Nanoleakage Tests Research Articles

Long-term hybrid stability and matrix metalloproteinase inhibition by fucosterol in resin-dentin bonding biomechanics

Fucosterols have been widely studied for their antioxidant, anticancer, and anti-inflammatory properties. However, they have not yet been studied in the field of dentistry. This study aimed to determine whether pretreatment of dentin with fucosterol before resin restoration enhances bond stability in resin-dentin hybrid layers. After applying 0.1, 0.5, and 1.0 wt% fucosterol to demineralized dentin, microtensile bond strength (MTBS) and nanoleakage tests were performed before and after collagenase aging, and the surface was observed using scanning electron microscope (SEM). The fucosterol-treated group showed better bond strength and less nanoleakage both before and after collagenase aging, and the corresponding structures were confirmed using SEM. MMP zymography confirmed that the activity of MMPs was relatively low along the concentration gradient of fucosterol, and the FTIR analysis confirmed the production of collagen crosslinks. In addition, fucosterol exhibits cytotoxicity against Streptococcus mutans, the main cause of dental decay. The results of this study suggest that fucosterol pretreatment improves bond strength and reduces nanoleakage at the resin-dentin interface, possibly through a mechanism involving collagen cross-link formation via the inhibition of endogenous and exogenous MMP activity. This study demonstrates the potential of fucosterol as an MMP inhibitor in dentin, which contributes to long-term resin-dentin bond stability and can be used as a restorative material.

Light-curable urushiol enhanced bisphenol A glycidyl dimethacrylate dentin bonding agent

ObjectivesThe low durability of composite resin restorations can be attributed to the degradation of the resin dentin bonding interface. Owing to the presence of hydrophilic components in the adhesive, the integrity of the resin dentin bonding interface is easily compromised, which, in turn, leads to a reduction in bond strength. The hydrophilic nature of the adhesive leads to water sorption, phase separation, and leaching of the resin component. Therefore, hydrophobic adhesives could effectively be used to stabilize the integrity and durability of the resin dentin bonding interface. MethodsWe synthesized a novel hydrophobic dentin adhesive by partially replacing bisphenol A glycidyl dimethacrylate (Bis-GMA) with a light-curable urushiol monomer. The properties of the produced adhesive, including the degree of conversion, viscosity, contact angle, water sorption/solubility, and mechanical strength, were comprehensively examined and compared to those of the commercially adhesive Adper Single Bond2 as a positive control. The adhesive properties were determined using microtensile bond strength measurements, laser confocal microscopy, scanning electron microscopy observations, and nanoleakage tests. Finally, the novel adhesive was subjected to biocompatibility testing to determine its potential cytotoxicity. ResultsAt a light-curable urushiol content of 20 %, the synthesized adhesive exhibited high degrees of conversion and hydrophobicity, low cytotoxicity, good mechanical properties, and outstanding adhesive strength. ConclusionsThe introduction of the light-curable urushiol into dentin adhesives can significantly enhance their hydrophobic, mechanical, and bonding properties, demonstrating potential to significantly improve restoration longevity. Clinical significanceThe integration of light-curable urushiol has endowed the experimental adhesives with several enhanced functionalities. These notable benefits underscore the suitability of this monomer for expanded applications in clinical practice.

New Monomer Capable of Dual Chemical Binding with Dentin to Improve Bonding Durability.

The water-rich nature of the dentin bonding microenvironment, coupled with the stresses on the bonding interface, contributes to the hydrolytic degradation of the hybrid layer, resulting in a decline in bonding durability and, ultimately, restoration failure. Currently, the 3-step etch-and-rinse technique remains the gold standard for dentin bonding, and the bonding mechanism mainly involves a physical interaction with little chemical bonding. In this study, we have developed a siloxane-modified polyurethane monomer (SPU) with acrylate and siloxane modifications that chemically binds to both collagen and hydroxyapatite in dentin. Formulated as a bisphenol A-glycidyl methacrylate alternative, the SPU monomer-based adhesive was designed to improve dentin bonding quality and durability. Attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscope, and hydroxyproline release assays were performed on SPU-treated collagen, hydroxyapatite, and acid-etched dentin slices to dentin. The physicochemical properties of the configured SPU adhesives were profiled for polymerization behavior, water contact angle, and tensile strain and strength. The bonding effectiveness was assessed through micro-tensile strength, nano-leakage tests conducted on the bonded samples before and after thermal cycle aging. Finally, we further conducted in vivo and in vitro experiments to assess the biocompatibility of adhesives. The results showed that the siloxane groups of SPU monomer could covalently bind to dentin collagen and hydroxyapatite. The incorporation of SPU in the adhesive led to a significant increase in adhesive polymerization (P < 0.05) and tensile strain at break up to 134.11%. Furthermore, the SPU adhesive significantly improved dentin bond strength (P < 0.05), reduced interfacial nano-leakage (P < 0.05), and displayed good biocompatibility. In conclusion, the application of SPU, which achieves dual chemical bonding with dentin, can improve the quality of the hybrid layer, buffer the interfacial stresses, enhance the interfacial resistance to hydrolysis, and provide a feasible strategy to extend the service life of adhesive restorations.

