Hideharu Hirose

Dimensional changes in stone models simulating full crown preparations with adjacent teeth resulting from long-term immersion of medium-viscosity additiontype silicone rubber impressions in disinfectant solutions

If impression materials could be immersed in disinfectant solutions for a longer period, then this form of disinfection would be easier to incorporate into dental preparation procedures. This study investigated the dimensional changes in stone models resulting from immersion of medium-viscosity hydrophilic addition-type silicone rubber impression material in disinfectant solutions for 30 min and 24 h. Impressions of a master die designed to simulate a full crown preparation with adjacent teeth were immersed in 2% glutaraldehyde and 0.55% ortho-phthalaldehyde solutions. The dimensional changes in the mesiodistal and buccolingual dimensions in the stone models were then measured using a three-dimensional coordinate system. It was found that the dimensional changes in the stone models caused by immersion of the impression materials were less than 15 μm. Immersion in 2% glutaraldehyde or 0.55% ortho-phthalaldehyde for 24 h was as clinically acceptable for medium-viscosity hydrophilic addition-type silicone rubber impressions as immersion for 30 min.

Micro-Inactivation of Coliforms by Low-Temperature and Atmospheric-Pressure Plasma Irradiation

In this study, we report on the inactivation technique to apply the oral surgery by micro low-temperature and atmospheric-pressure plasma irradiation utilizing a capillary nozzle. Emission spectrum of the micro-plasma showed OH and O radical, which were affected inactivation of coliform. Vibration temperature of the micro-plasma with 7998 K was calculated from peak-intensity at emission due to N2 2nd positive system. Inactivation region was larger than plasma irradiation spot, and it was increasing with plasma irradiation time.

Micro-Biocidal Activity of Yeast Cells by Needle Plasma Irradiation at Atmospheric Pressure

In this study, we report on the biocidal activity technique by needle helium plasma irradiation at atmospheric pressure using borosilicate capillary nozzle to apply for the oral surgery. The diameter of needle plasma was less than 50 m, and temperature of plasma irradiated area was less than body temperature. Needle plasma showed emission due to OH and O radical. Raman spectra and methylene blue stain showed yeast cells were inactivated by needle plasma irradiation.

Application of Coaxial Ion Gun for Film Generation and Ion Implantation

A magnetized coaxial plasma gun (MCPG) is here utilized for deposition on high-melting-point metals. MCPGs have hitherto been studied mostly in the context of nuclear fusion research, for particle and magnetic helicity injection and spheromak formation. During spheromak formation, the electrode materials are ionized and mixed into the plasmoid. In this study, this ablation process by gun-current sputtering is enhanced for metallic thin-film generation. In the proposed system geometry, only ionized materials are electromagnetically accelerated by the self-Lorentz force, with ionized operating gas as a magnetized thermal plasmoid, contributing to the thin-film deposition. This reduces the impurity and non-uniformity of the deposited thin-film. Furthermore, as the ions are accelerated in a parallel direction to the injection axis, vertical implantation of the ions into the substrate surface is achieved. To test a potential application of the developed system, experiments were conducted involving the formation of a buffer layer on hard ceramics, for use in dental materials.

Surface porosity of stone casts resulting from immersion of addition silicone rubber impressions in disinfectant solutions.

This study investigated the effects of immersion of addition silicone rubber impressions in disinfectant solutions on the surface porosity of the resulting stone casts. Five brands of type 2 and 3 addition silicone rubber impression materials and one brand of type 4 dental stone were used. Impressions of a master die designed to simulate an abutment tooth were immersed in disinfectant for 30 minutes. The disinfectants used were 2% glutaraldehyde solution and 0.55% ortho-phthalaldehyde solution. The surface porosities of stone casts obtained from two brands of impression materials immersed in disinfectant for 30 minutes were determined. Results suggest that impression materials immersed in disinfectant solutions need sufficient time before pouring into dental stone.

A Study on Tensile Bond Strength of Silicone-rubber Soft Relining Material: Denture Relinig to Various Denture Base Materials.

The tensile bond strength (TBS) to denture base materials of silicone-rubber soft relining materials (DRS: Denture Relining Soft type, GC) immersed in water at 37°C from 1 day to 8 weeks was investigated. Four denture base metals (18 K-Au alloy, Ag-Pd-Au alloy, Co-Cr alloy and Pure Ti) and two denture base resins (polycarbonate resin and polysulfon resin) were used. The TBS of DRS was 1.39-2.05 MPa to denture base metals and 1.59-1.81 MPa to denture base resin after 1-dayimmersion, and 1.59-2.75 MPa and 1.47-2.33 MPa respectively after 8-week immersion. These values were significantly superior to those of two ordinary silicone-rubber relining materials.

Studies on polyfunctional cyclophosphazene monomers for dental use (2)--physical properties of polymers.

The present studies were aimed at the development of monomers for dental resins, for which the authors substituted the 8 Cl atoms in P4N4Cl8 with hydrophobic groups (Ph, TF and OF) and a polymerizing group (EMA), and bulk-polymerized them in order to examine their physical properties. Attention was focused on the relationship between the number of substituted hydrophobic groups and the mechanical properties, thermal expansion coefficient, polymerization shrinkage, contact angle, refractive index, water sorption and solubility to establish a basis for the practical use of cyclophosphazene monomers as dental resin monomers. The results obtained were as follows : compressive strength, transverse strength and hardness under dry conditions decreased in accordance with the increased number of substituted hydrophobic groups, but their degree of decrease in mechanical strength under wet conditions (after immersion in water) was small, proving that in comparison with PNC-EMA 4006, having no hydrophobic group, the mechanical properties under wet conditions were improved. It was found that by hydrophobic group substitution, contact angle increased and water sorption decreased. On the other hand, thermal expansion coefficient increased in accordance with the number of substituted hydrophobic groups, but polymerization shrinkage in all cases was very small, 3.09-9.08 vol%. Solubility also showed low values, 0.053 0.160 wt% when the number of substituted hydrophobic groups was 1-2.