Morphological and mechanical characterization of the acid-base resistant zone at the adhesive-dentin interface of intact and caries-affected dentin

Bioactivity of human dental pulp-derived stem cells with boron-controlled S-PRG filler eluate by anion exchange

Surface pre-reacted glass-ionomer (S-PRG) filler is a bioactive glass filler capable of releasing various ions. A culture medium to which was added an S-PRG filler eluate rich in boron was reported to enhance alkaline phosphatase (ALP) activity in human dental pulp-derived stem cells (hDPSC). To clarify the role of boron eluted from S-PRG fillers, the modified S-PRG filler eluate with different boron concentrations was prepared by using an anion exchange material. Therefore, elemental mapping analysis of anion exchange material, adsorption ratio, hDPSCs proliferation and ALP activity were evaluated. For statistical analysis, Kruskal-Wallis test was used, with statistical significance determined at p<0.05. ALP activity enhancement was not observed in hDPSC cultured in the medium that contained the S-PRG filler eluate from which boron had been removed. The result suggested the possibility that an S-PRG filler eluate with controlled boron release could be useful for the development of novel dental materials.

The Effect of a Deproteinizing Pretreatment on the Bonding Performance and Acid Resistance of a Two-step Self-etch Adhesive on Eroded Dentin

OBJECTIVES

This study evaluated how deproteinization using sodium hypochlorite (6% NaOCl) or hypochlorous acid (50 ppm HOCl) with or without the subsequent use of an arylsulfinate salt-containing agent (Clearfil DC Activator; DCA; Kuraray Noritake Dental) affects the micro-tensile bond strength (μTBS) and formation of an acid-base resistant zone (ABRZ) of a two-step self-etch adhesive on eroded dentin.

METHODS

Coronal dentin surfaces of sound human molars were exposed to 48 cycles of demineralization (1% citric acid; 5 minutes) and remineralization (buffer solution with pH=6.4; 3.5 hours). They were then assigned to experimental groups according to the pretreatment used: none (negative control), NaOCl, NaOCl+DCA, HOCl, and HOCl+DCA. Sound dentin surfaces with no pretreatment were used as a positive control. The dentin surfaces were bonded with Clearfil SE Bond 2 (Kuraray Noritake Dental), and μTBS was measured either after 24 hours or 20,000 thermal cycles (TC). The μTBS data were statistically analyzed using a mixed-model analysis of variance (ANOVA) and t-tests with Bonferroni correction. Failure mode was determined with scanning electron microscopy (SEM), which was also used for the observation of ABRZ.

RESULTS

Among experimental groups, there was no significant difference between the negative control, HOCl, and HOCl+DCA after 24 hours, but the HOCl-pretreated groups exhibited significantly higher μTBS than the negative control after TC (p<0.01). Pretreatment with NaOCl and NaOCl+DCA resulted in significantly higher μTBS (p<0.001), but the highest μTBS was measured on sound dentin (p<0.001). TC decreased μTBS significantly in all groups (p<0.001) except for sound dentin and NaOCl+DCA (p>0.05). Adhesive failures prevailed in eroded groups, whereas cohesive failures were predominant on sound dentin. ABRZ was recognized in all groups but marked morphological differences were observed.

CONCLUSIONS

The combined use of 6% NaOCl and the arylsulfinate salt-containing agent partially reversed the compromised bonding performance on eroded dentin, while the effect of 50 ppm HOCl was negligible.

Investigating a Commercial Functional Adhesive with 12-MDPB and Reactive Filler to Strengthen the Adhesive Interface in Eroded Dentin

To compare the adhesive interface of eroded dentin formed by a functional dental adhesive and a gold standard strategy, by testing microtensile bond strength (μTBS), hardness/elastic modulus. Permanent sound human molars were randomly allocated to four experimental groups, all subject to artificial erosion (0.05 M citric acid; 3× daily, 5 days). Groups included control Clearfil SE Bond 2 (CFSE), and experimental group Clearfil SE Protect (CFP), at two different time points-immediate (24 h) and long term (3 months–3 M). Samples were sectioned into microspecimens for μTBS (n = 8) and into 2-mm thick slabs for nanoindentation assays (n = 3). Groups CFSE_3M and CFP_3M were stored in artificial saliva. Statistical analysis included two-way ANOVA for μTBS data, while hardness/modulus results were analyzed using Kruskal–Wallis H Test (significance level of 5%; SPSS v.27.0). Although no significant differences were found between mean μTBS values, for different adhesives and time points (p > 0.05), a positive trend, with μTBS rising in the CFP_3M group, was observed. Regarding hardness, no significant differences were seen in the hybrid layer, considering the two variables (p > 0.05), while the reduced elastic modulus rose in CFP_3M when compared to 24 h. Thus, CFP shows similar mechanical and adhesive performance to CFSE in eroded dentin, although it may comprise promising long-term results. This is advantageous in eroded substrates due to their increased enzymatic activity and need for remineralization.

