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Biomedical subjects

R Grajower

Publications and source records attributed to R Grajower.

At least 37 records · Page 2Linked to original sources
PubMed1982

Optical properties of composite resins.

The translucency and colour of a composite resin are characterized by two wavelength-dependent parameters: the absorption coefficient, K and the scattering coefficient, S. These parameters were calculated according to the Kubelka-Munk (1931) equations for two commercial resins. The calculations were based on reflectance spectra of samples of different thicknesses which were placed on a black and a white background. Employing the values of these parameters, calculated spectra were obtained of samples on the same as well as different backgrounds. The difference between the experimental and the calculated spectra was evaluated in terms of Friele-MacAdam-Chickering (Hemmendinger, 1970) colour differences. The Munsell colour values, corresponding to the spectra were evaluated. It was found that the colour of a resin sample of a specified thickness which is placed on a particular background may be predicted to a fair degree of accuracy from calculations employing the K and S values of the resin and the reflectance spectrum of the background. It has been demonstrated that illuminating the sample at 45 degrees instead of using diffuse illumination, affected the results only to a small extent. The effect of internal reflections at the resin surface on the relfectivity on the sample is discussed. An expression has been derived for computing the reflectivity of a sample on any background from its transmittance and reflectivity on a completely absorbing background.

Color↗
PubMed1981

Temporary space maintainers retained with composite resin. Part II: Fracture load in vitro.

The average fracture load during occlusal loading of pontics which were bonded to natural abutment teeth in vitro was found to be 56.1, 57.5 and 74.2 kg for natural, acrylic resin, and Restodent pontics, respectively. Coating the roots of the abutment teeth with a thin layer of silicone rubber before embedding them in stone slightly reduced the strength of the fixed partial dentures. Thermocycling the specimens with coated roots caused a considerable decrease in strength to fracture loads of 33.0, 17.9, and 37.3 kg for natural, acrylic resin, and Restodent pontics, respectively. Fracture of the enamel of natural tooth pontics was observed in a few specimens. The superior strength of the fixed partial dentures with natural tooth and Restodent pontics would indicate that these pontics are superior for clinical trials rather than acrylic resin pontics.

Acrylic Resins↗
PubMed1981

Addition of fluoride compounds to acrylic resin plates: bending strength and fluoride release.

The effect of incorporated CaF2 (2.04%), NaF (2.27%) and amine fluoride (0.71%) in acrylic resin plates, on bending strength and fluoride release by rinsing and immersion in synthetic saliva, was determined. Bending strength was reduced by 6.7, 9.5 and 20% respectively. The most elevated release of fluoride from the NaF containing--and the most protracted from the CaF2 containing--plates may be related to the solubilities of the compounds. It appears that the organic molecule of the AmF compound affects the strength of the acrylic plates most significantly. The F- concentrations released in the in vitro rinsing experiment may be presumed to occur in vivo at some higher level due to the larger size of dental appliances.

Acrylic Resins↗
PubMed1980

Copperplating copper band-compound impressions at constant voltage.

According to the experimental results, the electrodeposition of copper on impressions should be carried out with a voltage-stabilized power supply at 0.3 V. This method permits the copperplating of tube impressions of various sizes without the need for further adjustments of controls on the plating apparatus.

Acrylic Resins↗
PubMed1979

Reflectance spectra of composite resins on liners.

The reflectance spectra of two types of composite resins were determined on various backgrounds. It was found that the shade differences caused by different "whitish" liners were perceptible only for thin resin specimens and were smaller than those caused by varying the resin type and thickness. Employing a light brown liner gave rise to a difference in shade which was also perceptible on resin specimens of 2.5 mm thickness. Shade differences due to varying the thickness of the specimens were more pronounced on white than on black backgrounds. The clinical significance and the qualitative physical interpretation of the results were discussed.

Calcium Hydroxide↗
PubMed1979

The grinding efficiency of diamond burs.

Deterioration of round diamond burs during 8 minutes of operation was found to be more pronounced for burs with low particle densities than for burs with high particle density. No definitive relationship was found between the initial grinding rate and initial particle density.

Dental Enamel↗
PubMed1979

Tensile strength of the bond between resin to enamel etched with phosphoric acid containing fluoride.

The tensile bond strength of Epoxylite 9075 and Enamelite to enamel treated with NaF and SnF2, at two concentrations, in the etching acid (H3PO4) was determined. The average fracture stress of those samples in which fracture occurred in the resin only, may be considered as the tensile strength of the resin, 69.8 +/- 5.6 kg/cm2. The mean fracture stresses of the Epoxy 9075 systems etched with pure phosphoric acid or with acid solutions containing 0.5% F salts were significantly higher than those treated with acid solutions containing 2% F salts. Incorporation of NaF or SnF2 in the etching solutions highly increased the fluoride concentration of enamel. The fluoride increase dependend on the fluoride concentration of the etching solution and was greater for NaF than SnF2.

Acid Etching, Dental↗
PubMed1979

The bending strength of acrylic resin samples repaired under pressure.

The bending strength of heat-cured resin samples was found to be 49% higher than that of autopolymerizing resin samples cured under room conditions. Curing the latter resin in a pressure vessel at 32psi and 30 degrees C increased its strength by 4.5%. For this reason and because a less porous material is obtained, pressure-curing may be employed with advantage for the preparation of various appliances from S.C. resin. The effect of pressure-curing in increasing the strength of the repaired samples was not significant. It would also appear that pressure affects the porosity of small quantities of repair material less than when appliances are made from S.C. resins only. The increase in strength achieved by pressure-curing repairs, in which only small quantities of S.C. resin are used, is therefore questionable.

Acrylic Resins↗