Light Curing Composite Resin Color Performance

Dental resin composites were introduced commercially in the mid-1960s for restoration of anterior teeth to meet esthetic requirement. Despite continual improvements, facings made of these materials still display a number of inadequacies in clinical application. Apart from low resistance to abrasion and weak bond between the metal base and facings, the main disadvantages appear to stem from plaque retention and discoloration. During the last few years, several studies concerning the color stability of resin-based composites have shown that, for example, changes in color occur after UV irradiation. In vitro discoloration due to coloring agents, filtered coffee, tea, red wine has also been observed. Few studies have reported that the color of composite resins is affected by many factors, include the background environment, thickness of specimens, shades, light wavelengths, submersion in water, the sort of matrix, the sort, size and content of inorganic particles and temperature etc. The purposes of this series studies were to evaluate the color stability of light-curing composite resins precured and postcured, to examine the color difference influenced by pH buffer solution, red wine, coffee and tea underwent an accelerated aging test for color stability. PartiThree disks (10 mm in diameter, 10 mm thick) of each material were prepared in a mold. L*, a*, b* color parameters of 27 different shades of TPH, Sculpt It, Durafil, Charisma ( light-curing composite resins) were taken precure and postcure. Color difference between precure and pstcure (AE) was calculated as AE= ((AL*)2+(Aa*)2+(Ab*)2) m. PartnIn this test nine composite resins (shade A2) were used. A plastic mold (10-mm diameter x 4-mm height) was used to prepare 27 disk specimens. Color was measured by CIE L* a*b* relative to CDE source against a white and a black background, using a colorimeter. Color difference (AE*)was calculated as AE= ((AL*)2+(Aa*)2+(Ab*)2) 1/2. The heights of composite resins were recorded asAE玘1.5. The infinity optical thickness of composite resins when A E=1.5 was calculated by regression formulation. PartmThree kinds of light-cured composite resins and attached shads guides were used. A plastic mold (10-mm diameter x 4-mm height) was used to prepare disk specimens. Color was measured by CIE L* a*b* relative to CIE source against a white and a black background, using a colorimeter. Color change (AE)was calculated as AE= ((AL*)2+(Aa*)2+(Ab*)2) m. The heights of composite resins were recorded as AE^l.5. The infinity optical thickness of composite resins when delta E*=1.5 was calculated by regression formulation. PartlV.Eight kinds light-cured composite resins with some shade were studied, twenty one specimens of each resins were produced by a plastic mold (d=10mm,h= 10mm).The specimens were stored in commercial tea, coffee, red wine and McIIvain's buffer solution at different pH(4,6 and 8) at 60癈.the color values of the specimens were determined by a digital colorimeter on CIE L* a* b* color stem before and after immersion at 1,2,3,4 weeks, color difference(AE) was calculated as AE=[ (AL*)2+( A a*) 2+ (Ab*) T'2.The conclusions are as follows:1 > The results showed that the restoratives evaluated all underwent color changes during polymerization. Changes in L* and b* parameters during polymerization were significant for all materials. L* and b* parameters decreased for TPH, Sculpt It and Charisma, but increased for Durafil. The color difference (AE) were from 4.66 to 15.11.2^ The results indicated that composite resins with hybrid filler and opaque pigments were superior infinity optical thickness. Composite resins contain micro-filler were inferior infinity optical thickness.3^ There was significant difference in color difference and the infinityoptical thickness among materials and shades. The infinity optical thicknessgradual decreased in the same shade mark from 1 to 4, and from A to D theresults is not simple.4^ The buffer solution of pH at 4,6 caused severe color change...