(1/59) A method of predicting color stability of autopolymerizing acrylic resins using electron spin resonance.

Synopsis. Long periods can be required to determine the color stability of acrylic resins. The concentration of propagating radicals with unpigmented experimental resins (UER) and initiator solution (IS) of two initiator systems (binary and ternary) and five products were measured using electron spin resonance (ESR). The radical concentration was estimated from the area under the integrated ESR spectrum. The discoloration was measured using a color computer. Higher content of benzoylperoxide led to higher radical concentrations. The radical concentration for the ternary system increased slightly with time, but were lower than those of the binary system. Significant positive correlations were found between the radical concentration and delta E*ab for UER (r = 0.900, p < 0.01), IS (r = 0.953, p < 0.001) and the products (r = 0.808, p < 0.05). It was suggested that the color stability of these resins was predictable by measuring the radical concentration using ESR.  (+info)

(2/59) A method for evaluating color stability of light-cured composite resins using an experimental filter.

The purpose of this study was to investigate a method for evaluating color stability of light-cured composite resins using an experimental filter that simulates human enamel. The light transmission coefficients and their spectral distributions from 400 to 600 nm of twelve enamel specimens were measured. The experimental filter was designed so that its light transmittance characteristics were similar to those of enamel. Color stability tests for ten shades of two light-cured composite resins, which were irradiated directly and indirectly through the experimental filter with a light source, were performed. Despite different irradiation procedures, most materials exhibited significant color changes in the color stability test. Although the differences were small, the group of specimens irradiated indirectly through the filter showed significantly higher color differences in comparison with those irradiated directly. Our results indicate that the light attenuating effect of enamel affects the color stability of light-cured composite resins.  (+info)

(3/59) Gingival prostheses--a review.

Gingival replacement is often a component of comprehensive prosthodontics. Gingival prostheses may be fixed or removable and may be made from acrylics, composite resins, silicones or porcelain-based materials. Undercuts or dental attachments are used to secure removable prostheses, which are esthetically pleasing and easy to maintain. This paper describes several clinical situations in which gingival prostheses were used effectively.  (+info)

(4/59) Zirconia and alumina ceramics in comparison with stainless-steel heads. Polyethylene wear after a minimum ten-year follow-up.

Although alumina has been used in orthopaedic surgery since the 1970s, the long-term clinical results of zirconia have not been well documented in vivo. We studied hips with these two different ceramics during the same period and with a minimum follow-up of ten years. Because the size of the alumina and zirconia heads was different, hips with 32 mm alumina heads and those with 28 mm zirconia heads were compared with control hips with stainless-steel heads of the same size. Our aim was to compare the two ceramics. There was an increased linear rate of penetration of the femoral heads into the liner between years five and 12 for the zirconia and the stainless-steel groups. This was severe in the zirconia group (0.4 mm/year compared with 0.13 mm/year for the stainless-steel group). During the same 12-year period there was, however, no significant change in the rate of wear in the alumina group (0.07 mm/year). The mean wear at the most recent follow-up was 1360 mm3 for the 28 mm zirconia group, 683 mm3 for the 28 mm stainless-steel group, 755 mm3 for the 32 mm alumina group and 1314 mm3 for the 32 mm stainless-steel group. The monoclinic content rose on the surface of three zirconia heads which were retrieved at revision. This change was associated with an increase in the surface roughness. A change in the roundness with an increase in the sphericity deviation was also observed both in the articular and non-articular parts of the femoral heads. The increase in rate of wear in the zirconia group was only evident after eight years and may be linked to a long-term biodegradation of zirconia in vivo, associated with the altered roughness and roundness which was observed on the retrieved heads.  (+info)

(5/59) Color change in acrylic denture base resin reinforced with wire mesh and glass cloth.

In this study, the L*a*b* color system as a color system and light transmittance of the denture base resin reinforced with wire mesh and glass cloth were measured, and the color difference (deltaE*ab) was calculated using L*, a* and b* values which were measured both on a white calibration plate and on a null background. The thicknesses of test specimens, which were reinforced with wire mesh and glass cloth 0.5 and 1.0 mm below the surface, were 3 and 5 mm. L*, a* and b* values of wire mesh reinforcing specimens decreased in comparison with the non-reinforcing specimens (p<0.05). L* values of glass cloth-reinforcing specimens increased compared with the non-reinforcing specimens (p<0.05). The glass cloth is an effective reinforcing material and an aesthetically important property of denture base resin, since wire mesh makes the resin appear darker with the background condition greatly altering the color, while glass cloth makes the resin lighter.  (+info)

(6/59) Optical and color stabilities of paint-on resins for shade modification of restorative resins.

The purpose of this study was to examine the optical and color stabilities of the paint-on resin used for shade modification of restorative resins. Three shades of paint-on resin and two crown and bridge resins were used. The light transmittance characteristics of the materials during accelerated aging tests such as water immersion, toothbrush abrasion, ultraviolet (UV) light irradiation, and staining tests were measured. Discolorations of materials resulting from tests were also determined. There were no significant effects of water immersion, toothbrush abrasion and UV light irradiation on the light transmittance and visible color change of paint-on resins, whereas the staining tests significantly decreased the light transmittance and increased color change of the translucent shades of materials. Our results indicate that the paint-on resins exhibit stable optical properties and color appearance, which are at least as good as the crown and bridge resins.  (+info)

(7/59) Color stability of acrylic resin adhesives with different initiation modes.

The purpose of this study was to evaluate the color stability of two acrylic resin adhesives with different activation systems: a benzoyl peroxide (BPO)-amine redox system and a tri-n-butylborane (TBB) derivative system. The colorimetric values of the two resins in different shades (Clear and Ivory) were determined (n=5) 24 hours after polymerization as a baseline using the L*a*b* system of the Commission Internationale de l'Eclairage (CIE). The specimens were thereafter immersed in distilled water, and the color difference (deltaE*) values were calculated. After 24 weeks, the TBB-initiated material showed a significantly (p<0.05) lower color change than the BPO-amine-initiated material. The deltaE* values for the BPO-amine-initiated materials were 6.9 for Clear and 15.8 for Ivory, whereas those for the TBB-initiated materials were 1.3 and 1.8 respectively. Thus, it was concluded that the TBB-initiated material had superior color stability to that of the BPO-amine-initiated material.  (+info)

(8/59) Colorimetric analysis of silicone cosmetic prostheses for upper-limb amputees.

Every year the Italian National Insurance Institute of Accidents on Work (INAIL) Prosthesis Centre manufactures more than 300 silicone cosmetic upper-limb prostheses that are aesthetically similar to patients' missing limbs; however, the prostheses have the following drawbacks: subjectivity in color choice, high production costs, and long time frames for patient tests and prosthesis production. In an attempt to minimize these factors, we performed a study to test various systems that automatically detect the color of human skin. Such a system would allow us to reproduce a patient's exact skin color for silicone cosmetic prostheses. We analyzed the color identification systems available on the market and assessed the possibility of introducing such a system into the production cycle of the prostheses. We found that because of intrinsic factors of the materials, automatic color detection for prosthesis production is complex. Therefore, any of the systems we tested will require further development for full satisfaction of the needs of prostheses manufacturers.  (+info)