title: Nanomechanical properties of dental resin-composites.
abstract: OBJECTIVE
  To determine by nanoindentation the hardness and elastic modulus of resin-composites, including a series with systematically varied filler loading, plus other representative materials that fall into the categories of flowable, bulk-fill and conventional nano-hybrid types.
  
  
  METHODS
  Ten dental resin-composites: three flowable, three bulk-fill and four conventional were investigated using nanoindentation. Disc specimens (15mm×2mm) were prepared from each material using a metallic mold. Specimens were irradiated in the mold at top and bottom surfaces in multiple overlapping points (40s each) with light curing unit at 650mW/cm(2). Specimens were then mounted in 3cm diameter phenolic ring forms and embedded in a self-curing polystyrene resin. After grinding and polishing, specimens were stored in distilled water at 37°C for 7 days. Specimens were investigated using an Agilent Technologies XP nanoindenter equipped with a Berkovich diamond tip (100nm radius). Each specimen was loaded at one loading rate and three different unloading rates (at room temperature) with thirty indentations, per unloading rate. The maximum load applied by the nanoindenter to examine the specimens was 10mN.
  
  
  RESULTS
  Dependent on the type of the resin-composite material, the mean values ranged from 0.73GPa to 1.60GPa for nanohardness and from 14.44GPa to 24.07GPa for elastic modulus. There was a significant positive non-linear correlation between elastic modulus and nanohardness (r(2)=0.88). Nonlinear regression revealed a significant positive correlation (r(2)=0.62) between elastic moduli and filler loading and a non-significant correlation (r(2)=0.50) between nanohardness and filler loading of the studied materials. Varying the unloading rates showed no consistent effect on the elastic modulus and nanohardness of the studied materials.
  
  
  CONCLUSIONS
  For a specific resin matrix, both elastic moduli and nanohardness correlated positively with filler loading. For the resin-composites investigated, the group-average elastic moduli and nanohardnesses for bulk-fill and flowable materials were lower than those for conventional nano-hybrid composites.
authors.affiliation: School of Dentistry and Photon Science Institute, University of Manchester, UK. drelsafti@yahoo.com
authors.forename: S
authors.initials: S
authors.lastname: El-Safty
authors.forename: R
authors.initials: R
authors.lastname: Akhtar
authors.forename: N
authors.initials: N
authors.lastname: Silikas
authors.forename: D C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D003775:Dental Polishing; D003799:Dental Stress Analysis / Q000295:instrumentation; D018130:Diamond / Q000737:chemistry; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D053761:Nanocomposites / Q000737:chemistry* / Q000528:radiation effects; D036103:Nanotechnology / Q000295:instrumentation; D058105:Polymerization; D011829:Radiation Dosage; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C515951:Filtek Supreme Plus; C509998:Grandio; C553871:Surefil SDR Flow; C113300:TPH hybrid; C121818:Tetric ceram; C488393:Venus (composite resin); C527485:estelite flow quick; D014867:Water; D018130:Diamond