Mild Self-etch Adhesives Research Articles

Effect of Simulated Pulpal Pressure on Knoop Hardness of Two Self-etch Adhesives with Different Aggressiveness

Simulated pulpal pressure (PP) has been shown to affect the bond strength and nanoleakage of different adhesives at dentin interfaces but the effect of simulated PP on polymerization of adhesives has not been studied yet. Furthermore, it has been proposed that strong and mild self-etch adhesives have different polymerization behaviors. This study aimed to evaluate the effect of simulated PP on polymerization of two self-etch adhesives, Adper Prompt L-Pop (APLP) and Adper Easy Bond (AEB), by means of the Knoop hardness test. Sixty caries-free human molars were used to prepare deep dentin specimens with a mean remaining dentin thickness of 0.9 mm. The specimens were bonded in the absence or presence of PP. The specimens were assigned to four equal groups (n = 15) as follows: AEB/-PP, APLP/-PP, AEB/+PP, and APLP/+PP. Bonding procedures were completed; then the specimens' hardness was measured with the Knoop test. Data were analyzed with two-way ANOVA and the t test. In the absence of PP, the hardness of AEB was significantly higher than that of APLP (p < 0.001). In contrast, when PP was simulated, the hardness of APLP was higher than that of AEB (p = 0.002). The hardness of AEB was not influenced by the presence of PP (p = 0.153). Simulation of PP resulted in a significant improvement in the hardness of APLP (p < 0.001). The polymerization degree of strong self-etch adhesive was lower compared to mild self-etch adhesive. In the presence of hydrostatic PP, the polymerization degree of strong self-etch adhesive was higher than mild self-etch adhesive. Dentin moisture caused by positive PP might improve polymerization of strong self-etch adhesives.

Effect of a novel prime-and-rinse approach on short- and long-term dentin bond strength of self-etch adhesives.

This study investigated the effects of the prime-and-rinse approach, using a 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing primer, on the short- and long-term dentin microtensile bond strengths (MTBSs) of mild self-etch adhesives. Half of sixty human midcoronal dentin surfaces were polished as control (self-etch approach), and the other half were polished and further treated with a 15% MDP-containing primer and thoroughly sprayed with water as prime-and-rinse approach. The dentin surfaces were treated with a self-etch adhesive, and a composite resin was placed on the surfaces. The following materials were used: Clearfil S3 Bond+Clearfil Majesty; G-Bond+Gradia Direct; Adper Easy One+Z250; and i Bond+Charisma. The MTBS was examined after 24h and 14months in water storage. The resin-dentin interfaces were analysed using scanning electron microscopy/transmission electron microscopy. Pretreated dentin surfaces were further analysed using scanning electron microscopy and micro-Raman spectroscopy. Compared with the self-etch approach, the prime-and-rinse approach significantly increased the dentin MTBS, regardless of the duration of storage. The scanning electron microscopy/transmission electron microscopy findings revealed that the prime-and-rinse approach removed most of the dentin smear layer. The Raman spectra of the MDP-treated dentin reveal the characteristic spectra of collagen, hydroxyapatite, and the monomer. Therefore, the prime-and-rinse approach using MDP-containing primers prior to the application of mild self-etch adhesives significantly increases the short- and long-term MTBS of dentin.

Prime-and-rinse approach for improving the enamel micro-tensile bond strengths of self-etch adhesives

The study investigated the effects of prime-and-rinse approach using 15% MDP (10-methacryloyloxydecyl dihydrogen phosphate)-containing primer on the enamel micro-tensile bond strengths (MTBS) of (ultra-) mild self-etch adhesives, enamel surfaces and enamel-resin interfaces. The buccal enamel surfaces of 69 human third molars were polished and randomly assigned to three groups: Group A (control, self-etch approach): Polished enamel surfaces were not further pre-treated. The enamel surfaces were acid-etched (Group B, (selective) enamel etching) or primed with 15% MDP-containing primer (Group C, prime-and-rinse approach) for 15 s and thoroughly water-sprayed. The enamel surfaces were applied with self-etch adhesives and placed with composite resins (Adper Easy One + Filtek Z350 (3 M ESPE); Clearfil S3 Bond + Clearfil Majesty (Kuraray-Noritake Co.); G Bond + Gradia Direct (GC); iBond + Charisma (Heraeus-Kulzer)), respectively. The specimens were prepared for MTBS test and scanning/transmission electron microscopy observations. Compared with group A, groups B and C produced significantly higher enamel MTBS (p < .01), regardless of the adhesives used. Groups B and C possessed similar enamel MTBS (p > .05). The SEM findings showed that smear layer remained on the polished enamel surface was completely removed by acid etching and almost completely removed by prime-and-rinse approach. The TEM microphotographs reveal that smear layer was detectable at the resin-enamel interface in group A, not in groups B and C. The novel prime-and-rinse approach using MDP-containing primer before the application of (ultra-) mild self-etch adhesives could greatly increase the enamel MTBS. That might be an alternative to selective enamel etching.

Influence of nano-hydroxyapatite containing desensitizing toothpastes on the sealing ability of dentinal tubules and bonding performance of self-etch adhesives

ObjectivesTo evaluate the dentinal tubular occlusion of nano-hydroxyapatite (nHAp) containing desensitizing toothpastes and their influence on the resin-dentin bonding performance of two mild self-etch adhesives. Materials and methodsMid-coronal dentin specimens were prepared from obtained intact human third molars. They were immersed in 1% citric acid for 20 s to expose the dentinal tubules to simulate sensitive teeth and then randomly divided into four groups. The control group received no desensitizing treatment. Experimental groups were treated with two commercial nHAp containing desensitizing toothpastes (Biorepair and Dontodent) and an experimental pure nHAp paste respectively. Each group was further divided into two subgroups and bonded with either G-Bond or Clearfil S3 Bond. The micro-tensile bond strength was tested and failure mode distribution was analyzed. Moreover, the effect of desensitizers on dentinal tubular occlusion was observed by the field-emission scanning electron microscope (FESEM). Resin infiltration of the adhesives labeled by fluorescent Rhodamin B was evaluated under confocal laser scanning microscopy (CLSM). ResultsFESEM revealed that all the desensitizers noticeably occluded the dentinal tubules, and the extents were completer after application for 7 days. The majority of the occlusion still preserved even after acid challenge with cola or adhesive. CLSM demonstrated shorter resin tags were produced in the desensitized groups. When bonding with G-Bond, the pure nHAp group showed comparable bond strength to the control group, while Biorepair and Dontodent treatment decreased the bond strength. For groups bonded with Clearfil S3 Bond, all the desensitizers reduced the bond strengths compared to the control and no significant difference was found among the three groups. ConclusionNano-hydroxyapatite containing desensitizing toothpastes could occlude dentinal tubules effectively with a certain degree of acid resistance, which contributes to the relief of dentin hypersensitivity. While, the application of these nHAp desensitizers comprised the resin infiltration of G-Bond and Clearfil S3 Bond, resulting in decreased bond strengths of the resin-dentin bonding.

Effect of Scrubbing Technique with Mild Self-etching Adhesives on Dentin Bond Strengths and Nanoleakage Expression.

To evaluate the effect of a scrubbing technique with one-step self-etching adhesives on bond strengths and nanoleakage expression at the resin/dentin interface. Flat human dentin surfaces bonded with one of two mild self-etching adhesives, SE One (SE) or Scotchbond Universal (SU) applied either with scrubbing or without scrubbing technique, were prepared (n = 5). The microtensile bond strengths (μTBS), SE micrographs of morphological changes on treated dentin surfaces, and expression of nanoleakage along the bonded dentin interfaces as shown with TEM were evaluated. μTBS data were analyzed using two-way ANOVA and the post-hoc t-test at the significance level of 0.05. The scrubbing technique had a significant positive effect on the μTBS of SU (p < 0.05), while it produced no significant difference for SE (p > 0.05). Morphological evaluation of the treated dentin surfaces demonstrated that SU with scrubbing showed the highest etching ability, followed by scrubbing SE > nonscrubbing SE > nonscrubbing SU. In the nonscrubbing groups, nanoleakage formation using SU exhibited a reticular pattern throughout the hybridized complex, whereas with SE, water-tree nanoleakage was only found in the adhesive layer at dentinal tubule orifices. The scrubbing groups of both adhesives did not exhibit any nanoleakage expression. Using a scrubbing technique when applying mild self-etching adhesives could improve resin monomer infiltration into dentin, chase water on adhesive surfaces, and facilitate smear layer removal.

