The effect of Y-TZP surface treatments on flexural strength and resin shear bond strength to human dentin
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Introduction. This study evaluated the effect of mechanical surface treatment of yttria-partially stabilized zirconia (Y-TZP) on its flexural strength and the effect of mechanical and chemical surface treatments on its shear bond strength to human dentin using a resin cement. Materials and Methods. I: Flexural strength ; Sixty four bars of Y-TZP were prepared from Zircad blocks (Ivoclar Vivadent), finished using a 2mm CEREC diamond bur, sintered, then randomly assigned into 4 groups (n=16): (1) control, (2) airborne-particle abraded (APA); [50μm Al 2 O 3 at 3 bar], (3) silicoated [30 μm silica-modified Al 2 O 3 at 3 bar], and (4) wet hand-ground using a fine grit diamond bur at high speed. After storage for 24 hours at 37°C, flexural strength of the bars was determined using a three-point bending test in a Universal Testing Machine (Instron) with a 5 KN load cell at 1 mm/min crosshead speed. II: Shear bond strength ; 192 zirconia rods [2.5 mm in diameter] were milled from Zircad blocks by CEREC 3, sintered and randomly assigned into 16 groups; (n=12). Each group underwent a combination of the following mechanical and chemical treatments: mechanical : (1) control, (2) APA, (3) silicoating or (4) wet hand-grinding, chemical: (1) control, (2) acid-etching [5% HF acid/90 s.] followed by silanation [60 s.], (3) silanation only [60 s.], or (4) application of zirconia primer [3 minutes]. Dentin samples were prepared from extracted molars stored in 0.5% chloramine-T. Multilink Automix (Ivoclar Vivadent) was used to bond the rods to dentin using Ultradent positioning jigs. The specimens were light polymerized (20 sec/side). After 10 minutes of storage at 37°C, the samples were loaded to failure using a Universal Testing Machine (Instron) with a 5 KN load cell at 1 mm/min crosshead speed. III: Artificial Aging : The groups that achieved the highest bond strength values were duplicated, stored at 37°C and 100% humidity for 90 days and thermocycled [6,000 thermocycles (5-55°C), 10 sec dwell time] before they were loaded to failure. Results. Flexural strength : The APA group followed by the hand-ground groups achieved statistically the highest flexural strength values. Shear Bond Strength : The highest shear bond strength values were achieved for the following groups: silicoated+ silanated > hand-ground + zirconia primer > APA + silanated > zirconia primer > APA + zirconia primer. Artificial Aging : Artificial aging resulted in a significant drop in the shear bond strength values for the silicoated+ silanated and the zirconia primer groups. All groups except the zirconia primer maintained comparable shear bond strength values after artificial aging. Conclusions. Mechanical modification of the surface increased the flexural strength of Y-TZP. Mechanical and/or chemical conditioning of Y-TZP increased the resin bond strength to dentin. A combination of mechanical and chemical conditioning of the zirconia surface was essential to developing a durable long-term resin bond to zirconia.