Effect of double-layer application on the early enamel bond strength of universal adhesives

Tooth-composite bond failure with a universal and an etch-and-rinse adhesive depending on mode and frequency of application

OBJECTIVES

To evaluate the effect of an additional layer of universal adhesive on the interfacial enamel/dentin-composite gap formation in relation to application mode and aging, via spectral domain optical coherence tomography (SD-OCT) and scanning electron microscopy (SEM).

METHODS

In vitro class V cavities in 114 caries-free premolars were restored by applying one or two layers of a universal adhesive (Scotchbond Universal, SBU) in self-etch (se) and etch-and-rinse (er) mode or the reference adhesive OptiBond FL (OFL-er). The restorations were imaged by SD-OCT (six groups, n = 8) and SEM (n = 3) directly after filling (t1), water storage (t2, 24 h), embedding (t3), and thermo-mechanical loading (t4, TCML). The interfacial gaps were quantified using 26 parameters and analyzed using principal component analysis and linear mixed effect models.

RESULTS

Gap formation at enamel and dentin was significantly influenced by the adhesive, the application mode and number of layers (p < 0.001). This was due to the influence of the SBU-er mode (p < 1e-05), which showed significantly more gap formation and a greater range of variation with double application when compared to SBU-se and OFL. The fewest interfacial gaps occurred with one or two applications of OFL-er and one layer of SBU-er.

SIGNIFICANCE

Adhesive application mode and the number of adhesive layers are relevant factors in the tooth-composite bond failure. Double application worsened the adaptation of SBU to freshly prepared dentin conditioned with phosphoric acid.

Comparative evaluation of the effect of 37% orthophosphoric acid pre-etching on the microtensile enamel bond strength using universal adhesive and two-step self-etch adhesive systems - An in vitro study

Context

The significance of enamel etching has been well-researched and established. Limited literature is available comparing the enamel bond strengths of the two-step self-etch adhesive system and the newly introduced universal adhesive (UA) system with prior acid etching.

Aims

The aim of the study was to evaluate and compare the microtensile bond strength (μTBS) of composite to enamel with and without 37% orthophosphoric acid pre-etching using a recently introduced UA and a two-step self-etch adhesive.

Subjects and Methods

This in vitro, experimental study was conducted on 48 extracted human third molar teeth. Two enamel surface fragments were obtained per tooth, polished using 600-grit silicon carbide abrasive paper, and randomly divided into four groups-CLEARFIL SE BOND with and without acid pre-etching and G-Premio Bond with and without acid pre-etching. The samples were etched using 37% phosphoric acid gel for 30 s, followed by the bonding protocol. Composite resin blocks were built incrementally to a thickness of approximately 6 mm, and the restored samples were stored in distilled water for 24 h at 37°C. They were then sectioned, mounted, and subjected to a μTBS test using a universal testing machine.

Statistical Analysis Used

Statistical analysis of the data was performed using one-way ANOVA and Tukey's post hoc test using SPSS software version 22.0.

Results

Samples bonded with the UA subjected to prior acid etching protocol demonstrated the highest enamel μTBS. In contrast, those treated with the two-step self-etch adhesive without prior acid etching demonstrated the lowest enamel μTBS. Pre-etching with phosphoric acid significantly increased the enamel bond strength of both bonding agents, with the universal agent showing better results than the two-step adhesive system.

Conclusions

Enamel etching with phosphoric acid significantly increases the bond strength of self-etch adhesives. UA with prior acid etching showed the maximum enamel μTBS. Two-step self-etch adhesive without prior acid etching yielded enamel μTBSs unacceptable for long-term, durable bonding.

Effect of the Absence of HEMA on the Bonding Properties of Universal Adhesive Systems Containing 10-MDP: An In Vitro Study

OBJECTIVES

To evaluate the absence of 2-hydroxyethyl methacrylate (HEMA) on the adhesive properties with enamel and dentin of universal adhesive systems containing 10-methacryloyloxydecyl dihydrogen phosphate (MDP).