Fluoride-Releasing Self-Etch Adhesives Create Thick ABRZ at the Interface

A fluoride-releasing adhesive system is expected to promote mineralization of demineralized dentin/enamel around a composite restoration, thereby contributing to the longevity of the restoration. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) observations revealed the formation of an “acid–base resistant zone” (ABRZ) beneath the hybrid layer when dentin was treated with a self-etch adhesive system. A thicker ABRZ was formed from the upper slope to the end of the outer lesion, indicating greater resistance against an acid-base challenge, when a fluoride-releasing self-etch adhesive system was used. The slope formation of a fluoride-releasing adhesive is believed to be due to fluoride-release from the adhesive. Quantitative assessment of the acid resistance was performed at the interface using the region of interest (ROI) mode of a digital image analysis software package. The area of the ABRZ is influenced by the concentration of fluoride release from the adhesive resin. The threshold of fluoride concentration in the adhesive may exist to influence the morphology of the ABRZ. X-ray absorption fine structure (XAFS) analysis of the dentin treated with different concentrations of NaF-mouth rinses suggested that different fluoride concentrations result in the formation of different chemical compounds, such as fluorapatite and CaF₂-like structures, on the dentin surface. This may explain the differences in μTBS values and morphological appearance of the ABRZ. NaF is effective in enhancing the enamel/dentin bond durability and also helps create a high quality of ARBZ to improve the clinical success of restorations.

Effect of repair systems on dentin bonding performance

The purpose of this study was to investigate the influence of phosphoric acid etching, metal primer or silane coupling agent application on dentin bonding performance of a 2-step self-etch adhesive system. Human dentin surfaces were prepared and divided into four groups depending on the pre-treatment method: no pretreatment (Clearfil SE Bond 2, CONTROL); 40% phosphoric acid (K-Etchant GEL, K); metal primer (Alloy Primer, AP); or silane coupling agent (Porcelain Bond Activator, PB). The specimens were sectioned into beams, separated into 2 subgroups (n=20): no thermocyling or thermocycled (TC), and subjected to a µTBS test and an acid-base challenge for SEM observation. Statistically lower results were observed between K and AP groups, PB and CONTROL, and PB with/without TC (p<0.05). SEM images at the dentin-adhesive interface revealed that all groups produced an acid-base resistant zone (ABRZ), with a funnel-shaped erosion under the ABRZ for the K group.

Clinical efficacy of universal adhesives for the restoration of noncarious cervical lesions: A randomized clinical trial

Introduction

The efficacy of an adhesive agent is an important aspect in restoring noncarious cervical lesion (NCCL) as studies have proved that compromise in adhesive agent results in reduced bond strength. The purpose of this prospective randomized double-blind clinical trial was to evaluate the efficacy of the newly formulated "universal" dental adhesive in the restoration of NCCLs in permanent dentition using either a self-etch or a selective-etch approach.

Materials and Methods

The study was done following the consolidated standards of reporting trials. 100 NCCLs randomly divided into 2 groups were restored using G-Premio Bond adhesive and Genial flowable composite in selective etch mode and self-etch mode. Restorations were evaluated at 1 week, 6 months, and 12 months using modified US Public Health Service criteria for marginal staining, fracture, and postoperative sensitivity. Statistical analysis was performed using appropriate tests.

Results

Recall rates were 100%, 98%, and 78% at the evaluation time. The result showed that neither the self-etch nor the selective etch mode had significant difference in ALPHA/BRAVO/CHARLIE scores (P > 0.05). Percentage-wise comparison showed less changes reported in the selective etch group compared to self-etch group.

Conclusion

It was concluded that there was no statistical significance between the groups for the parameters evaluated, but selective etch performed better than self-etch group.

Effect of two bleaching regimens on enamel bonding performance

This study evaluated the post-bleaching bonding performance of a one-step and two-step self-etch adhesive (SEA) to bleached enamel using in-office or at-home bleaching. Bovine enamel surfaces were treated with an in-office or at-home bleaching agent and divided into four post-bleach time periods: immediate, one day (1d), one week (1w) and one month (1m) before application of SEA systems. Enamel was bonded using the following procedures: Group 1: one-step SEA application (BeautiBond Multi, BBM), Group 2: two-step SEA application (FL-Bond II, FLBII). Microshear bond strengths (µSBS) were measured 24-h after bonding for each of the post-bleaching time periods. Acid-base resistant zones (ABRZs) were observed under SEM. Data were analyzed using three-way ANOVA. Bleaching caused a significant decrease of the immediate µSBSs for both adhesives (p≤0.005) then increased. Thick ABRZs were observed in BBM and FLBII after bleaching. Enamel µSBSs were adversely affected by bleaching. Thick ABRZ was created with bleaching.

