Long-term Bond Strength Research Articles

Comparison of bond strength of universal adhesives using different etching modes: A systematic review and meta-analysis.

This review aims to evaluate whether the etch-and-rinse or self-etch mode is the better protocol for dentin adhesion by universal adhesives. A total of 15 articles were included in the meta-analysis. Two reviewers performed a literature search up to October 2020in four databases: PubMed, Web of Science, Embase, and the Cochrane Library. Without considering the difference in aging mode, the analysis of the immediate and long-term bond strength of dentin showed that there was no statistical significance between the etch-and-rinse and self-etch mode of universal adhesive, and the long-term bond strength decreased relative to the immediate. In vitro studies suggest that prior acid etching did not improve bond performance. Whether from the perspective of long-term bonding performance or simplifying operating procedures, the self-etch mode is preferred.

6 - Ceramic-Dentin Cement Thickness: Bond Strength and Residual Stress

This study aimed to test whether three different cement layer thicknesses (60, 120 and 180 μm) would provide the same bonding capacity between adhesively luted lithium disilicate and human dentin. Ceramic blocks were cut with a low-speed diamond saw with water cooling into 20 blocks, which were cemented to human flat dentin with adhesive protocol. The assembly was sectioned into 1 mm 2 cross-section beams composed of ceramic/cement/dentin. Cement layer thickness was measured, and three groups were formed. Half of the samples were submitted to aging simulation and the other half was immediately tested to evaluate the long-term bond strength. The microtensile test was performed in a universal testing machine. Bond strength (MPa) was calculated. The fractured specimens were examined under stereomicroscopy. Applying the finite element method, the residual stress of polymerization shrinkage according to cement layer thick-ness was also calculated using First Principal Stress as analysis criteria. ANOVA showed that the cement layer thickness factor significantly influenced the bond strength results for the aged samples (p=0.040) without difference between the groups for the immediately tested groups (p=0.772). The higher the cement layer thickness the higher the residual stress generated at the adhesive interface due to cement polymerization shrinkage. In conclusion, the cement layer thickness does not affect the immediate bond strength in lithium disilicate restorations; however, thinner cement layers are most stable in long-term showing constant bond strength and lower residual stress.

Effect of an extrafibrillar dentin demineralization strategy on the durability of the resin–dentin bond

ObjectivesThis study aimed to evaluate the potential of the extrafibrillar dentin demineralization strategy on the long-term dentin bond strength of an etch-and-rinse adhesive. MethodsA water-soluble glycol chitosan-EDTA (GCE), a chelating conditioner, was synthesized and subjected to size-exclusion dialysis to obtain molecules >40 kDa. The conjugation of EDTA to glycol chitosan was analyzed by Fourier transform infrared (FTIR) spectroscopy. Mid-coronal dentin surfaces of 80 teeth were either acid-etched with 35% phosphoric acid or conditioned with 25 mg/mL GCE (n = 40) and thoroughly water-sprayed before applying the etch-and-rinse adhesive Adper Single Bond Plus and placing Z250 composite resin (3 M Oral Care; St Paul, MN, USA). Resin-bonded specimens were prepared into beams with a cross-sectional area of about 0.9 mm2 vertically through the resin–dentin interfaces before the microtensile bond strengths (MTBS) were determined immediately or after 3, 6, or 12 months of water storage. The resin–dentin interfaces were analyzed using transmission electron microscopy (TEM). The MTBS data were analyzed using two-way ANOVA followed by the LSD post-hoc multiple comparisons (P < 0.05). ResultsFTIR spectra showed that EDTA was successfully conjugated to glycol chitosan. The phosphoric acid-etching group and GCE-conditioning group showed similar bond strength values after 24 h of water storage. The bond strength of the phosphoric acid-etching group after 12-month water aging was significantly reduced from 51.61 ± 3.30 MPa to 38.57 ± 4.81 MPa, while the bond strength of the GCE-conditioning group was not significantly reduced from 50.28 ± 3.62 MPa to 46.40 ± 4.71 MPa.The degradation of the hybrid layer could be detected in the phosphoric acid-etching group after 12 months of water aging, but not in the GCE-conditioning group. ConclusionThe extrafibrillar dentin demineralization strategy using GCE conditioner could defy the hybrid layer degradation of the dentin bond after 12 months of water aging and enhance the dentin bond durability of the etch-and-rinse adhesive Adper Single Bond Plus.

