Age of 3 self-etch one bottle adhesives-shear bond strength

Shelf life and expiration date of dental adhesives have clinical considerations and concerns that raise critical questions about their efficacy. Objectives: To measure and compare the shear bond strength of three adhesive at the beginning and the end of their shelf life on ground enamel and dentin. Methods: 120, intact human molars were divided into two groups (older/G1 and newer/G2 material). Half of each group was ground with 600 grit wet wheel to obtain flat enamel (E), while the second half was ground to obtain dentin surfaces (D). Adhesives: Clearfil S3 (CS3), G Bond (GB), I Bond (IB) were stored in refrigerator when not being used for testing. The adhesives were applied to the bonding area following manufacturer's instructions. A plastic tube (diameter=1.5mm) filled with composite-resin (Z100) was placed over the adhesive and cured for 40 seconds with an Optilux 501 curing light (output >500mW/cm²). Samples (n=10) were stored in water for 24 hours at 37°C in an incubator before testing. Specimens were then placed in a special fixture mounted on a Universal testing machine (INSTRON, model number 5562) and were loaded to failure at a crosshead speed of 1mm/min. The failure load was converted to bond strength by dividing by the bonding area. The data were analyzed with ANOVA and Tukey post-hoc test. Results: Statistical analysis showed no significant differences in shear bond strengths between the old and new materials for both enamel and dentin. 

Age	G1			G2
	CS3	GB	IB	CS3	GB	IB
E	30±5	21.4±6	31.44±8	27.5±5	21.2±5	29.6±3
D	22.7±5	20.2±7	25.46±4	26.9±6	19.2±4	27.2±5

Conclusion: Based on this study, shear bond strength of these materials was not influenced by the shelf life. Dental adhesives that have recent expiration date showed satisfactory shear bond strength that is comparable to newer adhesive that has further expiration date.