Electric-current-assisted Application of Self-etch Adhesives to Dentin

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.

Iontophoresis effects of two-step self-etch and total-etch systems on dentin permeability and sealing of composite restoration under simulated pulpal pressure

BACKGROUND

Studies demonstrated the bond strength enhancement and the decrease in degradation of the adhesive interface after applying either self-etch adhesives or two-step, etch-and-rinse adhesives under an electric field. However, the presence of dentinal fluid driven by the pulpal pressure in vivo is a profounding factor affecting both the sealing ability and bond strength of adhesives. This study aimed to evaluate the effect of three-step etch-and-rinse and two-step self-etch adhesives when applied with iontophoresis under simulated pulpal pressure on the permeability of dentin, resin infiltration, and the sealing ability of resin composite.

METHODS

The experiments were done on 32 recently extracted premolars, randomly assigned into four groups (n = 8) according to two adhesive systems (SBMP and SE), applied following the manufacturer's instructions (control) for two groups or with iontophoresis for the others (SBMPi and SEi). For the iontophoresis, the anodal current was applied at 75 μA for 20 s through the cavity electrode during the bond. The fluid flow rate of dentin was recorded after cavity preparation (smear-layer-covered dentin; T1), bonding (T2), and composite restoration (T3) during the maintained pulpal pressure of 20 mm Hg. The flow rates were expressed as a percentage relative to the initial smear-layer-covered value for each specimen. Results were analyzed using repeated measures ANOVA. Scanning electron microscopy (SEM) was performed to observe the resin/dentin interface.

RESULTS

There were no significant increases in the mean flow rates from T1 to T3 in the SBMP (P = 0.355), while these changes in the SE were significant between T1 (100%) and T2 (166.77%) and T1 and T3 (221.16%) (P = 0.002; one-way RM ANOVA; Holm-Sidak test). For the iontophoresis groups, the mean flow rates decreased significantly from T1 to T2 and T1 to T3 of both SBMPi (T2 = 86.43, and T3 = 79.53; P < 0.001) and SEi groups (T2 = 87.96, and T3 = 81.48; P = 0.004). The iontophoresis of both adhesives produced the optimal resin infiltration with improved quality of the hybrid layer and resin tags.

CONCLUSIONS

SBMP bonded with or without iontophoresis performed better sealing ability than SE under the same condition. Both adhesives applied with anodal iontophoresis significantly decreased the dentin permeability, contributing to the improved resin infiltration.

Removal of Accumulated Hard Tissue Debris (AHTD) from Root Canals with an Electric Current Device: A MicroCT Preliminary Report

In modern endodontics, removal of accumulated hard tissue debris (AHTD) from root canals is requested. In the last decade, different irrigating solutions and activation methods have been successfully tested. Sonic activation has been shown to be effective in the removal of AHTD. Electric current has been tested before in restorative dentistry, but not in endodontics. An experimental electric current delivering device was compared in the removal of AHTD, using microCT analyses. Fifteen single-rooted teeth were shaped with TruNatomy system endodontic files and divided into three groups: negative control group: specimens underwent no activation; EA group: specimens were activated with EndoActivator (EA); EB group: specimens were activated with ElectroBond (EB). The 2D images, 3D images and morphometric analysis from the microCT showed a statistically significant increased AHTD removal when EB was used. Results of the present preliminary study showed that the irrigant activation with ElectroBond is encouraging when compared to EndoActivator along the entire root canal system. The AHTD was significantly statistically reduced, validating the clinical use of electric fields in endodontics.

Sonic application of one-step self-etch adhesive in composite restorations of non-carious cervical lesions: A double-blind randomized clinical trial

OBJECTIVES

To evaluate the influence of the sonic device on the clinical performance of one-step self-etch adhesive systems in non-carious cervical lesions (NCCLs) after 18 months.

MATERIALS AND METHODS

Forty patients participated in this study. Eighty restorations were assigned to two groups (n = 40): Sonic application and Manual application. After the adhesive application (iBond Self-Etch, Kulzer, Hanau, Germany), NCCLs were restored using composite resin (Charisma, Kulzer, Hanau, Germany). The restorations were evaluated at baseline and after 18 months both according to the Word Dental Federation (FDI) and the United States Public Health Service (USPHS) criteria. Friedman repeated measures analysis of variance by rank and Wilcoxon test for significance in each pair were applied (α = 0.05).

