Evaluation of a conditioning method to improve core-veneer bond strength of zirconia restorations.
BACKGROUND
The high strength and fracture toughness of zirconia have supported its extensive application in esthetic dentistry. However, the fracturing of veneering porcelains remains one of the primary causes of failure.


OBJECTIVE
The purpose of this study was to evaluate, with shear bond strength testing, the effect of a simple and novel surface conditioning method on the core-veneer bond strength of a zirconia ceramic system.


METHODS
The shear bond strength of a zirconia core ceramic to the corresponding veneering porcelain was tested by the Schmitz-Schulmeyer method. Thirty zirconia core specimens (10 × 5 × 5 mm) were layered with a veneering porcelain (5 × 3 × 3 mm). Three different surface conditioning methods were evaluated: polishing with up to 1200 grit silicon carbide paper under water cooling, airborne-particle abrasion with 110 μm alumina particles, and modification with zirconia powder coating before sintering. A metal ceramic system was used as a control group. All specimens were subjected to shear force in a universal testing machine at a crosshead speed of 0.5 mm/min. The shear bond strength values were analyzed with 1-way ANOVA and Tukey's post hoc pairwise comparisons (α=.05). The fractured specimens were examined with a scanning electron microscope to observe the failure mode.


RESULTS
The mean (SD) shear bond strength values in MPa were 47.02 (6.4) for modified zirconia, 36.66 (8.6) for polished zirconia, 39.14 (6.5) for airborne-particle-abraded zirconia, and 46.12 (7.1) for the control group. The mean bond strength of the control (P=.028) and modified zirconia groups (P=.014) was significantly higher than that of the polished zirconia group. The airborne-particle-abraded group was not significantly different from any other group. Scanning electron microscopy evaluation showed that cohesive fracture in the veneering porcelain was the predominant failure mode of modified zirconia, while the other groups principally fractured at the interface.


CONCLUSIONS
Modifying the zirconia surface with powder coating could significantly increase the shear bond strength of zirconia to veneering porcelain.
Department of Prosthodontics State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, P.R. China.
Jili
J
Teng
Hang
H
Wang
Yunmao
Y
Liao
Xing
X
Liang
D000537:Aluminum Oxide / Q000737:chemistry; D017554:Carbon Compounds, Inorganic / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry; 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; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D033081:Shear Strength; D017655:Silicon Compounds / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
D017554:Carbon Compounds, Inorganic; D020099:Coated Materials, Biocompatible; D003764:Dental Materials; D017655:Silicon Compounds; C499362:yttria stabilized tetragonal zirconia; D014867:Water; D003776:Dental Porcelain; D015019:Yttrium; D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide; C022088:silicon carbide