Fatigue Limits of Enamel Bonds with Etch-and-Rinse and Self-Etch Adhesives

Fatigue testing of adhesive bonds to tooth structures has been shown to yield valuable information in examining the effectiveness of dental adhesives. Objective: The purpose of this study was to determine the shear fatigue limit (SFL) of composite to enamel bonds using modern adhesive systems. Methods: Ten specimens each were used to determine 24-hour composite (Z100 – 3M ESPE) to enamel shear bond strengths (SBS) with an etch-and- rinse system, Adper Single Bond (SB), and three self-etch adhesives - Adper Prompt-L-Pop (PLP), Clearfil SE (CSE) and Clearfil S3 (CS3). A staircase method of fatigue testing was used in a four-station fatigue cycler (Proto-tech) to determine the SFL of composite to enamel bonds with the adhesives (20 specimens for each adhesive) at 0.25 Hz for 40,000 cycles. ANOVA and Tukey's post hoc test were used for the SBS data and a modified t-test with Bonferroni correction was used for comparisons of the SFL. Results:

Adhesive	SBS (MPa)	SFL (MPa)	Ratio of SFL to SBS
SB	55.8±6.1 a	27.8±2.8 a	.50
CSE	47.8±2.8 b	22.1±4.1 b	.46
PLP	37.4±6.8 c	15.7±2.0 c	.42
CS3	31.8±2.2 c	12.2±1.5 d	.38
Different letters in columns indicate differences at the 5% significance level.

There was a significant difference (p<0.05) in the SBS and SFL between the etch-and-rinse adhesive and the three self-etch systems. The SBS of CSE was also significantly greater than the other two self-etch systems. There was a significant difference for SFL among all the adhesives with SB exhibiting the highest SFL. The ratio of SFL/SBS was less for the self-etch systems when compared to the etch-and-rinse system. Conclusions: The etch-and-rinse adhesive system produced significantly higher composite to enamel shear bond strength and fatigue limit than the self-etch systems.