Dentin Etching Research Articles

Influence of drying and HEMA treatment on dentin wettability

Objectives: The aim of this study was to evaluate the effect of drying time and primer pre-application (35% HEMA in water) on water spreading/infiltration on dentin. Methods: Freshly extracted molars were embedded in resin and sectioned on their coronal side. Flat occlusal dentin surfaces were prepared using wet SiC paper from nos. 80–4000. A computerized contact angle device complementing a special software (Wingoutt R) was used to measure the contact angle (θ) kinetics of a reference liquid (pure H 2O) in the ten groups each of ten dentin surfaces during 120 s: Gp1: etched (37% phosphoric acid for 15 s) and blot-dried; Gp2: 3 s dried; Gp3: 5 s air-dried; Gp4: 10 s air-dried; Gp5: 20 s air-dried; Gp6: 30 s air-dried; Gp7: 1 min dried with hair dryer; Gp8: 5 s air-dried and HEMA treated; Gp9: 30 s air-dried followed by HEMA treatment; Gp10: HEMA treated prior to 30 s air-drying. three drops were applied on each sample. 40 contact angles were recorded for each drop with a frequency of one measure every 3 s. A one-way ANOVA test was used for data analysis. A PLSD test was conducted to identify statistical differences between pairs of groups at a reliability level of 95%. Results: At each measurement time, air-drying, whatever its duration, significantly decreased the wetting ability of the pure water on the etched dentin in comparison with the blot-dried group. The contact angle increases with drying time. No significant differences in water contact angle were obtained between 3, 5 and 10 s in spite of a slight decrease in the spreading/infiltration ability of water the longer the drying time. HEMA increases the spreading/infiltration ability of water on 5 or 30 s air-dried etched dentin surfaces; 30 s air-drying did not alter the spreading/infiltration ability of the water on etched and HEMA treated dentin. Significance: Dentin hydrophobicity increases depending on air-drying time. HEMA-based primer allows to prevent collagen collapse, which may be created by air-drying and partly rewet the collapsed collagen network.

Etching kinetics of a self-etching primer

Self-etching primers are thought to offer significant advantages over total-etch adhesive systems. The hypothesis tested in this study was that there was no difference in etching characteristics between a self-etching primer and a phosphoric acid solution at the same pH. Etching was assessed using atomic force microscopy (AFM) evaluation of site-specific changes in the height of the peritubular and intertubular dentin as a function of exposure time. Human dentin disks ( n=6/group), prepared with an acid-resistant glass reference layer, were etched with a self-etching primer and with 0.0134 m phosphoric acid (both pH≅1.94). Depth changes relative to the reference layer were measured with the AFM after each etching interval, at 15 different locations, each in the peritubular and intertubular dentin. The total demineralization depth was measured in a scanning electron microscope. Peritubular dentin etching rate was linear while it could be measured (up to 15 s) and was greater for the self-etching primer ( p<0.0001). Intertubular dentin displayed a similar demineralization pattern with both acids, ultimately reaching a plateau in the majority of specimens. The self-etching primer attained a plateau after less recession than phosphoric acid ( p<0.0001). Dentin demineralization appears to be affected by other factors in addition to the pH of the etchant solutions.

Mapping of tooth deformation caused by moisture change using moiré interferometry

Bonding of composite restorative materials to teeth usually involves surface etching and drying of both dentin and enamel. These two hard tissues have very different water contents. Objectives: The purpose of this study was to evaluate the effects of changes in humidity on the dimensional changes in dentin disks constrained by enamel and in unconstrained dentin. Methods: Changes in humidity were used to induce changes in the moisture level of the hard tissues, which created a mechanical load across the dentin–enamel junction (DEJ). High-sensitivity moiré interferometry was used to measure the magnitudes of the strains. Diffraction gratings (with a sensitivity of 2400 lines/mm) were transferred to moist polished sections of human teeth, which were subsequently dehydrated and then hydrated again. The fringe patterns from moiré interferometry recorded the change in deformation between the moisture states. Results: The results indicated that there were wide variations in strain between the two specimen geometries. The strains were fairly constant through the bulk of the dentin in both specimen types. However, the strain gradients were very high across the dentin–enamel interface into the dentin in the unconstrained geometry, and nearly zero in the constrained geometry. Significance: Moiré interferometry is a powerful tool to study the deformation of materials that are not isotropic and are not linearly elastic. It provides full-field, high-resolution deformation fields in tooth specimens. Deformations observed in this study indicate that the DEJ zone is a unique material interface that needs to be better understood in terms of normal tooth function, and that its material properties be taken into account when natural hard tissues are restored.

