Shear Bond Strength of Three Adhesives to Unground-Enamel, Ground-Enamel, Dentin

Bonding agents continue to develop with basic changes from a total etch to self etching systems. However the self etching systems have a higher pH which decrease the bond to unground enamel. 

OBJECTIVES: To measure and compare the shear bond strength of two experimental self-etch adhesives with a commercially available self-etching adhesive on unground-enamel, ground-enamel and dentin.

METHODS: 90 extracted, intact, human molars were divided into 3 groups, 30 each. For the Unground-Enamel group (UE-Group1), flattest surface was used. Two other groups were ground with a series of abrasives ending with a 600 grit wet wheel to obtain flat enamel (GE-Group2) and dentin (D-Group3) bonding surfaces. The adhesives used were Clearfil SE (CSE/Kuraray), SCB Experimental O-(SEO/Coltene Whaledent), SCB experimental P-(SEP/Coltene). The adhesives were applied to the bonding area according to manufacturer's instructions. A plastic tube (diameter=1.5mm) filled with composite-resin (Synergy/Coltene Whaledent) was placed over the adhesive and cured for 40s with Coltolux LED curing light (750 Mw/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 5565) 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 2-factor ANOVA and Tukey/Kramer post-hoc tests (p=0.05).

RESULTS: Mean±SD in MPa

CSE-UE	SEO-UE	SEP-UE	CSE-GE	SEO-GE	SEP-GE	CSE-D	SEO-D	SEP-D
26.8±4	19.7±4	17.9±4	31.6±4	23.6±5	20.8±2	28.7±2	24.9±3	21.7±3

CONCLUSIONS: Based on the results of this study, Clearfil SE showed higher shear bond strength for all three substrates (p<0.05). Significant differences were found between dentin, ground enamel and unground enamel. This study was supported in part by a grant from Coltene/Whaledent.