Adhesion and sealing of different universal adhesive systems associated with bulk-fill resins after using endodontic irrigation solutions: An invitro study.

This study aimed to evaluate the interface of universal adhesive (UA) with bulk-fill resin (BF) and dentin, after endodontic irrigation. The pulp chamber of 96 molars was irrigated with chlorhexidine 2% (CHX) or sodium hypochlorite 5.25% (NaOCl) and restored according to three restorative protocols. Microtensile bond strength (μTBS) and nanoleakage tests were performed after 24 h of thermocycling. Kruskal Wallis, Mann-Whitney and Wilcoxon were performed (p < 0.05). Comparing restorative systems, a difference was found only when irrigated with CHX after 24 h. CHX provided higher μTBS than NaOCl after 24 h for two restorative protocols; after thermocycling, NaOCl provided the greatest μTBS than CHX for one group. Decreased μTBS was observed for all restorative systems when CHX was used after thermocycling. NaOCl demonstrated the highest nanoleakage. The composition of UA influenced the immediate adhesion and sealing to BF when CHX was used; ageing has a deteriorating effect on adhesion and sealing for all restorative systems.

Effects of Nd:YAG laser irradiation at different energy densities on dentin bond durability under simulated pulpal pressure.

To evaluate the effects of Nd:YAG laser irradiation on the microstructures of dentin surfaces and the long-term bond strength of dentin under simulated pulpal pressure. Under simulated pulp pressure, 30 freshly extracted caries-free third molars were cut into 2-mm-thick dentin samples and then divided into five groups: the control and laser groups (93.3J/cm2; 124.4J/cm2; 155.5J/cm2; 186.6J/cm2). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and Vickers hardness were used to analyze the surface morphology, composition, and mechanical properties of the dentin before and after laser irradiation. Another 80 caries-free third molars were removed and treated as described above, and the resin was bonded to the dentin surface with Single Bond Universal (SBU) adhesive in self-etch mode to make stick specimens. Microtensile bond strength (µTBS), confocal laser scanning microscopy (CLSM), and interfacial silver nanoleakage tests before and after 10,000 times thermocycling were then performed to analyze the bonding properties and interfacial durability of each group. SEM observations revealed that the surfaces of all laser group specimens were rough with open dentin tubules. Laser irradiation altered the surface composition of dentin while removing some collagen fibers but did not affect its surface hardness or crystallographic characteristics. Furthermore, laser irradiation with an energy density of 124.4J/cm2 significantly promoted the immediate and aging bond strengths and reduced nanoleakage compared to those of the control group. Under simulated pulp pressure, Nd:YAG laser pretreatment altered the chemical composition of dentin and improved the immediate and long-term bond strength. This study investigated the optimal parameters for Nd:YAG laser pretreatment of dentin, which has potential as a clinical method to strengthen bonding.

