title: Effect of ageing and immersion in different beverages on properties of denture lining materials.
abstract: OBJECTIVE
  To evaluate the color stability and hardness of two denture liners obtained by direct and indirect techniques, after thermal cycling and immersion in beverages that can cause staining of teeth.
  
  
  METHODS
  Seventy disc-shaped specimens (18 x 3 mm) processed by direct (DT) and indirect techniques (IT) were made from Elite soft (n=35) and Kooliner (n=35) denture liners. For each material and technique, 10 specimens were subjected to thermal cycling (3,000 cycles) and 25 specimens were stored in water, coffee, tea, soda and red wine for 36 days. The values of color change, Shore A hardness (Elite soft) and Knoop hardness (Kooliner) were obtained. The data were subjected to ANOVA, Tukey's multiple-comparison test, and Kruskal-Wallis test (P<0.05).
  
  
  RESULTS
  The thermal cycling promoted a decrease on hardness of Kooliner regardless of the technique used (Initial: 9.09± 1.61; Thermal cycling: 7.77± 1.47) and promoted an increase in the hardness in the DT for Elite Soft (Initial: 40.63± 1.07; Thermal cycling: 43.53± 1.03); hardness of Kooliner (DT: 8.76± 0.95; IT: 7.70± 1.62) and Elite Soft (DT: 42.75± 1.54; IT=39.30± 2.31) from the DT suffered an increase after the immersion in the beverages. The thermal cycling promoted color change only for Kooliner in the IT. Immersion in the beverages did not promote color change for Elite in both techniques. The control group of the DT of Kooliner showed a significant color change. Wine and coffee produced the greatest color change in the DT only for Elite Soft when compared to the other beverages.
  
  
  CONCLUSIONS
  The three variation factors promoted alteration on hardness and color of the tested denture lining materials.
authors.affiliation: Department of Dental Materials and Prosthodontics, Ribeirão Preto Dental School, University of São Paulo, Ribeirão Preto, SP, Brazil.
authors.forename: Vanessa M F
authors.initials: VM
authors.lastname: Leite
authors.forename: Marina X
authors.initials: MX
authors.lastname: Pisani
authors.forename: Helena F O
authors.initials: HF
authors.lastname: Paranhos
authors.forename: Raphael F
authors.initials: RF
authors.lastname: Souza
authors.forename: Cláudia H
authors.initials: CH
authors.lastname: Silva-Lovato
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D001628:Beverages; D002253:Carbonated Beverages; D003069:Coffee / Q000737:chemistry; D003116:Color; D003124:Colorimetry; D003764:Dental Materials / Q000737:chemistry*; D003822:Denture Liners; D006244:Hardness; D006801:Humans; D007101:Immersion; D008422:Materials Testing; D058105:Polymerization; D019904:Polymethyl Methacrylate / Q000737:chemistry; D012826:Silicone Elastomers / Q000737:chemistry; D013053:Spectrophotometry; D013499:Surface Properties; D013662:Tea / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D014920:Wine
chemical_list: D000180:Acrylic Resins; D003069:Coffee; D003764:Dental Materials; D012826:Silicone Elastomers; D013662:Tea; D014867:Water; C103363:kooliner; D019904:Polymethyl Methacrylate