title: Poly(methyl-methacrylate) nanocomposites with low silica addition.
abstract: BACKGROUND
  Poly(methyl-methacrylate) (PMMA) represents the most popular current denture material. However, its major drawbacks are insufficient ductility and strength.
  
  
  OBJECTIVE
  The purpose of this study was to improve the mechanical properties of PMMA in denture base application by adding small quantities of nanosilica.
  
  
  METHODS
  Silica nanoparticles were added to the liquid component of the tested materials. The standard heat polymerizing procedure was followed to obtain 6 PMMA--silicon dioxide (/SiO2) concentrations (0.023%, 0.046%, 0.091%, 0.23%, 0.46%, and 0.91% by volume). Microhardness and fracture toughness of each set of specimens was compared with the unmodified specimens. Furthermore, differential scanning calorimetry and scanning electron microscopy analyses were conducted, and the results obtained were correlated with the results of mechanical properties.
  
  
  RESULTS
  It was found that the maximum microhardness and fracture toughness values of the materials tested were obtained for the lowest nanosilica content. A nanosilica content of 0.023% resulted in an almost unchanged glass transition temperature (Tg), whereas the maximum amount of nanosilica induced a considerable increase in Tg. A higher Tg indicated the possible existence of a thicker interfacial layer caused by the chain immobility due to the presence of the particles. However, scanning electron microscopy results demonstrated extensive agglomeration at 0.91% nanosilica, which may have prevented the formation of a homogenous reinforced field. At a nanosilica content of 0.023%, no agglomeration was observed, which probably influenced a more homogenous distribution of nanoparticles as well as uniform reinforcing fields.
  
  
  CONCLUSIONS
  Low nanoparticle content yields superior mechanical properties along with the lower cost of nanocomposite synthesis.
authors.affiliation: Assistant Professor and Deputy Head of Department, Department of Production Engineering, Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia. Electronic address: sebab@uns.ac.rs.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Balos
authors.affiliation: Associate Professor and Vice Dean, Department of Material Engineering, Faculty of Technology, University of Novi Sad, Novi Sad, Serbia.
authors.forename: Branka
authors.initials: B
authors.lastname: Pilic
authors.affiliation: Professor and Director, Clinic of Dentistry, Clinical Center of Voivodina, Department of Dentistry, Medical Faculty, University of Novi Sad, Novi Sad, Serbia.
authors.forename: Dubravka
authors.initials: D
authors.lastname: Markovic
authors.affiliation: Assistant Professor, Department of Material Engineering, Faculty of Technology, University of Novi Sad, Novi Sad, Serbia.
authors.forename: Jelena
authors.initials: J
authors.lastname: Pavlicevic
authors.affiliation: Assistant Professor, Department of Production Engineering, Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia.
authors.forename: Ognjan
authors.initials: O
authors.lastname: Luzanin
mesh_terms: D002152:Calorimetry, Differential Scanning; D003432:Cross-Linking Reagents / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry*; D003819:Denture Bases; D005898:Glass / Q000737:chemistry; D006244:Hardness; D006358:Hot Temperature; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D020366:Methylmethacrylate / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D053761:Nanocomposites / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry; D019904:Polymethyl Methacrylate / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D044366:Transition Temperature
chemical_list: D003432:Cross-Linking Reagents; D003764:Dental Materials; D008689:Methacrylates; D020366:Methylmethacrylate; D012822:Silicon Dioxide; C004919:ethylene dimethacrylate; D019904:Polymethyl Methacrylate