Enhanced silane-aided bonding to silica-coated zirconia with novel silanes

Objectives: Adhesion promoters or specific resin-composite cements are needed for durable bonding to zirconia. Silica-coating combined with novel, experimental silane solutions might solve the problem. The adhesion promotion role of four experimental silane solutions in adhesion of resin-composite cement to silica-coated zirconia was investigated.

Methods: RelyX Unicem universal resin-composite cement (3M ESPE, Germany) was applied and photo-polymerized as stubs (n = 12/group) onto silica-coated (Rocatec sandblasting system, 3M ESPE, Germany) and silanized zirconia. For silanization, 1.0 vol% solutions of 3-methacryloyloxypropyltrimethoxysilane (abbr. MPS; Dow Corning, USA), 3-acryloyloxypropyltrimethoxysilane (ACPS; Toray Dow Corning Silicone, Japan), 3-styrylethyltrimethoxysilane (STYRX; ABCR, Germany) and 3-isocyanatopropyltriethoxysilane (ICS; ABCR, Germany ) were prepared in 95% ethanol (pH 4.5). A ready-to-use 3-methacryloyloxypropyltrimethoxysilane (RelyX Ceramic Primer, 3M ESPE, USA) was used as control. The silane solution activation was evaluated using Fourier Transformation Infra-Red (FTIR) spectroscopy. The shear bond strength was tested after dry storage or thermo-cycling (6000 cycles, 5-55 °C).

Results: After thermo-cycling: statistical analysis (ANOVA) revealed that the highest shear bond strength, 16.0 MPa (SD 2.5 MPa), was obtained using 3-acryloyloxypropyltrimethoxysilane. The lowest shear bond strength was 6.5 MPa (SD 2.6 MPa) with the control silane. All bond strengths enhanced during thermo-cycling. Visually estimated failure mode for thermo-cycled specimens was 50% cohesive.

All experimental silanes became activated within 1 h according to the FTIR spectroscopic analysis. The type of silane (p < 0.001) and storage conditions (p < 0.001) affected significantly the shear bond strength values.

Silane system	Shear bond strength + standard deviation (dry storage)/MPa	Shear bond strength + standard deviation (thermo-cycled)/MPa
MPS	10.3 (3.4)	13.6 (4.9)
ACPS	11.7 (2.3)	16.0 (2.5)
STYRX	10.3 (3.0)	14.9 (4.3)
ICS	6.8 (2.1)	8.5 (1.6)
Control	4.5 (1.3)	6.5 (2.6)

Conclusions: Silanization with three experimental silane solutions produced significantly higher shear bond strengths than the ready-to-use control silane.