Effect of surface conditioning and restorative material on the shear bond strength and resin–dentin interface of a new one-bottle nanofilled adhesive

Objectives: To determine the effect of different combinations of surface conditioning (DeTrey Conditioner 36, NRC, no etching) and restorative materials (Dyract AP, Spectrum TPH) on the shear bond strength of Prime and Bond NT to enamel and dentin, and to characterize the resin–dentin interface produced by these combinations. Methods: Shear bond strength was tested on 30 enamel and 30 dentin flat labial surfaces of extracted bovine teeth. The enamel and dentin specimens were randomly assigned to six groups of five teeth each and treated using different combinations of surface conditioners and restorative materials with Prime and Bond NT. Scanning electron microscope (SEM) observation of argon-ion-etched specimens was done to evaluate the resin–dentin interface. Results: The type of surface conditioning and restorative material had significant effects on dentin bond strengths. Etching the dentin prior to application of Prime and Bond NT significantly increased bond strength and caused formation of a hybrid layer for Spectrum TPH. For Dyract AP, dentin etching generally did not improve bond strength despite the formation of a hybrid layer. On enamel, Prime and Bond NT had consistently high bond strengths on etched specimens. Significance: The results showed that Dyract AP and Spectrum TPH, when used with Prime and Bond NT have different bonding mechanisms and the effect of surface conditioning on their shear bond strength differs. Clinicians should be aware of these effects in order to optimize bonding.

Reversal of compromised bonding to oxidized etched dentin.

The mechanism responsible for hydrogen-peroxide- or sodium-hypochlorite-induced reductions in dentin bond strength is unknown. This in vitro study tested the hypothesis that these oxidizing agents were responsible by attempting to reverse the effect with sodium ascorbate, a reducing agent. Human dentin was treated with these oxidants before or after being acid-etched and with or without post-treatment with sodium ascorbate. They were bonded with either Single Bond or Excite. Hydrogen peroxide reduced the bond strengths of both adhesives, while sodium hypochlorite produced reduction in adhesion of only Single Bond (p < 0.05). Following treatment with sodium ascorbate, reductions in bond strength were reversed. Transmission and scanning electron microscopy showed partial removal of the demineralized collagen matrix only by sodium hypochlorite. The observed compromised bond strengths cannot be attributed to incomplete deproteinization and may be related to changes in the redox potential of the bonding substrates.

Technique sensitivity: biological factors contributing to clinical success with various restorative materials.

Since the 1950s, clinicians have relied on various formulations of Ca(OH)2 to stimulate dentin bridge formation. Various studies (Kozlov and Massler, 1966; Massler, 1967; Brännström, 1978; Cox et al., 1987; Snuggs et al., 1993) have demonstrated that pulp healing and dentin bridging can occur against a pH spectrum of materials. Recent studies (Akimoto et al., 1998; Cox et al., 1998, 1999; Tarim et al., 1998; Kitasako et al., 1999; Hafez et al., 2000) have reported successful pulp healing and dentin bridging using adhesives for direct capping of exposed pulps. However, others (Costa et al., 1997; Stanley and Pameijer, 1997; Pameijer, 1998; Hebling et al., 1999; Carvalho et al., 2000) have reported unsatisfactory results when exposures were direct-capped with adhesives. Biological and technical factors, or a combination of both, might be postulated to explain these differences. Recent studies have demonstrated that biological success is dependent upon proper hemorrhage control at the exposure site. This review explores the differences and common factors influencing successful dentin bridging, focusing on data derived from animal studies conducted according to ISO usage guidelines for cavity preparation and material placement. In the past, there has been concern that etching of vital dentin leads to immediate pulp death due to low pH. Recent studies have reported that acidic cements cause breakdown of only the smear layer and fail to seal the restoration interface, leading to inflammation and necrosis. A properly hybridized dentinadhesive interface provides a "bacteriometic" seal to both dentin and pulp tissues. Recent ISO usage studies have shown a high incidence of dentin bridging with adhesives following proper hemorrhage control and removal of both operative debris and biofilm at the dentin-pulp interface by agents such as NaOCl. These are important technique-sensitivity factors to be considered for pulp healing and dentin bridge formation.

