The aim of this study was to ascertain whether zinc may improve the repair ability of demineralized dentin. Dentin disks were demineralized by phosphoric acid during 15 s and immersed in artificial saliva, remineralizing solution, a zinc chloride solution and a zinc oxide solution. Dentin specimens were analyzed after 24 h and 1 month of storage. Surface morphology was assessed by atomic force and scanning electron microscopy, mechanical properties were analyzed by nanohardness testing in a TriboIndenter, and chemical changes at the surfaces were determined by X-ray diffraction, Raman and energy-dispersive elemental analyses. After phosphoric acid application, dentin was only partially demineralized. Demineralized dentin was remineralized after 24 h of storage in any of the tested solutions (nanohardness increased and hydroxylapatite formation was detected by Raman). Remineralization was maintained up to 1 month in dentin stored in remineralizing solution, zinc chloride and zinc oxide. Zinc and phosphate were important for hydroxylapatite homeostasis. Scholzite formation was encountered in dentin stored in zinc-containing solutions. Zinc might allow to reach the balance between dentin demineralization and remineralization processes.

Introduction Demineralized collagen fibers at the hybrid layer are susceptible to degradation. Remineralization may aid to improve bond longevity. Objectives The aim of the present study was to infiltrate zinc and calcium-loaded polymeric nanoparticles into demineralized dentin to facilitate hybrid layer remineralization. Materials and methods Zinc or calcium-loaded polymeric nanoparticles were infiltrated into etched dentin, and Single Bond Adhesive was applied. Bond strength was tested after 24 h and 6 months storage. Nanomechanical properties, dye-assisted confocal laser microscopy, and Masson’s trichrome staining evaluation were performed to assess for the hybrid layer morphology, permeability, and remineralization ability after 24 h and 3 months. Data were analyzed by ANOVA and Student–Newman–Keuls multiple comparisons tests (p < 0.05). Results Immediate bond strength was not affected by nanoparticles infiltration (25 to 30 MPa), while after 6 months, bond strengths were maintained (22 to 24 MPa). After 3 months, permeability occurred only in specimens in which nanoparticles were not infiltrated. Dentin remineralization, at the bottom of the hybrid layer, was observed in all groups. After microscopy analysis, zinc-loaded nanoparticles were shown to facilitate calcium deposition throughout the entire hybrid layer. Young’s modulus at the hybrid layer increased from 2.09 to 3.25 GPa after 3 months, in specimens with zinc nanoparticles; meanwhile, these values were reduced from 1.66 to 0.49 GPa, in the control group. Conclusion Infiltration of polymeric nanoparticles into demineralized dentin increased long-term bond strengths. Zinc-loaded nanoparticles facilitate dentin remineralization within the complete resin–dentin interface. Clinical relevance Resin–dentin bond longevity and dentin remineralization at the hybrid layer were facilitated by zinc-loaded nanoparticles.

The aim of this study was to evaluate if mechanical cycling influences bioactivity at the resin–carious dentin interface after bonding with Zn-doped self-etching adhesives. Caries-affected dentin surfaces were bonded with: Clearfil SE bond (SEB), and 10 wt. % ZnO nanoparticles or 2 wt. % ZnCl2 were added into the SEB primer or bonding components. Bonded interfaces were stored during 24 h and then tested or submitted to mechanical loading. Microtensile bond strength was assessed. Debonded dentin surfaces were studied by field emission scanning electron microscopy. Remineralization of the bonded interfaces was evaluated through nanohardness (Hi) and Young's modulus (Ei), Raman spectroscopy/cluster analysis, and Masson's trichrome staining technique. New precipitation of minerals composed of zinc-base salts and multiple Zn-rich phosphate deposits was observed in samples infiltrated with the Zn-doped adhesives. At the hybrid layer, specimens treated with ZnO incorporated in the primer (SEB·P-ZnO), after load cycling, attained the highest Ei and Hi. Load cycling increased Ei at the bottom of the hybrid layer when both, SEB undoped and SEB with ZnCl2 included in the bonding (SEB·Bd-ZnCl2), were used. ZnO incorporated in the primer promoted an increase in height of the phosphate and carbonate peaks, crystallinity, relative mineral concentration, and lower collagen crosslinking. ZnCl2 included in the bonding attained similar results, but relative mineral concentration decreased, associated to higher crosslinking and restricted collagen maturation. In general, a substantial restoration of the mechanical properties of caries-affected dentin substrata occurred when SEB-Zn doped adhesives were used and load cycled was applied, leading to functional and biochemical remineralization.