Figure 1. Optical micrographs of Vickers indentation at the interface of (A) HF-treated E1 ceramic bonded to the adhesive resin (AR) and resin composite (RC), and (B) HF-treated E2 ceramic bonded to AR-RC. The adhesive resin (AR) layer varied (23-82 µm) in thickness (200x). (C) Schematic illustration of a bar specimen fixed to the flat ‘grips’ of the universal testing machine and loaded to failure in tension; (D) close-up view of the indented adhesion zone.