title: Effect of opacifiers on color stability of pigmented maxillofacial silicone A-2186 subjected to artificial aging.
abstract: OBJECTIVE
  This study was designed to determine the effect of opacifiers used at different ratios on the color stability of pigmented A-2186 silicone maxillofacial elastomers and to evaluate the color spectrophotometrically before and after artificial aging.
  
  
  METHODS
  Sixty experimental groups of elastomers were made using various concentrations (5%, 10%, and 15%) of 4 opacifiers (Georgia kaolin powder neutral, kaolin powder calcined, Artskin white, and dry pigment titanium white) with 1 of 5 dry earth cosmetic pigment groups (no pigment [control], red, yellow ochre, burnt sienna, and a mixture of all pigments). Five specimens of each elastomer were tested, for a total of 300 specimens. All specimens were placed in an aging chamber and artificially aged by exposure to light, water spray, fluctuating temperatures, and humidity. CIE L*a*b* values were measured by spectrophotometer. The color differences (Delta E*) at various exposure energies (150, 300, and 450 kJ/m(2)) were subjected to 4-way analysis of variance with repeated measures (super ANOVA). Mean values were compared with Tukey-Kramer intervals calculated at the 0.05 significance level.
  
  
  RESULTS
  The trained human eye can detect color changes (Delta E*) greater than 1.0. Adding all pigments to any of the kaolin groups did not protect silicone A-2186 from color degradation over time. Mixing red pigment in all groups at all times drastically increased DeltaE* values ranging from 0.1 to 1.3 up to 16.6 to 49.6. Yellow ochre had an effect only with 10% and 15% concentrations of kaolin powder calcined, increasing the value of Delta E* to greater than 1.0. Burnt sienna had an effect only with a 15% concentration of kaolin powder calcined, increasing the value of Delta E* at 300 and 450 kJ/m(2) to greater than 11.0. At the 5% concentration, kaolin powder calcined had the smallest color changes, followed by, in order, dry pigment titanium white, Artskin white, and Georgia kaolin. At the 10% concentration, Artskin white had the smallest color changes, followed by, in order, dry pigment titanium white, kaolin powder calcined, and Georgia kaolin. At the 15% concentration, Artskin white again had the smallest color changes, followed by, in order, dry pigment titanium white, Georgia kaolin, and the kaolin powder calcined. The smallest color changes in each kaolin group were at the 10% concentration for Artskin white, dry pigment titanium white, and kaolin powder calcined and at the 5% concentration for Georgia kaolin.
  
  
  CONCLUSIONS
  Mixing dry earth cosmetic pigments with opacifiers did not protect silicone A-2186 from color degradation over time, especially in the case of red pigment. The group in which pigments were mixed with 10% Artskin white had the smallest color changes over time, followed by, in order, the groups in which pigments were mixed with 10% dry pigment titanium white, 10% kaolin powder calcined, and 5% Georgia kaolin. Red pigment had a significant effect on all opacifiers, especially Georgia kaolin and kaolin powder calcined. Yellow ochre and burnt sienna had an effect only on 15% kaolin powder calcined. Among all the pigment groups tested, yellow ochre remained the most color stable over time.
authors.affiliation: Assistant Professor, Department of Restorative Dentistry and Biomaterials, The University of Texas, Houston Health Science Center, Dental Branch, Houston, TX 77030, USA.
authors.forename: Sudarat
authors.initials: S
authors.lastname: Kiat-Amnuay
authors.forename: James C
authors.initials: JC
authors.lastname: Lemon
authors.forename: John M
authors.initials: JM
authors.lastname: Powers
mesh_terms: D000704:Analysis of Variance; D001672:Biocompatible Materials / Q000737:chemistry*; D003116:Color; D004396:Coloring Agents / Q000737:chemistry*; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D020724:Elastomers / Q000737:chemistry; D006801:Humans; D006813:Humidity; D007616:Kaolin / Q000737:chemistry; D008027:Light; D008422:Materials Testing; D008447:Maxillofacial Prosthesis; D055095:Optics and Photonics; D017797:Prosthesis Coloring; D013053:Spectrophotometry; D013223:Statistics as Topic; D013696:Temperature; D013997:Time Factors; D014025:Titanium / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: C076788:A 2186; D001672:Biocompatible Materials; D004396:Coloring Agents; D004129:Dimethylpolysiloxanes; D020724:Elastomers; D014867:Water; D007616:Kaolin; D014025:Titanium