Effect of pretreatment with calcium‐containing desensitizer on the dentine bonding of mild self‐etch adhesives

Desensitizing agents are frequently applied to sensitive teeth and may affect subsequent resin bonding. The current study aimed to evaluate the bonding performance of two self-etch adhesives containing functional monomers to dentine pretreated with three new calcium-containing desensitizers. No desensitizer was applied in the control group. Groups 1, 2, and 3 were treated with an arginine-calcium carbonate-containing polishing paste, a casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-containing paste, and an experimental hydroxyapatite paste, respectively. G-Bond and Clearfil S(3) Bond were used for bonding after desensitizer treatments. The microtensile bond strength (μTBS) was tested (n = 20 beams per group) and failure mode distribution was analyzed. Scanning electron microscopy was used to observe the occlusion of dentinal tubules. The mean (±SD) μTBS values, expressed in MPa, of groups 1, 2, and 3 and the control group were, respectively, 30.81 (7.79), 44.41 (8.02), 31.49 (6.13), and 41.40 (8.67) for G-Bond and 39.63 (9.59), 32.55 (7.86), 37.50 (8.60), 27.90 (6.52) for S3 Bond. Most failures were recorded as adhesive failure (69.375%), instead of cohesive failure or mixed failure. The dentinal tubules were seldom plugged in group 2, but were mostly occluded in groups 1 and 3. Two-way anova indicated that desensitizer application in association with a compatible adhesive system should be used when endeavoring to control hypersensitivity without adverse interference in bonding.

Resistance to Degradation of Resin-Dentin Bonds Produced by One-Step Self-Etch Adhesives

The objective of this article is to evaluate the resistance to degradation of resin-dentin bonds formed with three one-step adhesives. Flat, mid-coronal dentin surfaces were bonded with the self-etching adhesives [Tokuyama Bond Force (TBF), One Up Bond F Plus (OUB), and G-Bond (GB)]. The bonded teeth were subjected to fatigue loading, chemical degradation, and stored in distilled water for four time periods (up to 12 months). Specimens were tested for microtensile bond strength and microleakage. Fractographic analysis was performed by scanning electron microscopy. Bonded interfaces were examined by light microscopy using Masson's trichrome staining. An atomic force microscope was employed to analyze phase separation and surface nanoroughness (Ra) at the polymers. Vickers microhardness and the degree of the conversion (DC) were also determined. ANOVA and multiple comparisons tests were performed. Bond strength significantly decreased after the chemical challenge, but not after load cycling. Aging decreased bond strength after 6 months in TBF and GB, in OUB after 12 months. An increase of the nonresin protected collagen zone occurred in all groups, after storing. TBF showed the highest roughness, microhardness, and DC values, and GB showed the lowest. Mild self-etch one-step adhesives (TBF/OUB) showed a higher degree of cure, lower hydrophilicity, and major resistance to degradation of resin-dentin bonds when compared to highly acidic self-etching adhesive (GB).