The effect of kaempferol on the dentin bonding stability through matrix metalloproteinases inhibition and collagen crosslink in dentin biomodification

Background/purposeNaturally derived collagen crosslinkers with matrix metalloproteinases (MMPs) inhibitory activity for dentin bonding have been previously studied. One of these crosslinkers is flavonoids. The purpose of this study was to investigate whether dentin pretreatment with kaempferol (KEM), one of the flavonoids, enhances dentin bond stability and nanoleakage at the dentin-resin interface through MMPs inhibition and collagen crosslinking. Materials and methodsThe experimental KEM-containing solution was used to pretreat demineralized dentin prior to the application of a universal adhesive. KEM is a natural flavonoid and those which did not take the experimental solution served as the control group (CON). Microtensile bond strength (μTBS) and nanoleakage tests were conducted before and after the thermocycling to evaluate the influence of KEM on dentin bond strength. The MMPs inhibition activity of KEM was analyzed via MMPs zymography using a confocal microscopy. Fourier-transform infrared (FTIR) spectroscopy was used to demonstrate that KEM inhibits MMPs and enhances collagen crosslinking. ResultsThe μTBS values of KEM group exhibited a higher bond strength after thermocycling. At the resin-dentin interface, the KEM group did not exhibit any signs of nanoleakage after thermocycling. Furthermore, MMPs zymography confirmed that there was a relatively low activity of MMPs in the presence of KEM. In FTIR analysis, the PO4 peak representing the cross-link between dentin and collagen was significantly higher in the KEM group. ConclusionOur findings suggest that pretreatment with KEM enhances the dentin bonding stability at the resin-dentin interface by acting as a collagen crosslinker and MMPs inhibitor.

Inhibition of matrix metalloproteinase-9 by 10-MDP and its calcium salt contributes to improved dentin-bonding durability

The activation of matrix metalloproteinases (MMPs) is responsible for degradation of the hybrid layer. The effect of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) on biodegradation of the hybrid layer remains unknown. This study aimed to evaluate the effects of 10-MDP and its Ca salt on MMP-9 activity and dentin-bonding durability. 10-MDP-Ca salt was synthesized and characterized by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The effects of chlorhexidine (CHX), 10-MDP, and 10-MDP-Ca salt on MMP activity were evaluated by in-situ zymography, MMP-9 inhibition assay, and hydroxyproline (HYP) assay. Dentin-resin bonded specimens were fabricated with using CHX or 10-MDP, including Single Bond 2 (Ctr), CHX + Single Bond 2 (CHX), 10-MDP + Single Bond 2 (10-MDP), and SBU (SBU). Micro-tensile bond strength (μTBS) and nanoleakage tests were performed after 24-h or two-years water storage. XRD and NMR confirmed the presence of 10-MDP-Ca salt. The relative inhibition percentages of recombinant MMP-9 for 10-MDP and 10-MDP-Ca salt were 8.04 ± 0.83% and 55.96 ± 1.82% respectively. HYP assay showed that 10-MDP, CHX, and 10-MDP-Ca salt conditioning decreased collagen degradation. Water storage weakened μTBS of all the groups, with the Ctr and CHX groups showing more significant decreases (P < 0.05). After aging, the Ctr and CHX groups also presented more nanoleakage, and the CHX group showed more in-situ zymography fluorescence than the 10-MDP and SBU groups. The capacity to inhibit MMP-9 activity, decrease HYP release, and reduce nanoleakage of 10-MDP and its salt contribute to improvement of dentin-bonding durability.

Effect of dentin pretreatment with dialdehyde carboxymethyl cellulose on dentin properties and long-term adhesion

ObjectivesThe aim of this in vitro study was to evaluate the effect of pretreatment of dentin with different concentrations (0, 1%, 2.5% or 5%) of dialdehyde carboxymethyl cellulose (DCMC) on the biodegradation rates, mechanical properties of the dentin and long-term dentin bonding (μTBS and nanoleakage). MethodsIn all tests, specimens were designated to 4 groups: Control (without DCMC), DCMC1%, DCMC2.5% and DCMC5%. For the biodegradation evaluation, dentin beams (n = 5) were prepared (2x2x6mm), dehydrated, and demineralized. After, the beams were immersed in test solutions for 24h. After, the biodegradation rate was quantified by hydroxyproline assay. The nano-indentation technique was used to measure nanohardness and elastic modulus. 2 mm thick dentin slices (n = 5) were prepared. After dentin etching, the pretreatment solution (according to groups) was applied for 1 min, followed by drying with absorbent paper. After bonding procedure and restoration, the specimens were polished and the nanohardness and modulus of elasticity were evaluated. For μTBS, the dentin of forty-eight teeth (n = 6) was etched and pretreated for 1 min according to groups, the adhesive system was applied, and resin composite buildups were constructed incrementally. Beams (1 mm2) were obtained and μTBS was evaluated after 24h and 1 year of water storage. 2 beams of each tooth were separated for nanoleakage tests (after 24h and 1 year of water storage). ResultsControl and DCMC1% presented higher biodegradation rates when compared to DCMC2.5% and DCMC5%. The nanohardness of dentin and hybrid layer was higher for DCMC1%, DCMC2.5% and DCMC5% when compared to Control. DCMC2.5 and DCMC5% increased the modulus of elasticity of hybrid layer, when compared to Control and DCMC1%. DCMC1%, DCMC2.5% and DCMC5% showed lower immediate μTBS than Control, but they showed no decrease in μTBS and nanoleakage after 1 year of storage. Control showed significant decrease of μTBS and significant increase of nanoleakage after aging. ConclusionsThe use of DCMC as a dentin pretreatment decreased the biodegradation rate, improved the mechanical properties of dentin, and preserved the long-term bond strength.

