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

Purpose: To evaluate the bond strength of two dentin-bonding systems to roo t canal dentin. Materials and Methods: 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 gr oups. The teeth of the first group were treated with All-Bond 2 dental adhe sive and those of the second group with Panavia F. The root canal dentin wa s conditioned as suggested by the manufacturers and, after the application of the dental adhesives, a layer of resin-based composite was polymerized o ver the adhesive layer. After the composite had completely set, the section s were prepared for microtensile test and kept in a wet environment at a re lative humidity of 90 +/- 2% measured with a digital relative humidity mete r and at a temperature of 22 degreesC for 24 hrs. The specimens were sectio ned perpendicularly to the bonded interface, into slabs 1.5 nun thick (10 s ections 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 t hen exactly established by three measurements performed in three points of each slab by a digital micrometer, The specimens were then subjected to a t ensile force at a crosshead speed of 0.2 mm/min. The test was observed usin g a confocal microscope and the failure modes were noted. The load at failu re was registered and the bonded area was measured using a confocal microsc ope at a magnification of x25 in conjunction with an image-processing progr am. The failure data were analyzed using the Wilcoxon-Gehan test with exact non-parametric inference. Results: The mean value at failure was the same for the two experimental groups (17.1 MPa). There was no statistically sign ificant difference between Panavia F and All-Bond 2 (P > 0.8671). Most of t he 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.