Hydrophobic Resin Layer Research Articles

The effect of an extra hydrophobic resin layer on the bond strength and durability of one-step universal adhesives used as a primer

ObjectivesTo determine the effect of an extra hydrophobic resin layer (EHL) on the bond strength and durability of three different pH one-step universal adhesives (UAs) utilized in self-etch (SE) mode, and to explore whether UAs can be used as a primer in two-step bonding system. MethodsThree different pH UAs were utilized: G-Premio Bond (GPB), Scotchbond Universal (SBU), All-Bond Universal (ABU), while the bonding agent of Clearfil SE Bond 2 (SE2) was selected as the EHL. For the EHL groups, EHL was applied after the air blow of each UA and before light curing. The microtensile bond strength (μTBS), fracture modes, interfacial structures and nanoleakage (NL) were evaluated after 24 h water storage and after 15,000 thermal cycling (TC). Elastic modulus (EM) and hardness (H) was tested by a nanoindenter after 24 h. ResultsSignificantly higher μTBS was achieved in the GPB+EHL group compared with GPB both at 24 h and after 15,000 TC, while the additional use of EHL did not improve the μTBS of SBU and ABU significantly both at 24 h and after 15,000 TC. GPB+EHL demonstrated lower NL than GPB. The mean EM and H of the adhesive layer in GPB+EHL was significantly decreased compared with GPB. ConclusionsThe results indicated that the bond strength and durability of low pH one-step UA (GPB) were significantly improved by additional application of EHL both at 24 h and after 15,000 TC, while no significant improvement was observed for ultra-mild one-step UAs (SBU and ABU). Clinical significanceThis study indicates that GPB can be used as a primer in a two-step bonding system, while SBU and ABU may not be as effective. These findings may help guide clinicians in selecting the appropriate UAs and bonding techniques for different clinical scenarios.

Effect of Extra Hydrophobic Resin Layer on Bonding of Universal Adhesive Systems to Enamel.

The objective of this study was to compare the effect of solvent in universal adhesives (UA) and the application of an extra layer of hydrophobic bonding resin on enamel shear bond strengths (SBS). Crowns of 224 bovine mandibular incisors were embedded in acrylic resin, wet-polished up to 600-grit silicon carbide paper and assigned to 3 UAs with different solvents (n=32): ethanol-based UA (ADU, AdheSE Universal, Ivoclar Vivadent); isopropanol-based UA (PBU, Prime&Bond Universal, Dentsply Sirona); and acetone-based UA (OPT, OptiBond Universal, Kerr Co). The same UAs were also applied with an extra layer of a hydrophobic bonding resin (HLB, Heliobond, Ivoclar Vivadent): ADU + HLB; PBU + HLB; and OPT + HLB. HLB alone was used as control. Enamel was etched with 37.5% H3PO4 (Kerr Gel Etchant, Kerr Co) for 15 seconds, rinsed with water, and air dried. UAs were applied according to the respective manufacturer's instructions. After adhesive application, composite cylinders (Filtek Z250, 3M Oral Care) were built up and light-cured (40 seconds/increment, 40 J/cm2) keeping the light tip in contact with the mold. Specimens were stored in water for 24 hours (24H) or for 6 months (6M). A knife-edged metallic rod (Ø=2.8-mm semicircular notch) loaded the composite cylinders until fracture. Mode of failure was analyzed with optical microscopy (40×). Statistics included twoway analysis of variance (ANOVA; adhesive strategy and water storage) and Tukey honestly significant difference (HSD) post hoc test (α=95%). Mean enamel SBS ranged from 3.6 (±2.2) MPa (HLB/6M) to 24.7 (±7.1) MPa (ADU + HLB/6M). ANOVA revealed significant differences for adhesive strategy (p≤0.001) but no significant differences for water storage (p>0.05). All UAs resulted in similar mean enamel SBS with or without an extra layer of HLB at 24H. After 6M, only ADU resulted in higher enamel SBS when an extra layer of HLB was applied. All UAs resulted in higher mean enamel SBS than HLB (control). Most failures were adhesive exception for PBU/HLB/6M, which had mostly mixed failures. UAs resulted in statistically higher enamel SBS than the nonsolvated hydrophobic bonding resin (control), regardless of the solvent in their composition. Application of an extra layer of hydrophobic bonding resin over UAs did not improve mean enamel SBS for isopropanol- and acetone-based UAs but did improve mean enamel SBS for the ethanol-based UA after 6M. Resin composite bonding to enamel using a hydrophobic bonding resin alone is not recommended.

