Adhesive Interface Micromorphology: Conventional vs. Low Vacuum Scanning Electron Microscopy

Methods: Adhesive interfaces were created on dentin-enamel discs with etch&rinse adhesives (Syntac Classic, OptibondFL, Excite) as well as self-etch adhesives (Clearfil Protect Bond, AQ Bond) and consecutively coated with a flowable composite (Tetric Flow). Adhesive interface micromorphology was evaluated (A) in CSEM mode after conventional SEM preparation (fixation, dehydration, HMDS drying) and (B) in the low vacuum mode (LVSEM) as well as the extended low vacuum mode (ELVSEM) on native specimens. Micromorphology was characterized using criteria published in the literature (hybrid layer, tags, lateral tags, lateral tubule hybridization). Additionally, chemical characterization of the adhesive interface was performed using energy-dispersive x-ray analysis (EDX). CSEM, LVSEM and ELVSEM evaluation were performed using the FEI Quanta 400 FEG SEM (FEI, Netherlands).

Results: Micromorphological characteristics of the adhesive interface as determined by CSEM could also be identified in LVSEM and ELVSEM modes. Within LVSEM and ELVSEM modes, the evaluation can be performed on native specimens without additional SEM preparation and without artefacts directly after exposure of the adhesive interface. LVSEM and ELVSEM mode allow for additional information due to imaging of material contrast. EDX analysis enabled chemical characterization of areas of interest within the resin-dentin interdiffusion zone.

Conclusions: Application of the new LVSEM and ELVSEM imaging modes is advantageous for micromorphological characterization of the adhesive interface as the original spatial arrangement between dentin and adhesive is maintained and SEM preparation as well as artefact formation is considerably reduced.