Bond Strength of Three-Step Etch-and-Rinse Adhesives with Modified Primer Application

Objectives: The purpose of this study was to evaluate the effect of variations in application technique of the primer component of three-step, etch-and-rinse adhesive agents on the shear bond strength of composite resin to dentin. Methods: The coronal enamel of 120 extracted human third molars was removed with a low-speed saw.  The teeth were mounted in PVC pipe with dental stone, and randomly divided into 12 groups of 10 teeth each. The flat dentin surfaces were bonded using the manufacturer’s directions (MD) for Adper Scotchbond Multipurpose (3M/ESPE) and Optibond FL (Kerr).   The variation from MD for each primer agent were: 1) application method (passive or active), or 2) application time (MD, MD+10 seconds, or MD+20 seconds). The adhesives were light cured and the specimens were placed in a jig (Ultradent).  Filtek Z250 (3M/ESPE) composite was light cured in 2-mm increments to 3-4 mm in height.  Specimens were stored for 24 hours in 37°C distilled water before testing in shear (Instron).  A mean and standard deviation were determined per group.  Data were analyzed with ANOVA/Tukey’s.   Results:   With Optibond FL, a two-way ANOVA found no significant difference between groups based on application time or method with no significant interaction (p>0.05).  With Adper Scotchbond MP, a two-way ANOVA found no significant differences based on application time or method (p>0.05), but there was a significant interaction (p=0.002).  One-way ANOVAs and t-tests found a significant difference between groups (p<0.001).  See table.  Conclusions: With Optibond FL, there was no significant difference in shear bond strength to dentin based on application time, or active versus passive application of the primer.  However, active application of the primer of Adper Scotchbond MP at the manufacturer’s recommended application time increased the bond strength compared to longer application times or passive application.

Application Time (seconds) Manufacturer’s Directions (MD) Mean Shear Bond Strength MPa (st dev) Scotchbond MP Optibond FL Active Passive Active Passive MD 17.46 (6.33) Aa 8.60 (4.66) Ba 14.27 (4.91) 9.92 (6.20) MD + 10 secs 11.19 (6.48) Ab 11.61 (2.91) Aa 10.20 (5.39) 7.80 (4.25) MD + 20 secs 9.21 (3.36) Ab 12.57 (6.53) Aa 8.50 (3.64) 9.33 (4.49)   Groups with the same lower case letter per column or upper case letter by row are not significantly different (p>0.05)