Effect of Frequency on Fatigue Limits of Dentin Bonds

Higher frequencies reduce the time to characterize the fatigue endurance of a resin composite bonded to mineralized tooth structures and expedite testing. Minimal information is available regarding the effect of frequency on shear fatigue limit (SFL) testing to dentin. Objectives: The purpose of this study was to examine the effect of frequency on SFL of dentin bonds using self-etch adhesives. Methods: Fifteen specimens each were used to determine initial shear bond strength (SBS) to dentin with three self-etch adhesive systems: 1) G-aenial Bond[GB] (GC), 2) OptiBond XTR[OX] (Kerr) and 2) Scotchbond Universal[SU] (3M ESPE). A staircase method of fatigue testing (25 specimens) was used with an ElectroPuls E1000 machine to determine the SFL of Z100 Restorative (3M ESPE) bonded to dentin with the three adhesives using 5Hz, 10Hz and 20Hz frequencies for 50,000 cycles. A stainless steel metal ring with an inner diameter 2.4 mm was used to bond the resin composite to flat ground (4000 grit) dentin surfaces for determination of both SBS and SFL. A releasing agent was used on the surface of metal rings in contact with the bonding site. An ANOVA and post hoc Tukey's test were used for analysis of the SBS data and a modified t-test with Bonferroni correction was used to compare the SFLs at the three frequencies. Results:

The SBS of OX was significantly greater (p<0.05) than SU and GB.  There was not a significant difference (p>0.05) in SFL using frequencies of 5Hz, 10Hz and 20Hz, but differences (p<0.05) in SFL were found among the adhesives systems at the same frequency. Conclusion: Frequencies of 5Hz, 10Hz and 20Hz did not result in differences in SFL for each of three self-etch adhesives. The results suggest that higher frequencies may be appropriate for fatigue testing of resin composite bonded to dentin.