Representative scanning electron microscopy images of permanent enamel after treatment with 37% orthophosphoric acid for 20 s (a); appearances of permanent enamel after treatment with Optibond All-in-one; passive application (b), manual active application (c), and rotary-brush active application (d). Phosphoric acid etched enamel showed no sign of smear layer and more irregular and rough surface properties (a) in comparison to enamel treated with Optibond All-in-one self-etch adhesive alone (b) or with both active application techniques (c, d).