Captopril inhibits matrix metalloproteinase activity and improves dentin bonding durability.

We investigated the inhibitory effects of captopril on matrix metalloproteinases (MMPs) and its effect as a primer on dentin bonding durability. One hundred fifty human third molars were selected. Flat surfaces of the middle dentin were exposed, etched 15s, and followed by pretreatment with a primer for 60s, including distilled water (control, the negative control primer), 2% chlorhexidine digluconate (CHD,the positive control primer), and captopril solution. Inhibitory effects of primers on MMPs were evaluated by hydroxyproline and gelatinase activity tests. All primers were applied on dentin followed by bonding. Some of the samples were sliced into slabs, placed in a fluorescent solution containing gelatin, and incubated for in situ zymography. Some were cut into sticks, and after aging for 1day, 12months, or 24months, microtensile bonding strength was tested. Some were cut into slabs, aged for 1day, 12months, or 24months, and taken out for nanoleakage tests to reveal interface defects. Hydroxyproline and gelatinase activity analyses showed that captopril exerted better inhibitory effects on MMPs, relative to 2% CHD (p < 0.05). A 0.2% captopril aqueous solution (0.2% CapW) was chosen to apply to the dentin. In situ zymography showed that inhibitory effects of captopril on gelatinase were significantly higher compared to 2% CHD (p < 0.01). Microtensile strength revealed that the bonding effects of the 0.2% CapW group lasted longer, compared to the control and 2% CHD groups (p < 0.05). Interface defects, detected by nanoleakage, were significantly reduced in the 0.2% CapW group, compared to the control and 2% CHD groups (p < 0.05). Captopril inhibits dentin MMP activities and effectively improves dentin bonding durability. Captopril is a promising dentin bonding primer for improving bonding durability.

Association of solvents improves selected properties of experimental dental adhesives.

The aim of the study was to evaluate how the association of solvents (tetrahydrofuran [THF], dimethyl sulfoxide [DMSO], ethanol [ET] or acetone [ACT]) with experimental dental adhesives affects selected properties of experimental dental adhesives and dentin bond durability. Six adhesive combinations were prepared containing: 30 % ET, 30 % ACT, 30 % THF, 28 % ET + 2 % DMSO (ET+DMSO), 15 % ethanol + 15 % THF (ET+THF), or 28 % THF + 2 % DMSO (THF+DMSO). Thirty-six molars (n = 6) were cut to expose the coronary dentin, and were randomly divided according to the adhesives. They were restored, and then cut into resindentin sticks (1 mm²), and stored in distilled water for 24 h or 6 months, until conducting the microtensile bond strength and nanoleakage tests. Other experiments performed with adhesives included viscosity assessment using a rheometer, and degree of conversion using Fourier-transform infrared spectroscopy (FTIR). The data were analyzed statistically using two-way ANOVA and Tukey's test (p < 0.05). The adhesive formulated exclusively with THF showed the highest viscosity, followed by ET+THF, which obtained the highest degree of conversion compared to ET, and THF alone. ET+DMSO obtained the highest 24-h and aged bond strengths (p < 0.05). ET+THF increased the nanoleakage slightly after 6 months, but attained the only gap-free adhesive interface among all the groups. The combination of alternative solvents, particularly THF, with conventional ones (ET) has improved chemical properties, and the dentin bonding of experimental simplified adhesives.

