title: Effect of extraoral aging conditions on mechanical properties of maxillofacial silicone elastomer.
abstract: OBJECTIVE
  The purpose of this study was to investigate the effect of extraoral human and environmental conditions on the mechanical properties (tensile strength and modulus, elongation, tear strength hardness) of maxillofacial silicone elastomer.
  
  
  METHODS
  Specimens were fabricated using TechSil-S25 silicone elastomer (Technovent Ltd, Leeds, UK). Eight groups were prepared (21 specimens in each group; eight tensile, eight tear, five hardness) and conditioned differently as follows (groups 1 through 8): Dry storage for 24 hours; dry storage in dark for 6 months; storage in simulated sebum solution for 6 months; storage in simulated acidic perspiration for 6 months; accelerated artificial daylight aging under controlled moisture for 360 hours; outdoor weathering for 6 months; storage in antimicrobial silicone-cleaning solution for 30 hours; and mixed conditioning of sebum storage and light aging for 360 hours. The conditioning period selected simulated a prosthesis being in service for up to 12 months. Tensile and tear test specimens were fabricated and tested according to the International Standards Organization (ISO) standards no. 37 and 34, respectively. Shore A hardness test specimens were fabricated and tested according to the American Standards for Testing and Materials (ASTM) D 2240. Data were analyzed with one-way ANOVA, Bonferroni, and Dunnett's T3 post hoc tests (p < 0.05). Weibull analysis was also used for tensile strength and tear strength.
  
  
  RESULTS
  Statistically significant differences were evident among all properties tested. Mixed conditioning of simulated sebum storage under accelerated artificial daylight aging significantly degraded mechanical properties of the silicone (p < 0.05).
  
  
  CONCLUSIONS
  Mechanical properties of maxillofacial elastomers are adversely affected by human and environmental factors. Mixed aging of storage in simulated sebum under accelerated daylight aging was the most degrading regime.
  
  
  CONCLUSIONS
  Accelerated aging of silicone specimens in simulated sebum under artificial daylight for 12 months of simulated clinical service greatly affected functional properties of silicone elastomer; however, in real practice, the effect is modest, since sebum concentration is lower, and daylight is less concentrated.
authors.affiliation: Biomaterials Research Group, School of Dentistry, University of Manchester, Manchester, UK. muhanad.hatamleh@manchester.ac.uk
authors.forename: Muhanad M
authors.initials: MM
authors.lastname: Hatamleh
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Polyzois
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D000465:Algorithms; D000890:Anti-Infective Agents / Q000737:chemistry; D001672:Biocompatible Materials / Q000737:chemistry*; D003624:Darkness; D003890:Desiccation; D004129:Dimethylpolysiloxanes / Q000737:chemistry; D055119:Elastic Modulus; D004548:Elasticity; D004777:Environment; D006244:Hardness; D006801:Humans; D006813:Humidity; D006863:Hydrogen-Ion Concentration; D008029:Lighting; D008422:Materials Testing; D008447:Maxillofacial Prosthesis; D055595:Mechanical Phenomena; D009757:Nylons / Q000737:chemistry; D012629:Sebum; D012826:Silicone Elastomers / Q000737:chemistry*; D013472:Sunlight; D013542:Sweat; D013718:Tensile Strength; D013997:Time Factors
chemical_list: D000890:Anti-Infective Agents; D001672:Biocompatible Materials; D004129:Dimethylpolysiloxanes; D009757:Nylons; D012826:Silicone Elastomers; C085707:poly(dimethylsiloxane)-polyamide copolymer