Objectives To evaluate the surface roughness and gloss of three nanohybrid resin composites after polishing with three different polishing systems. Materials and Methods A total number of 112 disc specimens (10 × 3 mm) were prepared from nanohybrid—Empress Direct (ID), Grandio (GR), Filtek Z550 (ZN) and a microhybrid resin composite restorative materials—Filtek Z250 (ZM). Following 24-hour storage in 37°C distilled water, each composite group (n = 28) was assigned into four groups (n = 7) according to finishing/polishing (F/P) system: Mylar strip, Optrapol, Politip, and Sof-Lex (SL). The surface roughness (Ra, mm) was measured by a novel three-dimensional method using an image analysis software attached to an environmental scanning electron microscope. A glossometer was used to measure the surface gloss. Results Statistical analysis used was ANOVA test. Two-way Anova test revealed that the “type of composite” and “F/P techniques” had a significant effect on both surface roughness and gloss of the tested resin composite materials (p < 0.05). Tukey’s post hoc test showed that ID, GR, and ZN revealed lower surface roughness and higher surface gloss than ZM within the same polishing system (p < 0.05). Sof-Lex polishing discs produced the lowest surface roughness and highest surface gloss values compared with Optrapol and Politip (p < 0.05). Conclusion The tested F/P systems provided comparable surface roughness and gloss for nanohybrid composites. The Sof-Lex system provided the best surface roughness and gloss for nanohybrid composites.

This study was designed to evaluate the effect of water absorption of three resin based composite materials on their color stability Methods: using scanning spectrophotometer. A total of 45 disc samples were constructed from microhybrid resin composite, polyacid modified resin composite and giomer. It should be mentioned that the selected shade is A2. Then inserted in water for water absorption test. Using five different drink [mouth rinse (37•C) (Chlorohexidine containing mouthwash), tea, coffee, red wine and de-ionized water (37•C)] with no exposure to a light source (neutral sample). Three specimens from each restorative material were made for each type of drink. All the color testing were carried out according to the CIE-L * a * b * -color system whereby L * indicates the brightness of a color, a * describes the red-green content and b * the yellow-blue content.

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A two-beam interferometric method is used to study the change of optical orientation functions and the molecular structure of annealed Egyptian poly(ethylene terephthalate) (PET) fibers. The acoustic method was used for measuring the density. The density results were used to calculate the degree of crystallinity of PET. It was found that annealing causes alignment to the fiber chains in the directions of the fiber axis. This alignment gives an increase in the optical orientation function and decrease in orientation angle. The value of Da/3a 0 , which depends upon the molecular structure of the polymer, remains constant. The obtained results of the optical and the density clarify that new reorientations occurred due to annealing at different conditions. The changes of the refractive index profile of annealed PET fibers are given. Microinterferograms and curves are given for illustration.

SYNOPSISPolyester (Egyptain manufacturers) fibers were annealed in the temperature range 80-190°C for time intervals from 1 to 10 h. The density of the annealed fibers was measured by a system based on the theory of vibrating strings. The fiber diameter was also determined, using the laser forward diffraction technique. Refractive indices and birefringence for annealed fibers at different temperatures and constant time, 1 h, were measured by the polarizing interference microscope. The behavior of fiber density and the mechanical loss factor at different annealing temperatures and times were discussed at different optical parameters. The results obtained clarify the effect of annealing time and temperatures on the optical, density, and mechanical loss factor behavior of polyester fibers. Microinterferograms are given for illustration. 0 1995 John Wiley & Sons, Inc. I NTRO DUCT10 NBirefringence is a measure of the total molecular orientation of a system; it is an excellent property to use for the study of orientation in polycrystalline polymer. The birefringence measurement is thus a rapid and powerful tool for the study of morphological characteristics of deformed polycrystalline polymers. Since birefringence is a measure of the total molecular orientation of the two-phase system, its examination in conjunction with other physical measurements (X-ray, density, mechanical loss factor, etc.) yields considerable insight into the characteristics of the bulk polymer.' One of the important parameters characterizing the crystalline structure of polymers is the degree of crystallinity. The relationship between the degree of crystallinity and the density of the polymer has great influence on the viscoelastic properties of crystalline polymers.' Also, it is known that annealing at different conditions leads to a change in the density and loss tangent, etc.2Long bundles of poly(ethy1ene terephthalate) (PET, manufactured in Egypt) make up a crystalline ~~ * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 56, 1355Vol. 56, -1366Vol. 56, (1995 0 1995 John Wiley & Sons, Inc.CCC 0021-8995/95/101355-12 polymer that is among the most convenient ones to s t~d y .~ It can be prepared in both the amorphous and the crystallized states within a broad range of values of the degree of cry~tallinity.~ The dynamic mechanical loss modulus is a measure of the energy dissipated by the polymer as a consequence of molecular relaxation processes in the noncrystalline region of the polymer. ' In this work, the density of polyester fibers, with different annealing conditions, was measured to estimate the variation due to the annealing process and, on the other hand, to describe how these variations may lead to understanding of the molecular structure response to the applied annealing process. An interferometric method and a resonance technique are used to determine the optical parameters, density, and mechanical loss factor. The relations among the density, mechanical loss factor, and optical parameters we...

This work reports measurement of the molecular orientation by two techniques for nylon 6 fibers drawn at room temperature. The changes in the strain and optical parameters are used to obtain some macrostructural parameters to evaluate the cold-drawing process values of the mechanical orientation functions, [P 2 (cos )], [P 4 (cos )], amorphous and crystalline orientation functions (F c and F a ), and the molar number of chain segments per unit volume (N e ). Also the crosslink density (N 0 ), the chain entanglement density (N s ), the average optical orientation F av , the dielectric constant (), the dielectric susceptibility (), the shrinkage stress (k s ), and other parameters were calculated. Relationships between the calculated parameters are given. The present study demonstrates changes in the molecular reorientation factors and the obtained new physical properties resulting from cold-drawing process.

INTRODUCTION: Matching dental ceramic translucency is the optimal esthetic goal in restorative dentistry. Several types of ceramics evolved over the years in an attempt to optimize physical mechanical and optical properties of the previous types. OBJECTIVES: The aim of this study is to compare and analyze light transmission, light reflection and light absorption of high translucency zirconia reinforced lithium silicate ceramic, low translucency zirconia reinforced lithium silicate ceramic, high translucency lithium disilicate glass-ceramic and low translucency lithium disilicate glass-ceramic. MATERIALS AND METHODS: Serial cutting of the E.max cad and Vita suprinity blocks was done using isomet 4000 micro-saw microtome. Ten ceramic specimens were obtained for each material, 5 of which were 1.5 mm thick and the other 5 were 1 mm thick to be veneered by 0.5 mm of the corresponding veneering material according to manufacturer's instruction. Spectrophotometric analysis was carried out for the forty ceramic specimens. RESULTS: Light transmission for the four groups of zirconia reinforced lithium silicate was significantly higher than their corresponding groups of lithium disilicate (p<0.005). Light reflection and light absorption for the four groups of zirconia reinforced lithium silicate was significantly lower than their corresponding groups of lithium disilicate (p<0.005). Veneering increased light transmission and light reflection however it decreased light absorption for both materials significantly. CONCLUSIONS: Translucency of zirconia reinforced lithium silicate is better than lithium disilicate. Veneering improved optical properties for both zirconia reinforced lithium silicate and lithium disilicate.

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