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Biomedical subjects

J B Moser

Publications and source records attributed to J B Moser.

At least 19 recordsLinked to original sources
PubMed1993

Color mixing in dental porcelain.

For esthetic reasons, pigments and opacifiers are added to porcelains used in restorative dentistry. The purpose of this study was to use Kubelka-Munk theory (Kubelka and Munk, 1931) to predict and analyse the colors of porcelains modified by the addition of two pigments and an opacifying agent. The base porcelain was composed of 88% potassium feldspar, 6% quartz and 6% kaolin. The porcelain was modified by the addition of a yellow (Pr-Zr-Si) or a brown (Fe-Cr-Zn) stain and an opacifier (10% SnO in base porcelain). After firing at 1200 degrees C for 30 min, reflectance spectra of the various combinations were obtained with a spectrophotometer. Reflectance spectra, except at low wavelengths, were influenced by increased scattering due to the addition of the opacifier. Calculated values from Kubelka-Munk theory for absorption coefficients and scattering coefficients with appropriate correction factors were compared with the values from the reflectance spectra of the combinations. In general, good agreement was obtained if the scattering coefficient of the opacifier is set equal to 1.0. Using the L*a*b* transform of the CIE color space, it was found that this transform provided uniform color intervals for equal changes in pigment concentration.

Analysis of Variance↗
PubMed1991

Adhesive properties of several impression material systems: Part II.

The effect of saliva contamination on the tensile adhesive bond strengths of four impression adhesive systems, (1) polysulfide, (2) polyether, (3) polyvinylsiloxane, and (4) condensation silicone impression adhesive, was studied. Standard acrylic resin tray samples of 1-inch square surface were made. Tray surfaces were contaminated with saliva either before or after the application of tray adhesives. Tensile tests were performed with a Universal Load testing machine. The tensile adhesive bond strengths of contaminated tray surface and contaminated adhesive were compared with a group of control. Contamination of all impression adhesives resulted in significantly lower bond strength. Except for the polyvinylsiloxane and polysulfide impression adhesive systems, saliva contamination of tray material significantly decreased adhesive bond strengths. Impression trays should be tried in the mouth, rinsed, and dried before adhesive is applied.

Adhesiveness↗
PubMed1991

The effect of oxidation heat treatment of porcelain bond strength in selected base metal alloys.

Base metal alloys have been widely used for fixed partial dentures in the past decade. The oxidation heat treatment (degassing) of these alloys is a controversial step to prepare the metal surface for bonding porcelain. This study evaluated the effect of oxidation heat treatment on the porcelain bond strength of base metal alloys and investigated composition changes that may have occurred during this process.

Analysis of Variance↗
PubMed1991

Adhesive properties of several impression material systems: Part I.

The tensile adhesive bond strength of five impression adhesive systems was studied: polysulfide, polyether, polyvinylsiloxane, condensation silicone impression, and polyvinylsiloxane putty adhesive systems. Results showed no significant difference in adhesive bond strength to autopolymerizing acrylic resin between the former four impression materials studied. Polyether and medium-viscosity polyvinylsiloxane demonstrated significantly higher adhesive bond strength to polystyrene than either polysulfide or condensation silicone. The medium-viscosity polyvinylsiloxane impression material showed significantly higher adhesive bond strength to polystyrene than autopolymerizing acrylic resin whereas polysulfide and condensation silicone impression materials adhered significantly better to autopolymerizing acrylic resin than polystyrene. The polyvinylsiloxane putty did not adhere to its impression adhesive. Variation of the speed of tensile testing between 5 to 20 inches per minutes did not affect the adhesive bond strength of a polysulfide impression material.

Adhesiveness↗
PubMed1990

Cu-Ti, Co-Ti and Ni-Ti systems: corrosion and microhardness.

Titanium alloys of 10 wt%-72 wt% Cu, 10 wt%-80 wt% Co and 20 wt%-84 wt% Ni were investigated. Ingots were fabricated in a vacuum/argon tungsten arc furnace. The surfaces of the alloys were examined by optical microscopy and SEM/EDS, and the Knoop hardness values of the alloys were measured. The corrosion resistance of the alloys was determined by a potentiodynamic polarization technique in buffered Ringer's solution. When a threshold composition of 30 wt% alloy was reached, a large decrease in corrosion resistance was found to occur. Knoop hardness measurements showed that similar hardness values of approximately 300 KHN can be obtained in all systems with lower alloy content. These values are similar to those obtained with a commercial dental titanium alloy.

