Fracture strength and microstructure of Y-TZP zirconia after different surface treatments.
BACKGROUND
Airborne-particle abrasion of the inner and outer surfaces of an yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) core is used in an attempt to enhance the bond strength between the core and the veneering porcelain and to increase the surface area for cementation. However, airborne-particle abrasion introduces surface flaws that act as stress concentrators that may compromise the mechanical strength of the ceramic.


OBJECTIVE
The purpose of this study was to investigate the effect of airborne-particle abrasion and heat treatment on the microstructure, biaxial flexural strength, and reliability of Y-TZP zirconia ceramics before veneering and cementation.


METHODS
Forty-eight disks (15 mm in diameter, 0.5 mm in thickness) of Y-TZP were divided into 6 groups. Three treatments (untreated, airborne-particle abrasion, and heat treatment after airborne-particle abrasion) were applied to the upper surfaces, and 2 treatments (untreated and airborne-particle abrasion) were applied to the lower surfaces to mimic the preparation for veneering and cementation. For airborne-particle abrasion, 110 μm Al2O3 particles were used. The maximum load at fracture was calculated with a biaxial flexural strength test. The upper surfaces were facing the loading piston, and the lower surfaces were facing the supporting jig during testing. Results were analyzed with 2-way ANOVA (α=.05). The treated and fractured surfaces were observed with a scanning electron microscope. The relative content of the monoclinic phase was quantified with an x-ray diffraction analysis.


RESULTS
The group with airborne-particle abraded lower surfaces showed significantly higher flexural strength than the untreated group (P<.001). The SEM images of the airborne-particle abraded zirconia specimens showed rough and irregular surfaces. The fracture initiated from the tension side, which was opposite to the applied load.


CONCLUSIONS
Within the limits of this in vitro study, the results showed that airborne-particle abrasion of the lower surfaces increases the flexural strength of Y-TZP zirconia.
Graduate student, Department of Prosthodontics, School of Dentistry, Chonnam National University, Gwangju, Korea.
Jin-Young
JY
Song
Sang-Won
SW
Park
Kwangmin
K
Lee
Kwi-Dug
KD
Yun
Hyun-Pil
HP
Lim
D000537:Aluminum Oxide / Q000737:chemistry; D002484:Cementation / Q000379:methods; D001840:Dental Bonding; D045662:Dental Etching / Q000379:methods*; D003764:Dental Materials / Q000737:chemistry*; D003775:Dental Polishing / Q000379:methods; D003776:Dental Porcelain / Q000737:chemistry; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D018130:Diamond / Q000737:chemistry; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
D003764:Dental Materials; C499362:yttria stabilized tetragonal zirconia; D003776:Dental Porcelain; D015019:Yttrium; D018130:Diamond; D015040:Zirconium; D000537:Aluminum Oxide