Mechanical and fracture behavior of veneer-framework composites for all-ceramic dental bridges.
OBJECTIVE
High-strength ceramics are required in dental posterior restorations in order to withstand the excessive tensile stresses that occur during mastication. The aim of this study was to investigate the fracture behavior and the fast-fracture mechanical strength of three veneer-framework composites (Empress 2/IPS Eris, TZP/Cercon S and Inceram-Zirconia/Vita VM7) for all-ceramic dental bridges.


METHODS
The load bearing capacity of the veneer-framework composites were evaluated using a bending mechanical apparatus. The stress distribution through the rectangular-shaped layered samples was assessed using simple beam calculations and used to estimate the fracture strength of the veneer layer. Optical microscopy of fractured specimens was employed to determine the origin of cracks and the fracture mode.


RESULTS
Under fast fracture conditions, cracks were observed to initiate on, or close to, the veneer outer surface and propagate towards the inner framework material. Crack deflection occurred at the veneer-framework interface of composites containing a tough framework material (TZP/Cercon S and Inceram-Zirconia/Vita VM7), as opposed to the straight propagation observed in the case of weaker frameworks (Empress 2/IPS Eris).


CONCLUSIONS
The mechanical strength of dental composites containing a weak framework (K(IC)<3 MPam(1/2)) is ultimately determined by the low fracture strength of the veneer layer, since no crack arresting occurs at the veneer-framework interface. Therefore, high-toughness ceramics (K(IC)>5 MPam(1/2)) should be used as framework materials of posterior all-ceramic bridges, so that cracks propagating from the veneer layer do not lead to a premature failure of the prosthesis.
Department of Materials, Nonmetallic Inorganic Materials, Wolfgang-Pauli-Strasse 10, ETH Hönggerberg, HCI G 539, 8093 Zürich, Switzerland. andre.studart@mat.ethz.ch
André R
AR
Studart
Frank
F
Filser
Peter
P
Kocher
Heinz
H
Lüthy
Ludwig J
LJ
Gauckler
D000537:Aluminum Oxide / Q000737:chemistry; D000538:Aluminum Silicates / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry; D003776:Dental Porcelain / Q000737:chemistry*; D017267:Dental Prosthesis Design; D019232:Dental Restoration Failure; D003801:Dental Veneers; D003829:Denture, Partial; D004548:Elasticity; D006801:Humans; D018020:Lithium Compounds / Q000737:chemistry; D008422:Materials Testing; D018583:Pliability; D017680:Potassium Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D015019:Yttrium / Q000737:chemistry; D015040:Zirconium / Q000737:chemistry
D000538:Aluminum Silicates; D003764:Dental Materials; C118557:Empress 2; C500744:Eris ceramic; D018020:Lithium Compounds; D017680:Potassium Compounds; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; C016447:feldspar; C070870:In-Ceram; D015019:Yttrium; C023506:Glass ceramics; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide