Bonding agents: adhesive layer thickness and retention to cavity surfaces with time

This study assessed bonding agent thickness, cover and the influence of long-term storage on bonding agent retention to enamel and dentine surfaces in cut occlusal cavities in 46 human molar teeth. Two specimens were etched and set aside. The remaining specimens were divided into two equal groups and treated with either Optibond or Scotchbond Multipurpose Plus (SMPP) up to the adhesive stage. Thereafter two specimens from each group were stored for 0, 1, 3, 7 and 14 days and 1, 2, 3, 6 and 12 months in 1% NaCl. After storage the cavity surfaces were examined in a scanning electron microscope (SEM) and scored as to bonding agent cover. One specimen from each treatment was then embedded in resin, two sections prepared midway through each cavity, polished and re-examined in the SEM to measure bonding agent thickness at 13 sites along the cavity surface. Both bonding agents showed highly variable and significant (P < 0.05) bonding agent cover and layer thickness according to cavity site, SMPP more so than Optibond. Pooling of SMPP adhesive was apparent in cavity angles. Mean film thickness was significantly different between Optibond (221 +/- 130 microns) and SMPP (118 +/- 106 microns). There was no significant difference in bonding agent thickness between long- and short-term storage.