Effect of Different Application Modalities on the Bonding Performance of Adhesive Systems to Dentin: A Systematic Review and Meta-Analysis.

Diverse types of dental adhesives exhibit different cytotoxic outcomes on cells in vitro. Currently, no standard adhesive application technique has so far been decisive for clinicians for better durability of resin-dentin bonds of adhesive systems. The purpose of this study was to systematically review the literature to evaluate the bonding performance of adhesive systems to dentin by using different application modalities. The systematic research strategy was conducted by two reviewers among multiple databases: PubMed, Scopus, Web of Science, Embase, and Scielo. In vitro studies reporting the effects of additional steps for the application of adhesive systems on the bond strength to dentin were selected. Meta-analysis was performed using Review Manager Software version 5.3.5 using the random effects model. The methodological quality of each in vitro study was assessed according to the parameters of a previous systematic review. The electronic research through different databases generated a total of 8318 references. After the examination of titles and abstracts, a total of 106 potentially relevant studies accessed the full-text evaluation phase. After full-text examination, 78 publications were included for the qualitative analysis, and 68 studies were included in the meta-analysis. Regarding the etch-and-rinse adhesive systems, the application modalities that improved the overall bond strength were the application of a hydrophobic resin layer (p = 0.005), an extended application time (p < 0.001), an application assisted by an electric current (p < 0.001), a double-layer application (p = 0.05), the agitation technique (p = 0.02), and the active application of the adhesive (p < 0.001). For self-etch adhesive systems, the techniques that improved the overall bond strength were the application of a hydrophobic resin layer (p < 0.001), an extended application time (p = 0.001), an application assisted by an electric current (p < 0.001), a double-layer application (p < 0.001), the agitation technique (p = 0.01), and the active application of the adhesive (p < 0.001). The in vitro evidence suggests that the application of adhesive systems using alternative techniques or additional strategies may be beneficial for improving their bond strength to dentin. The application modalities that favored the overall bond strength to dentin were an extended application time, a double-layer application, an application assisted by an electric current, the active application of the adhesive, and the application of a hydrophobic resin layer. Worth mentioning is that some techniques are intended to increase the degree of the conversion of the materials, and therefore, improvements in the biocompatibility of the materials can be expected.

Facile fabrication of nanocarriers with yolk-shell mesoporous silica nanoparticles for effective drug delivery

Drug delivery systems (DDSs) can greatly reduce the negative impact of chemotherapy in the treatment of tumors by alleviating issues such as low solubility, short half-life, and strong side effects of chemotherapeutic drugs. Therefore, engineering DDSs is of great significance. Herein, we report an innovative magnetic delivery system with a yolk-shell structure and targeting function, comprising a magnetic core and a mesoporous silica shell. The yolk-shell-structure was fabricated by the swelling-shrinkage process of resorcinol-formaldehyde resin upon soaking in or removal of hexane, while a silica shell was formed. The hydrophobic resin layer, hollow cavity, and channels of the shell improved the drug loading and afforded sustained drug release. The desired drug carriers (denoted as Fe3O4@YSSiO2-FA) were labeled with folate to promote biocompatibility and targeting functions. The prepared Fe3O4@YSSiO2-FA with particle sizes ranging from 100 to 200 nm had a loading capacity of 220 μg mg−1 for camptothecin (CPT) and afforded sustained release over 72 h in vitro. Fe3O4@YSSiO2-FA presented a lower protein adsorption capacity, a hemolysis rate of less than 1.2%, and weak cytotoxicity for A549 cells, with a cell viability of more than 74%, indicating that the proposed nanocarriers possess excellent biocompatibility. CPT-loaded Fe3O4@YSSiO2-FA showed higher cytotoxicity for KB cells (FA-receptor-positive) due to the higher cellular uptake compared to A549 cells (FA-receptor-negative), likely suggesting a preeminent tumor-specific targeting ability. The superior loading capacity, targeting ability, and biocompatibility demonstrate that Fe3O4@YSSiO2-FA possesses great potential as a carrier for DDSs. As expected, the developed strategy provides a facile alternative for fabricating efficient DDSs for antitumor applications.

Bonding Performance of Simplified Dental Adhesives with Three Application Protocols: An 18-month In Vitro Study.

