Influence of Bonded Surface Area and Crosshead-speed on Bond Strength

Objectives:

This study investigated the influence of the bonded surface area and the crosshead speed on the dentin bond strengths of self-etch adhesives.

Methods:  

The system used was a Clearfil tri-S Bond (Kuraray Medical) with a combination of resin composite Clearfil AP-X (Kuraray Medical). Bovine mandibular incisors were mounted in self-curing resin and the facial surfaces were wet ground with #600 silicon carbide (SiC) paper. The dentin surfaces were treated according to the manufacturer’s instructions. Adhesives were applied, and the resin composites were condensed into molds (2.4 or 4.0 mm in internal diameter), placed on to the dentin, and then light activated. Ten samples per test group were shear tested at crosshead speeds of 0.1, 0.5, 1.0, 5.0, and 10.0 mm/min. Bond strength values in MPa were calculated from the peak load at failure divided by the specimen surface area. Two-way ANOVA followed by the Tukey HSD test (P<0.05) were done.

Results:

The mean dentin bond strength in MPa (std dev) obtained were:

                                                                         Crosshead speed (mm/min)

                        Diameter             0.1                 0.5                 1.0                   5.0                  10.0

                         2.4 mm         27.5(1.6)^a       29.1 (1.8)^a      32.6 (3.5)^a,b      34.6 (3.5)^b,c      36.7 (3.1)^c

                         4.0 mm         13.5 (1.5)^d      15.2 (2.4)^d      17.1 (2.3)^e        18.8 (1.8)^e,f      19.7 (1.9)^f

The two-way ANOVA revealed no statistically significant interaction between the bonded surface area and the crosshead speed. The dentin bond strength increased with increasing crosshead speed. When the bond strengths were compared at the same crosshead speed, they decreased with increasing bonded surface area.

Conclusions:

The results showed that higher crosshead speeds were associated with higher dentin bond strengths. This relationship was more significant for specimens with a smaller dentin bonding surface area.