Nanofiller Particles and Bonding Durability, Water Sorption, and Solubility of Universal Adhesives

The aim of this study was to evaluate the influence of nanofiller particles in simplified universal adhesive on the long-term microtensile bond strength and silver nitrate up-take, as well as water sorption and solubility. Commercial adhesives Ambar Universal (FGM) in nanofilled-containing version (filled) and same lot without fillers (unfilled) were donated and applied by means of etch-and-rinse strategy. Microtensile bond strength was surveyed after 24-hours or 1-year water storage. Silver nitrate uptake was assayed using scanning electron microscopy (SEM). Water sorption and solubility experiments were performed based on ISO 4049:2009. Statistical analysis was performed using two-way ANOVA and Tukey test (p<0.05). The bond strength of both the adhesives were statistically similar at 24 hours (p>0.05), but the filled group attained significant bond strength reduction after aging when compared to initial bond strength (p<0.001). Conversely, unfilled adhesive presented stable adhesion after 1-year storage (p=0.262). Silver nitrate uptake was similar for both adhesives, with little silver impregnation at the hybrid and adhesive layers. Water sorption was higher with filled adhesive compared to the unfilled one (p=0.01). Conversely, solubility was higher in unfilled in comparison to filled one (p=0.008). The presence of nanofillers in universal adhesive achieves higher water sorption and dentin bond degradation, which did not occur in the unfilled adhesive.

Effect of Curcumin Suspension and Vitamin C on Dentin Shear Bond Strength and Durability. A Pilot Study

Background: Preserving the strength and durability of dentin bonds is a concern of dental researchers and practitioners. Objective: The aim of this study was to investigate the effect of treating etched dentin with vitamin C and curcumin suspension as cross-linking agents on the shear bond strength and durability of a universal dental adhesive. Methods: Extracted human third molar teeth were collected. Fifty-six flat coronal dentin surfaces were divided equally into four groups: (1) treated with adhesives; (2) etched with 37% H3PO4 for 10s before application of adhesives; (3) same as group (2), but with dentin treated with 2.5% curcumin suspension for 60s before the application of adhesive; and (4) same as group (3), but with the use of a 20% vitamin C suspension instead of a curcumin suspension. Filtek Z350XT composite was built for all samples. Half of the samples in each group were subjected to thermocycling. Shear bond strength was measured using a universal testing machine. Scanning electron microscopy was used to investigate the dentinal surfaces after treatment. Results: Treatment with curcumin suspension preserved immediate and long-term bond strength. Conversely, treatment of etched dentin with vitamin C solution significantly reduced the immediate bond strength, but a significant improvement was observed after aging. SEM showed that both cross-linking agents resulted in narrowing or closing of the dentinal tubules, with an adhesive mode of failure. Conclusion: The application of curcumin or vitamin C suspension to acid-etched dentin resulted in different effects on immediate and long-term shear bond strength when using universal adhesives.

Long-term bond strength of glass fiber post to composite resin does not depend on surface treatment with silane coupling agent or universal adhesive