To evaluate the influence of application protocol on the shear bond strength (SBS) and nanoleakage of simplified adhesives over 18 months. 810 dentin slices were obtained from 405 caries-free human molars. They were randomly assigned to 54 experimental groups resulting from the combination of "adhesive" (Adper Scotchbond 1XT [S1XT], Solobond M [SM], Scotchbond Universal Adhesive in etch-and-rinse mode [SUER] and self-etch mode [SUSE], Adper Easy Bond [EB], Clearfil S3 Bond Plus [CS3]), "application protocol" (manufacturer's instructions [MI], two extra layers of adhesive [EL], hydrophobic resin layer [HL]), and "aging time" (24 h [24H], 6 months [6M], and 18 months [18M] in water). SBS tests were carried out using a Watanabe device followed by failure mode analysis. For the nanoleakage study, specimens from 54 additional molars were prepared as previously described, immersed in ammoniacal silver nitrate, and evaluated with SEM. SBS data were analyzed with ANOVA followed by Tukey's post-hoc tests; failure mode data were analyzed using chi-squared tests (α = 0.05). Nanoleakage data were analyzed with the Kruskal-Wallis test followed by LSD tests (α = 0.05). After 18M, S1XT and SUSE achieved the highest mean SBS (p < 0.05). Regarding the application protocols, EL and HL provided higher mean SBS than those obtained with MI (p < 0.05). HL resulted in the highest mean SBS and the lowest mean nanoleakage after 18M. Simplified adhesives may need an extra hydrophobic resin layer to achieve a stable and durable adhesive interface. The self-etch approach should be recommended for the universal adhesive.

Improvement of Flame Retardant Properties of Polyurethane Composites Using Microencapsulation Technology

ABSTRACTOne kind of microencapsulated flame retardant containing melamine polyphosphate(MPP) and hydrophobic resin layer as core and shell material was synthesized by in situ polymerization technology. The structures and properties of microencapsulated MPP were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and water contact angle. Thermal behaviors of the composites containing microencapsulated MPP were analyzed by thermogravimetric analysis. Flame retardant tests indicated that the microencapsulated MPP with the polymer resin led to an improvement of the hydrophobicity. Results revealed that the flame retardancy of the composites was improved at the same fillers loading through the microencapsulation technology, which the char yields reached (~26.9wt%) and flame retardance grade (LOI-38%) with optimized MPP addition (~40%) to polymer matrix.

Laboratory evaluation of the effect of unfilled resin after the use of self-etch and total-etch dentin adhesives on the Shear Bond Strength of composite to dentin.

BackgroundBased on the frequent application of composite resins as tooth-colored fillings, this method is considered a viable alternative to dental amalgam. However, this method has the low bond strength of the composite to dentin. To solve this issue, various dental adhesive systems with different characteristics have been developed by dentistry experts.AimTo assess the effect of an additional layer of unfilled resin in self-etch and total-etch dentin adhesives on the shear bond strength (SBS) of composite to dentin. Moreover, we assessed the effects of sample storage in artificial saliva on the SBS of composite to dentin.MethodsMethods: This experimental study was conducted on 160 freshly extracted human first or second premolar teeth, which were randomly divided into 16 groups. The teeth were prepared from Mashhad University of Medical Sciences, Mashhad, Iran (2008–2009). Scotchbond Multi-purpose (SBMP), single bond (SB), Clearfil SE Bond, and Clearfil S3 Bond were applied to dentin surface with or without the placement of hydrophobic resin (Margin Bond) in accordance with the instructions of the manufacturers. To expose the coronal dentin, the teeth were abraded with 600 grit SiC paper. Immediately after restoration, half of the samples were tested in terms of SBS, while the other samples were evaluated in terms of SBS after three months of storage in artificial saliva. SBS rates of dental composites evaluated by universal testing machine and samples were studied by optical stereomicroscopy to verify the failure type. Data analysis was performed in SPSS V.16 using Kolmogorov-Smirnov test, independent-samples t-test, ANOVA, and Duncan’s logistic regression test.ResultsIn this study, a significant reduction was observed in the SBS rates of SB and S3 bond adhesive systems after storage with and without hydrophobic resin (p>0.000). Without storage in normal saline, a significant increase was observed in the SBS rate of the SE bond (p=0.013). In addition, SBS rate of SBMP significantly increased after storage with hydrophobic resin (p=0.001). Finally, the highest and lowest rates of SBS were observed in the SE and S3 bonds in all the experimental groups, respectively.ConclusionThe effects of using a hydrophobic resin layer on shear bond strength values seem to be effective. The mild self-etch adhesive exhibited the best resin-dentine bond strength after aging