RESULTS

After 18 months, 38 patients were evaluated. Twenty-three restorations were lost (19 for manual vs. 4 for sonic application). The retention rates (95% confidence interval) were 50% (CI 34.8%-65.1%) for manual application and 84.2% (CI 69.6%-92.6%) for sonic application (p < 0.05). Twelve restorations showed marginal staining (nine for manual vs. three for sonic application; FDI, p < 0.05) and nine some marginal discrepancy (seven for manual vs. two for sonic application; FDI, p < 0.05). No restorations showed postoperative sensitivity and caries recurrence at the time.

CONCLUSION

The sonic application increases the retention rate of iBond Self-Etch after 18 months of clinical evaluation in NCCLs.

CLINICAL RELEVANCE

The application of a simplified self-etch adhesive (iBond Self-Etch) associated to a sonic device seems to be an alternative to improve the clinical behavior in NCCLs.

Adhesive systems applied to dentin substrate under electric current: systematic review

Objectives

The purpose of this systematic review was to collect and discuss the technique of adhesive systems application on dentin substrate under electric current.

Materials and Methods

The first search strategy was based on data available at PubMed, LILACS, Scielo, Scopus, and Cochrane Library, using a combination of descriptors such as “dentin bond agents OR adhesive system AND electric current OR electrobond” or “dentin bonding agents OR dentin bonding agent application OR adhesive system AND electric current OR electrobond”, with no limit regarding the publication year. The second search strategy was based on the articles' references found previously. An additional search strategy was applied that concerned the proposed theme in the SBU-UNICAMP (Unicamp's Library System Institutional Repository).

Results

Twelve studies published between 2006 and 2020 were found. The analyses of the selected studies showed that the use of electric current during adhesive systems application on dentin, whether conventional or self-conditioning, increases resinous monomer infiltration in the dentin substrate, which improves the hybridization processes and the bond strength of the restorative material to dentin.

Conclusions

Despite the favorable results related to the use of this technique, there is still no specific protocol for the application of adhesive systems under electric current.

Electric current effects on bond strength, nanoleakage, degree of conversion and dentinal infiltration of adhesive systems

To evaluate the effect of three adhesive systems applied under electric current on microtensile bond strength (μTBS) and degree of conversion (DC). Molar teeth were restored with the aid of three adhesive systems (Adper Single Bond 2-SB2; Clearfil SE Bond-CSE; and Single Bond Universal-SBU) under different electric current intensities (0 μA; 25 μA; and 50 μA). Composite resin blocks were built up in increments (2 mm) and sectioned into 1 × 1 mm beams. The μTBS was tested after 24 h and 1 y distilled water storages. Samples (n = 10) from 24 h to 1 y storages were immersed in a 50% ammoniacal silver nitrate solution and submitted to scanning electron microscopy. The silver nitrate in the hybrid layer was quantified (ImageJ software). The adhesive systems' dentinal infiltration was analyzed using confocal laser scanning microscopy. Fourier transform near infrared spectroscopy was used to measure the DC. The μTBS data were submitted to two-way ANOVA (time vs. electric current) and Bonferroni's test (α = 0.05). Quantitative nanoleakage data were submitted to two-way ANOVA (electric current vs. adhesive) and Bonferroni's test (α = 0.05). DC data were submitted to one-way ANOVA and Tukey's test (α = 0.05) for each adhesive system. The electric current statistically increased the μTBS for SB2 and CSE in 24 h storage, as well as for SB2, CSE and SBU in 1 y storage. No significant difference was observed between storage time for CSE and SBU. When compared to the control, electric currents (25 μA and 50 μA) showed significantly higher DC mean values for SB2 and SBU, and had no effect on CSE. The electric currents (25 μA and 50 μA) reduced the adhesive system's nanoleakage after 1-year storage, and improved the infiltration of SB2 and CSE. Both electric current intensities improved dentinal interface stability.

