Inmaculada Cabello

A Zn-doped etch-and-rinse adhesive may improve the mechanical properties and the integrity at the bonded-dentin interface

OBJECTIVE The objective of the study was to determine if zinc-doped etch-and-rinse dentin adhesive may induce therapeutic effects within the resin-dentin interface. METHODS Human acid-etched dentin was infiltrated with Adper™ Single Bond Plus (SB, 3M ESPE, St. Paul, MN, USA), SB doped with 10wt.% ZnO nanoparticles (ZnO-SB) or SB doped with 2wt.% ZnCl2 (ZnCl2-SB). AFM/nanoindentation analysis was performed on fully hydrated specimens to evaluate the nanomechanical properties (Hi: hardness; Ei: modulus of elasticity) across the resin-dentin interface after different SBF storage periods (24h, 1m, 3m). Confocal laser microscopy (CLSM) was used to evaluate the ultramorphology and micropermeability at 24h and 3m of SBF storage. RESULTS SB control specimens exhibited a decrease in Hi in the hybrid layer (HL) and bottom of the hybrid layer (BHL) and a decrease in Ei in the HL after 3m of SBF storage, indicating that severe degradation occurred in the control interface. ZnO-SB bonded specimens preserved the initial Hi and Ei at the HL and BHL subsequent SBF storage; ZnCl2-SB bonded specimens showed a decrease in Ei, in the HL over time. CLSM analysis confirmed that both Zn-doped adhesives were able to preserve the integrity of the HL. SIGNIFICANCE Specific formulation of Zn-doped etch-and-rinse adhesives may offer the possibility to maintain the nano-mechanical properties along the dentin-bonded interface by inhibiting dentin MMPs and by protective mineral crystals formation within the resin-dentin interface. Clinical advantages may be expected by preserving and improving the integrity of the hybrid layer when Zn-doped adhesives are employed.

Zinc induces apatite and scholzite formation during dentin remineralization.

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.

In vitro mechanical stimulation promoted remineralization at the resin/dentin interface

INTRODUCTION Teeth are continuously subjected to mechanical loading during mastication, swallowing and parafunctional habits. The purpose of this study was to evaluate if mechanical loading is able to promote remineralization at etched and bonded dentin interfaces. METHODS Flat mid-coronal human dentin surfaces were subjected to different treatments: (1) demineralization by 37% phosphoric acid (PA) followed by application of an etch-and-rinse dentin adhesive: Adper™ Single Bond (SB) (PA+SB) or (2) treatment by 0.5M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA+SB); (3) application of an self-etch dentin adhesive: Clearfil SE Bond (SEB). Restorations were accomplished, incrementally, with resin composite. In half of the specimens, mechanical loading (100,000 cycles, 3Hz, 49N) was applied. AFM imaging/nano-indentation, Raman spectroscopy/cluster analysis and dye assisted confocal microscopy evaluation (CLSM), were employed to detect remineralization at the interfaces. RESULTS In general, load cycling increased mechanical properties at the resin-dentin interface. Cluster analysis demonstrated a regular increase of the mineral-matrix ratio in EDTA+SB and SEB loaded specimens. CLSM showed a reduced micropermeability and nanoleakage after loading in bonded interfaces, and a most pronounced reduction in SEB samples. INTERPRETATION In vitro load cycling promoted remineralization at resin-dentin interfaces. Mineral content increased and nanomechanical properties were improved at both the hybrid layer and bottom of the hybrid layer. Higher mineral concentration in correspondence with a lesser concentration of demineralized dentin was observed, after loading.

Load cycling enhances bioactivity at the resin–dentin interface

OBJECTIVES The purpose of this study was to evaluate if mechanical loading promotes bioactivity at the resin interface after bonding with three different adhesive approaches. METHODS Dentin surfaces were subjected to three different treatments: demineralisation by (1) 37% phosphoric acid (PA) followed by application of an etch-and-rinse dentin adhesive Single Bond (SB) (PA+SB), (2) by 0.5 M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA+SB), (3) application of a self-etch dentin adhesive: Clearfil SE Bond (SEB). Bonded interfaces were stored in simulated body fluid during 24 h or 3w. One half of each tooth was submitted to mechanical loading. Remineralisation of the bonded interfaces was assessed by AFM imaging/nano-indentation, Raman spectroscopy/cluster analysis, dye assisted confocal microscopy evaluation (CLSM) and Massons trichrome staining. RESULTS Loading cycling for 3w promoted an increase of mechanical properties at the resin-dentin interface. Cluster analysis demonstrated an augmentation of the mineral-matrix ratio in SB-loaded specimens. CLSM showed an absent micropermeability and nanoleakage after loading EDTA+SB and SEB specimens. Trichrome staining reflected a narrow demineralised dentin matrix after loading, almost not observable in EDTA+SB and SEB. SIGNIFICANCE In vitro mechanical loading promoted mineralization in the resin-dentin interfaces, at 24 h and 3w of storage.

Bioactivity of zinc-doped dental adhesives

UNLABELLED Design of restorative materials should be focused on promoting not only adhesion but also dentine self-repair processes. OBJECTIVE To ascertain if ZnO and ZnCl2-doped resins are materials able to induce calcium (Ca) and phosphate (P) deposition. METHODS 48 resin disks were prepared with the following materials: (1) single bond -3M/ESPE-, (2) single bond+ZnO particles 20wt% and (3) single bond+ZnCl2 2wt%. Specimens were polymerised and polished. Bioactivity was tested through a simulated body fluid solution (SBFS) immersion test. At time 24h, 7 d and 21 d surfaces were analyzed by stereomicroscope, high resolution scanning electron microscope (HRSEM), energy-dispersive analysis (EDX), confocal laser Raman, and X-ray diffraction (XRD) for morphological and chemical composition. RESULTS Under the stereomicroscope, crystal formations were encountered in both zinc-doped resin adhesives after 7 d of immersion. It was, detected by EDX, that the ZnO-doped resin produced Zn, Ca and P deposition (globular formations were observed by HRSEM) after 7 d. Zn and P crystals were detected by HRSEM and EDX in the experimental ZnCl2-doped resin after 7 d and 21 d. Hopeite formation was identified by Raman on both Zn-doped resins. Single bond did not produce mineral or crystal precipitation. CONCLUSIONS ZnO-doped resin induced Ca and P deposition after SBFS immersion. On ZnCl2-doped resin hopeite formation was detected, if this hopeite may be further converted into apatite, after SBFS immersion, remains to be ascertained. CLINICAL SIGNIFICANCE Bonding with ZnO-doped resin may facilitate incorporation of Ca and P at the interfacial bonding zone.

Differential resin-dentin bonds created after caries removal with polymer burs.

The objective of this article was to investigate the effect of carbide and polymer burs caries removal methods on the bond strength of different adhesives to dentin. Resin restorations were performed in sound and caries-affected dentin, after using polymer or carbide burs and bonding with four different adhesive (Single bond, SB; Clearfil SE bond, SEB; FL-Bond II, FLB; and Fuji II-LC, FUJI). Microtensile bond strength (MTBS) was measured. Data were analyzed with ANOVA and Student-Newman-Keuls tests. Debonded surfaces were observed by scanning electron microscopy. Bonded interfaces were examined using light microscopy (Massons trichrome staining). In sound dentin, MTBS was similar for SEB and SB, and higher than that of FLB and FUJI. Bond strength to carbide bur prepared dentin was similar for SB, SEB, and FLB; FUJI presented the lowest. SB applied on polymer bur excavated dentin presented similar values to those of the carbide bur group; MTBS attained by SEB, FLB, and FUJI decreased when bonding to dentin treated with polymer burs; FUJI yielded pretesting failures in all specimens. Polymer burs created a thick smear layer that was not infiltrated by tested self-etching agents. The bonding effectiveness of self-etching and glass-ionomer-like adhesives to dentin decreased when polymer burs were used.

Bond strength and bioactivity of Zn-doped dental adhesives promoted by load cycling.

The purpose of this study was to evaluate if mechanical loading influences bioactivity and bond strength at the resin-dentin interface after bonding with Zn-doped etch-and-rinse adhesives. Dentin surfaces were subjected to demineralization by 37% phosphoric acid (PA) or 0.5 M ethylenediaminetetraacetic acid (EDTA). Single bond (SB) adhesive—3M ESPE—SB+ZnO particles 20 wt% and SB+ZnCl2 2 wt% were applied on treated dentin to create the groups PA+SB, SB+ZnO, SB+ZnCl2, EDTA+SB, EDTA+ZnO, and EDTA+ZnCl2. Bonded interfaces were stored in simulated body fluid for 24 h and tested or submitted to mechanical loading. Microtensile bond strength (MTBS) was assessed. Debonded dentin surfaces were studied by high-resolution scanning electron microscopy. Remineralization of the bonded interfaces was assessed by atomic force microscope imaging/nanoindentation, Raman spectroscopy/cluster analysis, and Massons trichrome staining. Load cycling (LC) produced reduction in MTBS in all PA+SB, and no change was encountered in EDTA+SB specimens, regardless of zinc doping. LC increased the mineralization and crystallographic maturity at the interface; a higher effect was noticed when using ZnO. Trichrome staining reflected a narrow demineralized dentin matrix after loading of dentin surfaces that were treated with SB-doped adhesives. This correlates with an increase in mineral platforms or plate-like multilayered crystals in PA or EDTA-treated dentin surfaces, respectively.

Surface microanalysis and chemical imaging of early dentin remineralization.

This study reports physical and chemical changes that occur at early dentin remineralization stages. Extracted human third molars were sectioned to obtain dentin discs. After polishing the dentin surfaces, three groups were established: (1) untreated dentin (UD), (2) 37% phosphoric acid application for 15 s (partially demineralized dentin-PDD), and (3) 10% phosphoric acid for 12 h at 25° C (totally demineralized dentin-TDD). Five different remineralizing solutions were used: chlorhexidine (CHX), artificial saliva (AS), phosphate solution (PS), ZnCl2, and ZnO. Wettability (contact angle), ζ potential and Raman spectroscopy analysis were determined on dentin surfaces. Demineralization of dentin resulted in a higher contact angle. Wettability decreased after immersion in all solutions. ζ potential analysis showed dissimilar performance ranging from -6.21 mV (TDD + AS) up to 3.02 mV (PDD + PS). Raman analysis showed an increase in mineral components after immersing the dentin specimens, in terms of crystallinity, mineral content, and concentration. This confirmed the optimal incorporation and deposition of mineral on dentin collagen. Organic content reflected scarce changes, except in TDD that appeared partially denatured. Pyridinium, as an expression of cross-linking, appeared in all spectra except in specimens immersed in PS.

Resistance to degradation of resin-dentin bonds produced by one-step self-etch adhesives.

The objective of this article is to evaluate the resistance to degradation of resin-dentin bonds formed with three one-step adhesives. Flat, mid-coronal dentin surfaces were bonded with the self-etching adhesives [Tokuyama Bond Force (TBF), One Up Bond F Plus (OUB), and G-Bond (GB)]. The bonded teeth were subjected to fatigue loading, chemical degradation, and stored in distilled water for four time periods (up to 12 months). Specimens were tested for microtensile bond strength and microleakage. Fractographic analysis was performed by scanning electron microscopy. Bonded interfaces were examined by light microscopy using Massons trichrome staining. An atomic force microscope was employed to analyze phase separation and surface nanoroughness (Ra) at the polymers. Vickers microhardness and the degree of the conversion (DC) were also determined. ANOVA and multiple comparisons tests were performed. Bond strength significantly decreased after the chemical challenge, but not after load cycling. Aging decreased bond strength after 6 months in TBF and GB, in OUB after 12 months. An increase of the nonresin protected collagen zone occurred in all groups, after storing. TBF showed the highest roughness, microhardness, and DC values, and GB showed the lowest. Mild self-etch one-step adhesives (TBF/OUB) showed a higher degree of cure, lower hydrophilicity, and major resistance to degradation of resin-dentin bonds when compared to highly acidic self-etching adhesive (GB).

Self-etching zinc-doped adhesives improve the potential of caries-affected dentin to be functionally remineralized

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 Youngs modulus (Ei), Raman spectroscopy/cluster analysis, and Massons 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.