Current perspectives on dental adhesion: (2) Concepts for operatively managing carious lesions extending into dentine using bioactive and adhesive direct restorative materials

This article reviews the current concepts for operatively managing carious lesions extending into dentine with minimal removal of tooth structure and restoring with dentine adhesives and direct composite resin. It looks sequentially at the operative steps involved including remineralisation with bioactive cements, bonding to caries-affected dentine including smear-layer modification using HOCl, creation of an acid-base resistance zone,steps to optimise the performance of all-in-one adhesives, and incremental placement of direct composite resin to improve bond strengths to cavity floor dentine. It explores how understanding the phenomenon of colour-shifting at the composite resin-enamel/dentine restoration borders can help in creating near "invisible" restoration margins through a "chameleon" effect. With the increased risks of transmission of Covid-19 when aerosol generating procedures are carried out in Dentistry, following a minimally invasive approach to managing dental caries should be given serious consideration.

The concept of super enamel formation -Relationship between chemical interaction and enamel acid-base resistant zone at the self-etch adhesive/enamel interface

Self-etch adhesive (SEA) systems simplify bonding procedures. It is believed that good mechanical retention and chemical bonding are both important factors to obtain reliable bonding to enamel. The enamel acid-base resistant zone (ABRZ) has been confirmed at the adhesive/enamel interface by scanning electron microscopic observation. However, the formation of enamel ABRZ is influenced by the type and components of adhesive systems. Chemical interactions by a functional monomer with hydroxyapatite strongly support the explanation of the mechanism for enamel ABRZ formation. The ABRZ created by MDP-containing SEA systems has shown good potential to resist acid attack from simulated recurrent caries models. In addition, fluoride release may enhance acid resistance. It has been proposed that such a reinforced enamel be termed "Super Enamel". The concept of the formation of super enamel may contribute to protecting enamel, and conserve tooth structure leading to improved restoration longevity.

Effect of fluoride mouthrinse and fluoride concentration on bonding of a one-step self-etch adhesive to bovine root dentin

This study investigated the effect of fluoride mouthrinses on bonding of a one-step self-etch adhesive to bovine root dentin. Application of a NaF solution (0, 450, 900, or 9,000 ppm) to bovine root dentin surfaces was performed for 30 s (immediate) or before bonding of an all-in-one adhesive. Microtensile bond strength (µTBS) testing and scanning electron microscopic (SEM) observation of the acid-base resistance zone (ABRZ) were performed. µTBS values and calculated ABRZ areas were analyzed by using two-way ANOVA and the t-test with Bonferroni correction. The significance level was set at P = 0.05 (n = 30). Fracture mode was analyzed with the Mann-Whitney U test with Bonferroni correction. The significance level set at P = 0.00178 (n = 30). µTBS did not significantly differ between the control, 450 ppm F, and 900 ppm F specimens (P > 0.05) but was significantly lower in 9,000 ppm F specimens (P < 0.05). SEM showed a significant increase in acid resistance at the adhesive-dentin interface, including the ABRZ, after fluoride application.

Influence of FCP-COMPLEX on bond strength and the adhesive-artificial caries-affected dentin interface

FCP-COMPLEX is a newly developed solution containing fluoride, calcium, and phosphoric acid that has the potential to reinforce caries-affected dentin. This study evaluated the effect of FCP-COMPLEX on micro-tensile bond strength (µTBS) and acid-challenge at the dentin-adhesive interface. FCP-COMPLEX, 2% NaF, and distilled water were applied to artificial caries-affected dentin (ACAD) and the effect on acid-induced damage after resin composite restoration was observed. Scanning electron microscopy and X-ray absorption fine structure (XAFS) were used to evaluate tooth morphology. The µTBS test revealed no effect of FCP-COMPLEX either immediately or after 3 months' storage. The area of acid damage in caries-affected dentin was reduced by FCP-COMPLEX. XAFS analysis revealed that absorbed fluorine on the surface would form CaF₂. In conclusion, FCP-COMPLEX significantly reduced the damage of acidic attack at the ACAD-adhesive interface, while the µTBS value was maintained after storage.