Etching characteristics of dentin: effect of ferric chloride in citric acid.

Citric acid etchants with ferric chloride (10-3) promote adhesion and are effective etchants. We used atomic force microscopy (AFM) to determine the dentin etching characteristics of 10% citric acid etchant with various additions of ferric chloride. AFM was used to measure the surface recession and morphology of dentin etching for a variety of 10% citric + Fe-Cl etchants. Commercial 10-3 was used as the control. Dentin disks were prepared and partially masked during etching so that the unetched dentin served as a reference. AFM images of the same samples were taken at each of the seven experimental steps using 10% citric acid with various quantities of ferric chloride ranging from 0 to 3% (denoted 10-0, 10-1, 10-1.8 and 10-3, respectively) which altered the pH from 1.63 to 0.42. Changes in depth (nm) relative to the reference height for intertubular dentin were determined after etching 15 s; clinical air drying, rewet for 1-5 min; desiccation for 24 h; rehydration for 24 h. Differences of log(depth change) were tested with mixed effects cell mean models. Overall differences were significant (P < 0.001). Significant differences were found between etchants and the extent of collapse on drying was dependent on pH and Fe-Cl content. Following long-term rehydration, samples recovered, but those with 0 or 1% Fe-Cl did not recover as completely (P < 0.01). Etching and collapse depended on Fe-Cl content. The collapse was nearly reversed on rehydration. Ten per cent citric acid with ferric chloride did not prevent the collapse of etched dentin. Ferric chloride additions reduced pH and increased the collapse of dentin on drying for either brief or prolonged periods. Brief rewetting can reverse the effect of brief air drying. For fully desiccated samples the effect was not reversed after 30 s, but was largely or completely reversed at 24 h in solution depending on Fe-Cl content.

Effects of rotary instrumentation and different etchants on removal of smear layer on human dentin

Statement of problem. Various methods of rotary preparation and conditioning of teeth affect surface topography and may affect the retention of dental restorations.Purpose. This study microscopically evaluated dentin surfaces prepared by different rotary instruments and etched using several types of acid etchants that have been deemed suitable dentin conditioners.Material and methods. Occlusal surfaces of 35 extracted human molars were ground wet with 320-grit silicon carbide paper to the depth of the central groove and then prepared with diamond (n = 5) and finishing burs (n = 30). Five specimens from each group were used for SEM evaluation of mechanical preparation effects. Dentin specimens (n = 5) prepared with finishing burs were then etched with 1 of 5 etchants (25% polyacrylic acid, 10% phosphoric acid, 10% citric acid, 20% lactic acid, or 32% phosphoric acid) for 10 seconds. Specimens were critical-point dried and freeze fractured for SEM analysis.Results. Diamond rotary instruments created more undulating surfaces than finishing burs. Fine grooves were observed running perpendicular to undulations and parallel to the direction of instrument rotation. Specimens prepared with finishing burs exhibited a smooth surface interrupted by only a slight granularity. The amorphous smear layer was partially removed after the application of 25% polyacrylic acid (pH 1.53), but all dentinal tubules contained plugs. The number of dentin tubules containing plug material and the amount of material in the tubules decreased noticeably with 10% phosphoric acid (pH 0.86), and the dentin surface had an appearance similar to the specimen etched with 10% citric acid (pH 1.70). The surfaces treated with 20% lactic acid (pH 1.40) produced a clearly etched surface with minimal demineralization. Etching of dentin with 32% phosphoric acid (pH 0.16) revealed significant changes in dentin with the evidence of increased tubule diameter.Conclusion. Differences related to the method of instrumentation were found in the surface characteristics of dentin. The degree of smear layer removal was related to the pH of the acid etchant. (J Prosthet Dent 2001;85:67-72.)

