Microtensile bond strength and confocal microscopy of dental adhesives bonded to root canal dentin

To evaluate the bond strength of two dentin-bonding systems to root canal dentin.

Six central incisors, extracted for periodontal reasons, were endodontically treated, no obturation of the root canal space was performed. The teeth were cut parallel to their long axis. One half of each tooth was randomly assigned to one of two experimental groups. The teeth of the first group were treated with All-Bond 2 dental adhesive and those of the second group with Panavia F. The root canal dentin was conditioned as suggested by the manufacturers and, after the application of the dental adhesives, a layer of resin-based composite was polymerized over the adhesive layer. After the composite had completely set, the sections were prepared for microtensile test and kept in a wet environment at a relative humidity of 90 +/- 2% measured with a digital relative humidity meter and at a temperature of 22 degrees C for 24 hrs. The specimens were sectioned perpendicularly to the bonded interface, into slabs 1.5 mm thick (10 sections for each experimental group). The slabs were then trimmed by super fine diamond burs for the microtensile bond test with the narrowest region located at the respective bonded interface. The thickness of the slab was then exactly established by three measurements performed in three points of each slab by a digital micrometer. The specimens were then subjected to a tensile force at a crosshead speed of 0.2 mm/min. The test was observed using a confocal microscope and the failure modes were noted. The load at failure was registered and the bonded area was measured using a confocal microscope at a magnification of x25 in conjunction with an image-processing program. The failure data were analyzed using the Wilcoxon-Gehan test with exact non-parametric inference.

The mean value at failure was the same for the two experimental groups (17.1 MPa). There was no statistically significant difference between Panavia F and All-Bond 2 (P> 0.8671). Most of the specimens showed a debonding of the adhesive from the hybrid layer. The results showed that the bond strength of the two bonding systems tested to the dentin of the root canal are slightly lower than to those obtained with the latest adhesive systems, in the coronal dentin.