Effect of self-etch adhesives on the internal adaptation of composite restoration: a CP-OCT Study

Despite improvements in dental adhesive materials, internal adaptation remains a challenge in bonded restorations. The aim of this study was to compare microgaps and internal floor adaptation between two different self-etch adhesives in class-V cavities using cross-polarization optical coherence tomography (CP-OCT). In this in vitro study, standardized round class-V cavities were prepared in 20 non-carious human upper central incisor teeth. They were randomly divided into two groups, TN and SE, with each group receiving a different dental adhesive. In TN group, the adhesive used was all-in-one Tetric N-Bond Self-Etch (TN; Ivoclar/Vivadent, Liechtenstein), while SE group was bonded with two-step self-etch Clearfil SE Bond 2 adhesive (SE; Kuraray Noritake Dental Inc, Japan). The prepared cavities were restored with flowable composite and then stored in distilled water for 24 h. Next, they were immersed in silver nitrate, followed by immersion in a photo-developing solution. Optical comparison was carried out by CP-OCT to assess microgaps and composite adaptation at the cavity floor. A Mann-Whitney test was applied to the data, which showed a statistically significant difference in composite adaptation among the two groups (p < 0.001) with the SE group showing superior adaptation. CP-OCT is a reliable tool for non-invasive imaging that gives an insight into composite performance. Better adaptation was found with the two-step self-adhesive for the composite used in this study.

Effect of fluoride mouthrinse on adhesion to bovine root dentin

The purpose of this study was to evaluate the effect of fluoride mouthrinses on dentin bonding performance of a two-step selfetch adhesive; Clearfil SE Bond. Bovine root dentin surface was treated with either 450, 900, or 9,000 ppm F solutions for 30 s (immediate), and continually treated for one month (one month) before the bonding procedures. Microtensile bond strength (µTBS) test and scanning electron microscopic (SEM) observation of the acid-base resistance zone (ABRZ) were performed. Chemical state of fluorine on dentin surface was analyzed by X-ray absorption fine structure (XAFS). The 450 and 900 ppm F fluoride mouthrinses did not influence the µTBS to dentin, while the 9,000 ppm F fluoride solution adversely affected the µTBSs. The fluoride application to dentin significantly enhanced acid resistance at the adhesive/dentin interface including the ABRZ. The XAFS analysis indicated different concentrations of fluoride might create different chemical compounds on the dentin surface, influencing the µTBS results.

Microtensile Bond Strength of Resin-Modified Glass Ionomer Cement to Sound and Artificial Caries–Affected Root Dentin With Different Conditioning

In this laboratory study, the microtensile bond strengths (μTBS) of resin-modified glass ionomer cement (RM-GIC) to sound and artificial caries–affected bovine root dentin (ACAD) using three different conditioning agents were evaluated after 24 hours and three months. The fractured interface was examined with a scanning electron microscope (SEM). Specimens were created on bovine root dentin that was embedded in epoxy resin. For the ACAD specimens, artificial carious lesions were created. The RM-GIC (Fuji II LC) was applied either directly (no treatment), after application of self conditioner, cavity conditioner, or 17% ethylenediamine tetraacetic acid (EDTA) applied for 60 seconds, on sound dentin and ACAD, then light cured. They were stored in artificial saliva for 24 hours or three months. Following this, the specimens were cut into sticks for the μTBS test, and the failure mode of the debonded specimens was examined by using SEM. Pretest failures were excluded from the statistical analysis of the μTBS values because of their high incidence in some groups. Results showed that the μTBS values were significantly affected by the dentin substrate as well as the conditioning agent. Self conditioner provided the highest and most stable μTBS values, while cavity conditioner showed stable μTBS values on sound dentin. Both self conditioner and cavity conditioner had significantly higher μTBS values than the no treatment groups. EDTA conditioning reduced the μTBS after three months to sound dentin, while it showed 100% pretest failure with ACAD for both storage periods.

Morphological evaluation of artificial caries-affected dentin after applying FCP-COMPLEX

FCP-COMPLEX is a newly-developed solution that contains fluoride, calcium, and phosphoric acid. It has the potential to reinforce caries-affected dentin. The purpose of this study was to evaluate the effect of FCP-COMPLEX on the morphology of bovine artificial caries-affected dentin (ACAD). FCP-COMPLEX, 2% sodium fluoride solution, and distilled water were applied to bovine ACAD and the effect on acid-induced damage was observed. Scanning electron microscopy was used to evaluate morphology after acid application. Energy dispersive X-ray spectroscopy was used for mapping and quantitative analyses of the dentin surface, and for line analysis of dentin-adhesive interface. The FCP-COMPLEX precipitated on the dentin surface and fluoride, calcium, and phosphorus were detected at a higher level in the FCP-COMPLEX group. The area of acid damage in caries-affected dentin was reduced by FCP-COMPLEX. In conclusion, FCP-COMPLEX significantly increased the deposition of fluoride onto bovine ACAD and inhibited demineralization.

