Shear bond strength of immediately repaired light-cured composite resin restorations

The goal of this study was to examine the extent to which the state of the surface of newly placed restorations made of one of two commercial formulations of composite resin (Pertac-Hybrid and Z-100) affects the interfacial bond strength when such restorations are immediately repaired with the same resin. Three groups of specimens for each material were prepared: one group in which there was an air-inhibited film on the surface of the initial layer of the restoration, another in which that film was prevented from being formed, and a third in which that surface was abraded prior to placement of the repair layer. All specimens were stored for 6 weeks in water at 23 degrees C before being loaded to fracture in shear at a rate of 5 mm/min. The shear bond strength results were treated using the three-parameter Weibull equation and a clearly defined index of performance (I), which is a measure of both the magnitude and variability of the shear bond strength. It was found that, for two states of the surface of the initial layer, I for Pertac-Hybrid specimens is about the same as that for Z-100 specimens. For specimens made of either material, there was a demonstrable difference in I between specimens with or without an air-inhibited film on the initial layer, while abrading the surface of that layer severely degraded I.