Occlusal cavity preparations were made in vivo in 18 human premolars and randomly appointed to three groups ( n = 6 ) , according to the following bonding procedures : ( 1 ) OptiBond Solo , a single-bottle adhesive system , was applied following 15 seconds etching with 37 % phosphoric acid and rinsing ; ( 2 ) Clearfil Liner Bond 2V , a self-etching adhesive system was applied ; and ( 3 ) no bonding material was used , with the untreated smear layer acting as a control .