Comparing the effect of a desensitizing material and a self-etch adhesive on dentin sensitivity after periodontal surgery: a randomized clinical trial

Objectives

This double-blind randomized placebo-controlled clinical trial evaluated the ability of a desensitizing agent and a self-etch adhesive on cervical dentin sensitivity (CDS) after periodontal surgery.

Materials and Methods

Ninety hypersensitive teeth of 13 subjects were included in the study. After periodontal surgery, the teeth of each posterior sextant treated with one of the following materials: G1: Clearfil S³ Bond (Kuraray Dental), G2: Gluma Desensitizer (Heraeus Kulzer), and G3: placebo (water). The sensitivity was assessed using evaporative stimuli before treatment (baseline, T0), 1 day after treatment (T1), after 1 week (T2), and after 1 month (T3) according to visual analog scale (VAS).

Results

Following the treatment, all the 3 groups showed significant reduction of CDS in T1 compared to T0. Reduction of CDS between T1 and T2 was observed only in G1 but there was no significant difference between T2 and T3 in this group. Although we observed a significant difference in T3 compared to T1 and T2 in G2 and G3, comparison of treatment groups in each assessment time showed a significant difference only in T3. According to paired comparison, this was due to the difference between G2 and G3.

Conclusions

Dentin sensitivity following periodontal surgery will decrease spontaneously over time, but treating the sensitive teeth with Gluma Desensitizer and Clearfil S³ Bond can have some benefits.

Microleakage and Shear Bond Strength of Composite Restorations Under Cycling Conditions

OBJECTIVES

The aim of this study was to evaluate microleakage and shear bond strength of composite restorations under different cycling conditions.

METHODS AND MATERIALS

Class V cavities were prepared in the buccal and lingual surfaces of 30 human molars (n=60). A further 60 molars were used to prepare flat enamel and dentin specimens (n=60 each). Cavities and specimens were divided into six groups and pretreated with an adhesive (self-etch/Clearfil SE Bond or etch-and-rinse/Optibond FL). Composite was inserted in the cavities or adhered to the specimens' surfaces, respectively, and submitted to cycling (control: no cycling; thermal cycling: 10,000 cycles, 5°C to 55°C; thermal/erosive cycling: thermal cycling plus storage in hydrochloric acid pH 2.1, 5 minutes, 6×/day, 8 days). Microleakage was quantified by stereomicroscopy in enamel and dentin margins after immersion in silver nitrate. Specimens were submitted to shear bond strength testing. Statistical analysis was done by two-way analysis of variance and Kruskal-Wallis tests (p<0.05).

RESULTS

Microleakage in enamel margins was significantly lower in the control group compared with thermal cycling or thermal/erosive cycling. Erosive conditions increased microleakage compared with thermal cycling (significant only for Clearfil SE Bond). No significant differences were observed in dentin margins. Bond strength of enamel specimens was reduced by thermal cycling and thermal/erosive cycling when Clearfil SE Bond was used and only by thermal/erosive cycling when Optibond FL was used. No differences were observed among dentin specimens.

CONCLUSIONS

Thermal/erosive cycling can adversely affect microleakage and shear bond strength of composite resin bonded to enamel.

Dentin bonding performance and interface observation of an MMA-based restorative material

The purpose of this study was to evaluate bonding performance and dentin interface acid resistance using a 4-META/MMA-TBB based restorative material (BF) compared to a conventional 4-META/MMA-TBB resin cement (SB), and the effect of sodium fluoride (NaF) addition to the materials. Dentin surfaces were treated with 10% citric acid-3% ferric chloride (10-3) or 4-META containing self-etching primer (TP), followed by application of BF or SB polymer powders with or without NaF, to evaluate microtensile bond strength (µTBS) in six experimental groups; 10-3/SB, 10-3/BF, TP/SB, TP/BF, TP/SB/NaF and TP/BF/NaF. SEM observation of the resin-dentin interface was performed after acid-base challenge to evaluate interfacial dentin resistance to acid attack. TP/BF showed highest µTBS, while NaF polymers decreased µTBS. TP/BF showed funnel-shaped erosion at the interface, however, NaF polymers improved acid resistance of interface. In conclusion, BF demonstrated high µTBSs and low acid-resistance at the interface. NaF addition enhanced acid resistance but decreased µTBS.

