title: Damage tolerance of indirect restorative materials (including PICN) after simulated bur adjustments.
abstract: OBJECTIVE
  To analyze the damage tolerance of indirect restorative materials after grinding with diamond burs to simulate adjustments by clinicians and technicians.
  
  
  METHODS
  Seven commercially available restorative materials (Mark II, ENAMIC, In-Ceram Alumina, VM 9, In-Ceram YZ, IPS e.max CAD) and an experimental one (PICN) were analyzed. Forty bending bars per material were fabricated according to manufacturer's instructions and lapped with 15 μm diamond suspension. The initial flexural strength was determined in three-point-bending on 10 specimens. Additionally the elastic modulus and Poisson's ratio were determined by the resonant frequency method. The remaining bending bars were divided into six groups (n=5) and subjected to standardized grinding with three different diamond grit burs (coarse, 151 μm; medium, 107 μm and extra fine 25 μm) and two grinding directions (transversal and longitudinal). The ground specimens were subsequently loaded to fracture and analyzed by SEM.
  
  
  RESULTS
  Except for the YTZP bending bars, the initial materials strength of all tested materials decreased significantly with all diamond burs upon adjustments in both transversal and longitudinal grinding directions. The resistance of the ground materials to strength reduction follow the order from highest to least damage tolerant material: PICN>ENAMIC>Mark II>VM 9>In-Ceram Alumina>IPS e.max CAD. The loss in strength of all examined materials after longitudinal grinding is generally less compared to transversal grinding. The lowest loss in strength occurred for VM 9 (7.79%) and ENAMIC (9.18%) upon longitudinal grinding direction with extra fine and medium diamond grit bur, respectively.
  
  
  CONCLUSIONS
  The damage tolerance of restorative materials upon adjustments depends on specific mechanical properties and the adjustment procedure. The outcomes of the simulated grinding protocols of this study can be adopted clinically in terms of the selection of appropriate materials, burs and adjustment parameters.
authors: Research and Development Department, VITA Zahnfabrik, Ballyweg 6, 79713 Bad Saeckingen, Germany; Department of Oral Rehabilitation, School of Dentistry, University of Otago, PO Box 647, Dunedin, New Zealand. Electronic address: a.coldea@vita-zahnfabrik.com.
authors: Andrea
authors: A
authors: Coldea
authors: Research and Development Department, VITA Zahnfabrik, Ballyweg 6, 79713 Bad Saeckingen, Germany; Institute for Material Sciences and Engineering, University of Basel, Hebelstrasse 3, 4056 Basel, Switzerland.
authors: Jens
authors: J
authors: Fischer
authors: Department of Oral Rehabilitation, School of Dentistry, University of Otago, PO Box 647, Dunedin, New Zealand; Biomaterials Unit, Faculty of Dentistry, University of Sydney, Sydney, NSW, Australia.
authors: Michael V
authors: MV
authors: Swain
authors: Research and Development Department, VITA Zahnfabrik, Ballyweg 6, 79713 Bad Saeckingen, Germany.
authors: Norbert
authors: N
authors: Thiel
mesh_terms: D000537:Aluminum Oxide; D002516:Ceramics; D017076:Computer-Aided Design; D003748:Dental Equipment; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D018130:Diamond; D055119:Elastic Modulus; D006244:Hardness; D008422:Materials Testing; D013499:Surface Properties
chemical_list: D003764:Dental Materials; C000613958:ENAMIC; C520133:IPS e.max CAD LT; C483026:In-Ceram Alumina; C485633:In-Ceram Zirconia; C000613959:VM 9 feldspar ceramic; C082340:Vita Mark II; D003776:Dental Porcelain; C070870:In-Ceram; D018130:Diamond; D000537:Aluminum Oxide
keywords: Adjustments; Damage tolerance; Dental ceramics; Grinding; Interpenetrating phase composite; Mechanical properties