Effect of processing induced particle alignment on the fracture toughness and fracture behavior of multiphase dental ceramics.
OBJECTIVE
To investigate the processing induced particle alignment on fracture behavior of four multiphase dental ceramics (one porcelain, two glass-ceramics and a glass-infiltrated-alumina composite).


METHODS
Disks (Ø12 mm x 1.1mm-thick) and bars (3 mm x 4 mm x 20 mm) of each material were processed according to manufacturer instructions, machined and polished. Fracture toughness (K(Ic)) was determined by the indentation strength method using 3-point bending and biaxial flexure fixtures for the fracture of bars and disks, respectively. Microstructural and fractographic analyses were performed with scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction.


RESULTS
The isotropic microstructure of the porcelain and the leucite-based glass-ceramic resulted in similar fracture toughness values regardless of the specimen geometry. On the other hand, materials containing second-phase particles with high aspect ratio (lithium disilicate glass-ceramic and glass-infiltrated-alumina composite) showed lower fracture toughness for disk specimens compared to bars. For the lithium disilicate glass-ceramic disks, it was demonstrated that the occurrence of particle alignment during the heat-pressing procedure resulted in an unfavorable pattern that created weak microstructural paths during the biaxial test. For the glass-infiltrated-alumina composite, the microstructural analysis showed that the large alumina platelets tended to align their large surfaces perpendicularly to the direction of particle deposition during slip casting of green preforms.


CONCLUSIONS
The fracture toughness of dental ceramics with anisotropic microstructure should be determined by means of biaxial testing, since it results in lower values.
Gonzaga
Carla C
CC
Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, Brazil.
Okada
Cristina Yuri
CY
Cesar
Paulo F
PF
Miranda
Walter G
WG
Yoshimura
Humberto N
HN
D000465:Algorithms; D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D016880:Anisotropy; D001031:Apatites / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D055598:Chemical Phenomena; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing; D003776:Dental Porcelain / Q000737:chemistry; D004577:Electron Probe Microanalysis; D005898:Glass / Q000737:chemistry; D006801:Humans; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D055595:Mechanical Phenomena; D008855:Microscopy, Electron, Scanning; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D001031:Apatites; D003764:Dental Materials; C118557:Empress 2; C075815:IPS-Empress ceramic; C483026:In-Ceram Alumina; D018020:Lithium Compounds; C506670:d.SIGN ceramic; C493120:lithia disilicate; D003776:Dental Porcelain; C078519:leucite; C023506:Glass ceramics; D000537:Aluminum Oxide