METHODS AND MATERIALS

One hundred and twelve caries-free third molars were used to test adhesion to dentin (n=64) and enamel (n=48). For each substrate, teeth were divided into eight experimental groups: four different adhesives each using two adhesive strategies. The adhesives used were: (1) Scotchbond Universal (SBU, 3M Oral Care, St Paul, MN, USA) as a HEMA-containing universal adhesive; (2) Gluma Bond Universal (GBU, Kulzer, Hanau, Germany); (3) Solare Universal Bond (SUB, GC, Tokyo, Japan); and (4) Zipbond Universal (ZIP, SDI, Victoria, Australia) as HEMA-free universal adhesives. The adhesive strategies used were etch-and-rinse (ER) and self-etch (SE). For dentin tests, the occlusal third of the crown of all teeth was removed and an adhesive protocol was applied. After completing the restoration, specimens were sectioned into bonded sticks (0.8 mm 2) and tested for microtensile bond strength (μTBS), in situ degree of conversion (DC), and nanoleakage (NL) by scanning electron microscopy. For enamel tests, teeth were sectioned into four parts (buccal, lingual, and proximal), and an adhesive protocol was applied. After completing the restoration, the specimens were tested for their microshear bond strength (μSBS). For in situ degree of conversion (DC) and nanoleakage (NL) evaluation of enamel, the specimens were sectioned in slices to be evaluated. The data for each substrate were subjected to two-way ANOVA and Tukey's test (α=0.05) for each property evaluated.

RESULTS

The SBU and ZIP adhesives showed the highest μSBS, and DC (dentin and enamel) and lower NL (dentin) values compared to GBU and SUB (p=0.001). However, SBU showed better results in terms of μTBS and μSBS (SE strategy), and DC (dentin and enamel) than ZIP. Strategy ER presented higher values of μTBS and μSBS when compared to strategy SE (p=0.001), except for SBU.

CONCLUSION

The effect of the absence of HEMA in commercial universal adhesive systems on enamel and dentin adhesive properties appears to be material-dependent.

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

OBJECTIVE

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).

METHODS AND MATERIALS

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%).

RESULTS

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.

CONCLUSIONS

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.

Bond durability of a two-step adhesive with a universal-adhesive-derived primer in different etching modes under different degradation conditions

This study investigated the enamel and dentin bond durability of a two-step adhesive system, using a universal adhesive-derived primer (G2-Bond Universal [GU]), and compared it with the two conventional, two-step, self-etch adhesive systems (Clearfil SE Bond 2 [CS] and OptiBond XTR [OX]) under thermal cycling (TC) and long-term water storage (WS). The shear bond strengths to bovine enamel and dentin were determined using the etch-and-rinse and self-etch modes. Twelve specimens per test group were prepared and further divided into the following subgroups: 1) subjected to TC, 2) long-term WS, and 3) WS for 24 h (baseline). The enamel and dentin bond durability of GU was superior to those of CS and OX in different etching modes and under different degradation conditions. The latest two-step adhesive system, which utilizes universal adhesives' benefits in its primer, might offer durable clinical bonding performances and can be widely used in a clinical setting.

Eighteen-month clinical evaluation of a new universal adhesive applied in the "no-waiting" technique: a randomized clinical trial

OBJECTIVE

The aim of this double-blind, randomized clinical trial was to evaluate the 6- and 18-month clinical performances of a new universal adhesive applied in the "no-waiting" (NW) technique to non-carious cervical lesions (NCCLs) using two evaluation criteria.

MATERIALS AND METHODS

One hundred and seventy-six restorations were assigned to four groups according to the adhesive system, adhesive strategy, and application mode: Prime&Bond Active (PB) applied using the etch-and-rinse (ER) and self-etch (SE) strategies with 20 s applications and Clearfil Universal Bond Quick (CQ) applied using the ER and SE strategies with the NW technique. The composite resin restorations were evaluated at baseline and after 6 and 18 months using the World Dental Federation (FDI) and US Public Health Service (USPHS) criteria. The Friedman repeated measures analysis of variance and Wilcoxon test were used for statistical analyses (α = 0.05).

RESULTS

No significant differences were observed among any of the groups or criteria after 6 months (p > 0.05). After 18 months, 10 restorations were lost (p > 0.05) (2 with PB-ER [95.5%; 95%CI: 92-100%], 4 with PB-SE [90.9%; 95%CI: 82-98%], 0 with CQ-ER [100%; 95%CI: 92-100%], and 4 with CQ-SE [90.9%; 82-98%]). The restorations performed with the SE strategy showed more marginal discrepancies than those performed with the ER strategy, mainly when the FDI criteria were used (p < 0.05). Those that used the PB-SE showed fewer marginal discrepancies than those that used the CQ-SE (FDI; p < 0.05). A few restorations showed marginal discrepancies after the USPHS analysis (p > 0.05).

CONCLUSIONS

The results when using the CQ-SE and -ER strategies with the NW technique were similar to those when using the PB-SE and -ER strategies in standard applications to non-carious cervical lesions after 6 and 18 months of clinical evaluation.

CLINICAL RELEVANCE

After 6 and 18 months, the application of Clearfil Universal Bond Quick with the "no-waiting" technique showed similar clinical performance compared to the standard application of Prime & Bond Active applied using the standard application time (20 s).

TRIAL REGISTRATION

ClinicalTrials.gov identifier RBR-5f9gps.

Effect of immediate dentin sealing procedure using different universal adhesive systems on the shear bond strength of self-adhesive resin cement

Objective: The aim of this in vitro study was to investigate the effect of immediate dentin sealing (IDS) procedure using different universal adhesive systems on the shear bond strength (SBS) of dual-cure self-adhesive luting cement. Materials and Method: Sixty sound human molar teeth were used. The coronal dentin surfaces were exposed with model trimmer device and ground with 600-grit silicon carbide paper under water cooling to obtain standard smear layers. Specimens were randomly divided into 4 groups according to the different types of universal adhesive systems used (n=15): Group 1 (control; C): no immediate dentin sealing; Group 2: Clearfil Universal Bond Quick (UBQ); Group 3: Single Bond Universal (SBU); Group 4: OptiBond Universal (OBU). Adhesive systems were applied in self-etch mode according to the manufacturers’ instructions. Then, self-adhesive luting cement (Nova Resin Cement) was bonded using cylinder-shaped silicone mold (diameter: 3 mm, height: 2 mm). The specimens were stored in distilled water for 24 h and subjected to SBS test at a crosshead speed of 1 mm/min using universal testing machine. Debonded surfaces were observed with a stereomicroscope under 15× magnification to determine the failure mode. Data were statistically analyzed with Kruskal Wallis and Dunn test (p&lt;0.05). Results: Control group showed statistically lower shear bond strength than IDS-treated groups (p&lt;0.05). Group 2 (UBQ) showed statistically higher SBS than Group 3 (SBU) (p&lt;0.05). IDS-treated groups showed predominantly mixed failures while control group showed adhesive failure patterns. Conclusion: IDS procedures using universal adhesive systems improved the SBS of the self-adhesive luting cement. Besides, the highest shear bond strengths were obtained with Clearfil Universal Bond Quick which contains MDP and amide monomers.

Investigation of the Effects of Adhesive Materials of Different Types and Thicknesses on Dental Tissue Stress via FEM Analysis

The aim of this study was to investigate the types and thicknesses of adhesive materials used in restorative treatment in dentistry in class I occlusal and class II disto-occlusal cavities and to examine the effects of stress distribution on enamel, dentin, restoration material, and adhesive material using the finite element stress analysis method. A 3-dimensional geometry of the tooth was obtained by scanning the extracted 26 numbered upper molar tooth with dental tomography. The 3D geometry obtained by using the Geomagic Design X 2020.0 software was divided into surfaces, and necessary arrangements were made. With the Solidworks 2013 software, 2 different cavity modeling, class I occlusal and class II disto-occlusal, with a cavity angle of 95 degrees on the 3D model, as well as 10, 30, and 50 micrometers thick, four types of adhesive materials and the modeling of the bulk-fill composite material on it were made. With finite element stress analysis, the stress distribution was analyzed using the Abaqus software. The materials used in the study are included in the simulation as isotropic linear elastic. Periodontal ligament and jawbone were not included in the analysis. A total of 600 N pressure was applied on the models. In our study, it was observed that the amount of stress on the tooth structures changed when the thickness, elastic modulus, and Poisson ratios of the adhesive material were changed. In addition, when all models are examined, it is seen that when the thickness is increased, more stress is placed on the adhesive material compared to the restoration, while when 50-micrometer-thick adhesive material is used, more stress is placed on the restoration compared to the adhesive material.

Influence of bonding agent application method on the dentin bond durability of a two-step adhesive utilizing a universal-adhesive-derived primer

This study investigated the effect of the bonding agent application method on the dentin bond durability of a two-step adhesive utilizing a universal-adhesive-derived primer. The bonding durability of a universal adhesive was compared with those of two conventional two-step adhesives by shear bond strength testing after thermal cycling. The primer was applied (with or without phosphoric acid pre-etching), and the specimens were divided into three groups based on the bonding agent application method used as follows: (i) strong air-flow application, (ii) gentle air-flow application, and (iii) gentle air-flow + second bonding application. The shear bond strength was determined after thermal cycling. All the factors (bonding agent application method, adhesive system, and storage condition) significantly influenced the dentin shear bond strength both with and without phosphoric acid pre-etching. The specimens exposed to gentle air-flow showed a higher shear bond strength than did those exposed to strong air-flow and gentle air-flow + second bonding. The bond durability of the tested adhesive systems was influenced by the bonding agent application method, and this trend was material dependent. The G2-Bond Universal exhibited the same or greater dentin bond durability to the other two-step adhesive systems.

Bonding effects of cleaning protocols and time-point of acid etching on dentin impregnated with endodontic sealer

Objectives

This study aimed to investigate the bonding effects of cleaning protocols on dentin impregnated with endodontic sealer residues using ethanol (E) or xylol (X). The effects of dentin acid etching immediately (I) or 7 days (P) after cleaning were also evaluated. For bonding to dentin, universal adhesive (Scotchbond Universal; 3M ESPE) was used. The persistence of sealer residues, hybrid layer formation and microshear bond strength were the performed analysis.

Materials and Methods

One hundred and twenty bovine dentin specimens were allocated into 4 groups (n = 10): G1 (E+I); G2 (X+I); G3 (E+P); and G4 (X+P). The persistence of sealer residues was evaluated by SEM. Confocal laser scanning microscopy images were taken to measure the formed hybrid layer using the Image J program. For microshear bond strength, 4 resin composite cylinders were placed over the dentin after the cleaning protocols. ANOVA followed by Tukey test and Kruskal-Wallis followed by Dunn test were used for parametric and non-parametric data, respectively (α = 5%).

Results

G2 and G4 groups showed a lower persistence of residues (p < 0.05) and thicker hybrid layer than the other groups (p < 0.05). No bond strength differences among all groups were observed (p > 0.05).

Conclusions

Dentin cleaning using xylol, regardless of the time-point of acid etching, provided lower persistence of residues over the surface and thicker hybrid layer. However, the bond strength of the universal adhesive system in etch-and-rinse strategy was not influenced by the cleaning protocols or time-point of acid etching.