Dimensional changes of demineralized dentin treated with HEMA primers

Objectives: The purpose of this study was to measure the dimensional changes of demineralized dentin before and after application of HEMA (2-hydroxyethyl methacrylate) by confocal laser scanning microscopy (CLSM). Methods: The middle portion of bovine dentin was ground, polished, and covered with a vinyl tape with a 4-mm hole punched through it. A strip of polysiloxane impression material was then placed across the center of the dentin surface to preserve a strip of the original unetched surface. Dentin surfaces were etched with 32% phosphoric acid for 60 s and rinsed with water. The impression material was then removed and the following sequential steps were performed: the dentin surface was mildly air-dried, then strongly air-dried, then treated with either 35 wt.% HEMA/water or 100 wt.% HEMA and mildly air-dried, and then strongly dried again. The shrinkage of the demineralized dentin surface from the original unetched level was measured by CLSM in each step and results analyzed by one-way ANOVA. Results: The dimensional changes of demineralized dentin after mild air drying were approximately −1 μm and, following strong air drying, resulted in −5 μm shrinkage. Following the application of 35 wt.% HEMA/water, the height of the demineralized dentin changed to a level of −3.3 μm, but then shrank to −4.8 μm after strong drying. ANOVA indicated that re-expansion of the shrunken etched dentin was significant ( p<0.05); however, the treated surface collapsed when it was strongly dried again ( p<0.05). 100% HEMA did not re-expand the shrunken demineralized dentin under any of the application on protocols ( p>0.05). Significance: Thirty-five wt.% HEMA in water re-expanded the collapsed demineralized dentin matrix, however not to the original level. One hundred wt.% HEMA did not cause any re-expansion.

Dentin etch chemistry investigated by Raman and infrared spectroscopy

Dentin etch chemistry investigated by Raman and infrared spectroscopy

Citric acid etching of cervical sclerotic dentin lesions: an AFM study.

Atomic force microscopy (AFM) has been used to determine microstructural changes, etching rates of peritubular dentin, and intertubular dentin recession during demineralization in dilute acidic solutions. These studies have not included many forms of altered dentin, including noncarious sclerotic root dentin associated with Cl V (abfraction) lesions. We sought to determine microstructural changes and recession rates during demineralization in citric acid (pH 2.5, 0.018M) for the transparent/sclerotic zone. Highly polished dentin disks were prepared from teeth with noncarious C1 V lesions (n = 3) and compared with normal root dentin (n = 3). Samples were etched at 5-s intervals for 1 min and at longer intervals up to 30 min. The depth changes in various portions of the dentin with respect to the reference layer were measured and changes in microstructure observed in solution in the wet cell of the AFM. In sclerotic dentin, most tubule lumens were occluded with crystalline deposits that etched more slowly than the other dentin components, but etching rates could not be determined due to their irregular geometry. The intertubular dentin recession quickly reached a plateau after a depth change of <1 microm for all dentin types, in agreement with prior work. Mixed linear regression models indicated an important difference between the etching of sclerotic intertubular dentin and that of non-sclerotic root dentin that became apparent after 600 s (p = 0.037). The sclerotic intertubular dentin underwent less depth change at the plateau (558 nm) compared to normal root dentin (744 nm). In addition, normal root dentin underwent significantly greater recession than coronal dentin (p = 0.002). The results of this study indicate that intertubular sclerotic dentin from Cl V lesions etches differently than normal root dentin, and this may help explain the difficulties in restoring such lesions with current bonding procedures.