Effect of Diode Laser (810 nm) Irradiation on Marginal Microleakage of Multi-mode Adhesive Resins in Class V Composite Restorations

Introduction: Some studies have shown that laser irradiation on unpolymerized adhesives can improve composite-dentin adhesion. The aim of the present study was to evaluate the effect of the diode laser (810 nm) on the microleakage of multi-mode adhesive systems at enamel and dentin margins of composite restorations. Methods: Classic class V boxes were prepared on 48 sound premolar teeth and randomly divided into 6 groups (n=16). In the control groups, Scotchbond Universal (SBC), G-Premio (GBC), and Ambar U (AMC) were used by a self-etch mode. In the test groups (SBL, GBL, ABL), the 810 nm diode laser was irradiated (1 W) for 10 seconds before the polymerization of the adhesive. The boxes were restored by the resin composite. After finishing and polishing, the samples were thermocycled (5°C to 55°C) for 1000 cycles and then immersed in 0.1% methylene blue dye (48 hours). Dye penetration through the gingival and occlusal margins was measured by Stereomicroscope. The data were analyzed at the 5% significance level using Kruskal-Wallis and Mann-Whitney U tests. Results: Significant differences were found between the control and test groups (P < 0.05). The occlusal margins of the SBL and GBL groups and the cervical margin of the SBL group exhibited the lowest microleakage (P < 0.05). The AM control group showed maximum microleakage at cervical and occlusal margins. Conclusion: The irradiation of the 810 nm diode laser on the unpolymerized universal adhesive systems in a self-etch mode caused a significant reduction in enamel and dentin marginal microleakage of composite restorations.

Optimization of direct currents to enhance dentine bonding of simplified one-step adhesive

The aim of this study was to investigate the effects of different direct current intensities on dentine bonding effectiveness of Clearfil S(3) Bond and on cell viability of human dental pulp cells (HDPCs). Thirty-five-third molars were sectioned and ground to provide flat surfaces. Clearfil S(3) Bond was applied under different current conditions for 30 s and then resin composite was built up. Specimens were processed for microtensile bond strength (µTBS) testing and for nanoleakage investigation using scanning electron microscopy. Primary HDPCs isolated from premolars were stimulated with different intensities of electric current for 30 s. Then, cell viability was tested using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Specimens bonded with application of electrical current intensities of 50, 60, 70, and 90 µA exhibited a significant increase in immediate µTBS compared with all other groups. Bonded interfaces prepared using electrically assisted current application showed reduced interfacial nanoleakage upon scanning electron microscopy. Electric current application, from 20 to 70 µA, had no effect on the viability of HDPCs. This study provides further evidence for its future clinical use.

Effect of sonic application mode on the resin-dentin bond strength and nanoleakage of simplified self-etch adhesive

OBJECTIVES

This study aims to evaluate the effect of different application modes on the immediate and 6-month resin-dentin bond strength (μTBS) and nanoleakage in the hybrid and adhesive layers.

MATERIALS AND METHODS

Three 1-step self-etch adhesives (One Coat 7.0 (OC), Clearfil S(3) Bond (CS), and FuturaBond NR (FB)) were applied on a flat superficial dentin surface of 30 human molars under manual mode or sonic vibration at a frequency of 170 Hz (SV). Composite build-ups were constructed incrementally; specimens were sectioned to obtain resin-dentin sticks with cross-sectional area of 0.8 mm(2) and tested in tension (0.5 mm/min) immediately (IM) or after 6 months (6M) of water storage. Two bonded sticks, from each tooth at each storage time, were immersed in a silver nitrate solution, photo-developed, and analyzed under scanning electron microscopy. The amount of nanoleakage was measured using the ImageTool 3.0 software. Data, from each adhesive, were analyzed by two-way ANOVA and Tukey's test (α = 0.05).

RESULTS

OC and CS showed higher μTBS and lower nanoleakage in the IM period when applied with SV groups. For FB, no significant difference was observed between the two modes of application. All materials showed lower nanoleakage in the SV groups. Higher nanoleakage was observed after 6M for OC and FB.

CONCLUSIONS

The sonic application mode at an oscillating frequency of 170 Hz can improve the resin-dentin μTBS, reduce the nanoleakage, and retard the degradation of the resin-dentin μTBS of Clearfil S(3) Bond and One Coat 7.0 adhesives.