Paucity of Nanolayering in Resin-Dentin Interfaces of MDP-based Adhesives

Self-assembled nanolayering structures have been reported in resin-dentin interfaces created by adhesives that contain 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP). These structures have been hypothesized to contribute to bond durability. The objective of the present study was to determine the extent of nanolayering in resin-dentin interfaces after application of commercialized 10-MDP-containing self-etch and universal adhesives to human dentin. Seven commercialized adhesives were examined: Adhese Universal (Ivoclar-Vivadent), All-Bond Universal (Bisco, Inc.), Clearfil SE Bond 2, Clearfil S3 Bond Plus, Clearfil Universal Bond (all from Kuraray Noritake Dental Inc.), G-Premio Bond (GC Corp.), and Scotchbond Universal (3M ESPE). Each adhesive was applied in the self-etch mode on midcoronal dentin according to the respective manufacturer’s instructions. Bonded specimens (n = 6) were covered with flowable resin composite, processed for transmission electron microscopy, and examined at 30 random sites without staining. Thin-film glancing angle X-ray diffraction (XRD) was used to detect the characteristic peaks exhibited by nanolayering (n = 4). The control consisted of 15%wt, 10%wt, and 5%wt 10-MDP (DM Healthcare Products, Inc.) dissolved in a mixed solvent (ethanol and water weight ratio 9:8, with photoinitiators). Experimental primers were applied to dentin for 20 s, covered with hydrophobic resin layer, and examined in the same manner. Profuse nanolayering with highly ordered periodicity (~3.7 nm wide) was observed adjacent to partially dissolved apatite crystallites in dentin treated with the 15% 10-MDP primer. Three peaks in the 2θ range of 2.40° (3.68 nm), 4.78° (1.85 nm), and 7.18° (1.23 nm) were identified from thin-film XRD. Reduction in the extent of nanolayering was observed in the 10% and 5% 10-MDP experimental primer-dentin interface along with lower intensity XRD peaks. Nanolayering and characteristic XRD peaks were rarely observed in specimens prepared from the commercialized adhesives. The sparsity of nanolayering in resin-dentin interfaces created by commercialized adhesives challenges its clinical effectiveness as a mechanism for improving bond longevity in dentin bonding.

Permeabilidade dentinária e morfologia da interface adesiva de diferentes sistemas adesivos

ObjectiveCompare dentine permeability of different adhesive systems with and without hydrophobic resin. Analyze the influence of pulpal pressure on the morphology of the adhesive interface. MethodsFor the permeability assay, teeth were randomly allocated in 4 groups (n=9), according to the adhesive systems: Futurabond U (Voco) self‐etch; Futurabond U etch‐and‐rinse; Scotchbond 1XT (3M‐Espe); Easybond (3M‐Espe) with subsequent application of an hydrophobic resin [Adhesive; Scotchbond Multipurpose system (3M‐Espe)]. Hydraulic conductance of each specimen was measured on a permeability apparatus. To characterize the morphology of the adhesive interface in scanning electron microscope, 3 specimens from each group subjected to pulpal pressure were used, and new specimens (n=3) were prepared without pulpal pressure, according to the same adhesive system, forming the 4 groups described before. Permeability of the different adhesive systems was compared with Anova and Tukey post‐hoc (p<0.05). Permeability before and after the hydrophobic resin layer was compared with a paired t student test for repeated measures. ResultsPermeability was significantly lower with Futurabond U self‐etch when compared to the etch‐and‐rinse groups (p<0.05), both before and after hydrophobic resin layer application. Hydrophobic resin layer lead to a significant reduction on the permeability for all adhesive systems (p<0.05). Hybrid layer was not identified on the self‐etch groups as opposed to the etch‐and‐rinse groups. Adhesive interface had alterations when the pulpal pressure was applied. ConclusionHydrophobic resin layer reduced the permeability in all adhesive systems tested. Structural defects were present in all groups when the adhesive procedures were performed under pulpal pressure.