Influence of hydrophobic layer of Bis-EMA with different ethoxilations on adhesive's bonding efficacy and mechanical properties

ObjectivesThe aim of this study was to evaluate the effects of a hydrophobic layer of Bis-EMA 4 (B4, 4 ethoxilations), Bis-EMA 10 (B10, 10 ethoxilations) or Bis-EMA 30 (B30, 30 ethoxilations) on dentin adhesion and mechanical properties of a universal adhesive. Materials and methodsExtracted human molars were cut and restored using self-etching mode of Ambar Universal (AU, FGM) adhesive and divided according to the hydrophobic layer employed (n = 8): only AU (Control), SBMP (Scotchbond Multi-Purpose adhesive, 3 M, Commercial Control), B4, B10 and B30. Microtensile bond strength (μTBS) and nanoleakage tests were performed after 24h and 6 months water storage. Interface micro-permeability was surveyed by confocal microscopy. Dynamic-mechanical analysis (DMA) of each adhesive combination (50 wt% Ambar + 50 wt% BisEMA or 100% Ambar) were assessed. The data were statistically analyzed using two-way ANOVA and Tukey's test (p < 0.05). ResultsSBMP achieved the highest μTBS, followed by B4, B10 and Control, whilst B30 presented significantly lowest μTBS when compared with further groups (p < 0.001). After ageing, the only group depicting significant μTBS reduction was Control (p = 0,009). B4 and SBMP were almost devoid of silver deposits and did not show any signs of gaps, even after ageing. B4 presented the lowest micropermeability and the best mechanical behavior on DMA, showing the highest rubbery zone and increased glass transition temperature. ConclusionsBis-EMA-4 might be a suitable monomer for a hydrophobic layer in adhesive strategy, reducing hydrolytic degradation and increasing the durability and mechanical properties of adhesive interfaces.

Evaluation of the interaction of chlorhexidine and MDP and its effects on the durability of dentin bonding

ObjectiveThis study aimed to evaluate the potential interaction of chlorhexidine (CHX) and 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and its effects on the durability of dentin bonding. MethodsTwo commercial adhesives were tested: a MDP-free adhesive (Single Bond 2, SB2) and a MDP-containing adhesive (Single Bond Universal, SBU). Teeth were randomly assigned to six groups and tested for micro-tensile bond strength (μTBS): Ctr, direct bonding with SB2; CHX, CHX conditioning and SB2; MDP, MDP conditioning and SB2; CHX+MDP, combined CHX and MDP conditioning and SB2; SBU, direct bonding with SBU; CHX+SBU, CHX conditioning and SBU. The potential interaction of CHX and MDP was assessed by measuring nanoleakage, in situ zymography, and chemoanalytic characterization via Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR). Specimens for μTBS and nanoleakage tests were first subjected to water storage for 24h or 6 months. ResultsThe initial μTBS values of the Ctr and CHX groups were significantly lower than those of the other four groups (P<0.05). Water storage for 6 months significantly weakened all groups (P<0.05), with the Ctr group showing the lowest μTBS. This group also showed more obvious nanoleakage than the other five groups. In situ zymography revealed that the Ctr group showed the strongest fluorescence and that the CHX+MDP group showed greater fluorescence than either CHX or MDP group. FTIR, XPS, and NMR indicated that MDP can interact with hydroxyapatite. NMR detected no Ca2+ salt peak for MDP when it was combined with CHX. SignificanceThe application of either CHX or MDP alone can improve dentin bond durability. However, CHX may interfere with the formation of MDP–Ca salts.

Long-term Evaluation of Dentin Matrix Stability and Gelatinolytic Activity after Dentin Pretreatment with Caffeic Acid Phenethyl Ester.

