title: Investigations towards nano-hybrid resin-based composites.
abstract: OBJECTIVE
  Clinical data indicate an increased trend in material fracture as reason for failure in composite restorations, questioning whether modern resin-based composites (RBCs) are able to fulfil the rising aesthetical demands and to provide at the same time a sufficient mechanical stability also in larger cavities. Nano-hybrid RBCs are promoted as materials with improved mechanical properties. The aim of this study was to analyse differences in mechanical properties within and between modern flowable and non-flowable nano-hybrid and micro-hybrid RBCs by measuring mechanical properties at macro- and micro-scale.
  
  
  METHODS
  Thirty-four RBCs with traditional and new monomer formulation or photo-polymerization initiator technology-15 nano-hybrid, nine micro-hybrid and ten flowable-were therefore considered. Flexural strength, flexural modulus (E(flexural)), indentation modulus, Vickers hardness (HV) and creep were measured after the samples had been stored in water for 24 h at 37°C. Differences within the materials as well as within material categories were statistically analysed using one-way ANOVA with Tukey HSD post hoc test (α = 0.05) as well as partial eta-square statistics.
  
  
  RESULTS
  The category of micro- and nano-hybrid RBCs performed in all properties superior compared to the flowable RBCs. The former two categories differ significantly only with regard to three parameters, with nano-hybrid RBCs showing higher HV respectively lower E(flexural) and filler weight. The micro-mechanical parameters proved to be more sensitive to differences in filler amount and RBCs type than the macro-mechanical properties.
  
  
  CONCLUSIONS
  Only few differences were found between nano-hybrid and micro-hybrid RBCs as a material category and thus, from laboratory tests, no clear advantages in the mechanical stability in stress-bearing areas of nano-hybrid RBCs are expected clinically. Similar is valid for materials with new monomer formulation or photo-polymerization initiator technology. However, several of the measured nano-hybrid RBCs showed consistently higher mechanical properties than the mean values of the micro-hybrid RBCs.
authors.affiliation: Department of Restorative Dentistry, Dental School of the Ludwig-Maximilians-University, Goethestr. 70, 80336, Munich, Germany. nicoleta.ilie@dent.med.uni-muenchen.de
authors.forename: Nicoleta
authors.initials: N
authors.lastname: Ilie
authors.forename: Adam
authors.initials: A
authors.lastname: Rencz
authors.forename: Reinhard
authors.initials: R
authors.lastname: Hickel
mesh_terms: D003188:Composite Resins / Q000737:chemistry* / Q000145:classification; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D006244:Hardness; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D008689:Methacrylates / Q000737:chemistry; D053761:Nanocomposites / Q000737:chemistry*; D058567:Photoinitiators, Dental / Q000737:chemistry; D018583:Pliability; D058105:Polymerization; D062047:Silorane Resins / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014520:Urethane / Q000031:analogs & derivatives / Q000737:chemistry; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: C520091:CeramX; D003188:Composite Resins; D003764:Dental Materials; C507124:Estelite sigma; C466112:Esthet-X; C474035:Filtek Supreme; C470230:Gradia; C509998:Grandio; D008689:Methacrylates; C551012:N'Durance composite resin; D058567:Photoinitiators, Dental; D062047:Silorane Resins; C510232:Simile composite resin; C501891:Tetric EvoCeram; C488393:Venus (composite resin); C528099:diurethane dimethacrylate; C507210:premise composite resin; C555513:silorane composite resin; D014867:Water; D014520:Urethane