Immediate bond performance of resin composite luting systems to saliva-contaminated enamel and dentin in different curing modes

The purpose of this study was to evaluate the immediate shear bond strength of resin composite luting systems to tooth with or without saliva contamination in different curing modes. The Knoop hardness number of the resin composite luting agents was measured. Four combinations of resin composite luting systems were used. The shear bond strength to bovine teeth was measured with and without saliva contamination in different curing modes at different storage periods. The Knoop hardness number of the resin composite luting agents was also evaluated. Significantly lower enamel and dentin shear bond strengths and Knoop hardness number values were observed in all resin composite luting systems at 5 min versus 24 h, regardless of the curing mode or saliva contamination. The influence of the curing mode of the resin composite luting systems on shear bond strengths and Knoop hardness number was dependent on material. For the saliva contamination conditions, only G-CEM ONE EM did not show any significant difference in shear bond strength among the groups with and without saliva contamination, regardless of curing mode, storage period, or tooth substrate. All the resin composite luting systems showed lower shear bond strengths and Knoop hardness number values immediately after setting.

Evaluation of developmentally hypomineralised enamel after surface pretreatment with Papacarie Duo gel and different etching modes: an in vitro SEM and AFM study

PURPOSE

This study aimed at investigating the surface morphology and nanotopography of normal enamel (NE) and developmentally hypomineralised enamel (HE) when subjected to various pretreatment protocols under scanning electron microscopy (SEM) and atomic force microscopy (AFM).

METHODS

Sixteen NE, 16 creamy/white (CW) HE and 16 yellow/brown (YB) HE specimens sectioned from extracted hypomineralised first permanent molars (FPMs) were included in this study. They were randomly distributed into 12 experimental groups (n = 4). Each group involved the following: (1) deproteinisation with Papacarie Duo^® gel or no deproteinisation, and (2) the use of Scotchbond™ Universal Adhesive (Scotchbond) in self-etch (SE) mode or 37% phosphoric acid etchant. Subsequently, the surface morphology and nanotopography of pretreated enamel specimens were evaluated under SEM and AFM, respectively.

RESULTS

SEM observation showed that deproteinisation with Papacarie Duo^® gel before phosphoric acid etching led to favourable etching patterns. This was consistent across all groups irrespective of the type of enamel specimen and the severity of hypomineralisation. In contrast, AFM results identified three factors that influenced surface parameters: (1) type of enamel specimen, (2) severity of hypomineralisation and (3) etching mode. YB HE recorded higher surface roughness values than CW HE and NE when subjected to the same pretreatment protocol. Deproteinisation and the application of Scotchbond in SE mode led to minimal topographic changes; however, acid etching was associated with an increase in surface roughness.

CONCLUSION

Deproteinisation with Papacarie Duo^® gel followed by acid etching contributed to improved etching patterns on HE.

Comparative evaluation of different adhesive strategies of a universal adhesive in class II bulk-fill restorations: A 48-month randomized controlled trial

OBJECTIVES

To compare the clinical performance of the universal adhesive used in etch-and-rinse (ER) and self-etch (SE) adhesive strategies for 48-month in class II bulk-fill restorations.

METHODS

A total of 84 class II bulk-fill resin composite (Tetric EvoCeram Bulk Fill) restorations were placed in 35 participants by one operator using the universal adhesive's (Adhese Universal VivaPen) etch-and-rinse or self-etch mode randomly. The restorations were evaluated by two calibrated examiners at baseline and after 6-, 12-, 24-, 36- and 48-month using modified USPHS criteria. The comparison of the two adhesive strategies for each evaluation criteria was performed with the chi-square test. The baseline scores were compared with those at the recalls using the Friedman and Cochran's Q-test (p < .05).

RESULTS

At 48-month, 74 restorations were evaluated in 30 participants (recall rate: 85.7%). Marginal discoloration was statistically more frequent in SE approach (p < .05), whereas no significant difference was observed between the two strategies in terms of marginal adaptation (p > .05). There were statistically significant differences between the baseline and 48-month recall in the SE group in terms of marginal adaptation and discoloration (p < .05). In ER group, significant differences were found between baseline and 48-month only for marginal adaptation (p < .05). None of the restorations showed post-operative sensitivity. Secondary caries was observed in one restoration from SE group.

