease in external osmotic pressure by 0.16 Osm induced a simultaneous increase in [Ca(2+)](c) with both depolarization of the membrane and increase in the membrane conductance. Decrease in external osmotic pressure by 0.05 Osm induced a simultaneous increase in [Ca(2+)](c) with membrane depolarization but the increase in membrane conductance started later than the other two processes. There was a close temporal relationship between the increase in [Ca(2+)](c) and membrane depolarization on the initial response of turgor regulation induced by hypotonic treatment.

Biological Transport↗