This study evaluated the effect of glass fiber post (GFP) surface treatment with or without a silane coupling agent, associated with adhesive systems with or without silane in their composition, on the long-term bond strength to resin composite. Sixty GFPs (Whitepost DC no. 2, FGM) were cleaned using 70% ethanol, and randomly divided into two groups, either with or without pretreatment with silane (Ceramic Primer, 3 M ESPE), for 60 s. Each group was further subdivided into three groups, according to the adhesive system applied over the GFP (n = 10): UAS (Scotchbond Universal, 3 M ESPE), E&R – etch-and-rinse adhesive system (Adper Single Bond Plus, 3 M ESPE), and a control group with no adhesive system. The GFPs were centralized in a cylindrical matrix, and a nanoparticulate resin composite (Filtek Supreme Ultra, 3 M ESPE) was inserted and photoactivated. After 48 h, the samples were sectioned in slices, two of which were immediately (48 h) submitted to the push-out bond strength test, and another two, after 6 months of storage in water. The failure mode was evaluated with a stereomicroscope under 40× magnification, and classified using scores. Three-way ANOVA (α = 0.05) showed that the triple interaction of pretreatment with silane, use of adhesive and time period were significant (p = 0.019). After 48 h, the application of silane resulted in a significant increase in bond strength values, regardless of the adhesive application (p = 0.013), but this effect was no longer observed after 6 months (p = 0.677). Application of UAS did not influence bond strength values, regardless of silane application or storage time (p > 0.05). As for E&R, significantly higher bond strength was observed after 6 months, compared with 48 h (p = 0.040). When post silanization was performed with no adhesive system, there was no difference in bond strength between 48 h and 6 months storage time (p > 0.05). When there was neither silanization, nor an adhesive system, a significantly higher bond strength was observed after 6 months, compared with 48 h (p < 0.05). Most of the failure types were classified as mixed in both of the water storage time periods. The long-term bond strength of the GFP to composite resin did not depend on post surface treatment with silane, or application of either a UAS or a E&R system.

Effect of Cement Layer Thickness on the Immediate and Long-Term Bond Strength and Residual Stress between Lithium Disilicate Glass-Ceramic and Human Dentin

This study tested whether three different cement layer thicknesses (60, 120 and 180 μm) would provide the same bonding capacity between adhesively luted lithium disilicate and human dentin. Ceramic blocks were cut to 20 blocks with a low-speed diamond saw under cooling water and were then cemented to human flat dentin with an adhesive protocol. The assembly was sectioned into 1 mm2 cross-section beams composed of ceramic/cement/dentin. Cement layer thickness was measured, and three groups were formed. Half of the samples were immediately tested to evaluate the short-term bond strength and the other half were submitted to an aging simulation. The microtensile test was performed in a universal testing machine, and the bond strength (MPa) was calculated. The fractured specimens were examined under stereomicroscopy. Applying the finite element method, the residual stress of polymerization shrinkage according to cement layer thickness was also calculated using first principal stress as analysis criteria. Kruskal–Wallis tests showed that the ‘‘cement layer thickness’’ factor significantly influenced the bond strength results for the aged samples (p = 0.028); however, no statistically significant difference was found between the immediately tested groups (p = 0.569). The higher the cement layer thickness, the higher the residual stress generated at the adhesive interface due to cement polymerization shrinkage. In conclusion, the cement layer thickness does not affect the immediate bond strength in lithium disilicate restorations; however, thinner cement layers are most stable in the short term, showing constant bond strength and lower residual stress.

Dry bonding to dentin: Broadening the moisture spectrum and increasing wettability of etch-and-rinse adhesives

ObjectiveTo determine whether the effect of dentin moisture on the etch-and-rinse bonding may be minimized by dry-bonding protocols utilizing aqueous or ethanolic dimethyl sulfoxide (DMSO) pretreatments. MethodsH3PO4-etched mid-coronal dentin surfaces from human molars were randomly blot- or air-dried for 30 s and pretreated with DMSO/H2O or DMSO/EtOH solutions. Untreated samples served as control. Moisture control was performed by either blot- or air-drying. Samples were bonded with a multistep etch-and-rinse adhesive. Restored crown segments (n = 8/group) were stored in distilled water for 24 h and sectioned for microtensile bond strength testing. Resin-dentin beams (0.8 mm2) were tested under tension until fracture (0.5 mm/min) after 24 h and two years of storage in artificial saliva at 37 °C.SEM nanoleakage evaluation was performed on aged samples. Collagen wettability was also measured by sessile drops of the hydrophilic and hydrophobic bonding resins (n = 8/group). Data were examined by factorial ANOVA followed by the Tukey test (α = 0.05). ResultsDry bonding to untreated collagen produced inferior immediate and long-term bond strengths than wet bonding (p < 0.05). Regardless of initial hydration and moisture control, DMSO-dry bonding produced initially higher and stable bond strengths after aging (p < 0.05). DMSO-pretreated groups presented improved collagen wettability with lower silver uptake (p < 0.05). SignificanceDespite the common belief that etch-and-rinse adhesives must be applied onto moist collagen, DMSO-dry bonding protocols not only improved bonding performance and hybrid layer integrity, but also brought more versatility to collagen hybridization by reducing overdrying-related issues.

