title: Viscoelastic properties of uncured resin composites: Dynamic oscillatory shear test and fractional derivative model.
abstract: OBJECTIVE
  In this study we analyze viscoelastic properties of three flowable (Wave, Wave MV, Wave HV) and one universal hybrid resin (Ice) composites, prior to setting. We developed a mathematical model containing fractional derivatives in order to describe their properties.
  
  
  METHODS
  Isothermal experimental study was conducted on a rheometer with parallel plates. In dynamic oscillatory shear test, storage and loss modulus, as well as the complex viscosity where determined. We assumed four different fractional viscoelastic models, each belonging to one particular class, derivable from distributed-order fractional constitutive equation. The restrictions following from the Second law of thermodynamics are imposed on each model. The optimal parameters corresponding to each model are obtained by minimizing the error function that takes into account storage and loss modulus, thus obtaining the best fit to the experimental data.
  
  
  RESULTS
  In the frequency range considered, we obtained that for Wave HV and Wave MV there exist a critical frequency for which loss and storage modulus curves intersect, defining a boundary between two different types of behavior: one in which storage modulus is larger than loss modulus and the other in which the situation is opposite. Loss and storage modulus curves for Ice and Wave do not show this type of behavior, having either elastic, or viscous effects dominating in entire frequency range considered.
  
  
  CONCLUSIONS
  The developed models may be used to predict behavior of four tested composites in different flow conditions (different deformation speed), thus helping to estimate optimal handling characteristics for specific clinical applications.
authors.affiliation: Clinic of Dentistry, Faculty of Medicine, University of Novi Sad, Serbia.
authors.forename: Ljubomir M
authors.initials: LM
authors.lastname: Petrovic
authors.affiliation: Mathematical Institute, Serbian Academy of Arts and Sciences, Belgrade, Serbia.
authors.forename: Dusan M
authors.initials: DM
authors.lastname: Zorica
authors.affiliation: Clinic of Dentistry, Faculty of Medicine, University of Novi Sad, Serbia.
authors.forename: Igor Lj
authors.initials: ILj
authors.lastname: Stojanac
authors.affiliation: Department of Pharmacy, Faculty of Medicine, University of Novi Sad, Serbia.
authors.forename: Veljko S
authors.initials: VS
authors.lastname: Krstonosic
authors.affiliation: Institute for Food Technology, University of Novi Sad, Serbia.
authors.forename: Miroslav S
authors.initials: MS
authors.lastname: Hadnadjev
authors.affiliation: Mathematical Institute, Serbian Academy of Arts and Sciences, Belgrade, Serbia.
authors.forename: Marko B
authors.initials: MB
authors.lastname: Janev
authors.affiliation: Clinic of Dentistry, Faculty of Medicine, University of Novi Sad, Serbia.
authors.forename: Milica T
authors.initials: MT
authors.lastname: Premovic
authors.affiliation: Department of Mechanics, Faculty of Technical Sciences, University of Novi Sad, Trg D. Obradovica 6, 21000 Novi Sad, Serbia. Electronic address: atanackovic@uns.ac.rs.
authors.forename: Teodor M
authors.initials: TM
authors.lastname: Atanackovic
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D008422:Materials Testing; D008956:Models, Chemical; D044367:Phase Transition; D012212:Rheology; D033081:Shear Strength; D013499:Surface Properties; D014783:Viscosity
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C471181:wave flowable composite
keywords: Dynamic oscillatory shear test; Flowable and universal hybrid resin; Resin composites; Uncured; Viscoelasticity of fractional order