CONCLUSIONS

The tested bulk-fill restorative exhibited better clinical performance only in terms of marginal discoloration when the universal adhesive was used with ER strategy.

CLINICAL RELEVANCE

Though ER approach of the tested universal adhesive appears to be advantageous in terms of marginal discoloration, both adhesive strategies had similar impact on the clinical success of bulk-fill resin restorations.

Do universal adhesives provide the benefits from double-application or an extra bonding layer in composite repair?

This study aimed to determine whether the application of extra hydrophobic resin (EHR) or double layer (DL) improves microtensile bond strength (μTBS) of two universal adhesives to composite resin. Composite blocks were fabricated and exposed to thermal cycles. The specimens were horizontally sectioned into two halves. Scotch Bond Universal (SBU) and Clearfil S3 Bond Universal (CSBU) were applied to the ground composite surface according to the manufacturers' instructions, or with DL application or EHR application. The repair composite was incrementally placed to bonded planes. Composite sticks were achieved and tensed with a universal testing machine, followed by examining the fracture surfaces by a scanning electron microscope. Data were evaluated by Weibull analysis (shape and scale [σ_θ and σ_0.10 ] parameters) using the maximum likelihood method. The σ_θ and σ_0.10 , respectively, estimate strength at 63.2 and 10% probability of failure. Shape parameter values showed significant differences among treatments. DL application of CSBU did not affect μTBS values at σ_θ of failure but caused to decrease μTBS values at σ_0.10 of failure. DL application of SBU reduced μTBS values at σ_θ of failure. DL or EHR coating did not improve μTBS of SBU. EHR application increased μTBS of CSBU, whereas DL application did not benefit.

Is the presence of 10-MDP associated to higher bonding performance for self-etching adhesive systems? A meta-analysis of in vitro studies

OBJECTIVE

The purpose of this systematic review and meta-analysis was to analyze the literature on the bond strength of self-etching (SE) adhesives containing 10-MDP or other acidic functional monomers, comparing the bonding performance of both compositions.

METHODS

This study is registered in PROSPERO (CRD42020175715) and it followed the PRISMA Statement. The literature search was performed in PubMed, Web of Science, SciELO, Scopus, LILACS, IBECS, and BBO from the starting coverage date through 30 June 2021. Study eligibility criteria consisted of in vitro studies that evaluated the bond strength (microtensile, microshear, tensile or shear testing) to sound dentin/enamel of a minimum of two distinct SE systems, with at least one material containing 10-MDP and one other being comprised of a distinct acidic composition. Statistical analyses were carried out with RevMan 5.3.5 and using random-effects models with the significance level at p < 0.05. Also, Bayesian network meta-analysis (NMA) was conducted using MetaInsight V3 tool.

RESULTS

From 740 relevant studies evaluated in full-text analysis, 210 were incorporated to the systematic review and 206 in meta-analysis. The majority of studies was classified as having medium risk of bias (56.7%), followed by low (35.2%) and high (8.1%) risk of bias. Data from a total of 64 adhesive systems were collected, which favored the 10-MDP-based group at both dentin (overall effect: 6.98; 95% CI: 5.61, 8.36; p < 0.00001) and enamel (overall effect: 2.79; 95% CI: 1.62, 3.96; p < 0.00001) substrates. Microtensile testing was more frequently used (73.4%) in the included studies. Adhesives based on 10-MDP showed greater bonding performance than adhesives comprised of monomers such as PENTA, 6-MHP, 4-META, 4-MET, pyrophosphate esters, mixed composition or monomers derived from sulfonic acid (p ≤ 0.01); whereas similar bond strength values were verified between 10-MDP-based materials and those containing PEM-F, acrylamide phosphates, 4-AET, MAC-10, or monomers derived from polyacrylic and phosphonic acids (p ≥ 0.05). Adhesives based on GPDM were the only ones that resulted in greater bonding potential than the 10-MDP-based group (p = 0.03). Dental bonds in dentin were favored with the application of 2-step 10-MDP-based adhesives; whereas in enamel the dental bonds were favored for both 2-steps versions of adhesives, regardless of the presence of 10-MDP. Indirect evidence from NMA revealed that 1-step 10-MDP-free and universal 10-MDP-free adhesives seemed to perform worst in dentin and enamel, respectively.

