A 3D analysis of mechanically stressed dentin–adhesive–composite interfaces using X-ray micro-CT

Dentin bonding systems (DBS) have been developed in order to bond restorative materials (i.e. composite) to tooth tissues when function and integrity have to be re-established. Adhesion to dentin results from the penetration of DBS into the demineralised substrate constituted by a conditioned collagen network. The long-term stability of a restored tooth is mainly affected by the seal of the restorative material on the dental structures. Although leakage through the dentin–DBS interface has been widely reported, 3D investigation technique and accurate non-destructive measurements of leakage as functions of mechanical cycling have never been provided. To address these issues, the properties of the material interface are analysed using micro-tensile static and dynamic tests, assisted by the finite element modelling and by the X-ray computed micro-tomography. The dual energy absorption technique, with the synchrotron beam light, has been developed to investigate, in a non-destructive manner, the effect of mechanical cycling on leakage of a silver nitrate staining solution at the dentin–DBS interface. The effect of the pulpal roof on the stress distribution in the coronal dentin–DBS–composite interface has been investigated and the level at which the state of stress can be assumed to be uniform within acceptable limits has been defined. The tensile static and dynamic results suggest that the adhesive strength for the multi-step DBS resulted significantly higher than the other investigated DBS. Imaging results indicate that 3D leakage occurs radially at the dentin–adhesive interface through the interface itself rather than through the unconditioned dentin bulk; moreover, the dynamic tensile loading allows a more diffuse staining penetration.