Long-Term Microtensile Bond Strength of Surface Modified Zirconia

Objective: To compare long-term microtensile bond strength of zirconia, surface-modified via a novel treatment, to current surface conditioning methods, when bonded to dental composite.

Methods: Two ProCAD (porcelain) and ten sintered ZirCAD (ZrO₂) blocks (18x14x12mm) were obtained from manufacturers. Twelve Herculite XRV composite blocks were fabricated (18x14x12mm). Bonding surface of blocks was polished through 1200-grit SiC and air-abraded (50μm alumina, 0.28MPa, 20 s).  Blocks were then separated into six groups: 1) porcelain (control), HF-etched/silane-treated, 2) ZrO₂, tribochemical-coated/silane-treated, 3) ZrO₂, primer-treated, 4) ZrO₂, modified via novel 3.2nm silica layer/silane-treated, 5) ZrO₂, modified via novel 5.8nm silica layer/silane-treated, and 6) ZrO₂, modified via novel 30.4nm silica layer/silane-treated.  Blocks were bonded to composite using Clearfil Esthetic cement.  Blocks were stored in distilled water (37°C, 1wk), then cut into microtensile bars (n=8/gp), then bond strengths measured using a universal testing machine at zero, one, and three months.  All groups were statistically analyzed (ANOVA, Tukey's, p<0.05).

Results:

Microtensile Bond Strength, MPa±SD
Material	Baseline			1 months				3 months
Composite	60.3±17.6d			-				-
Porcelain	25.6±5.6a1			38.9±8.1a2				40.2±8.7a2
Air Abrasion	15.0±6.8bc1			18.1±5.8bc1				14.3±0.8b1
CoJet	24.0±11.1ac1			25.7±10.0b1				44.9±12.5a2
3.2-nm	25.2±4.3a1			27.5±5.9ab12				35.0±5.2a2
5.8-nm	18.2±5.8ab1			13.2±2.2c1				16.5±10.1b1
30.4-nm	12.1±3.4b1			20.±5.6bc2				15.8±5.1b12
Superscript letters indicate significant difference (p < 0.05) between groups for same time interval.  Superscript numbers indicate significant difference for groups at different time intervals.

Conclusion: CoJet-modified and 3.2-nm novel silica-coated zirconia were the only groups that displayed microtensile bond strength to resin composite that were statistically comparable to porcelain after three months.

This research supported by NIH-NIDCR R01 DE013511 and through a NSU-HPD research grant.