Apatite crystal protection against acid-attack beneath resin–dentin interface with four adhesives: TEM and crystallography evidence

ObjectivesInteraction between specific functional groups and apatite crystals may contribute to adhesion. The present study investigated effects of four adhesives with different compositions on protection of crystals beneath the hybrid layer against acid-attack using transmission electron microscopy (TEM) and selected area electron diffraction (SAED). MethodsHuman dentin was bonded with four adhesives; two with a carboxylic-based functional co-polymer (PAA): three-step etch-and-rinse Scotchbond Multi-Purpose (SMP, 3M ESPE) and one-step self-etch Adper Easy Bond (AEB, 3M ESPE), and two with a phosphate-based functional monomer (MDP): two-step etch-and-rinse Clearfil Photo Bond (CPB, Kuraray Medical) and two-step self-etch Clearfil SE Bond (CSE, Kuraray Medical). The specimens were the either left untreated (control) or subjected to acid–base challenge with demineralizing solution (pH 4.5) and 5% NaClO. All specimens were processed and observed by TEM. SAED was used to identify the presence or absence of apatite crystallites at the base or beneath hybrid layer before and after acid–base challenge. ResultsAn apatite-rich zone was observed beneath the partially demineralized hybrid layer of CSE. The zone was thinner in AEB, but a demineralization-susceptible area was found beneath it. The etch-and-rinse adhesives (SMP and CPB) demonstrated completely or predominantly demineralized hybrid layers, which were devoid of the acid-resistant apatite-rich zone. SignificanceTEM/SAED evidence disclosed that the preserved dentin apatite crystals beneath the thin hybrid layer of the mild self-etch adhesives were protected against acid. Diffusion of reactive components beyond the hybrid layer, and their chemical bonding potential with the remaining crystals created the acid–base resistant zone.

Mild self-etch adhesives

Mild self-etch adhesives

Nanolayering of phosphoric acid ester monomer on enamel and dentin

Following the “adhesion–decalcification” concept, specific functional monomers possess the capacity to primary chemically interact with hydroxyapatite (HAp). Such ionic bonding with synthetic HAp has been demonstrated for 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), manifest as self-assembled “nanolayering”. In continuation of that basic research this study aimed to explore whether nanolayering also occurs on enamel and dentin when a 10-MDP primer is applied following a common clinical application protocol. Therefore, the interaction of an experimental 10-MDP primer and a control, commercially available, 10-MDP-based primer (Clearfil SE Bond primer (C-SE), Kuraray) with enamel and dentin was characterized by X-ray diffraction (XRD), complemented with transmission electron microscopy interfacial ultrastructural data upon their reaction with enamel and dentin. In addition, XRD was used to study the effect of the concentration of 10-MDP on nanolayering on dentin. Finally, the stability of the nanolayers was determined by measuring the bond strength to enamel and dentin when a photoinitiator was added to the experimental primer or when interfacial polymerization depended solely on the photoinitiator supplied with the subsequently applied adhesive resin. XRD confirmed nanolayering on enamel and dentin, which was significantly greater on dentin than on enamel, and also when the surface was actively rubbed with the primer. Nanolayering was also proportional to the concentration of 10-MDP in the primer. Finally, the experimental primer needed the photoinitiator to obtain a tensile bond strength to dentin comparable with that of the control C-SE primer (which also contains a photoinitiator), but not when bonded to enamel. It is concluded that self-assembled nanolayering occurs on enamel and dentin, even when following a clinically used application protocol. The lower bonding effectiveness of mild self-etch adhesives to enamel should be ascribed in part to a lower chemical reactivity (nanolayering) with enamel HAp.

Effect of dentin location and long-term water storage on bonding effectiveness of dentin adhesives

Dentin is a variable substrate with properties that change considerable in a single surface. The purpose of this study was to evaluate the bonding effectiveness to these different dentin locations and evaluate these differences over time. After bonding procedures with five different adhesives, small micro-tensile bond strength (µTBS) beams were prepared and dichotomously divided in 'center' and 'periphery' dentin specimens. After 1 week, 3, 6 and 12 months of water storage the µTBS of specimens of each group was determined, enabling a paired study design. The bond strengths of both etch&rinse adhesives were insensitive to regional variability. For the two-step self-etch adhesives, a marked increase in bond strengths was observed with increasing amount of intertubular dentin. Regional variability did not affect the long-term bonding effectiveness for any of the adhesives tested. In conclusion, only for the mild self-etch adhesives, µTBS to 'periphery' dentin was higher than for the 'center' specimens.