Nanoleakage in Hybrid Layer and Acid-Base Resistant Zone at the Adhesive/Dentin Interface

The aim of interfacial nanoleakage evaluation is to gain a better understanding of degradation of the adhesive-dentin interface. The acid-base resistant zone (ABRZ) is recognized at the bonded interface under the hybrid layer (HL) in self-etch adhesive systems after an acid-base challenge. The purpose of this study was to evaluate nanoleakage in HL and ABRZ using three self-etch adhesives; Clearfil SE Bond (SEB), Clearfil SE One (SEO), and G-Bond Plus (GBP). One of the three adhesives was applied on the ground dentin surface and light cured. The specimens were longitudinally divided into two halves. One half remained as the control group. The others were immersed in ammoniacal silver nitrate solution, followed by photo developing solution under fluorescent light. Following this, the specimens were subjected to acid-base challenges with an artificial demineralization solution (pH4.5) and sodium hypochlorite, and prepared in accordance with common procedures for transmission electron microscopy (TEM) examination. The TEM images revealed silver depositions in HL and ABRZ due to nanoleakage in all the adhesives; however, the extent of nanoleakage was material dependent. Funnel-shaped erosion beneath the ABRZ was observed only in the all-in-one adhesive systems; SEO and GBP, but not in the two-step self-etch adhesive system; SEB.

Effect of chemomechanical caries removal on bonding of resin-modified glass ionomer cement adhesives to caries-affected dentine

BACKGROUND

This study evaluated the effect of: (1) chemomechanical caries removal (CMCR); (2) dentine surface treatments and (3) dentine substrates on adhesion of resin-modified glass ionomer cement (RMGIC) adhesives.

METHODS

One hundred and twenty permanent molars exhibiting moderate cavitation on the occlusal surface into dentine were used. Seventy-five carious molars were used for bond strength testing; the remaining 45 for micromorphological evaluation of the bonded interface. Caries was excavated with NaOCl-based CMCR (Carisolv), enzyme-based CMCR (Papacarie), or conventional rotary caries removal methods. Dentine surface treatment was performed using 37% phosphoric acid, 25-30% PAA or 20% PAA + 3% AlCl3 .

RESULTS

Three-way ANOVA revealed that all three factors 'caries removal methods', 'dentine surface treatments' and 'dentine substrates' did not significantly affect bond strength (p > 0.05). Scanning electron microscopy micrographs showed that the acid-base resistant layer was thicker in caries-affected dentine compared to sound dentine.

CONCLUSIONS

NaOCl- and enzyme-based CMCR methods have no adverse effect on adhesion of RMGIC adhesives to sound and caries-affected dentine. Dentine surface treatment with 37% phosphoric acid for 5 s has no negative effect on bonding of RMGIC adhesives to dentine compared with using polyacrylic acid for 10 s. RMGIC adhesives bonded well to both sound and caries-affected dentine.

Effect of fluoride concentration in adhesives on morphology of acid-base resistant zones

This study aimed to investigate the effect of fluoride concentration in adhesives on morphology of acid-base resistant zone (ABRZ). Seven experimental adhesives with different concentrations of NaF (0 wt%; F0 to 100 wt%: F100) were prepared based on the formulation of a commercially available adhesive (Clearfil Protect Bond, F100). The resin-dentin interface of the bonded specimen was subjected to demineralizing solution and NaOCl, sectioned, polished and argon-ion etched for SEM observation. Fluoride release from each adhesive was measured using an ion-selective electrode. Fluoride ion release from the adhesive linearly increased with higher NaF concentration. The ABRZ area increased significantly with higher NaF concentration except for F0, F10, and F20 (p<0.05). F100 showed the largest ABRZ, where a slope of acid-resistant dentin was clearly observed at the bottom of the ABRZ. The concentration of NaF in the two-step self-etching adhesive resin influenced the amount of dentin structure remaining after acid-challenge.

Effect of partially demineralized dentin beneath the hybrid layer on dentin-adhesive interface micromechanics

OBJECTIVE

To investigate the presence of non-infiltrated, partially demineralized dentin (PDD) beneath the hybrid layer for self-etch adhesive systems, and its effect on micromechanical behavior of dentin-adhesive interfaces (DAIs). This in-vitro laboratory and computer simulation study hypothesized that the presence of non-infiltrated PDD beneath the hybrid layer does not influence the mechanical behavior of the DAI of self-etch adhesive systems.

METHODS

Fifteen sound third molars were restored with composite resin using three adhesive systems: Scotchbond Multipurpose (SBMP), Clearfil SE Bond (CSEB) and Adper Promp L-Pop (APLP). The thickness and length of all DAIs were assessed using scanning electron microscopy, and used to generate three-dimensional finite element models. Elastic moduli of the hybrid layer, adhesive layer, intertubular dentin, peritubular dentin and resin tags were acquired using a nano-indenter. Finite element software was used to determine the maximum principal stress. Mixed models analysis of variance was used to verify statistical differences (P<0.05).