Influence of the activation mode on long-term bond strength and endogenous enzymatic activity of dual-cure resin cements

ObjectiveTo investigate the long-term microtensile bond strength (µTBS), interfacial nanoleakage expression (NL), and adhesive stability of dual-cure resin cements with/out light activation to dentin.Materials and methodsComposite overlays (N = 20) were luted to deep dentin surfaces with RelyX Ultimate (RXU, 3M) or Variolink EstheticDC (VAR, Ivoclar-Vivadent). A universal adhesive was used for bonding procedures (iBond universal, Heraeus Kulzer). The resin cements were either self-cured (SC; 1 h at 37 °C) or dual-cured (DC; 20s light-cure followed by 15 min self-cure at 37 °C). Specimens were submitted to µTBS immediately (T0) or after 1 year of laboratory storage (T12). The fracture pattern was evaluated using scanning electron microscopy (SEM). Data were statistically analyzed with two-way ANOVA/Tukey test. Further, the NL was quantified and analyzed (chi-square test) and in situ zymography was performed to evaluate the endogenous enzymatic activity within the hybrid layer (HL) at T0 and T12 (Mann–Whitney test). The significance level for all statistical tests was set at p = 0.05.ResultsDC resulted in higher bond strength and decreased fluorescence at the adhesive interface, irrespective of the material and the storage period (p < 0.05). Significantly lower bonding performances (p < 0.05) and higher endogenous enzymatic activity (p < 0.05) were observed within the HL at T12 compared to T0 in all tested groups.ConclusionsLight-curing the dual-cure resin cements, more than the cement materials, accounted for good bonding performances and higher HL stability over time when used with a universal adhesive.Clinical significanceThe curing condition influences the bonding performances of dual-cure resin cements to dentin when used with a universal adhesive.

Short- and Long-Term Dentin Bond Strength of Bioactive Glass-Modified Dental Adhesives.

This study investigated the short- and long-term effects of dental adhesives doped with nano-sized bioactive glass 45S5 (BAG) on the resin–dentin interfacial bond strength. Two etch-and-rinse adhesives (Adper Scotchbond Multi-Purpose (ASB) and Solobond Plus (SB)) and one self-etch adhesive (Clearfil SE Bond (CF)) were doped with different concentrations of BAG (5, 10, and 20 wt%). The unmodified (0 wt% BAG) commercial adhesives served as control groups. Dentin of 120 molars (n = 10 per group) was treated with the different adhesives, followed by buildups with a conventional composite restorative material. From each tooth, 14 sticks were prepared for micro-tensile bond strength (µTBS) testing. The sticks were stored in simulated body fluid at 37 °C and tested after 24 h or six months for µTBS and failure mode. Data were analyzed using Kruskal–Wallis tests in combination with post-hoc Conover-tests and Wilcoxon signed-rank tests at a level of significance of α = 0.05. After 24 h and six months, both etch-and-rinse adhesives with a low BAG content (up to 10 wt% for ASB and 5 wt% for SB) showed similar µTBSs as their respective control groups (0 wt% BAG). CF showed a significant decrease in µTBS even after addition of 5 wt% BAG. At a high concentration of added BAG (20 wt%), all three adhesives showed a significant decrease in µTBS compared to the unmodified controls. The CF control group showed significantly lower µTBS after 6 months of storage than after 24 h. In contrast, the µTBS of all CF groups modified with BAG was unaffected by aging. In conclusion, the tested etch-and-rinse adhesives can be modified with up to 5 wt% (SB), or 10 wt% (ASB) of BAG without reducing their short- and long-term dentin bond strength. Moreover, the addition of nano-sized BAG may prevent long-term bond strength deterioration of a self-etch adhesive.