Enamel-Smear Compromises Bonding by Mild Self-Etch Adhesives

In light of the increased popularity of less acidic, so-called ‘ultra-mild’ self-etch adhesives, adhesion to enamel is becoming more critical. It is hypothesized that this compromised enamel bonding should, to a certain extent, be attributed to interference of bur debris smeared across enamel during cavity preparation. High-resolution transmission electron microscopy revealed that the enamel smear layer differed not only in thickness, but also in crystal density and size, depending on the surface-preparation method used. Lab-demineralization of sections clearly disclosed that resin-infiltration of an ultra-mild self-etch adhesive progressed preferentially along micro-cracks that were abundantly present at and underneath the bur-cut enamel surface. The surface-preparation method significantly affected the nature of the smear layer and the interaction with the ultra-mild adhesive, being more uniform and dense for a lab-SiC-prepared surface vs. a clinically relevant bur-prepared surface.

Enzymatic degradation of adhesive–dentin interfaces produced by mild self‐etch adhesives

Endogenous matrix metalloproteinases (MMPs) released by adhesive procedures may degrade collagen in the hybrid layer and so compromise the bonding effectiveness of etch-and-rinse adhesives. In this study, endogenous enzymatic degradation was evaluated for several simplified self-etch adhesives. In addition, primers were modified by adding two MMP inhibitors: chlorhexidine, a commonly used disinfectant, but also a non-specific MMP inhibitor; and SB-3CT, a specific inhibitor of MMP-2 and MMP-9. Gelatin zymography of fresh human dentin powder was used to identify the enzymes released by the adhesives. Micro-tensile bond strength (μTBS) testing was used to assess the mechanical properties of resin-dentin interfaces over time. In none of the experimental groups treated with the mild self-etch adhesives was MMP-2 and/or MMP-9 identified. Also, no difference in the μTBS was measured for the inhibitor-modified and the control inhibitor-free adhesives after 6 months of water storage. It is concluded that in contrast to etch-and-rinse adhesives, the involvement of endogenous MMP-2 and MMP-9 in the bond-degradation process is minimal for mild self-etch adhesives.

Self-Etching Adhesives Increase Collagenolytic Activity in Radicular Dentin

Endogenous matrix metalloproteinases (MMPs) release from crown dentin and their activation results in degradation of hybrid layers created by dentin adhesives. This study tested the hypothesis that instrumented intraradicular dentin possesses latent collagenolytic activity that is activated by mild self-etching adhesives. Root dentin shavings were produced from 50 cleaned and shaped, saline-irrigated root canals using Gates Glidden drills and rinsed with sodium azide to prevent bacterial growth. Dried dentin powder aliquots were treated with two clinically-relevant MMP inhibitors, 2% chlorhexidine for 10 minutes and 17% EDTA for 1 minute. Additional dentin powder was mixed with Clearfil Liner Bond 2V or Clearfil Tri-S Bond for 1 minute followed by extracting the adhesives with acetone. Dentin powder was also treated with 2% chlorhexidine for 10 minutes before or after adhesive application. Collagenolytic activities of the nine groups were assayed with a fluorometer in 96-well plates, by recording the changes in fluorescence before and after addition of fluorescein-labeled type I collagen. Epoxy resin-embedded powders were examined with TEM for the extent of demineralization. Instrumented, mineralized intraradicular dentin possessed low but detectable collagenolytic activity that was inhibited by chlorhexidine (p < 0.001) and EDTA (p < 0.001). Both adhesives partially demineralized the dentin powder and activated latent MMPs, with 14- to 15-fold increases in collagenolytic activities (p < 0.001) that were significantly (p < 0.001) but incompletely inactivated after 10 min application of chlorhexidine. Mild self-etching adhesives activate latent MMPs without denaturing these enzymes, and may adversely affect the longevity of bonded root canal fillings and posts.

