Influence of Silane Coupling Agent Application Techniques on the Interfacial Properties and Shear Bond Strength of Two Veneer Preparation Designs: An In Vitro Study

This in vitro study evaluated the effect of two silane coupling agent application techniques (dry air and thermally activated warm air) on the interfacial properties and shear bond strength (SBS) of lithium disilicate veneers fabricated with two designs: incisal overlap and window. Materials and Methods: The interfacial characteristics of lithium disilicate specimens were evaluated using contact angle measurements and ATR–FTIR spectroscopy to investigate the effect of different silane application techniques. Forty lithium disilicate veneer specimens were divided by preparation design (incisal overlap or window) and silane application technique (dry air or warm air) (n = 10). Forty flat lithium disilicate specimens were prepared for contact angle and ATR–FTIR analyses. Wettability was assessed using the sessile drop method, while SBS was measured using a universal testing machine. ATR–FTIR evaluated chemical changes within the silane layer. Results: Warm-air silane application significantly improved SBS and wettability compared with dry-air application. The incisal overlap/warm-air group exhibited the highest SBS (19.3 ± 1.7 MPa), whereas the window/dry-air group showed the lowest (12.5 ± 1.4 MPa). Contact angle measurements demonstrated significantly lower values following thermal activation (p < 0.001). ATR–FTIR analysis suggested modifications in carbonyl-containing organic species at the interface following thermal activation. Conclusions: Thermal activation of silane improved interfacial properties and bond strength. Incisal overlap preparations demonstrated superior bonding performance, while warm-air silane application enhanced adhesion across both designs.