RESULTS

Elastic moduli and morphology were found to differ between the adhesive systems, as well as the presence and extension of PDD.

SIGNIFICANCE

Both self-etch adhesive systems (APLP and CSEB) had PDD. The DAI stress levels were higher for the one-step self-etch adhesive system (APLP) compared with the etch-and-rinse adhesive system (SBMP) and the self-etch primer system (CSEB).

Self-Etch Adhesive Systems: A Literature Review

This paper presents the state of the art of self-etch adhesive systems. Four topics are shown in this review and included: the historic of this category of bonding agents, bonding mechanism, characteristics/properties and the formation of acid-base resistant zone at enamel/dentin-adhesive interfaces. Also, advantages regarding etch-and-rinse systems and classifications of self-etch adhesive systems according to the number of steps and acidity are addressed. Finally, issues like the potential durability and clinical importance are discussed. Self-etch adhesive systems are promising materials because they are easy to use, bond chemically to tooth structure and maintain the dentin hydroxyapatite, which is important for the durability of the bonding.

Resistance of dentin coating materials against abrasion by toothbrush

Thin-film coating of root dentin surface by all-in-one adhesives has been shown to be an effective option to prevent root surface caries. The purpose of this study was to investigate the wear resistance against toothbrush abrasion of two all-in-one coating materials; Shield Force (SF) and Hybrid Coat (HC). Bovine dentin surfaces were covered with one of the coating materials; SF or HC. After storage in water for 24 h, the testing surface was subjected to the toothbrush abrasion test up to 50,000 cycles either in water or toothpaste slurry. The remaining thickness of the coating material was measured using SEM. Toothpaste slurry significantly increased rate of tooth brush abrasion of the coating materials. While SF and HC wore at a similar pace under toothbrush abrasion, SF had a thicker coat and could protect dentin longer, up to 50,000 cycles.

Phosphoric Acid-Etching Promotes Bond Strength and Formation of Acid-Base Resistant Zone on Enamel

This study examined the effect of phosphoric acid (PA) etching on the bond strength and acid-base resistant zone (ABRZ) formation of a two-step self-etching adhesive (SEA) system to enamel. An etch-and-rinse adhesive (EAR) system Single Bond (SB) and a two-step SEA system Clearfil SE Bond (SE) were used. Human teeth were randomly divided into four groups according to different adhesive treatments: 1) SB; 2) SE; 3) 35% PA etching→SE primer→SE adhesive (PA/SEp+a); (4) 35% PA etching→SE adhesive (PA/SEa). Microshear bond strength to enamel was measured and then statistically analyzed using one-way analysis of variance and the Tukey honestly significant difference test. The failure mode was recorded and analyzed by χ2 test. The etching pattern of the enamel surface was observed with scanning electron microscope (SEM). The bonded interface was exposed to a demineralizing solution (pH=4.5) for 4.5 hours and then 5% sodium hypochlorite with ultrasonication for 30 minutes. After argon-ion etching, the interfacial ultrastructure was observed using SEM. The microshear bond strength to enamel of the SE group was significantly lower (p&lt;0.05) than that of the three PA-etched groups, although the latter three were not significantly different from one another. The ABRZ was detected in all the groups. In morphological observation, the ABRZ in the three PA-etched groups were obviously thicker compared with the SE group with an irregular wave-shaped edge.

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

OBJECTIVES

Interaction 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).

METHODS

Human 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.

RESULTS

An 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.

SIGNIFICANCE

TEM/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.

Effect of functional monomers in all-in-one adhesive systems on formation of enamel/dentin acid-base resistant zone

This study aimed at evaluating the effect of functional monomers in all-in-one adhesive systems on formation of acid-base resistant zone (ABRZ) in enamel and dentin. Experimental adhesive systems containing one of three functional monomers; MDP, 3D-SR and 4-META were applied to enamel or dentin surface and light-cured. A universal resin composite was then placed. The specimens were subjected to a demineralizing solution (pH 4.5) and 5% NaClO for acid-base challenge and then observed by SEM. The ABRZ was clearly observed in both enamel and dentin interfaces. However, enamel ABRZ was thinner than dentin ABRZ in all adhesives. Morphology of the ABRZ was different between enamel and dentin, and also among the adhesives. Funnel-shaped erosion was observed only in the enamel specimen with the 4-META adhesive. The formation of enamel/dentin ABRZ was confirmed in all adhesives, but the morphology was influenced by the functional monomers.

Effect of thermal and mechanical loading on marginal adaptation and microtensile bond strength of a self-etching adhesive with caries-affected dentin

Aim:

This study evaluated the effect of thermal and mechanical loading on marginal adaptation and microtensile bond strength in total-etch versus self-etch adhesive systems in caries-affected dentin.