Chemical Phenomena↗
PubMed1990

Casting pure titanium into commercial phosphate-bonded SiO2 investment molds.

Pure titanium was cast into five different phosphate-bonded SiO2 investment mold materials (at 350 degrees C) with an argon-arc melting and pressure casting machine. The mesh castability, the fit of the MOD inlay castings, and the Knoop hardness and the micro-structure in cross-sections of castings were examined. The setting and thermal expansion, the compressive strength, and the X-ray diffraction analysis of the investments were also measured. The castability, the fit, and the thickness of the reacted layer differed in degree among these investments, in spite of the same phosphate-bonded SiO2-type investment. A significant correlation was obtained between the thermal expansion (at 350 degrees C) and the casting accuracy.

Analysis of Variance↗
PubMed1989

Studies of Ti alloys for dental castings.

Casting of Ti has been recently investigated in dentistry. The purpose of this study was to examine the alloying effect on the cast Ti. Metallurgical structures, mechanical properties, and in vitro corrosion resistance were, therefore, studied for cast Ti and for four selected cast Ti alloys such as Ti-6AI-4V, Ti-15V, Ti-20Cu, and Ti-30Pd. A "Castmatic" dental casting machine was utilized, which involved argon-arc melting and subsequent argon/vacuum-pressurized casting. The photomicrographs revealed quite large grains in the cast structures. XRD analyses on cast Ti metals showed the quasi-equilibrium phases present. The strength of cast Ti could be significantly increased by alloying. Cross-sectional microhardness measurements of cast Ti alloys showed U-type hardness distribution due to the surface mold reaction. All the cast Ti alloys examined showed a strong passivity trend in the corrosion test. The present results suggest that cast Ti alloys have promising features for future dental uses.

Dental Alloys↗
PubMed1989

Evaluation of the viscoelastic behavior of a light-cured denture resin.

A visible light-cured reline resin presently marketed is used directly in the mouth to record the tissue. The viscosity of the material will therefore have an effect on the success of the reline. This article compares the viscoelastic properties of the currently marketed visible light-cured material with a medium-body rubber base material. A cone and plate viscometer was used to help derive the apparent viscosity and flow index of the materials. Readings were recorded with varying shear rates at 25 degrees C and 37 degrees C. The visible light-cured resin was found to have a higher apparent viscosity and flow index than the medium-body rubber base at low shear rates. Temperature had an indirect relationship with the viscosity.

Dental Impression Materials↗
PubMed1987

Visual and instrumental discrimination steps between two adjacent porcelain shades.

Two different porcelain systems were compared over the B1 to B2 shade ranges visually and spectrophotometrically. Six samples of each porcelain were made by blending weighed increments of opaque and body porcelain and firing the blended compositions onto Option metal disks according to manufacturer's instructions. Compositional blends varied incrementally by 20% in steps. Selective blending of porcelain shades was shown to have an effect in improving the range of choices within the shade guide system. The human eye was capable of detecting small-step changes between two steps of the Vita shade guide. Systematic color changes occurred with compositional changes between B1 and B2. It appears from the overall results observed that a desired blending of porcelains at smaller intervals than full shade guide steps could be done more easily with Jelenko than with Vita porcelain. The visual rankings agreed more closely with the manufacturer's expectations than did the instrumental measurements.

Color↗
PubMed1986

Evaluation of light transmission characteristics of protective eyeglasses for visible light-curing units.

Eyeglasses with protective filters are recommended for users of visible light-curing units to decrease the intensity of blue light reaching the eyes. The transmission curves of 20 commercially available filter glasses are obtained. The irradiance from eight curing units through these glasses is measured. The reduction in irradiance through the filter glasses is related to the transmission curves.

Evaluation Studies as Topic↗
PubMed1985

Ultraviolet light stability of composite resins.

The ultraviolet light color stability of seven commercial composite resins was evaluated after 1, 8, and 15 days of exposure. Color differences between exposed and unexposed specimens stored for identical time periods were determined. Samples exposed to ultraviolet light showed large changes in Munsell Hue and Chroma, with smaller but significant changes in Value. Unexposed samples showed small changes in the Munsell components in some cases opposite those observed for the exposed samples. Statistical analysis showed that although significant color changes were observed, brands of composite resins could not be distinguished by length of storage in the dark. Time of exposure was a significant variable at 24 hours and 8 days. At 15 days a number of composite resins did not undergo additional significant color change. Scanning electron microscope showed a significant roughening of the surface of exposed composites with resin breakdown and exposure of the composite filler.

Chemical Phenomena↗