title: The mechanical properties of nanofilled resin-based composites: the impact of dry and wet cyclic pre-loading on bi-axial flexure strength.
abstract: OBJECTIVE
  To determine the influence of nano-sized filler particles and agglomerates of nanoparticles ('nanoclusters') in resin-based composite (RBC) materials on the bi-axial flexure strength (BFS) following cyclic pre-loading and storage in a 'dry' or 'wet' environment.
  
  
  METHODS
  Seven commercially available RBC restoratives, Heliomolar (Ivoclar Vivadent, Schaan, Liechtenstein), Z100 MP Restorative, Filtek Z250, Filtek Supreme (3M ESPE, St. Paul, MN, USA) in Body (FSB) and Translucent (FST) shades, Grandio and Grandio Flow (VOCO, Cuxhaven, Germany), containing differing filler particle types and morphologies were investigated. Specimens were pre-loaded at 20, 50 or 100 N for 2000 cycles and stored in a 'dry' or 'wet' environment prior to BFS testing.
  
  
  RESULTS
  A general linear model analysis of variance highlighted a reduction in the BFS following pre-loading, however, individual RBC materials responded differently. The RBCs containing agglomerated nano-sized particles or 'nanoclusters' (Filtek Supreme) demonstrated distinctive and unique patterns of response to pre-loading. Cyclic pre-loading at 20 and 50 N significantly increased the Weibull modulus of both FSB (8.53+/-1.91 and 10.23+/-2.29) and FST (16.89+/-3.78 and 10.91+/-2.45) compared with FSB and FST control (no pre-cyclic load) specimens (5.98+/-1.34 and 7.99+/-1.78, respectively). BFS of FSB and FST was maintained or significantly increased compared with the other materials following 20 and 50 N cyclic pre-load (P<0.05).
  
  
  CONCLUSIONS
  The 'nanoclusters' provided a distinct reinforcing mechanism compared with the microhybrid, microfill or nanohybrid RBC systems resulting in significant improvements to the strength and reliability, irrespective of the environmental storage and testing conditions. Silane infiltration within interstices of the nanoclusters may modify the response to pre-loading induced stress, thereby enhancing damage tolerance and providing the potential for improved clinical performance.
authors.affiliation: Biomaterials Unit, School of Dentistry, University of Birmingham, St. Chads Queensway, Birmingham B4 6NN, UK.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Curtis
authors.forename: William M
authors.initials: WM
authors.lastname: Palin
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
authors.forename: Adrian C C
authors.initials: AC
authors.lastname: Shortall
authors.forename: Peter M
authors.initials: PM
authors.lastname: Marquis
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D017609:Barium Compounds / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003890:Desiccation; D055119:Elastic Modulus; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D053761:Nanocomposites / Q000737:chemistry*; D010316:Particle Size; D018583:Pliability; D011140:Polyurethanes / Q000737:chemistry; D012821:Silanes / Q000737:chemistry; D017640:Silicates / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D000538:Aluminum Silicates; D017609:Barium Compounds; D003188:Composite Resins; D003764:Dental Materials; C474035:Filtek Supreme; C444701:Filtek Z250; C509998:Grandio; C513708:Heliomolar; D011140:Polyurethanes; D012821:Silanes; D017640:Silicates; C083568:Z100 composite resin; C415406:barium borosilicate; D014867:Water; D012822:Silicon Dioxide; D015040:Zirconium; C028541:zirconium oxide