Materials and Methods:

Forty class II cavities were prepared on extracted proximally carious human mandibular first molars and were divided into two groups: Group I — self-etch adhesive system restorations and Group II — total-etch adhesive system restorations. Group I and II were further divided into sub-groups A (Without thermal and mechanical loading) and B (With thermal and mechanical loading of 5000 cycles, 5 ± 2°C to 55 ± 2°C, dwell time 30 seconds, and 150,000 cycles at 60N). The gingival margin of the proximal box was evaluated at 200X magnification for marginal adaptation in a low vacuum scanning electron microscope. The restorations were sectioned, perpendicular to the bonded surface, into 0.8 mm thick slabs. All the specimens were subjected to microtensile bond strength testing. The marginal adaptation was analyzed using descriptive studies, and the bond strength data was analyzed using the one-way analysis of variance (ANOVA) test.

Results and Conclusions:

The total-etch system performed better under thermomechanical loading.

Micro-tensile bond strength and interfacial characterization of an adhesive bonded to dentin prepared by contemporary caries-excavation techniques

OBJECTIVES

To evaluate the micro-tensile bond strength (μTBS) and interfacial characteristics of adhesive-dentin bonds produced after caries-removal with contemporary techniques.

METHODS

Carious molars were cut at the base of the fissure, exposing 'sound' and 'carious' dentin at different spots. After caries-excavation, a composite was bonded using a 2-step self-etch adhesive. The μTBS was measured and the mode of fracture analyzed using a stereomicroscope and imaged by Feg-SEM, while additional non-fractured specimens were histologically analyzed after Masson's trichrome staining in order to identify potentially incompletely resin-enveloped collagen.

RESULTS

μTBS to residual caries-excavated dentin was lower than to sound dentin. The different caries-removing techniques had a significant effect on the μTBS. Er:YAG laser guided by a LIF-feedback system (Kavo) resulted in the lowest μTBS (26.8% lower than to 'sound' dentin) and a distinct layer of incompletely resin-enveloped collagen at the interface. Although different degrees of collagen exposure were seen for other caries-removing techniques, such as a thick layer for CeraBur (Komet-Brasseler), some unprotected collagen areas for Cariex (Kavo), or completely resin-enveloped collagen for a tungsten-carbide-bur (Komet), the μTBS appeared not directly affected (10%, 16.6%, and 15.3% lower than to 'sound' dentin, respectively). Carisolv (MediTeam) resulted in the highest μTBS (only 1% reduction compared to that to 'sound' dentin), followed by the tungsten-carbide-bur aided by Caries Detector (Kuraray) (4.8% reduction). Enzymatic caries excavation using the experimental SFC-VIII (3M-ESPE) aided by a disposable plastic instrument resulted in a 19.4% reduction in μTBS as compared to that to 'sound' dentin.

SIGNIFICANCE

The dentin bonding receptiveness depends to a large extent on the caries-excavation method employed.

The role of functional monomers in bonding to enamel: acid-base resistant zone and bonding performance

OBJECTIVES

To investigate the effects of two functional monomers on caries-inhibition potential and bond strength of two-step self-etching adhesive systems to enamel.

METHODS

Clearfil SE Bond and similar experimental formulations different in the functional monomer were used. Four combinations of primer and bonding agents were evaluated: (1) Clearfil SE Bond which contains MDP in both primer and bonding (M-M); (2) Clearfil SE Bond primer and Phenyl-P in bonding (M-P); (3) Phenyl-P in primer and Clearfil SE Bond bonding (P-M); (4) Phenyl-P in primer and bonding (P-P). Ground buccal enamel surfaces of human sound premolars were treated with one of the systems and the bonded interface was exposed to an artificial demineralising solution (pH 4.5) for 4.5 h, and then 5% NaOCl with ultrasonication for 30 min. After argon-ion etching, the interfacial ultrastructure was observed using SEM. Micro-shear bond strength to enamel was measured for all groups and results were analysed using one-way ANOVA and Turkey's HSD, while failure modes were analysed by chi-square test.

RESULTS

An acid-base resistant zone (ABRZ) was found with all adhesive systems containing MDP either in primer or bond; however, ultramorphology and crystallite arrangement in the ABRZ were different among groups. P-P was the only group devoid of this protective zone. Micro-shear bond strength in M-M was significantly higher than those in M-P, P-M and P-P, while the latter three were not different from each other. Failure modes were significantly different (p<0.05).

CONCLUSIONS

Functional monomers in two-step self-etching systems influence both the bonding performance and the formation of ABRZ on enamel.