All teeth were embedded in epoxy resin and subsequently sectioned longitudinally in a bucco-lingual direction with a water-cooled diamond disk (Isomat 2000, Buehler, Lake Bluff, IL, USA) to achieve two sections with four surfaces to score per tooth (one section at buccal pit and the other at 4mm apart occlusally).
[2001] reported that FS after 15 and 20 years showed 40% of the failed FS on the mandibular first molar had failed because of caries or restoration in the buccal pits, while the FS in the occlusal fissures showed complete retention.