CLINICAL SIGNIFICANCE

Sonic application mode at an oscillating frequency of 170 Hz can be helpful and easy to use in dental practice to guaranty long-lasting restorations.

Overview of Clinical Alternatives to Minimize the Degradation of the Resin-dentin Bonds

The incorporation of hydrophilic and acidic resin monomers substantially improved the initial bonding of contemporary etch-and-rinse (ER) and self-etch (SE) adhesives to intrinsically wet dental substrates, providing quite favorable immediate results, regardless of the bonding approach used. However, in the long term, the bonding effectiveness of most simplified ER and SE adhesives drop dramatically. This review examines the fundamental processes that are responsible for the aging mechanisms involved in the degradation of the resin-bonded interfaces and some possible clinical approaches that have been effective in minimizing or even preventing the degradation of the adhesive interfaces produced with simplified adhesives. The incorporation of some of the feasible approaches - described in this review - may improve the quality of the adhesive restorations performed in clinical practice, while manufacturers develop bonding materials that are less susceptible to the aging mechanisms present in the oral environment.

Electrical properties of resin monomers used in restorative dentistry

OBJECTIVES

The application of an electric field has been shown to positively influence the impregnation of the resin monomers currently used in dentin bonding systems during hybrid layer formation. This study presents an experimental characterization of the electrical properties of these monomers with the aim of both correlating them to their chemical structures and seeking an insight into the mechanisms of the monomer migration under an applied electric field.

METHODS

Some common monomers examined were TEGDMA (triethyleneglycoldimethacrylate), HEMA (2-hydroxyethyl methacrylate), UDMA (urethane dimethacrylate), 2-MP (bis[2-(methacryloyloxy)ethyl] phosphate, TCDM di(hydroxyethyl methacrylate) ester of 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic anhydride) and Bis-GMA [2,2-bis(4-2-hydroxy-3-methacryloyloxypropoxyphenyl)propane]. A customized cell produced for the measurement of the electrical properties of monomers was manufactured and electrical conductivity and permittivity of resin monomers were measured.

RESULTS

The permittivity of the tested monomers is largely affected by electrical frequency. The large values of permittivity and dielectric losses observed as frequency decreased, indicate a dominant effect of ionic polarization, particularly evident in materials showing the highest conductivity. Permittivity and conductivity of the tested monomers showed a similar behavior, i.e. materials with the lowest permittivity also show small values of conductivity and vice versa.

SIGNIFICANCE

The results of the present study revealed a good correlation between electrical properties and Hoy solubility parameters and, in particular, the higher the polar contribution (polar forces plus hydrogen bonding) the higher the permittivity and conductivity. The most relevant outcome of this study is that the electrophoretic mechanism prevails on the electroendoosmotic effect in determining the monomer migration under the application of electric fields.

Effects of pH, ionic strength, and applied voltage on migration of dental monomers in an organic matrix

OBJECTIVES

The application of an electric field has been shown to positively influence the bonding of dentin bonding systems (DBS) by improving adhesive impregnation into dentin. However, the mechanism responsible for this phenomenon has not been completely elucidated. The aim of this study was to clarify the effects of pH, matrix ionic strength, and applied voltage on the migration of commonly used DBS monomers in a model matrix (agarose gel).

METHODS

Some common monomers examined were bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane); HEMA (2-hydroxyethyl methacrylate); 2-MP (bis[2-(methacryloyloxy) ethyl] phosphate); TCDM [di(hydroxyethyl methacrylate) ester of 5-(2,5,-dioxo tetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid]; and TEGDMA (triethylene glycol dimethacrylate). Agarose gels poured into a horizontal 10-well electrophoretic cell were used to mimic the collagen fibrils of the dentin organic matrix. The role of pH, matrix ionic strength, and voltage on monomer migration was assayed by modifying the experimental conditions.

RESULTS

Results of experiments performed at pH 3.1, 6.3, 8.5, and 12.3; at low, medium, and high ionic strength; and at 50 and 100 V clearly showed that DBA monomer migration toward both the anode and the cathode can be affected by each of these parameters.

SIGNIFICANCE

Migration of acrylic monomers toward the anode or cathode can be achieved as desired by selective choice of pH, ionic strength, and applied voltage. Additional studies are needed to evaluate the synergistic effects of DBS monomer blends on migration in an electric field.

