Video rate confocal microscopic imaging of dentin/adhesive interfacial failure under load

To obtain information on interfacial failure by recording video rate images of the interface as it failed, while simultaneously recording the load applied.

Fluorescent labeled adhesives were used to retain resin-based composite bobbins on the flat exposed dentin surface of teeth included in epoxy resin blocks. The teeth were secured in a miniature straining stage while the bobbins were loaded in shear mode and the interface viewed with a tandem scanning confocal microscope. Images of the interface during failure were recorded with the aid of computer image processing and storage. The dynamic failure pattern, site of failure (after repositioning the fractured bobbin under the microscope) and shear bond stress were analyzed for four dentin adhesives [OptiBond (OB), Scotchbond Multi-Purpose Plus (SBMP+), Clearfil Liner Bond 2 (CFLB2) and ESPE Bonding System (EBS)]. Control specimens without fluorescent dyes were also studied. Four dynamic patterns of failure were observed: snap, slip/stick, peel and shock wave were seen respectively with OB, SBMP+, CFLB2 and EBS adhesive. The shear bond strengths were ranked EBS*>OB>SBMP+>CFLB2* (*statistically different at alpha=0.05). No significant difference was found between specimens with and without fluorescent dye.