To investigate the long-term effect of 0.05% or 0.1% caffeic acid phenethyl ester (CAPE) on dentin matrix stability and hybrid layer stability, using an etch-and-rinse (Adper Scotchbond Multipurpose/ASB) or a self-etch adhesive (Clearfil SE Bond/CSE). Dentin matrix specimens were assigned to five groups: 0.05% or 0.1% CAPE, green tea (GT), and the controls distilled water (DW) and dimethyl sulfoxide (DMSO). Following immersion of specimens for 1 h, modulus of elasticity (ME) and dentin mass change (MG) were determined at 3 post-treatment time points: immediately afterwards and at 3 and 6 months. Collagen solubilization (CS) was estimated by hydroxyproline (HYP) quantification. Resin-dentin interfaces with both adhesives were assessed with in situ zymography tests to evaluate gelatinolytic activity (GA). The dentin pretreatments were actively applied for 60 s. The sealing ability of aged resin-bonded slices was assessed by nanoleakage tests. GT increased immediate ME, which decreased significantly after 3 months (p < 0.0001). The CAPE groups did not differ from the control groups. GT provided a significant increase in dentin matrix mass after treatment (p < 0.0001). No significant differences regarding MG were observed for CAPE 0.1%, CAPE 0.05%, DW, and DMSO groups after 3 and 6 months. Cumulative HYP release revealed that CAPE groups and GT were statistically similar to DW and DMSO; the GT group exhibited statistically significantly less HYP release than did CAPE groups (p = 0.0073). Treatment with 0.05% or 0.1% CAPE presented lower GA when applied to ASB before acid conditioning (p < 0.05), but no differences were detected when the CAPE groups were applied to CSE. CAPE at 0.1% significantly reduced nanoleakage for CSE, and 0.05% CAPE with CSE presented levels of nanoleakage similar to those of the CSE control group. CAPE at 0.05% or 0.01% did not influence ME, MG, or CS, but reduced GA when applied to ASB before acid conditioning. CAPE at 0.1% with CSE promoted adhesive layer integrity.

SEM-EDS nanoleakage evaluation of universal-adhesive-systems with etch-and-rinse and self-etch approach

Introduction: For adhesive systems to be considered efficient they should maintain restorations stable and with adherence. They also should be capable to seal restorations margins against oral fluids and microorganisms for a long period [1,2]. Adhesive interface permeability to water and other oral fluids is possible even in restorations without detectable pores since their entry can be done through nanometric defects [2,3]. This adhesive interface degradation by hydrolysis can negatively affect adhesion durability leading to an adhesive interface degradation, process that Sano in 1995, called nanoleakage [4,5]. The aim of this study was the nanoleakage evaluation of universal adhesive systems, by SEM-EDS with Etch-and-rinse and Self-Etch approach. Materials and methods: This work was approved by the IUEM Ethics Committee. 24 intact human molars extracted for orthodontic or periodontal reasons were randomly divided into 12 groups (n = 2), 6 control and 6 experimental. Three universal adhesive systems, Futurabond® U, Prime & Bond® Active™ and Scotchbond™ Universal, were tested in their etch-and-rinse and self-etch approaches. Teeth were cut in a hard tissues microtome to expose superficial dentin and were polished with a 400 grit SiC paper. Adhesives were applied according to manufacturer’s instructions and resin build-ups were obtained with Filtek Z250 resin (colour A2) with 2 mm increments up to a maximum of 6–8 mm. Samples were sectioned in the X direction on a hard tissue microtome in order to obtain slices of 0.7 mm. 10 slices were selected for each group. In the control groups samples were stored in 5 ml of oil (VV Lubricant) for 3 months in an oven at 37 °C in order to avoid the hydrolytic degradation process and the experimental groups were stored in 5 ml of deionized water for 3 months in an oven at 37 °C so that it was possible to observe the hydrolytic degradation. After the incubation period samples were prepared and subjected to SEM-EDS nanoleakage tests. Statistical analyses with a Mixed Linear Model (MM), with Akaike (AIC), Hurvich andTsai (AICC), Bozdogan (CAIC) and the Bayes and Schwarz (BIC) information criteria were done. Results: No significant differences were found between universal adhesives. However, there was a significant difference concerning the adhesion strategy. The previous acid conditioning caused a greater expression of the nanoleakage. Discussion and conclusions: In our study we verify that when universal adhesives were applied with the etch-and-rinse approach the adhesive interface percentage infiltrated with silver nitrate is significantly higher that when adhesives were applied in the self-etch approach. These results are in accordance with other studies found in literature. Marchesi et al. [6] observed that nanoinfiltration was significantly reduced when Scotchbond Universal adhesive was applied as self-etch. In another study Luque-Martinez et al. [7] studied three universal adhesives: Scotchbond Universal, All-Bond Universal e Prime&Bond Elect and found that all presented significantly higher nanoinfiltration when applied as etch & rinse. The same results were found by Muñoz et al. [8] for the All-Bond Universal and G-Bond adhesives. The self-etch application of these universal adhesives seemed to contribute to the stability and durability of the adhesive interface.