The Effect of Deproteinizing Agents on Bond Strength of Resin-based Materials to Enamel: A Systematic Review and Meta-Analysis of In Vitro Studies.

To systematically review the literature to evaluate whether the bond strength of resin-based materials to enamel is affected by deproteinizing agents. This systematic review and meta-analysis was conducted according to the PRISMA statement. PubMed, ISI Web of Science, Cochrane Library, SciELO, Scopus, LILACS, IBECS, and BVS databases were screened up to December 2020. Eligibility criteria included in vitro studies that reported the effect of a deproteinizing agent applied before or after acid etching on the immediate or long-term bond strength of resin-based materials to enamel. The meta-analysis was carried out using Review Manager (version 5.3.5). A global comparison was performed with the standardized mean difference based on random-effect models at a significance level of α = 0.05. A total of 23 studies were included in the meta-analysis. In all the studies, only the immediate bond strength was evaluated. The bond strength of the materials was improved by the application of NaOCl or papain prior to enamel etching with phosphoric acid (p ≤ 0.006). None of the deproteinizing agents had a significant effect when applied after etching with phosphoric acid (p ≥ 0.27). Based on in vitro studies, deproteinization with sodium hypochlorite or papain-based agents increases the immediate bond strength of resin-based materials to enamel only when used prior to phosphoric-acid etching.

Comparative assessment of long-term bond strength between fiber post and root dentin with and without 6.5% cocoa seed extract pretreatment – An in vitro study

Background: Cocoa seed extract (CSE) is a natural cross-linker or biomodifier, which contains proanthocyanidin that increases the immediate resin-dentin bond strength as well as reduces the dentinal matrix degradation. There are very few studies which shows the long-term effects of the cross-linking agents on radicular dentin. Aim: The aim of this study was to assess and compare the effect of 6.5% cocoa seed extract (CSE) on long-term push out bond strength between fiber post and root dentin cemented by using two different adhesive systems – total etch adhesive system and self-etch adhesive system. Materials and Methods: Sixty extracted permanent maxillary central incisors were decoronated to standardize the root length. Root canal preparation followed by postspace preparation was done. Specimens were then randomly divided into four groups according to the adhesive technique and CSE pretreatment – Group 1: Total-etch adhesive + without 6.5% CSE treatment, Group 2: Total-etch adhesive + with 6.5% CSE treatment for 10 min, Group 3: Self-etch adhesive + without 6.5% CSE treatment, and Group 4: Self-etch adhesive + with 6.5% CSE treatment for 10 min. Fiber posts were cemented with resin cement, and then, specimens were stored in an incubator for 180 days. Specimens were then tested for pushout bond strength using the universal testing machine. Statistical analysis was performed using the one-way ANOVA followed by Tukey's post hoc analysis. Results: CSE-treated groups showed higher bond strength than nontreated group. Group 2 showed significantly higher bond strength among all groups. Conclusion: The pretreatment with Proanthocyanidines containing CSE can be a natural alternative to improve the long-term resin–dentin bond strength.

Heat damage and bond-slip performance of steel arch frame-concrete in high-geothermal tunnels

According to the real construction environment in high-geothermal tunnel, push-out test on fifty-four I-shaped steel and concrete samples subjected to different relative humidity and variable temperature curing conditions were carried out to evaluate the bond slip performance at the interface. The study results indicated that there are three models of crack evolution in failure process under different curing conditions. Compared with the samples cured under standard condition, higher curing temperature contributes to the early development of bond strength, but the long-term bond strength decreased significantly. Relative humidity is beneficial for increasing the intensity and shearing stiffness, enhancing bonding properties and reducing the loss of long-term bond strength of samples cured under VTC condition. More initial defects lead to the weak slip resistance of the interface under hot and dry environment. According to the regression analysis of experiment data, the formula of characteristic strength and segmental constitutive equation of the bond-slip under coupling effect of temperature and humidity are obtained. The parametric finite element model (FEM) of the new constitutive relation proposed in this paper was established using parametric design language. The final results may contribute to provide a reference for related support design and construction in high geothermal tunnel.