Adhesive systems: important aspects related to their composition and clinical use

This literature review article addresses the types and the main components of different etch-and-rinse and self-etch adhesive systems available in the market, and relates them to their function, possible chemical interactions and influence of handling characteristics. Scanning electron microscopy (SEM) images are presented to characterize the interface between adhesives and dentin. Adhesive systems have been recently classified according to their adhesion approaches in etch-and-rinse, self-etch and glass ionomer. The etch-andrinse systems require a specific acid-etch procedure and may be performed in two or three steps. Self-etch systems employ acidic monomers that demineralize and impregnate dental substrates almost at the same time. These systems are separated in one or two steps. Some advantages and deficiencies were noted for etch-and-rinse and self-etch approaches, mainly for the simplified ones due to some chemical associations and interactions. The SeM micrographs illustrate different relationships between adhesive systems and dental structures, particularly dentin. The knowledge of composition, characteristics and mechanisms of adhesion of each adhesive system is of fundamental importance to permit the adoption of ideal bonding strategies under clinical conditions.

24-month clinical evaluation in non-carious cervical lesions of a two-step etch-and-rinse adhesive applied using a rubbing motion

The aim of this clinical trial was to evaluate the effects of application mode on the clinical performance of a two-step etch-and-rinse adhesive in class V cavities over 24 months. Forty patients with at least three similar-sized non-carious cervical lesions participated in this study. A total of 120 restorations with Prime & Bond NT were placed, 40 in each group. The adhesive was applied with no rubbing action, with slight rubbing action, or with vigorous rubbing action. The restorations were placed incrementally using the composite resin Esthet-X. The restorations were evaluated at baseline and after 6, 12, and 24 months following the modified United States Public Health Service criteria. Statistical analysis was conducted using Friedman repeated measures analysis of variance by rank and using the Wilcoxon signed-rank test for significance at each pair (α = 0.05). The 24-month retention rates of Prime & Bond NT were 82.5% for the no rubbing group, 82.5% for the slight rubbing group, and 92.5% for vigorous rubbing group. No significant difference in the retention rates in each recall period was detected among groups (p > 0.05); however, the retention rates in the 24-month recall was statistically lower than the baseline only for no rubbing or slight rubbing groups. The use of a vigorous application mode can be a clinical approach to improve the retention of restorations placed in non-carious cervical lesions.

Dental adhesion review: Aging and stability of the bonded interface

OBJECTIVE

Most of current dental adhesive systems show favorable immediate results in terms of retention and sealing of bonded interface, thereby counteracting polymerization shrinkage that affects resin-based restorative materials. Despite immediate efficacy, there are major concerns when dentin bonded interfaces are tested after aging even for short time period, i.e. 6 months.

METHODS

This study critically discusses the latest peer-reviewed reports related to formation, aging and stability of resin bonding, focusing on the micro and nano-phenomena related to adhesive interface degradation.

RESULTS

Most simplified one-step adhesives were shown to be the least durable, while three-step etch-and-rinse and two-step self-etch adhesives continue to show the highest performances, as reported in the overwhelming majority of studies. In other words, a simplification of clinical application procedures is done to the detriment of bonding efficacy. Among the different aging phenomena occurring at the dentin bonded interfaces, some are considered pivotal in degrading the hybrid layer, particularly if simplified adhesives are used. Insufficient resin impregnation of dentin, high permeability of the bonded interface, sub-optimal polymerization, phase separation and activation of endogenous collagenolytic enzymes are some of the recently reported factors that reduce the longevity of the bonded interface.

SIGNIFICANCE

In order to overcome these problems, recent studies indicated that (1) resin impregnation techniques should be improved, particularly for two-step etch-and-rinse adhesives; (2) the use of conventional multi-step adhesives is recommended, since they involve the use of a hydrophobic coating of nonsolvated resin; (3) extended curing time should be considered to reduce permeability and allow a better polymerization of the adhesive film; (4) proteases inhibitors as additional primer should be used to increase the stability of the collagens fibrils within the hybrid layer inhibiting the intrinsic collagenolytic activity of human dentin.