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ABSTRACT
In dentistry, adhesion promotion with 3-methacryloyloxypropyltrimethoxysilane is usually sufficient, but its hydrolytic stability is a continuous concern. The hydrolytic stability of an alternative, 3-isocyanatopropyltriethoxysilane, was compared with that of conventional 3-methacryloyloxypropyltrimethoxysilane. Two silanes, both in 0.1 and 1.0 vol-% in ethanol-water, were evaluated in the attachment of an experimental bis-phenol-A-diglycidyldimethacrylate (Bis-GMA) resin to grit-blasted (with two different systems) titanium. Silane hydrolysis was monitored by FTIR spectrometry. Bis-GMA resin was applied and photo-polymerized on titanium. The specimens were thermocycled (6000 cycles, 5-55°C). Surface analysis was carried out with scanning electron microscopy. Statistical analysis (ANOVA) showed that the highest shear bond was achieved with 0.1% 3-isocyanatopropyltriethoxysilane (12.5 MPa) with silica-coating, and the lowest with 1.0% 3-methacryloyloxypropyltrimethoxysilane (3.4 MPa) with alumina-coating. The silane, its concentration, and the grit-blasting method significantly affected the shear bond strength (p < 0.05). SEM images indicated cohesive failure of bonding, and, in conclusion, 3-isocyanatopropyltriethoxysilane is a potential coupling agent.
KEY WORDS: silanization, FTIR, silica-coating, trialkoxysilanes, titanium.
INTRODUCTION
The resin system most associated with restorative dentistry is bis-phenol-A-diglycidyldimethacrylate, Bis-GMA (Bowen, 1956). It can be polymerized quickly via a free-radical mechanism. Bis-GMA yields a cross-linked polymer that is also used in veneering composites. The relatively large Bis-GMA monomer molecule has the effect of reducing polymerization shrinkage on setting. The effective shrinkage is further reduced through the incorporation of an inert silanized filler (Bowen and Rodriguez, 1962; Bowen and Marjenhoff, 1992; Venhoven et al., 1994). Bis-GMA is an extremely viscous liquid, and it needs to be diluted with monomers such as methylmethacrylate to be applicable. In prosthodontics, the bonding of veneering composite to metal alloys is required. Titanium is popular in biomedicine and dentistry, due to its excellent biocompatibility. Ti is a commonly used metal, e.g., in a CAD/CAM milled implant fixed partial denture substructure that is veneered with a particulate filled composite. The extremely thin and compact oxide layer on Ti is mainly thermodynamically stable rutile TiO^sub 2^, but non-stoichiometric oxides also occur (Murray and Wriedt, 1990).
Bifunctional trialkoxysilane esters may join essentially different materials together. Two frequently used are vinyltriethoxysilane (Bowen, 1963; Clark and Plueddemann, 1963) and 3-methacryloyloxypropyltrimethoxysilane (Paffenbarger et al., 1967). Silanes alter the surface energy and wettability of an inorganic substrate, and they have an organofunctional group that can...