The pursuit of resin-dentin bond durability: Simultaneous enhancement of collagen structure and polymer network formation in hybrid layers

ObjectiveImperfect polymer formation as well as collagen’s susceptibility to enzymatic degradation increase the vulnerability of hybrid layers over time. This study investigated the effect of new dimethyl sulfoxide (DMSO)-containing pretreatments on long-term bond strength, hybrid layer quality, monomer conversion and collagen structure. MethodsH3PO4-etched mid-coronal dentin surfaces from extracted human molars (n = 8) were randomly treated with aqueous and ethanolic DMSO solutions or following the ethanol-wet bonding technique. Dentin bonding was performed with a three-step etch-and-rinse adhesive. Resin-dentin beams (0.8 mm2) were stored in artificial saliva at 37 °C for 24 h and 2.5 years, submitted to microtensile bond strength testing at 0.5 mm/min and semi-quantitative SEM nanoleakage analysis (n = 8). Micro-Raman spectroscopy was used to determine the degree of conversion at different depths in the hybrid layer (n = 6). Changes in the apparent modulus of elasticity of demineralized collagen beams measuring 0.5 × 1.7 × 7 mm (n = 10) and loss of dry mass (n = 10) after 30 days were calculated via three-point bending and precision weighing, respectively. ResultsDMSO-containing pretreatments produced higher bond strengths, which did not change significantly over time presenting lower incidence of water-filled zones. Higher uniformity in monomer conversion across the hybrid layer occurred for all pretreatments. DMSO-induced collagen stiffening was reversible in water, but with lower peptide solubilization. SignificanceImproved polymer formation and higher stability of the collagen-structure can be attributed to DMSO’s unique ability to simultaneously modify both biological and resin components within the hybrid layer. Pretreatments composed of DMSO/ethanol may be a viable-effective alternative to extend the longevity of resin-dentin bonds.

Bonding to dentin using an experimental zirconium oxynitrate etchant

ObjectiveTo investigate, by means of microtensile bond strength test (μTBS), nanoleakage expression analysis (NL), gelatin zymography and in situ zymography, the effects of an experimental metal salt-based zirconium oxynitrate etchant [ZrO(NO3)2,] – ZON with two simplified adhesives on long-term bond strength and endogenous enzymatic activities. MethodsMiddle/deep coronal dentin surfaces (N = 32) were conditioned either with a traditional 37 % H3PO4 etchant (TE) or with ZON. Further, a single-component etch-and-rinse adhesive (EF) or a universal adhesive (AU) were applied and μTBS and NL tests were performed. Additional freshly extracted teeth were processed for gelatin zymography and in situ zymography evaluation. The tests were performed at baseline and (T0) and after 1-year-aging (T12). Bond strength and in situ zymography results were analyzed using analysis of variance (ANOVA) (three-way and one-way, respectively), while Chi-squared test was used for the NL results. Statistical significance was preset at α = 0.05. ResultsAll the investigated factors (adhesive system, dentin conditioner and aging) significantly influenced μTBS, with the AU and ZON performing better compared to EF and TE, respectively, and with lower bond strength values after aging (p < 0.05). Incremented silver nitrate deposits were observed at the adhesive interfaces after aging, especially for the TE groups (p < 0.05). Further, the experimental groups treated with ZON had significantly lower levels of enzymatic activity compared to TE, as shown by gelatin and in situ zymography (p < 0.05). ConclusionsThe experimental etchant demonstrated promising results in hybrid-layer preservation over time when used with simplified bonding systems, and could therefore be recommended in the clinical practice.