Hydrolytic Stability of Self-etch Adhesives Bonded to Dentin

Functional monomers chemically interact with hydroxyapatite that remains within submicron hybrid layers produced by mild self-etch adhesives. The functional monomer 10-MDP interacts most intensively with hydroxyapatite, and its calcium salt appeared most hydrolytically stable, as compared with 4-MET and phenyl-P. We investigated the hypothesis that additional chemical interaction of self-etch adhesives improves bond stability. The micro-tensile bond strength (muTBS) of the 10-MDP-based adhesive did not decrease significantly after 100,000 cycles, but did after 50,000 and 30,000 cycles, respectively, for the 4-MET-based and the phenyl-P-based adhesives. Likewise, the interfacial ultrastructure was unchanged after 100,000 thermocycles for the 10-MDP-based adhesive, while that of both the 4-MET- and phenyl-P-based adhesives contained voids and less-defined collagen. The findings of this study support the concept that long-term durability of adhesive-dentin bonds depends on the chemical bonding potential of the functional monomer.

A challenge to the conventional wisdom that simultaneous etching and resin infiltration always occurs in self-etch adhesives

This study provided morphological evidence that discrepancies between the depth of demineralisation and the depth of resin infiltration can occur in some mild self-etch adhesives. Sound dentine specimens derived from extracted human third molars were bonded with 5 one-step and 5 two-step self-etch adhesives. One millimeter thick slabs containing the resin–dentine interfaces were immersed in 50 wt% aqueous ammoniacal silver nitrate and processed for TEM examination. A zone of partially etched but uninfiltrated dentine was identified beneath the hybrid layers in the milder versions of both one-step and two-step self-etch adhesives. This zone was characterised by the occurrence of silver deposits along the interfibrillar spaces of mineralised collagen fibrils. The silver infiltrated interfibrillar spaces were clearly identified from the one-step self-etch adhesives Xeno III, iBond, Brush&Bond and the experimental adhesive, and were thinner and only occasionally observed in the two-step self-etch adhesives Clearfil SE Bond and Clearfil Protect Bond. The more aggressive one-step and two-step adhesives that exhibit more abrupt transitions from completely demineralised to mineralised dentin were devoid of these silver-infiltrated interfibrillar spaces beneath the hybrid layers. Incomplete resin infiltration observed in some self-etch adhesives may be caused by the reduced etching potential of the acidic monomers toward the base of hybrid layers, or the presence of acidic but non-polymerisable hydrolytic adhesive components, creating potential sites for the degradation of the bonded created by these self-etch adhesives.

A challenge to the conventional wisdom that simultaneous etching and resin infiltration always occurs in self-etch adhesives

This study provided morphological evidence that discrepancies between the depth of demineralisation and the depth of resin infiltration can occur in some mild self-etch adhesives. Sound dentine specimens derived from extracted human third molars were bonded with 5 one-step and 5 two-step self-etch adhesives. One millimeter thick slabs containing the resin–dentine interfaces were immersed in 50 wt% aqueous ammoniacal silver nitrate and processed for TEM examination. A zone of partially etched but uninfiltrated dentine was identified beneath the hybrid layers in the milder versions of both one-step and two-step self-etch adhesives. This zone was characterised by the occurrence of silver deposits along the interfibrillar spaces of mineralised collagen fibrils. The silver infiltrated interfibrillar spaces were clearly identified from the one-step self-etch adhesives Xeno III, iBond, Brush&Bond and the experimental adhesive, and were thinner and only occasionally observed in the two-step self-etch adhesives Clearfil SE Bond and Clearfil Protect Bond. The more aggressive one-step and two-step adhesives that exhibit more abrupt transitions from completely demineralised to mineralised dentin were devoid of these silver-infiltrated interfibrillar spaces beneath the hybrid layers. Incomplete resin infiltration observed in some self-etch adhesives may be caused by the reduced etching potential of the acidic monomers toward the base of hybrid layers, or the presence of acidic but non-polymerisable hydrolytic adhesive components, creating potential sites for the degradation of the bonded created by these self-etch adhesives.