The effect of long-term storage on nanoleakage

To evaluate the durability of dentin bonding over time, the nanoleakage of four dentin bonding systems (Single Bond, Stae, Clearfil SE Bond and PermaQ uik) over 24 hours, three months, six months and 12 months, was investigate d. Flat occlusal dentin surfaces from extracted human molars were finished with wet 600-grit silicon carbide paper and bonded with one of the dentin b onding systems following manufacturers' instructions. The bonded surface wa s covered with <1 mm. thick layer of Silux Plus resin composite and light c ured for 40 seconds. The specimens in each dentin-bonding group were random ly assigned to four sub-groups and kept in phosphate buffered saline soluti on (pH 7.4) containing 0.01% sodium azide at 37 degreesC for 24 hours, thre e, six or 12 months. The margins of all specimens were finished and polishe d with Sof-Lex disks after initial 24-hour storage. At the end of each stor age time, the surrounding tooth surfaces except for 1 mm adjacent to the re storation were coated with nail varnish. The samples were immersed in a 50% w/v solution of silver nitrate for 24 hours, placed in photodeveloping sol ution and exposed to fluorescent light for eight hours. The samples were cu t longitudinally and bucco-lingually, polished, mounted on stabs, carbon co ated and observed in a Field Emission-SEM using backscattered electron mode . The results showed that systems using phosphoric acid as the etchant had a line of silver deposition at the base of the hybrid layer. Silver depositio n increased in all systems over 12-months storage, with PermaQuik changing the least. Nanoleakage of the dentin bonding systems increased slightly dur ing the 12-month storage period, indicating that they may be subject to hyd rolytic attack over time.