Effect of side-group methylation on the performance of methacrylamides and methacrylates for dentin hybridization

The stability of the bond between polymeric adhesives to mineralized substrates is crucial in many biomedical applications. The objective of this study was to determine the effect of methyl substitution at the α- and β-carbons on the kinetics of polymerization, monomer hydrolytic stability, and long-term bond strength to dentin for methacrylamide- and methacrylate-based crosslinked networks for dental adhesive applications. MethodsSecondary methacrylamides (α-CH3 substituted=1-methyl HEMAM, β-CH3 substituted=2-methyl HEMAM, and unsubstituted=HEMAM) and OH-terminated methacrylates (α- and β-CH3 mixture=1-methyl HEMA and 2-methyl HEMA, and unsubstituted=HEMA) were copolymerized with urethane dimethacrylate. The kinetics of photopolymerization were followed in real-time using near-IR spectroscopy. Monomer hydrolysis kinetics were followed by NMR spectroscopy in water at pH 1 over 30 days. Solvated adhesives (40 vol% ethanol) were used to bond composite to dentin and microtensile bond strength (μTBS) measured after 24h and 6 months storage in water at 37°C. ResultsThe rate of polymerization increased in the following order: OH-terminated methacrylates≥methacrylamides>NH2-terminated methacrylates, with minimal effect of the substitution. Final conversion ranged between 79% for 1-methyl AEMA and 94% for HEMA. 1-methyl-HEMAM showed the highest and most stable μTBS, while HEMA showed a 37% reduction after six months All groups showed measurable degradation after up to 4 days in pH 1, with the methacrylamides showing less degradation than the methacrylates. Additionally, transesterification products were observed in the methacrylamide groups. SignificanceAmide monomers were significantly more stable to hydrolysis than the analogous methacrylates. The addition of a α- or β-CH3 groups increased the rate of hydrolysis, with the magnitude of the effect tracking with the expected base-catalyzed hydrolysis of esters or amides, but opposite in influence. The α-CH3 substituted secondary methacrylamide, 1-methyl HEMAM, showed the most stable adhesive interface. A side reaction was observed with transesterification of the monomers studied under ambient conditions, which was not expected under the relatively mild conditions used here, which warrants further investigation.

Immediate and long-term microshear bond strength of resin-based cements to core build-up materials.

BackgroundTo evaluate the microshear bond strength (μ-SBS) between resin-based cements and core build-up materials after water storage. Material and MethodsCylinders (1x1 mm) of conventional dual-cure resin cement (RelyX ARC, 3M ESPE), universal dual-cure resin cement (RelyX Ultimate, 3M ESPE) or self-adhesive resin cement (RelyX U200, 3M ESPE) were adhered to disks (6x2 mm) made with commercial core build-up materials (Bis-Core, Bisco or LuxaCore Z, DMG) or conventional nanocomposite resin (Filtek Z350 XT, 3M ESPE). The specimens (n=10) were submitted to μ-SBS test using a universal testing machine and fracture pattern analysis at 48 hours or after 9 months of water storage. The data were evaluated by three-way ANOVA for repeated measures and Tukey’s test (α=0.05). ResultsAfter 48 hours, regardless of the resin-based cement used, the μ-SBS to the conventional resin composite (Filtek Z350 XT) was greater compared to other materials. However, after 9 months, there was a statistically significant decrease in μ-SBS values between the conventional resin composite and evaluated luting agents. The μ-SBS values of core build-up commercial materials (Bis-Core and LuxaCore Z) did not change over time. Regardless of the composite used and storage time, there was no statistically significant difference between the resin-based cements. After 48 h, the most prevalent failure was mixed for all groups. However, after 9 months, the core build-up materials showed a predominantly mixed fracture pattern whereas the resin composite presented an adhesive pattern. ConclusionsCommercial core build-up materials achieved stable bonding performance with resin-based cements over time. Key words:Composite resins, resin cement, dental restoration failure.

Effect of active application of self-etching ceramic primer on the long-term bond strength of different dental CAD/CAM materials.

