title: Effect of vulcanization temperature and dental stone colour on colour degradation of maxillofacial silicone elastomers.
abstract: BACKGROUND
  Colour degradation is a major problem in maxillofacial silicone elastomers. Recent studies have focused on colour stability and the mechanical properties of the silicone elastomers. A colour match is also essential for the acceptance of the prosthesis by the patient. The aim of this study is to assess the colour degradation of the silicone elastomer after being moulded in different colours of dental stones at two different vulcanization temperatures.
  
  
  METHODS
  Five different colours of dental stones were used to fabricate a total of 120 silicone blocks using a Cosmesil M511 maxillofacial silicone elastomer. Vulcanization was completed at two different temperatures (25 and 100° Celsius). Colour measurements were obtained with a Conica Minolta spectrophotometer. The CIEDE2000 formula was used to calculate the colour differences (∆E00). Two-way ANOVA, one-way ANOVA with Bonferroni corrected post-hoc p values and independent samples t-test were used for the statistical analyses.
  
  
  RESULTS
  High temperature vulcanization causes lightening of the maxillofacial silicone elastomers without regard to the dental stone colour (p = 0.001). Specimens moulded in green stone lightened least at room temperature (p = 0.999). Compared to the control group, at high temperature, all specimens moulded in coloured dental stones darkened significantly (p < 0.001 for white, blue and yellow; p = 0.006 for green; p = 0.045 for reddish-brown). In the high temperature group, the shift to a green chroma was significant in the white, yellow and green dental stones groups (p = 0.001, p = 0.002, p < 0.001, respectively). The mean b* of the high temperature control group was higher than that of the room temperature control group (p < 0.001). The only ∆E00 score lower than the perceptibility threshold for dental materials (∆E00 = 1.30) was between the room temperature control group and the room temperature green dental stone group (∆E00 = 0.96).
  
  
  CONCLUSIONS
  Green and blue dental stones cause less colour degradation in silicone elastomers. Reddish-brown dental stones cause the most colour degradation in silicone elastomers. At 100 °C, the colour of the silicone elastomer lightens and yellows even if the elastomer is vulcanized in a stainless steel mould. White, yellow and reddish-brown dental stones make the silicone elastomer appear more yellow even if the elastomer is vulcanized at room temperature.
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul University, 34093, Capa-Istanbul, Turkey. ebrusan@yahoo.com.
authors.forename: Ebru Demet
authors.initials: ED
authors.lastname: Cifter
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul University, 34093, Capa-Istanbul, Turkey.
authors.forename: Meltem
authors.initials: M
authors.lastname: Ozdemir-Karatas
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul University, 34093, Capa-Istanbul, Turkey.
authors.forename: Emrah
authors.initials: E
authors.lastname: Baca
authors.affiliation: Department of Chemistry, Faculty of Engineering, Istanbul University, 34320, Avcilar-Istanbul, Turkey.
authors.forename: Adem
authors.initials: A
authors.lastname: Cinarli
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul University, 34093, Capa-Istanbul, Turkey.
authors.forename: Ali
authors.initials: A
authors.lastname: Balik
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul University, 34093, Capa-Istanbul, Turkey.
authors.forename: Erkan
authors.initials: E
authors.lastname: Sancakli
authors.affiliation: Department of Prosthodontics, Faculty of Dentistry, Istanbul University, 34093, Capa-Istanbul, Turkey.
authors.forename: Bilge
authors.initials: B
authors.lastname: Gokcen-Rohlig
mesh_terms: D002133:Calcium Sulfate; D003116:Color; D003735:Dental Casting Technique; D003760:Dental Impression Materials; D003764:Dental Materials; D008422:Materials Testing; D008447:Maxillofacial Prosthesis; D012826:Silicone Elastomers; D013696:Temperature
chemical_list: D003760:Dental Impression Materials; D003764:Dental Materials; D012826:Silicone Elastomers; D002133:Calcium Sulfate
keywords: CIEDE2000; Colour change; Dental stone; Maxillofacial silicone elastomer; Spectrophotometric analysis; Temperature