A new adhesion concept based on a dual surface modification for resin Ti adhesion

Abstract

The objective of this resin Ti adhesion study was to compare and contrast the effect of two novel dual surface modification methods on the surface morphology, changes in surface chemistry and to evaluate their enclosed mold micro-shear bond strength variation on artificial ageing. A total amount of 168 c.p. grade 2 titanium specimens were first manually polished, then 24 of them were randomly selected as control specimens. To study the effect of dual surface modification (silicatization followed by etching), 72 polished titanium specimens were silicatized (Rocatec™ Plus, 3M ESPE, 110 μm silica-coated alumina powder) according to the manufacturer’s protocol and then 36 of the silicatized specimens were etched with a blend of HNO3–HCl at 60 °C for 2 mins. The reversed dual surface modification (etching followed by silicatization) was done for the remaining 72 titanium specimens. They were first etched with a blend of HNO3–HCl at 60 °C for 2 mins, and then 36 of the etched specimens were silicatized with the same protocol as mentioned above. As a final treatment one third of all differently modified sample groups were silanized by Monobond™ Plus (Ivoclar Vivadent), and the other third with an experimental silane primer blend, 1.0 vol% 3-acryloxypropyltrimethoxysilane + 0.3 vol% 1,2-bis-(triethoxysilyl)ethane. One third of each sample groups was left without silanization. SEM, EDX, XPS, AFM, and surface roughness profilometry were conducted to study the effects of different surface modifications. Two enclosed mold resin stubs were bonded on each surface treated titanium specimens to evaluate the enclosed mold micro-shear bond strength. The specimens were artificially aged for 1 day, 1 week, 4 weeks, and 8 weeks, followed by adhesion strength testing and failure mode analyses. SpeedCem™ (Ivoclar Vivadent) was used as resin cement. The highest surface roughness was detected on the titanium specimens, silicatized and followed by etching with and without silanization (group E), while the lowest surface roughness was observed in two groups, silanized polished titanium (group A, control) and etched polished titanium with and without silanization (group C). The surface roughness of titanium only silicatized (group B) and specimens silicatized after etching (group D) exhibited similar surface roughness, higher than groups A and C, but lower than group E. These results were supported by the SEM images and AFM analysis. The EDX and EM-μSBS analyses pointed out that specimens which had higher [Si] and [Al], exhibited higher EM-μSBS values. The highest EM-μSBS values were observed in Ti specimens which were silicatized only or those which were silicatized after etching, i.e., groups B and D. Adhesive and mixed mode of fractures were observed in the specimens after EM-μSBS tests. A novel approach of silicatized titanium surface after etching might prevent the removal of embedded SiO2 and Al2O3, allowing the formation of a durable chemical bond with a silane blend.