Purpose: To investigate the influence of relative humidity and application time on bond strength to dentin of different
classes of adhesive systems.
Materials and Methods: A total of 360 extracted human molars were ground to mid-coronal dentin. The dentin specimens
were treated with one of six adhesive systems (Syntac Classic, OptiBond FL, Clearfil SE Bond, AdheSE, Xeno
Select, or Scotchbond Universal), and resin composite (Filtek Z250) was applied to the treated dentin surface under
four experimental conditions (45% relative humidity/application time according to manufacturers’ instructions; 45%
relative humidity/reduced application time; 85% relative humidity/application time according to manufacturers’ instructions;
85% relative humidity/reduced application time). After storage (37°C, 100% humidity, 24 h), shear bond
strength (SBS) was measured and data analyzed with nonparametric ANOVA followed by Kruskal-Wallis tests and
Mann-Whitney U-tests with Bonferroni-Holm correction for multiple testing (level of significance: = 0.05).
Results: Increased relative humidity and reduced application time had no effect on SBS for Clearfil SE Bond and
Scotchbond Universal (p = 1.00). For Syntac Classic, OptiBond FL, AdheSE, and Xeno Select there was no effect
on SBS of reduced application time of the adhesive system (p ≥ 0.403). However, increased relative humidity
significantly reduced SBS for Syntac Classic, OptiBond FL, and Xeno Select irrespective of application time
(p ≤ 0.003), whereas for AdheSE, increased relative humidity significantly reduced SBS at recommended application
time only (p = 0.002).
Conclusion: Generally, increased relative humidity had a detrimental effect on SBS to dentin, but reduced application
time had no effect.