title: Dynamic visco-elastic properties of dental composite resins.
abstract: OBJECTIVE
  This study aimed to examine the visco-elastic properties of dental composites by dynamic mechanical analysis under the influence of clinically relevant temperatures and variable frequencies, after being stored in air or distilled water for up to 3 months.
  
  
  METHODS
  Two direct (Diamond Lite and Grandio) and two indirect (Artglass and Vita Zeta LC) composites were used. Samples were immediately tested (baseline) or stored at 37 degrees C, either in air or distilled water for 1 day, 7 or 90 days before testing. During dynamic testing, elastic modulus, viscous modulus and loss tangent were determined over a frequency range from 0.1 to 10 Hz at constant temperatures between 5 and 55 degrees C.
  
  
  RESULTS
  Results were analyzed by one-way ANOVA and Turkey's-test. Elastic and viscous moduli were higher for direct than for indirect composites. No such evidence was found for loss tangent. Only the elastic modulus showed statistically relevant differences in the direct and indirect materials groups: Grandio showed higher modulus than Diamond Lite, while Artglass had higher modulus than Vita Zeta LC. The elastic modulus reduced with increasing temperature and decreasing frequency, while the loss tangent showed the opposite trend. The influence of temperature and frequency on viscous modulus was not conclusive. The elastic modulus was more sensitive to moisture than viscous modulus and loss tangent but all three properties showed no overall consistent trend in the results following the storage periods.
  
  
  CONCLUSIONS
  Dynamic mechanical analysis was a valuable tool to characterize the visco-elastic properties of dental composites, thus giving us a greater insight into material behavior.
authors.affiliation: Department of Prosthodontics, Section Medical Materials and Technology, University Hospital Tuebingen, Osianderstr. 2-8, D-72076 Tuebingen, Germany. renata.mesquita@med.uni-tuengen.de
authors.forename: Renata V
authors.initials: RV
authors.lastname: Mesquita
authors.forename: Detlef
authors.initials: D
authors.lastname: Axmann
authors.forename: Jürgen
authors.initials: J
authors.lastname: Geis-Gerstorfer
mesh_terms: D000388:Air; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D004548:Elasticity; D004853:Epoxy Resins / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D010636:Phenols / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D013314:Stress, Mechanical; D013696:Temperature; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: C498018:Artglass (dental composite); D003188:Composite Resins; D003764:Dental Materials; C509997:Diamond Lite; D004853:Epoxy Resins; C509998:Grandio; D008689:Methacrylates; D010636:Phenols; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C509999:Vita Zeta LC; D014867:Water; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate