Effect of zinc-doping in physicochemical properties of dental adhesives

Purpose: To evaluate changes in the physicochemical properties, water sorption (WS), solubility (SO), modulus of elasticity (E), ultimate tensile strength (UTS), and microhardness (MH) tests were undertaken in zinc-doped dental adhesives.Methods: Two bonding resins, Adper Single Bond Plus (SB) and Clearfil SE Bond (SEB), were zincdoped by mixing them with 5, 10 or 20wt% of ZnO powder, or with 1 or 2wt% ZnCl2. Resin disks were made of each adhesive blend for the evaluation of WS, SO, and MH, and dumbbell-shaped specimens were prepared for E and UTS testing.Results: An increase in WS and SO was observed for adhesives doped with ZnCl2. A reduction in WS was observed for the adhesive blends containing 10% or 20wt% ZnO, while the SO was not altered in any of the ZnO-doped adhesives. An increase in E values was observed only for the SB adhesive doped with ZnCl2. For SEB-blends, the incorporation of zinc compounds did not alter the E values. UTS values decreased when SEB was doped with ZnO. SBblends doped with 20wt% ZnO significantly increased their MH, and the addition of zinc to the SEB-blends augmented the MH values in all cases.This investigation was supported by grants CICOM/FEDER MAT2014-52036P and AUIP-JA 201

In vitro mechanical stimulation facilitates stress dissipation and sealing ability at the conventional glass ionomer cement-dentin interface.

Objective: The aim of this study was to evaluate the induced changes in the chemical and mechanical performance at the glass-ionomer cement-dentin interface after mechanical load application. Methods: A conventional glass-ionomer cement (GIC) (Ketac Bond), and a resin-modified glass-ionomer cement (RMGIC) (Vitrebond Plus) were used. Bonded interfaces were stored in simulated body fluid, and then tested or submitted to the mechanical loading challenge. Different loading waveforms were applied: No cycling, 24 h cycled in sine or loaded in sustained hold waveforms. The cement-dentin interface was evaluated using a nano-dynamic mechanical analysis, estimating the complex modulus and tan δ. Atomic Force Microscopy (AFM) imaging, Raman analysis and dye assisted confocal microscopy evaluation (CLSM) were also performed. Results: The complex modulus was lower and tan delta was higher at interfaces promoted with the GIC if compared to the RMGIC unloaded. The conventional GIC attained evident reduction of nanoleakage. Mechanical loading favored remineralization and promoted higher complex modulus and lower tan delta values at interfaces with RMGIC, where porosity, micropermeability and nanoleakage were more abundant. Conclusions: Mechanical stimuli diminished the resistance to deformation and increased the stored energy at the GIC-dentin interface. The conventional GIC induced less porosity and nanoleakage than RMGIC. The RMGIC increased nanoleakage at the porous interface, and dye sorption appeared within the cement. Both cements created amorphous and crystalline apatites at the interface depending on the type of mechanical loading.This work was supported by the Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (FEDER) [Project MAT2017-85999-P]

Ex vivo detection and characterization of remineralized carious dentin, by nanoindentation and single point Raman spectroscopy, after amalgam restoration

The aim of this study was to assess the mechanical and chemical performance of sound and caries-affected dentin (CAD), after Zn-free vs containing amalgam restorations placement and thermocycling. Dentin surfaces were studied by Atomic Force Microscopy (AFM) analysis for surface morphological characterization (including fibril diameter assessment), nano-indentation (to measure nano-hardness-Hi and modulus of Young-Ei), and single point Raman spectroscopy for chemical analysis. Measurements were performed before amalgam placement, after amalgam removal, and after 3 months of thermocycling (100,000cy/5 ºC and 55 ºC). Restorations increased both Hi and Ei at intertubular dentin of CAD. The highest values of Hi were achieved at intertubular dentin after restoring with Zn-containing amalgams. Remineralization of dentin was attributed to the increase of both amorphous and crystalline new mineral, as lower degrees of crystal imperfections in junction with crystal disorders, and improvement in structural stability of collagen were found. Higher presence of minerals were also confirmed after the decrease of fluoridated apatite and the increase of the total water content. Proteoglycans, lipids, and proteins, augmented in both sound and CAD, providing support for the mineral growing. The increase of bands assigned to vibration of carbonate calcium phosphate contributed to a decrease of crystallinity.Project MAT2014-52036-P supported by the Ministry of Economy and Competitiveness (MINECO) and European Regional Development Fund (FEDER)

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 (CAD) 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 (MTBS) was assessed. Debonded dentin surfaces were studied by field emission scanning electron microscopy (FESEM). 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. Load cycling increased the percentage of adhesive failures. New precipitation of minerals composed of zinc-base salts and multiple Zn-rich phosphate deposits were 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 un-doped 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. Staining techniques permitted to observe no signs of exposed protein at the resin-dentin interface after using SEB·PZnO.This work was supported by grant MINECO/FEDERMAT2014-52036-P

Functional and molecular structural analysis of dentine interfaces promoted by a Zn-doped self-etching adhesive and an in vitro load cycling model

The aim of this study was to evaluate if mechanical cycling influences bioactivity and bond strength of resin–dentine interface after bonding with Zn-doped self-etching adhesives. Sound dentine surfaces were bonded with Clearfil SE Bond (SEB), 10 wt% ZnO microparticles or 2 wt% ZnCl2 were added into the SEB primer (P) or bonding (Bd) for Zn-doping. Bonded interfaces were stored in simulated body fluid (24 h), and then tested or submitted to mechanical loading. Microtensile bond strength testing was performed. Debonded dentine surfaces were studied by scanning electron microscopy. Remineralisation of the bonded interfaces was assessed by nano-indentation, Raman spectroscopy, and Masson׳s trichrome staining. Load cycling (LC) increased the percentage of adhesive failures in all groups. LC increased the Young׳s modulus (Ei) at the hybrid layer (HL) when SEB, SEB·P-ZnO and SEB·P-ZnCl2 were applied, but decreased when both ZnO and ZnCl2 were incorporated into the bonding. Ei was higher when Zn compounds were incorporated into the primer (SEB·P). ZnO promoted an increase, and ZnCl2 a decrease, of both the relative presence of minerals and crystallinity, after LC. LC increased collagen crosslinking with both SEB·P-ZnO and SEB·P-ZnCl2. The ratios which reflect the nature of collagen increased, in general, at both HL and BHL after LC, confirming recovery, better organisation, improved structural differences and collagen quality. After loading, trichrome staining reflected a deeper demineralised dentine fringe when Zn-doped compounds were incorporated into SEB·Bd. Multiple Zn-rich phosphate deposits and salt formations were detected. Mineral precipitates nucleated in multilayered platforms or globular formations on peritubular and intertubular dentine.This work was supported by grant MINECO/FEDER MAT2011-24551 and MAT2014-52036-P

On modeling and nano-analysis of caries-affected dentin surfaces restored with Zn-containing amalgam and in vitro oral function

The aim of this research was to assess the influence of mechanical loading on the ability of Zn-free vs Zn-containing amalgams to promote remineralization at the dentin interface. Sound (SD) and caries-affected dentin surfaces (CAD) were restored using Zn-free or Zn-containing dental amalgams. Mid-coronal dentin surfaces were studied by 1) Atomic Force Microscopy (AFM) analysis (including plot and phase imaging, nanoindentation test (modulus of Young (Ei), nano-roughness measurements, and fibril diameter assessment), 2) Raman spectroscopy/cluster analysis, 3) X-ray diffraction (μXRD2), 4) field emission electron microscope (FESEM) and energy-dispersive analysis (EDX), for morphological, mechanical, and physico-chemical characterization. Analyses were performed before amalgam placement and after amalgam removal, at 24 hours and 3 weeks of load cycling. Zn-free and Zn-containing amalgams restorations promoted an increase in the modulus of Young of CAD surfaces, after three weeks of load cycling; at this time, Zn-containing amalgams attained higher Ei than Zn-free restorations. Zn-containing amalgams induced tubular occlusion after load cycling, in both sound and CAD. Zn free-amalgams promoted remineralization of both intertubular and peritubular dentin in CAD substrata. These minerals were identified as calciumphosphate deposits, and crystals as hydroxyl-apatite with augmented crystallographic maturity but with some components of lattice distortion. Crosslinking of collagen diminished and secondary structure of collagen increased in CAD substrate restored with Zn-containing amalgam after 3 w of load cycling, indicating an advanced preservation, molecular organization and orientation of collagen fibrils after load cycling. Plot and phase images permitted to observe the topographical changes which were promoted by the mineral deposits; in general, the indexes related to higher remineralization gave rise to a decrease of nano-roughness and an augmentation of the bandwidth of the collagen fibrils. Zn-containing amalgam restorations submitted to mechanical stimuli promote remineralization of the partially mineral-depleted subjacent substrate at the caries-affected dentin.This work was supported by Grant Nos. MINECO/FEDER MAT2014-52036-P and FIS2013-41821-R

Microscopía electrónica con electrones secundarios y retrodispersos en el esmalte del diente fluorótico

Introducción: El objetivo del presente trabajo consistió en definir los patrones morfológicos del esmalte en dientes fluoróticos mediante la utilización de la Microscopía Electrónica de Barrido con electrones secundarios y retrodispersos. Material y Métodos: Se estudiaron 20 piezas dentarias permanentes de pacientes con fluorosis dental y 5 dientes controles. Todas las muestras fueron procesadas para su estudio morfológico. Resultados: Se distinguen tres zonas en dientes fluoróticos: zona externa, zona subsuperficial o lesión fluorótica y zona interna. La zona subsuperficial presenta un triple patrón morfológico característico. Discusión: Este estudio permite sistematizar patrones estructurales que en un futuro pueden constituir una base para el desarrollo de futuras estrategias reparativas en dientes fluoróticos.Introduction: The aim of the present study was to establish histological patterns of fluorotic teeth by scanning electron microscopy (SEM) using secondary and retrodispersive electrons. Material and Methods: We studied 20 permanent teeth belonging to pacients whith dental fluorosis and 5 control teeth. All samples were processed for morphological study and scanning electron microscopy (SEM). Results: We distinguished three areas in fluorotic teeth: external area, subsuperficial area (or fluorotic lesion) and internal area. Subsuperficial area showed three different types of morphological patterns, which were characteristic of fluorotic lesions. Discussion: This study provides systematic structural patterns which in the future can provide a basis for developing future strategies reparative in fluorotic teeth

Mineralización del esmalte en la fluorosis dentaria. Estudio microscópico y microanalítico

Tesis Univ. Granada. Departamento de Histología. Leída el 11 de diciembre de 200

A zinc chloride-doped adhesive facilitates sealing at the dentin interface: A confocal laser microscopy study

The aim of this study was to understand the effect of Zn-doping of adhesives and mechanical load cycling on the micromorphology of the resin-dentin interdiffusion zone (of sound and caries affected dentin). The investigation considered two different Zn-doped adhesive approaches and evaluated the interface using confocal laser scanning microscopy. Sound and carious dentin-resin interfaces of unloaded specimens were deficiently resin-hybridized, in general. These samples showed a rhodamine B-labeled hybrid layer and adhesive layer completely affected by fluorescein penetration (nanoleakage) through the porous resin-dentin interface, but thicker after phosphoric acid-etching and more extended in carious dentin. Zn-doping promoted an improved sealing of the resin-dentin interface at dentin, a decrease of the hybrid layer porosity, and an increment of dentin mineralization. Load cycled augmented the sealing of the Zn-doped resin-dentin interfaces, as porosity and nanoleakage diminished, and even disappeared in caries-affected dentin substrata conditioned with EDTA. Sound and carious dentin specimens treated with the xylenol orange technique produced a clearly outlined fluorescence when resins were Zn-doped, due to a consistent Ca-mineral deposits within the bonding interface and inside the dentinal tubules, especially when load cycling was applied on specimens treated with Zn-doped bonding components of self-etching adhesives. Micropermeability at the resin-dentin interface diminished after combining EDTA pretreatment, ZnCl2-doping and mechanical loading stimuli on restorations. It is clearly preferable to include the zinc compounds into the bonding constituents of the self-etching adhesives, instead of into the primer ingredients. The promoted new mineral segments contributed to reduce or avoid both porosity and nanoleakage from the load cycled Zn-doped resin dentin interface.This work was supported by the Ministry of Economy and Competitiveness (MINECO) [Project MAT2014-52036-P] and European Regional Development Fund (FEDER)