Effect of alternative modes of application on microleakage of one-step self-etch adhesives

Background/purposeContemporary one-step self-etch adhesives are certainly the most user-friendly adhesives; however, typically could not compete with the more traditional multi-step adhesives. This in vitro study evaluated the efficacy of two modes of application (double application or placement of a hydrophobic resin coating) for the reduction of microleakage, using three different one-step self-etch adhesives (AdheSE One VivaPen, Ivoclar Vivadent, Schaan, Liechtenstein; Xeno V, Dentsply De Trey, Konstanz, Germany; OptiBond All-In-One, Kerr Italia S.r.l, Scafati, Italy). Materials and methodsWe prepared Class V cavities with the occlusal margin in enamel and gingival margin in dentin on both buccal and lingual surfaces of 108 human molar teeth. Cavities were divided into nine groups according to the combination of adhesives and application modes used (n = 24). For applying adhesives, we followed three types of procedures: (1) according to the manufacturers’ directions; (2) using a double-application method; and (3) with the additional placement of a hydrophobic resin layer after following the manufacturers’ directions. We restored the cavities with a composite resin. After thermocycling (500 cycles at 5°C/55°C) and immersion in 0.5% basic fuchsin, we sectioned the teeth and evaluated them for microleakage using a stereo microscope (20×). Enamel and dentin margins were scored separately, and we analyzed the data using Kruskal–Wallis, Bonferroni-corrected Mann–Whitney U, and Wilcoxon signed-rank tests. ResultsApplication of a hydrophobic resin over the cured Xeno V adhesive decreased the amount of microleakage at the enamel margins, compared with the application according to the manufacturer’s instructions (P = 0.005). Both application modes decreased the amount of microleakage at the dentin margins with AdheSE One VivaPen adhesive, compared with application according to the manufacturer’s instructions (P < 0.001). With the OptiBond All-In-One adhesive, no significant difference between application modes was observed. ConclusionAlternative modes of application did not adversely affect the sealing ability of one-step self-etch adhesives. Depending on the type of adhesive, alternative modes of application may contribute to low microleakage values.

Microshear bond strength of self-etching systems associated with a hydrophobic resin layer

To evaluate in vitro the microshear bond strength of adhesive systems applied to dentin according to manufacturers' instructions, associated or not with a hydrophobic layer of unfilled resin. Six self-etching adhesives (Clearfil SE Bond, Kuraray Medical; AdheSE, Ivoclar Vivadent; Xeno III, Dentsply; I Bond, Heraeus-Kulzer; Bond Force, Tokuyama; Futurabond DC, Voco) were tested. The labial dentin of sixty bovine incisors was exposed, and the teeth were divided into two groups according to the application or not of an extra hydrophobic resin layer (Scotchbond Multi Purpose Plus, bottle 3). Six composite cylinders (Filtek Z250, 3M ESPE) were built up on each treated surface. Specimens were stored in distilled water at 37ºC for 24 h and then subjected to the microshear bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. Microshear bond strength values were analyzed by 2-way ANOVA and Tukey's post-hoc test. Failure mode was determined using a stereomicroscope under 20X magnification. The application of the hydrophobic resin layer did not affect bond strength, except for AdheSE. However, the bond strengths with the hydrophobic layer were similar among the six tested systems (Clearfil: 17.1 ± 7.9; AdheSE: 14.5 ± 7.1; Xeno lll: 12.8 ± 7.7; I Bond: 9.5 ± 5.8; Bond Force: 17.5 ± 4.1; Futurabond: 7.7 ± 2.3). When used as recommended by the manufacturers, Bond Force presented statistically higher bond strength than AdheSE and I Bond (p < 0.05) (Clearfil 10.4 ± 4.9; AdheSE 1.6 ± 1.6; Xeno lll: 9.0 ± 3.8; I Bond: 3.0 ± 1.5; Bond Force: 14 ± 3.9; Futurabond: 8.8 ± 3.8). Failure mode was predominantly adhesive. The bond strength of the self-etching systems tested was not significantly affected by the application of a hydrophobic layer, but a significant improvement was observed in AdheSE.

Ten-year observation of dentin bonding durability of 4-META/MMA-TBB resin cement —a SEM and TEM study

This study aimed to assess dentin bond durability of 4-META/MMA-TBB resin cement over ten years, by evaluating the tensile bond strength, and SEM and TEM observations. Tensile bond strength of Super Bond C&B (SB) to bovine dentin was evaluated at 1 day and after 10 years. The mode of failure after debonding was observed by SEM. Interfacial ultrastructure and nanoleakage was observed by TEM at the baseline and after 10 y. The tensile bond strength significantly dropped after 10 y. The failure pattern shifted from cohesive failure in resin towards adhesive failure or cohesive failure in dentin. TEM observation revealed degradation of both resin and collagen networks within the hybrid layer and nanoleakage at the base of the hybrid layer after 10 y. The bond strength of SB to dentin significantly decreased, and the hybrid layer degraded, while the overlying hydrophobic resin layer showed little disintegration over 10 y.