SIGNIFICANCE

Adhesives containing 10-MDP showed higher bonding performance than materials formulated with other acidic ingredients, although this result relied on the type of mechanical testing, type of the substrate, acidic composition of the adhesive, and the application category of the SE system. This review summarized the effects of the foregoing factors on the adhesion to dental substrates.

Effect of Adhesive Application Method on the Enamel Bond Durability of a Two-Step Adhesive System Utilizing a Universal Adhesive-Derived Primer

This study aimed to evaluate the effect of the adhesive application method on the durability of the enamel bond and the thickness of the adhesive layer. A new-generation two-step universal adhesive system, G2-Bond Universal, and two conventional two-step adhesive systems were utilized. The shear bond strength to bovine enamel was measured after thermal cycling in both etch-and-rinse and self-etch modes. Fifteen specimens were divided into three groups as follows: Group I, wherein a strong air stream was applied over the bonding agent for 5 s; Group II, wherein a gentle air stream was applied over the bonding agent for 5 s; and Group III, which was prepared as in Group II, followed by the application of a second layer of the bonding agent and a gentle air stream for 5 s. The durability of the enamel bond and thickness of the tested adhesives were influenced by the application method in both etching modes. The application method used in Group II appeared to be most suitable in terms of the bonding of the adhesives to the enamel. The new-generation two-step self-etch adhesive, comprising a universal adhesive-derived primer and a hydrophobic bonding agent, showed superior bond performance to the conventional two-step adhesive systems.

Effect of different adhesive strategies and storage time on bond strength of bifunctional monomers to simulated endodontically-treated dentin

Adhesive strategies were evaluated on the bond strength of bi-functional monomers bonded to endodontically-treated-dentin (ETD). Superficial dentin was removed on human molars. Teeth were immersed in 5 mL 2.5% NaOCl, followed by immersion in 5 mL 17% EDTA. Dentin surface impregnated with epoxy resin-based sealer was then divided four groups (n=10): Scotchbond Multi-Purpose (SBMP); Single Bond Universal (SBU); Optibond All-in-One (OPB); and Tetric-N-Bond Universal (TBU). After 24-h or 1-year-of-storage specimens were submitted to microtensile bond strength (µTBS) and failure classification. A confocal laser scanning microscope (CLSM) evaluated the hybrid layer formation. Two-way ANOVA and Tukey-HSD test were performed (α=5%). The µTBS did not present statistical differences among adhesive strategies after 24-h. Significant differences were found after 1-year-of-storage. CLSM analysis showed water infiltration and consequently degradation of the hybrid layer after 1-year-of-storage. The use of SBU universal adhesive on the self-etching mode on ETD produced more stable bond over the 1-year-of-storage.

Update on Enamel Bonding Strategies

Optimal strategies for the application of an adhesive differ between enamel and dentin because of the differences in their composition. The development of adhesive systems has mainly focused on the bonding of dentin, rather than on the enamel, by etching with phosphoric acid (PA). Dental adhesive technologies continue to rapidly advance, and various adhesive systems have been developed since the study of Buonocore in 1955. He introduced the enamel acid-etch technique. Then, the etch-and-rinse (ER) system was developed, and subsequently, the self-etch (SE) system. Universal adhesives are a new generation of one-bottle SE adhesives that can be applied with either ER mode or SE mode, or a combined system involving selective enamel etching mode. Since the combination of PA etching and the SE system differs from conventional ER systems, the enamel bonding strategy should be carefully considered. This concise review of the literature on reliable enamel bonding strategies should prove helpful to clinicians to choose an appropriate adhesive system to achieve optimal clinical outcomes.