title: Viscoelastic stability of resin-composites aged in food-simulating solvents.
abstract: OBJECTIVE
  To study time-dependent viscoelastic deformation (creep and recovery) of resin-composites, after conditioning in food-simulating solvents, under a compressive stress at 37°C.
  
  
  METHODS
  Five dimethacrylate-based composites: (Spectrum TPH, Premise Body, Tetric Ceram HB, Filtek P60, X-tra fil), and two Ormocers (Experimental Ormocer V 28407, Admira) were studied. Three groups of cylindrical specimens (4mm×6mm) were prepared and then conditioned in 3 solvents: methyl ethyl ketone (MEK), ethanol, and water for 1 month at 37°C. The compressive creep-strain under 35MPa in 37°C water was recorded continuously for 2h and then the unloaded recovery-strain was monitored for another 2h. The data were analyzed by one-way ANOVA and Bonferroni's test.
  
  
  RESULTS
  The materials all exhibited classic creep and recovery curves, with most parameters being significantly different (p<0.0001) for each solvent condition. All materials showed lower creep-strain in water than in ethanol or MEK solvents. Maximum creep-strain and permanent-set gave negative linear-regression (r(2)>0.98) with logarithm of the solvent solubility-parameter. The % mean (SD) creep-strain ranged from a minimum of 0.82 (0.01) for the Exp. Ormocer in water to the maximum of 4.19 (0.30) for Admira in MEK. Similar trends were found for permanent-set. The dimethacrylate-based composites behaved as an intermediate group, apart from X-tra fil that had similar stability to the Exp. Ormocer.
  
  
  CONCLUSIONS
  The viscoelastic stability (low creep and permanent-set) of the Exp. Ormocer, compared to many dimethacrylate-based composites, in food-simulating solvents may be due to its diluent-free formulation. This was closely matched by a highly-filled dimethacrylate material (X-tra fil).
authors.affiliation: DRBBA-Research Group, Operative Dentistry Division, Conservative Dental Science Department (CDS), Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia. hmarghalani@kau.edu.sa
authors.forename: Hanadi Y
authors.initials: HY
authors.lastname: Marghalani
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D002074:Butanones / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D004548:Elasticity; D000431:Ethanol / Q000737:chemistry; D005502:Food; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D063225:Organically Modified Ceramics / Q000737:chemistry; D011312:Pressure; D012833:Siloxanes / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D002074:Butanones; D003188:Composite Resins; D003764:Dental Materials; C438835:Filtek P60 Composite Resin; D008689:Methacrylates; D063225:Organically Modified Ceramics; D012833:Siloxanes; D012997:Solvents; C467914:TPH spectrum; C121818:Tetric ceram; C529733:X-tra fil composite resin; C479084:admira; C507210:premise composite resin; D014867:Water; D000431:Ethanol; C005222:methylethyl ketone
keywords: Creep; Food-simulating solvent; Ormocer; Resin-composite; Viscoelasticity