title: Confocal examination of subsurface cracking in ceramic materials.
abstract: OBJECTIVE
  The original ceramic surface finish and its microstructure may have an effect on crack propagation. The purpose of this study was to investigate the relation between crack propagation and ceramic microstructure following cyclic fatigue loading, and to qualitatively evaluate and quantitatively measure the surface and subsurface crack depths of three types of ceramic restorations with different microstructures using a Confocal Laser Scanning Microscope (CLSM) and Scanning Electron Microscope (SEM).
  
  
  METHODS
  Twenty (8 x 4 x 2 mm(3)) blocks of AllCeram (AC), experimental ceramic (EC, IPS e.max Press), and Sensation SL (SSL) were prepared, ten glazed and ten polished of each material. Sixty antagonist enamel specimens were made from the labial surfaces of permanent incisors. The ceramic abraders were attached to a wear machine, so that each enamel specimen presented at 45 degrees to the vertical movement of the abraders, and immersed in artificial saliva. Wear was induced for 80K cycles at 60 cycles/min with a load of 40 N and 2-mm horizontal deflection. The specimens were examined for cracks at baseline, 5K, 10K, 20K, 40K, and 80K cycles.
  
  
  RESULTS
  Twenty- to 30-microm deep subsurface cracking appeared in SSL, with 8 to 10 microm in AC, and 7 microm close to the margin of the wear facets in glazed EC after 5K cycles. The EC showed no cracks with increasing wear cycles. Seventy-microm deep subsurface cracks were detected in SSL and 45 microm in AC after 80K cycles. Statistically, there was significant difference among the three materials (p < 0.05). Bonferroni multiple comparison of means test confirmed the ANOVA test and showed that there was no statistical difference (p > 0.05) in crack depth within the same ceramic material with different surface finishes.
  
  
  CONCLUSIONS
  The ceramic materials with different microstructures showed different patterns of subsurface cracking.
authors.affiliation: Division of Prosthodontics, College of Dentistry, University of Saskatchewan, Saskatoon, Canada. maged.etman@usask.ca
authors.forename: Maged K
authors.initials: MK
authors.lastname: Etman
mesh_terms: D000537:Aluminum Oxide; D003743:Dental Enamel; D003764:Dental Materials / Q000737:chemistry* / Q000145:classification; D003776:Dental Porcelain / Q000737:chemistry* / Q000145:classification; D019232:Dental Restoration Failure; D019554:Dental Restoration Wear / Q000145:classification*; D003799:Dental Stress Analysis / Q000379:methods; D005898:Glass / Q000737:chemistry; D006801:Humans; D018613:Microscopy, Confocal; D013499:Surface Properties
chemical_list: C105314:AllCeram; D003764:Dental Materials; C508050:IPS e.max Press; C493120:lithia disilicate; D003776:Dental Porcelain; D000537:Aluminum Oxide