The effect of five-year storage prior to bonding on enamel/composite bond strength

The purpose of this study was to examine the effect of pre-bonding storage durations on the shear strength of light-cured composite bonded to enamel. Thirty whole extracted human molars--12 with a storage time of five years, 12 with a storage time of three or fewer months, and six with a storage time of 24 hours or less--were mounted in improved dental stone in copper tubing. The molars were faced 90 degrees to the horizontal with a milling device to produce 120 surfaces, 48 each for two groups, and 24 for one group. Composite buttons 2.3 mm in diameter were bonded to the enamel using the acid-etch light-curing system. The samples were tested in shear utilizing a cross-head speed of 0.5 cm/min with a 500-kg load cell. The results showed that: there was no significant difference, at the 0.05 confidence level, in composite/enamel bond strength between teeth stored for 24 hours, three months, and five years prior to bonding; the lingual surface developed the highest composite/enamel bond strength in all three groups; and enamel fracture occurred 29% of the time on de-bonding.