Marginal permeability of one step self-etch adhesives: Effects of double application or the application of hydrophobic layer

Aim:The purpose of this in vitro investigation was to evaluate the influence of double application and application of hydrophobic layer on marginal adaptation of four self-etch adhesive systems (XENOIII, ALLBONDSE, CLEARFIL SE TRI BOND, FUTURA BOND).Materials and Methods:One hundred and twenty class V cavities were prepared on intact, extracted human premolars and were divided into three groups of ten teeth each for all four adhesives. Group 1: Application of bonding agents as per manufacturer directions. Group 2: Double application of bonding agents. Group 3: Application of hydrophobic layer. The specimens were restored with composite and light cured. After thermocycling and immersion in 2% Basic Fuchsin dye solution, the teeth were sectioned and dye penetration was observed under a stereomicroscope at 20× magnification. All the samples were scored and results were analyzed using Kruskal-Wallis and Mann-Whitney tests.Results:Group 3, in which the adhesive systems were coated with hydrophobic layer, showed significantly decreased microleakage, followed by Group 1 and Group 2 for all the adhesive systems. And there is no significant different between Group 1 and Group 2.Conclusion:Marginal permeability of one-step adhesives can be minimized by the application of more hydrophobic resin layer, and the double application of one-step self-etch system can be safely performed without jeopardizing the performance of adhesives.

Influence of hydrophobic layer and delayed placement of composite on the marginal adaptation of two self-etch adhesives

Aim:The purpose of this in vitro investigation was to evaluate the influence of hydrophobic layer and delay in placement of composite on marginal adaptation of two self-etch adhesive systems (XENO-III and ALL-BOND SE).Materials and Methods:Eighty class V cavities were prepared on intact, extracted human premolars and were divided into 4 groups of 10 teeth each. Group 1: Application of bonding agents as per manufacturer directions and immediate placement of composite; Group 2: Application of bonding agent and composite similar to group1, with hydrophobic layer curing before composite placement; Group 3: Application of bonding agent similar to group 1, with 2 min delay in composite placement; and Group 4: Application similar to group 2 with 2-min delay in composite placement. The specimens were restored and light cured. After thermocycling and immersion in 2% basic Fuchsin dye solution, the teeth were sectioned and dye penetration was observed under a stereomicroscope at 20× magnification. All the samples were scored and results were analyzed using Kruskal-Wallis and Mann-Whitney tests.Results:In group 1, the microleakage along the both enamel and dentin margin was significantly higher than the other groups for both the adhesive systems. There is no significant difference between groups 2, 3 and 4.Conclusion:The addition of a more hydrophobic resin layer and delay in composite placement significantly improves the marginal adaptation of self-etch adhesive resin systems.

Can the durability of one-step self-etch adhesives be improved by double application or by an extra layer of hydrophobic resin?

Objectives This study evaluated the immediate and 6-month resin–dentin μ-bond strength (μTBS) of one-step self-etch systems (Adper Prompt L-Pop [AD] 3M ESPE; Xeno III [XE] Dentsply De Trey; iBond [iB] Heraeus Kulzer) under different application modes. Materials and methods Dentin oclusal surfaces were exposed by grinding with 600-grit SiC paper. The adhesives were applied according to the manufacturer's directions [MD], or with double application of the adhesive layer [DA] or following the manufacturer's directions plus a hydrophobic resin layer coating [HL]. After applying the adhesive resins, composite crowns were built up incrementally. After 24-h water storage, the specimens were serially sectioned in “ x” and “ y” directions to obtain bonded sticks of about 0.8 mm 2 to be tested immediately [IM] or after 6 months of water storage [6M] at a crosshead speed of 0.5 mm/min. The data from each adhesive was analyzed by a two-way repeated measures ANOVA (mode of application vs. storage time) and Tukey's test ( α = 0.05). Results The adhesives performed differently according to the application mode. The DA and HL either improved the immediate performance of the adhesive or did not differ from the MD. The resin–dentin bond strength values observed after 6 months were higher when a hydrophobic resin coat was used than compared to those values observed under the manufacturer's directions. Conclusions The double application of one-step self-etch system can be safety performed however the application of an additional hydrophobic resin layer can improve the immediate resin–dentin bonds and reduce the degradation of resin bonds over time.