title: Mechanical and structural characterization of discontinuous fiber-reinforced dental resin composite.
abstract: This study evaluated several fiber- and matrix related factors and investigated different mechanical properties of discontinuous i.e. short fiber-reinforced composite (SFRC) (everX Posterior, eXP). These were compared with three conventional composites, microfilled G-ænial Anterior (GA), nanofilled Supreme XTE (SXTE) and bulk-fill Filtek Bulk-Fill (FBF).
  
  
  
  Fracture toughness (KIC), flexural strength (FS), flexural modulus (FM), compressive strength (CS), diametral tensile strength (DTS), apparent horizontal shear strength (AHSS) and fracture work (Wf) were determined for each composite (n=8) stored dry or in water. SEM analysis of the fiber diameter (df) (n=6) and orientation (n=6) were performed. The theoretical critical fiber length (lfc) and the aspect ratio (l/d) of SFRC were calculated and the volume fraction of discontinuous fibers (Vf%) and the fiber length (lf) of SFRC were evaluated. The results were statistically analyzed with two-way ANOVA (α=0.05).
  
  
  
  The mechanical properties of SFRC (eXP) were generally superior (p<0.05) compared with conventional composites. GA had the highest FM (p>0.05), whereas FBF had the highest AHSS (p<0.05). The fiber related properties Vf%, l/d, lf, lfc and df of eXP were 7.2%, 18-112, 0.3-1.9mm, 0.85-1.09mm and 17μm respectively. SEM results suggested an explanation to several toughening mechanisms provided by the discontinuous fibers, which were shown to arrest crack propagation and enable a ductile fracture. Water exposure weakened the mechanical properties regardless of material type. Wf was unaffected by the water storage.
  
  
  
  The properties of this high aspect ratio SFRC were dependent on the fiber geometry (length and orientation) and matrix ductility.
  
  
  
  The simultaneous actions of the toughening mechanisms provided by the short fibers accounted for the enhanced toughness of this SFRC, which toughness value matched the toughness of dentin. Hence, it could yield an inherently uniform distribution of stresses to the hard biological tissues.
authors.affiliation: Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4 B, 20520 Turku, Finland. Electronic address: jasmina.bijelic@utu.fi.
authors.forename: Jasmina
authors.initials: J
authors.lastname: Bijelic-Donova
authors.affiliation: Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4 B, 20520 Turku, Finland.
authors.forename: Sufyan
authors.initials: S
authors.lastname: Garoushi
authors.affiliation: Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4 B, 20520 Turku, Finland.
authors.forename: Lippo V J
authors.initials: LV
authors.lastname: Lassila
authors.affiliation: Dental Materials Science, Dental School, Ghent University, De Pintelaan 185/P8, B-9000 Gent, Belgium.
authors.forename: Filip
authors.initials: F
authors.lastname: Keulemans
authors.affiliation: Department of Biomaterials Science and Turku Clinical Biomaterials Centre-TCBC, Institute of Dentistry, University of Turku, Itäinen Pitkäkatu 4 B, 20520 Turku, Finland; City of Turku Welfare Division, Oral Health Care, Lemminkäisenkatu 2, 20520 Turku, Finland.
authors.forename: Pekka K
authors.initials: PK
authors.lastname: Vallittu
mesh_terms: D003188:Composite Resins; D019245:Compressive Strength; D003799:Dental Stress Analysis; D006244:Hardness; D008422:Materials Testing; D018583:Pliability; D033081:Shear Strength; D013314:Stress, Mechanical; D013718:Tensile Strength
chemical_list: D003188:Composite Resins
keywords: Aspect ratio; Critical fiber length; Fiber orientation; Short fiber-reinforced composite; Toughening mechanism; Volume fraction