title: Indirect restorations for severe tooth wear: fracture risk and layer thickness.
abstract: OBJECTIVE
  This in vitro study investigated static failure risk related to restoration layer thickness for different indirect materials and compare them to direct composites.
  
  
  METHODS
  Two ceramics (IPS e-max CAD, EmpressCAD (Ivoclar Vivadent)), two indirect composites (Estenia (Kuraray), Sinfony (3M)) and two direct composites (Clearfil AP-X (Kuraray), Tetric EvoCeram (Ivoclar Vivadent)) were chosen. Of each material, 25 discs varying in thickness (0.5-3.0mm) were prepared and cemented to bovine dentine. For measuring compressive strength, samples were placed in a universal testing device. Each sample was uniaxially loaded until failure occurred. For each material a regression model based on the Weibull distribution was used to estimate the relation between restoration layer thickness and failure. Using these models, the chance of failure, standard error and 95% confidence interval for that chance is estimated. Groups of materials were compared as well.
  
  
  RESULTS
  Except for Tetric Evoceram, all materials show a significant positive association between layer-thickness and compressive strength, with an increased strength of increased thickness. ProCAD performed significantly worse than all other materials, especially when compared to the other ceramic material (IPS e-max CAD) (p=0.001).
  
  
  CONCLUSIONS
  For most tested materials, a thicker layer offers more strength, however, this property seems to be material/brand specific.
  
  
  CONCLUSIONS
  As direct composites showed the best results within the limitations of this in vitro study, dentists should consider these materials as a good choice for restoring severe tooth wear, and may offer superior performance compared to indirect composites and ceramics. For some brands of materials thicker layers result in a stronger restoration.
authors.affiliation: Department of and Restorative Dentistry, Radboud University Nijmegen Medical Centre, Philips van Leydenlaan 25, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands. Electronic address: j.hamburger@dent.umcn.nl.
authors.forename: J T
authors.initials: JT
authors.lastname: Hamburger
authors.affiliation: Department of Preventive and Restorative Dentistry, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: N J M
authors.initials: NJ
authors.lastname: Opdam
authors.affiliation: Department of Preventive and Restorative Dentistry, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: E M
authors.initials: EM
authors.lastname: Bronkhorst
authors.affiliation: Department of Preventive and Restorative Dentistry, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: M C D N J M
authors.initials: MC
authors.lastname: Huysmans
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000818:Animals; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry; D019245:Compressive Strength; D001840:Dental Bonding; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000648:ultrastructure; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013499:Surface Properties; D057085:Tooth Wear / Q000473:pathology / Q000628:therapy*
chemical_list: D000538:Aluminum Silicates; C112828:Clearfil AP-X; D003188:Composite Resins; D003764:Dental Materials; C520133:IPS e.max CAD LT; D008689:Methacrylates; D011140:Polyurethanes; C454801:ProCAD Ceramic; D019279:Resin Cements; C477352:Sinfony composite resin; C501891:Tetric EvoCeram; C493120:lithia disilicate; C091839:urethanetrimethacrylate; D003776:Dental Porcelain; C078519:leucite
keywords: Adhesion; Ceramics; Composite; Compressive strength; Layer thickness; Tooth wear