title: Effect of short-term water storage on the elastic properties of some dental restorative materials--A resonant ultrasound spectroscopy study.
abstract: OBJECTIVE
  This study was aimed to determine if short-term water storage would change elastic properties of dental composite materials.
  
  
  METHODS
  Particulate filler composite resin and continuous unidirectional E-glass FRC materials were photopolymerized and additionally post-polymerized by heat for testing elastic properties with the Resonance Ultrasound Spectroscopy method as a function of time in water storage. The test specimens were stored in 37 degrees C water for up to 30 days.
  
  
  RESULTS
  About 1% weight increase due to water sorption was observed in both materials with both polymerization methods. Water sorption did not change the resonance frequencies towards lower values, indicating no significant decrease in elastic properties in these materials. Because of high damping of the polymer composite materials leading to wide resonance peaks and low number of the recorded peaks, accurate determination of the elastic properties was not possible.
  
  
  CONCLUSIONS
  Results suggest that the most likely explanation for the previously observed decrease in bending stiffness of FRC materials is the decreased yield limit of the hydrated polymer matrix. It is important to recognize that water sorption has the effect on mechanical properties of dental composite materials by changing the yield limit of the matrix rather than by changing the elastic properties of the material.
authors.affiliation: Laboratory of Ceramic Materials, Institute of Materials Science, Kiilto Oy, PL 250, 33101, Tampere, Finland. pirjo.pastila@tut.fi
authors.forename: Pirjo
authors.initials: P
authors.lastname: Pastila
authors.forename: Lippo V J
authors.initials: LV
authors.lastname: Lassila
authors.forename: Mikko
authors.initials: M
authors.lastname: Jokinen
authors.forename: Jyrki
authors.initials: J
authors.lastname: Vuorinen
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
authors.forename: Tapio
authors.initials: T
authors.lastname: Mäntylä
mesh_terms: D000042:Absorption; D003188:Composite Resins; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D004356:Drug Storage; D004548:Elasticity; D005898:Glass; D044367:Phase Transition; D018583:Pliability; D013057:Spectrum Analysis / Q000379:methods; D014463:Ultrasonography / Q000379:methods; D014867:Water
chemical_list: D003188:Composite Resins; C444701:Filtek Z250; C496140:everStick; C009753:fiberglass; D014867:Water