title: Fracture toughness of cross-linked and non-cross-linked temporary crown and fixed partial denture materials.
abstract: OBJECTIVE
  Temporary crowns and fixed partial dentures are exposed to considerable functional loading, which places severe demands on the biomaterials used for their fabrication (= temporary crown & bridge materials, t-c&b). As the longevity of biopolymers is influenced by the ability to withstand a crack propagation, the aim of this study was to investigate the fracture toughness of cross-linked and non-cross-linked t-c&bs.
  
  
  METHODS
  Four different t-c&bs (Luxatemp AM Plus, Protemp 3 Garant, Structur Premium, Trim) were used to fabricate bar shaped specimens (2mmx5mmx25mm, ISO 13586). A notch (depth 2.47mm) was placed in the center of the specimen using a diamond cutting disc and a sharp pre-crack was added using a razor blade. 60 specimens per material were subjected to different storage conditions (dry and water 37 degrees C: 30min, 60min, 4h, 24h, 168h; thermocycling 5-55 degrees C: 168h) prior to fracture (3-point bending setup). The fracture sites were inspected using SEM analysis. Data was subjected to parametric statistics (p=0.05).
  
  
  RESULTS
  The K(IC) values varied between 0.4 and 1.3MPam(0.5) depending on the material and storage time. Highest K(IC) were observed for Protemp 3 Garant. Fracture toughness was significantly affected by thermocycling for all dimethacrylates (p<0.05) except for Structur Premium. All dimethacrylates showed a linear-elastic fracture mechanism, whereas the monomethacrylate showed an elasto-plastic fracture mechanism.
  
  
  CONCLUSIONS
  Dimethacrylates exhibit a low resistance against crack propagation immediately after curing. In contrast, monomethacrylates may compensate for crack propagation due to plastic deformation. However, K(IC) is compromised with increasing storage time.
authors.affiliation: Department of Prosthetic Dentistry, Justus-Liebig-University, Schlangenzahl 14, D-35392 Giessen, Germany. markus.balkenhol@dentist.med.uni-giessen.de
authors.forename: Markus
authors.initials: M
authors.lastname: Balkenhol
authors.forename: Heiko
authors.initials: H
authors.lastname: Köhler
authors.forename: Katharina
authors.initials: K
authors.lastname: Orbach
authors.forename: Bernd
authors.initials: B
authors.lastname: Wöstmann
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry; D003442:Crowns; D003764:Dental Materials / Q000737:chemistry*; D003794:Dental Restoration, Temporary; D003830:Denture, Partial, Fixed; D003833:Denture, Partial, Temporary; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D011109:Polymethacrylic Acids / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D003188:Composite Resins; D003432:Cross-Linking Reagents; D003764:Dental Materials; D008689:Methacrylates; D011109:Polymethacrylic Acids; C098586:luxatemp; D014867:Water; C091347:vinyl ethyl methacrylate; D017438:Bisphenol A-Glycidyl Methacrylate; C069714:Protemp