Novel self-bonding composites: resin-dentin interfacial chemistry

Abstract

Introduction: The biggest shortcoming of adhesive restorations is their susceptibility to bond degradation, when the substrate is dentin [1]. Since the quality of the resin-dentin interface relies mainly on its nanostructure [2], it is important to study the hybridization process in self-adhesive composites. Knowledge of the resin-dentin interface chemistry will provide insight into bonding, and possible susceptibility towards degradation [3].

Materials and methods: 9 primary teeth, obtained with informed consent from the Eastman Dental Hospital, previously approved by the EDI/EDH Joint Research & Ethics Committee were sectioned to obtain flat dentin surfaces, polished with 500 SiC grit paper and etched before material placement. The teeth were randomly divided (n = 3) between 3 materials - Activa ™ BioActive Restorative and 2 experimental composites. The experimental flowable composites had different levels of monocalcium phosphate (MCPM) and antibacterial polylysine (PLS) powders added to the filler phase. Restored teeth were stored in DI water for 24 h and vertically sectioned to obtain slabs perpendicular to the interface. Raman spectroscopy (Horiba Jobin Yvon, Paris, France) was used to research the chemistry of the resin-dentin interface. Three different lines were analysed in each sample to ensure reproducibility. Means corresponding to resin and dentin peaks were calculated and plotted using Microsoft Excel Tools (v15.30, Redmond, Washington, USA). FE-SEM (Phillip XL-30, Eindhoven, The Netherlands) was used to gather microstructural imaging of the interface.

Results: Differences in chemical composition of the resin-dentin interface was found within interfacial regions ranging from 4 to 8 μm deep. Spectra obtained in mineralized dentin confirmed material diffusion and penetration in all cases. Doubling the hydrophilic additives in experimental composites, increased the resin infiltration depth by almost two-fold and affected the apatite to collagen ratio variation within the interface. SEM imaging confirmed resin tag formation, with all materials.

Discussion and conclusions: No distinct hybrid layer was found at the interfaces, which is in accordance with previous studies [4,5]. However, resin infiltration was observable with all materials, providing evidence of envelopment and micromechanical interlocking. A gradual transition from dentin to pure material confirmed the presence of an interdiffusion zone [6] which was enhanced with increased hydrophilic additives. These results confirm micromechanical interlocking with dentin is achieved in both the experimental and commercial materials.