title: Effect of opacifiers and UV absorbers on pigmented maxillofacial silicone elastomer, part 2: mechanical properties after artificial aging.
abstract: BACKGROUND
  There are reports of dissatisfaction with color instability and reduced lifetime of extraoral maxillofacial prostheses. Previous studies showed that UV mineral-based light-protecting agent (LP) improved color stability of MDX4-4210/Type A silicone elastomer. However, effects of this agent and opacifiers on mechanical properties of the elastomer are unknown.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effect of 2 commonly used opacifiers and LP, a new opacifier, when combined with pigments on the mechanical properties of MDX4-4210/Type A silicone elastomer before and after artificial aging.
  
  
  METHODS
  Two commonly used opacifiers, titanium white dry pigment (TW) and silicone intrinsic white (SW) and LP were each combined with MDX4-4210/type A. Artists' oil pigment was then combined with the LP and TW groups, and silicone intrinsic pigments were combined with the SW group with 5 colors (no pigment=control, red, yellow, blue, or a combination of the 3 pigments). Ten dumbbell-shaped and 10 trouser-shaped specimens of each opacifier + pigment mixture, plus a control group with no opacifier and no pigment, were made for a total of 320 specimens. Half of the specimens (n=5) were aged in a chamber at 450 kJ/m(2). Specimens were tested for hardness (ASTM D2240), tensile strength (ASTM D412), tear strength (ASTM D624), and percentage elongation in a universal testing machine. A 3-way ANOVA and the Fisher PLSD test were performed (α=.05) for each mechanical property.
  
  
  RESULTS
  After accelerated aging, values of Shore A hardness were the lowest for LP with all 5 pigments and the control, followed by SW and TW (P<.001). After accelerated aging, tear strength, tensile strength, and elongation decreased significantly (P<.001) for LP, whereas changes for SW and TW varied depending on the pigment.
  
  
  CONCLUSIONS
  The mechanical properties of specimens with the light-protecting opacifier were adversely affected after being subjected to artificial aging. SW and TW preserved the mechanical properties of silicone in this study.
authors.affiliation: Department of Oral Health Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Caroline Tram
authors.initials: CT
authors.lastname: Nguyen
authors.forename: Mark S
authors.initials: MS
authors.lastname: Chambers
authors.forename: John M
authors.initials: JM
authors.lastname: Powers
authors.forename: Sudarat
authors.initials: S
authors.lastname: Kiat-Amnuay
mesh_terms: D020099:Coated Materials, Biocompatible; D003124:Colorimetry; D004548:Elasticity; D006244:Hardness; D008422:Materials Testing; D008447:Maxillofacial Prosthesis; D055595:Mechanical Phenomena; D017797:Prosthesis Coloring; D033081:Shear Strength; D012826:Silicone Elastomers; D013473:Sunscreening Agents; D013718:Tensile Strength; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D020099:Coated Materials, Biocompatible; D012826:Silicone Elastomers; D013473:Sunscreening Agents