title: Effect of time passage on some physical properties of silicone maxillofacial elastomers.
abstract: OBJECTIVE
  Changes in color and other physical properties of silicone facial prosthesis are the main reasons for its replacement. The purpose of this study was to investigate the effect of time passage on some physical properties such as tensile strength, modulus of elasticity, elongation at break, tear strength, hardness, color stability, and contrast ratio (CR) of 2 silicone facial elastomers after being sealed in glass containers and kept in the dark for 1 year.
  
  
  METHODS
  Specimens from 2 silicone elastomers (Silasto 30 and Premium 2) were made and stored in the dark. Tensile and tear strength tests were conducted according to International Organization for Standardization specification nos. 37 and 39, respectively, in a universal testing machine. Shore A hardness was measured according to the American Society for Testing Materials specification D 2240. Color changes (ΔΕ*) were determined in the CIE L*a*b* system using a tristimulus colorimeter, and CR also was calculated. Data were analyzed by paired and unpaired t-tests at a significance level of α = 0.05.
  
  
  RESULTS
  Elongation at break, modulus of elasticity, and hardness were significantly changed, whereas changes in CR were observed only in 1 of the 2 elastomers. Tensile and tear strengths were not significantly changed for both of them. Within the limitations of this study, color changes (ΔΕ) were unacceptable.
  
  
  CONCLUSIONS
  Most of the physical properties studied were significantly affected because of time passage. Mechanical and physical properties of silicone maxillofacial elastomers can be changed with time passage (natural aging in the dark). The average time of replacing a facial prostheses is 6 to 18 months; thus, it is important that the findings of this study covered a period of 12 months. Time passage seems to be a critical factor contributing to the overall deterioration of a silicone maxillofacial elastomer.
authors.affiliation: Division of Removable Prosthodontics, University of Athens, Athens, Greece.
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Polyzois
authors.forename: Panagiota N
authors.initials: PN
authors.lastname: Eleni
authors.forename: Magdalini K
authors.initials: MK
authors.lastname: Krokida
mesh_terms: D003116:Color; D055119:Elastic Modulus; D006244:Hardness; D008027:Light; D008422:Materials Testing; D008447:Maxillofacial Prosthesis; D017797:Prosthesis Coloring; D012826:Silicone Elastomers / Q000737:chemistry*; D018709:Statistics, Nonparametric; D013718:Tensile Strength; D013997:Time Factors
chemical_list: D012826:Silicone Elastomers