Water treeing - A potential mechanism for degradation of dentin adhesives

Purpose: To test the hypothesis that water channels are present along the adhesive-dentin interface that can be detected using transmission electron microscopy examination of tracer penetration. Materials and Methods: Different total-etch adhesives (Single Bond, Excite, and PQ1) and self-etch adhesives (Prompt L-Pop, Reactmer Bond, and an experimental self-etch adhesive) were bonded to dentin and enamel. Bonded resin-tooth slabs were immersed in 50 wt% conventional silver nitrate or 50 wt% basic, ammoniacal silver nitrate for 24 hours, exposed to a photodeveloping solution, and prepared for transmission electron microscopy. Results: With both types of silver nitrate, all adhesives exhibited nanoleakage within hybrid layers. In addition, water trees in the form of interconnecting, dendritic silver deposits were seen along the surface of the hybrid layers that extended perpendicularly into the adhesive layers. With ammoniacal silver nitrate, additional isolated, unconnected silver grains were observed within the adhesives.