Strength, fracture toughness and microstructure of a selection of all-ceramic materials. Part I. Pressable and alumina glass-infiltrated ceramics.
OBJECTIVE
The present study, divided into two parts, aimed to compare the strength, fracture toughness and microstructure of a range of all-ceramic materials. In part I, three hot-pressed glass-ceramics (IPS-Empress, Empress 2 and a new experimental ceramic) and alumina glass-infiltrated ceramics (In-Ceram Alumina), processed by both slip casting and dry pressing, were compared.


METHODS
Tensile strength was appraised on 10 bar-shaped specimens (20 x 4 x 1.2 mm3) for each material with the three-point bending method; the fracture toughness was measured from 20 specimens (20 x 4 x 2 mm3), by using the indentation strength technique. Data were compared with ANOVA and the Sheffé post hoc test (p = 0.05). The volume fraction of each phase, the dimensions and shapes of the grains, porosity and the crack patterns were investigated using SEM.


RESULTS
The average and standard deviation in strength (MPa) and fracture toughness (MPa m(1/2)) were: IPS-Empress 106(17)1, 1.2(0.14)1; Empress 2 306(29)2, 2.9(0.51)2, new experimental ceramic 303(49)2, 3.0(0.65)2, In-Ceram Alumina dry-pressed 440(50)2, 3.6(0.26)2, In-Ceram Alumina slip 594(52)3, 4.4(0.48)3. Values with the same superscript number showed no significant statistical difference. Microscopy revealed the relationship between the glass matrix and the crystalline phase and the characteristics of the latter were correlated to the strengthening and toughening mechanisms of these glass-ceramics.


CONCLUSIONS
The mechanical properties and microstructure of core materials have been advocated as crucial to the clinical long-term performance of all-ceramic dental restorations. This investigation provides the clinician with data regarding strength, fracture toughness and microstructure of a broad range of current materials.
Guazzato
Massimiliano
M
Biomaterials Science Research Unit, Faculty of Dentistry, University of Sydney, United Dental Hospital, 2 Chalmers Street, Surry Hills, NSW 2010 Australia. mgua2483@mail.usyd.edu.au
Albakry
Mohammad
M
Ringer
Simon P
SP
Swain
Michael V
MV
D000538:Aluminum Silicates / Q000737:chemistry; D000704:Analysis of Variance; D002516:Ceramics / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D016062:Porosity; D018709:Statistics, Nonparametric; D013718:Tensile Strength
D000538:Aluminum Silicates; C118557:Empress 2; C075815:IPS-Empress ceramic; C483026:In-Ceram Alumina; D018020:Lithium Compounds; D003776:Dental Porcelain; C023506:Glass ceramics