title: A comparison of the fracture resistance of three machinable ceramics after thermal and mechanical fatigue.
abstract: BACKGROUND
  Mechanical and thermal fatigue may affect ceramic restorations in the oral environment.
  
  
  OBJECTIVE
  The purpose of this study was to determine the influence of thermal and mechanical cycling on the fracture load and fracture patterns of 3 machinable ceramics.
  
  
  METHODS
  Seventy-two human third molar teeth were prepared for bonding ceramic specimens of Sirona CEREC Blocs, IPS e.maxCAD, or inCoris ZI meso blocks. The 24 specimens of each ceramic were divided into 4 groups (n=6), which underwent no preloading (control), thermocycling (5°C-55°C, 2000 cycles), mechanical cycling (10(5) cycles, 100 N), and thermocycling (5°C-55°C, 2000 cycles) plus mechanical cycling (10(5) cycles, 100 N). The specimens were subsequently loaded to failure, and both stereomicroscopy and scanning electron microscopy were used to investigate the fracture patterns. The data were analyzed with 2-way ANOVA and the Fisher exact probability test (α=.05).
  
  
  RESULTS
  Mechanical and thermal cycling had a significant influence on the critical load to failure of the 3 ceramics. No significant difference was found between mechanical cycling for 10(5) times and thermocycling for 2000 times within the same ceramic. The specimens of inCoris ZI experienced significantly higher fracture loads for all the groups. The fracture patterns of the 3 machinable ceramics showed that failure mainly occurred at the cement-dentin interface.
  
  
  CONCLUSIONS
  The effects of combined thermal and mechanical cycling on the fracture load of ceramics were more significant than any individual mode of cyclic fatigue. Overall, the inCoris ZI resisted thermal and mechanical fatigue better than the Sirona CEREC and IPS e.maxCAD.
authors.affiliation: Graduate student, Department of Prosthodontics, 9th People's Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai.
authors.forename: Rui
authors.initials: R
authors.lastname: Yang
authors.affiliation: Professor, Department of Mechanical Engineering, University of Maryland Baltimore County, Baltimore, Md.
authors.forename: Dwayne
authors.initials: D
authors.lastname: Arola
authors.affiliation: Graduate student, Department of Prosthodontics, 9th People's Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai.
authors.forename: Zhihui
authors.initials: Z
authors.lastname: Han
authors.affiliation: Professor, Department of Prosthodontics, 9th People's Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai. Electronic address: xiuyinzhangxyz@163.com.
authors.forename: Xiuyin
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D017076:Computer-Aided Design; D003764:Dental Materials / Q000737:chemistry*; D003776:Dental Porcelain / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000033:anatomy & histology; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D008964:Molar, Third / Q000033:anatomy & histology; D058105:Polymerization; D017680:Potassium Compounds / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D012464:Saliva, Artificial / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
chemical_list: D000538:Aluminum Silicates; D003764:Dental Materials; C520133:IPS e.max CAD LT; D017680:Potassium Compounds; D019279:Resin Cements; D012464:Saliva, Artificial; C493120:lithia disilicate; D014867:Water; D003776:Dental Porcelain; C016447:feldspar; C074543:Cerec; C023506:Glass ceramics; D015040:Zirconium; C028541:zirconium oxide