BackgroundThe objective of this in vitro study was to evaluate the effect of the active application of self-etching ceramic primer (ME&P) on the bond strength of different dental CAD/CAM materials (Lithium Disilicate ceramic (LD), Leucite ceramic (LE), Zirconia reinforced lithium silicate ceramic (ZLS), and Hybrid ceramic (HC)) with thermocycling aging. Material and MethodsThe samples were randomly divided into 16 groups (n = 20). Dual resin cement cylinders were made and light cured for 10 s (1.200 mW/cm2) for the shear bond strength test. 3-way ANOVA revealed that the factors were statistically significant (P< 0.05). ResultsThe aging process had a negative impact on the bond strength for all groups except for Lithium Disilicate, with active application. ZLS and LE showed promising results with high bond strength values for the ME&P active application; however, after aging the bond strength value was significantly reduced. HC showed reduced bond strength values regardless the ME&P application. ConclusionsIn order to obtain a durable bond strength, the recommended protocol of 20 s of active application followed by 40 s of sitting time in the self-etching ceramic primer should be followed when using reinforced-glass ceramics as restorative materials. Key words:Dentistry, dental materials, silane, shear strength, computer-aided design

The mussel-inspired polydopamine surface treatment influences bond strength of glass fiber posts to radicular dentin

The aim of this study was to compare the efficacy of silane and a novel bioinspired polydopamine functionalization on the adhesion strength of glass fiber posts cemented to root dentin. Sixty-four surface treated posts [polydopamine (group 1 = 32) or silane (group 2 = 32)] were cemented in root canals of 64 extracted and decoronated mandibular premolars by using 3 commercial brands of self-adhesive resin cements (subgroups A, B and C) or a total-etch resin cement (subgroup D). The samples were subjected to push-out bond strength testing at 24 h and at 6 months after storage in water. Each sample was subdivided into six slices (three slices of the coronal and three slices of the apical) to determine the push-out bond strength in the coronal and apical third. The mean bonding strength value of the 3 slices both for the coronal and apical third was calculated as megapascals (MPa) and the data were statistically analyzed using post hoc Tukey HSD and Student t tests using four-way ANOVA (P = 0.05). Failure modes were investigated using scanning electron microscopy (SEM). The number of adhesive failures at the dentin-cement interface dropped when polydopamine was used (12–33%). Failure between the post and cement interface also dropped (4–13%) in all the resin cement groups, except the Subgroup C (17%). Polydopamine treatment significantly increased the adhesion strength for all cements compared to silanization at 24 h (P < 0.05), however at 6 months, only for the self-adhesive cements (P < 0.05). Polydopamine surface treatment improves the short-term bond strength of fiber-posts cemented to root canal dentin. The positive effect of polydopamine on long-term bond strength did not appear to be significant for the total-etch resin cement.

Addition of EGCG to self-etching primer: effect on adhesive properties and bond stability to dentin

This study evaluated how adding EGCG to a SEP (Clearfil SE Bond, Kuraray) affects the physicomechanical properties of adhesive, and the long-term microtensile bond strength (µTBS) to dentin. Flexural strength (FS, n = 10) and degree of conversion (DC, n = 5) of the adhesive were analyzed after adding EGCG to SEP in two forms (powder or diluted in water), and in different concentrations (0.00%–control, 0.01%, 0.02% and 0.05%). The µTBS was tested by randomly dividing dentin fragments into 4 groups (n = 10): EGCG-SEP: EGCG (0.01%) added to SEP; EGCG-PRE: EGCG (0.01%) dentin pretreatment; CHX-PRE: 2% chlorhexidine dentin pretreatment; SEP: SEP applied without modification. After restoration of the dentin surface, beam-shaped specimens were submitted to µTBS after 24 h or 12 months of storage in artificial saliva. Particle size (PS), polydispersity index (PDI) and zeta potential (ZP) of EGCG-SEP and SEP solutions were measured at different storage periods (baseline, 14 or 28 days). Data was submitted to ANOVA or Kruskal–Wallis tests (α = 0.05). FS (p = 0.485) and DC (p = 0.6067) were not different among the groups. CHX-PRE and EGCG-PRE had significantly higher µTBS means than EGCG-SEP, but none differed from SEP (p = 0.053). µTBS decreased significantly after 12 months of storage (p < 0.001). PS (p < 0.001), and ZP (p = 0.003) means in EGCG-SEP were statistically higher and more negative, respectively, than SEP. PDI did not differ among the groups (p > 0.05). Incorporation of EGCG into SEP did not change adhesive properties; however, it influenced solution stability and did not prevent the decrease in long-term µTBS to dentin.