Bond degradation resistance of self adhesive sealer bonded to radicular dentin using an alternative adhesive strategy

ObjectiveThis study was carried out to evaluate the effect of an alternative adhesive strategy; double layering dentin bonding procedure in root canal obturation on the durability of root canal sealing using Resilon/Epiphany dual cure resin composite sealer system. Materials and methodsOne hundred and twenty freshly extracted human upper central incisors teeth with straight root canals were used. The crowns were removed at the level of Cemento-Enamel Junction (CEJ). All roots were instrumented with a crown-down technique. The root canals were filled with either single or double layering bonding techniques, aged for 7 days and 3 months, and then sectioned perpendicular to the longitudinal axis of each root into a series of 1.0 mm thick cross-sectional slices. Durability of sealing was tested by both micropush out and nanoleakage tests. For the micropush out test, each root slice was subjected to compressive loading via a computer controlled materials testing machine, while for nanoleakage, the slices were immersed in the tracing solution of ammoniacal silver nitrate for 24 h in complete darkness. Photomicrographs were obtained by Environmental Scanning Electron Microscope. ResultsThe micropush out bond strength increased significantly with the double layering technique. On the other hand, it was not affected by aging. Only one nanoleakage pattern start to emerge as early as 7 days after sealing and continue after that. ConclusionsThe current study supports the concept that double layering bonding strategy might be successfully adapted to endodontics to optimize bond strength of endodontic self-adhesive sealers to radicular dentin and to reduce nanoleakage.

Nanoleakage related to bond strength in RM-GIC and adhesive restorations

This was to investigate the nanoleakage of Resin Modified Glass Ionomer Cement (RMGIC) and composite resin (CR) restorations in sound and caries-affected primary dentine, submitted to load cycling and cariogenic challenge in vitro. Occlusal cavities were prepared in 60 sound exfoliated primary second molars and 30 specimens were subjected to chemical induction of artificial caries lesions and the others were restored without caries induction. All prepared teeth were divided into 2 groups according to restorative materials. From each dentine condition 5 restored teeth and restorative material were subjected to microtensile bond strength and nanoleakage tests immediately or after load-cycling or submitted to the pH-cycling procedure before testing. The adhesive presented bigger areas of silver leakage at the interfaces on caries-affected dentine (2.46±0.47)mm2 than sound dentine (0.90±0.19)mm2. RMGIC nanoleakage was not influenced by the sound (1.75±0.11)mm2 or caries-affected (2.08±0.39) condition of the substrate. A significant moderate inverse correlation was revealed between the bond strength and silver leakage area at the interface, (r= -0.55, p<0.001). Nanoleakage is greater in caries-affected primary teeth dentine than sound dentine in adhesive restorations although at the interfaces of RMGIC does not differ. As nanoleakage increases, bond strength decreases significantly.

The nanoleakage patterns of different dentin adhesive systems

Previous studies have focused on marginal gaps as the major pathway of microleakage. But Sano et al. described the occurrence of microleakage in the absence of gaps and the subsurface porosity of demineralized dentin. Yu and Davis described microleakage within or beneath smear layers and resin-bonded dentin using silver nitrate and SEM/EDS techniques. These results indicate that investigators should examine microleakage pathways at high magnification rather than simply relying on macroscopic dye penetration. Dentin adhesive systems with their micromechanical adhesion to dentin has greatly reduced microleakage. However, the ideal sealing that the adhesive resin completely penetrates the demineralized dentin is rarely achieved, leaving some porous regions within the exposed collagen network. These porosities can be penetrated by solution such as silver nitrate, even in gap-free bonding between denin and restorative composite resin, and this has been termed nanoleakage. The nanoleakage tests can provide much useful information on the sealing ability of dentin adhesive systems and the quality of the hybrid layer . The pore size of nanoleakage is so small that penetration of bacteria into the compound zone The Nanoleakage Patterns of Different Dentin Adhesive Systems