Early and 24-hour bond strength and degree of conversion of etch-and-rinse and self-etch adhesives

Purpose: To evaluate early and 24-hour microtensile bond strength (μTBS) and the degree of conversion (DC) of one representative adhesive system from each of the four current bonding approaches. Methods: 40 human molars were sectioned occluso-gingivally into two halves. Resin composite was bonded incrementally to flat, mid-coronal dentin, using the adhesives Adper Scotchbond MP (MP); Adper Scotchbond 2 (SB); Clearfil SE Bond (SE); and Adper Prompt LPop (LP) according to the respective manufacturer's instructions (n= 10). One half was immediately sectioned into sticks and subjected to μTBS test. As the sectioning process took approximately 1 hour, the results were designated as 1-hour bond strengths. The other half was stored in distilled water at 37°C for 24 hours before being sectioned and tested. The DC of these systems was measured using Fourier Transform-Raman spectroscopy in three periods: immediately, 1 and 24 hours after polymerization. Data were analyzed with ANOVA and Tukey's tests. Results: There were no significant differences between the 1-hour and 24-hour bond strengths (P>0.05), or among the DC measured immediately, 1 hour and 24 hours after polymerization (P>0.05). However, significant differences were observed among adhesives (P<0.05). μTBS values obtained, in MPa (1 hour/24 hour), were: SB (48.6 + 1.3/48.4 + 3.5) = SE (51.9 + 4.7/53.3±2.9) > MP (35.3 ±10.9/38.6 + 6.7) > LP (25.5 + 1.1/26.0 + 1.5). The DC, in percentage (immediately/lhour/24 hour), were: SE (81/82/87) > MP (79/77/81) > SB (60/63/65) > LP (39/37/42).