Morphological alterations associated with the cytotoxic and cytostatic effects of citric acid on cultured human dental pulp cells

Citric acid exerts potential harmful effects on the pulp when used for root surface demineralization, smear layer removal, and dentin etching. Using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay, we found that incubation of cultured human dental pulp cells in medium containing 0.5% (pH 4.74) or 1.0% (pH 3.42) of citric acid for 2 h lead to 25% and 48% of cell death, respectively. Cytotoxicity of citric acid was associated with its acidity. Exposure of cells to pure 1% citric acid (pH 2.26) for 60 s lead to immediate cell death. Cytotoxicity was usually preceded by cell retraction, cell surface blebbing, and finally uptake of trypan blue, implicating the presence of cell membrane damage. A medium containing 0.05% citric acid can retard the growth of pulp cells. These results indicate that adequate protection of the pulp is important, especially when the remaining dentin is thin in deep carious lesions or in the presence of accessory canals on the root surface.

Design, formulation, and evaluation of isocyanatoacrylate copolymer dental adhesives.

Experiments have recently been completed to explore the development of isocyanatoacrylate copolymers as new dental adhesives. A main goal of this work was to test the utility of solubility parameter differences between the candidate adhesives and etched dentin as a predictor of relative bond strength. All candidate adhesive mixtures contained 2-isocyanatoethyl methacrylate (IEM), a selected amount of tri-n-butylborane oxide (TBBO) initiator, and one of 13 methacrylate comonomers. Reactivity ratios were computed for comonomer pairs as indicators of relative reactivity. The concentration of TBBO was optimized for each comonomer mixture to obtain working times of 2-6 min and setting times of 6-10 min. The solubility parameter difference Deltadelta (J/cm(3))(1/2) was calculated for each test mixture with respect to an etched dentin substrate, as an approximation of wetting ability. Using standard techniques for shear bond strength evaluation, mean shear bond strength values ranging between 7-15.5 MPa were obtained for comonomer adhesives in bonding Z-100 composite to treated dentin. Shear bond strength values showed a good correlation (r = -0.612, P </= 0.05) with solubility parameter differences. This study illustrates the usefulness of reactivity ratios and solubility parameters in the design and development of effective dentin bonding agents.

Dentin demineralization: Effects of dentin depth, pH and different acids

Objectives This investigation sought to determine: 1) if dentin demineralization rates are proportional to acid concentration for demineralization in phosphoric acid (10% or 1.76M, 0.025M, 0.0001 M, with pH=0.95, 2.0, 4.0 respectively); 2) if the etching characteristics are independent of dentin depth; and 3) if the etching characteristics for phosphoric acid were comparable to those for citric acid over a similar pH range. Methods Highly polished dentin disks from freshly extracted, non-carious, third molars were prepared with a reference layer. Samples were prepared from either superficial or deep coronal dentin. The samples were etched for periods of up to 30 min using phosphoric acid solutions (pH = 0.95, 2.0, 4.0) in a wet cell of an atomic force microscope (AFM). Depth changes with respect to the reference layer were determined for the intertubular and peritubular dentin to quantify structural changes. The results were compared with similar studies using citric acid (pH = 1.0, 2.15 or 3.4). Etching characteristics were statistically compared using 2-way repeated measures ANOVA at p < 0.05 and the Tukey's multiple comparison test. Results The relation between time and recession for peritubular dentin was initially linear. The intertubular dentin recession started rapidly but then reached a plateau within a very short interval for etching solutions at pH = 2.0 and 4.0. At the highest concentration, the recession decreased with time, but a clear plateau was not established. There was no statistical difference between peritubular etching rates of superficial and deep dentin surfaces with phosphoric acid at any concentration. There was also no difference in the intertubular dentin recession at the location of the plateau that depended on dentin depth. Etching rates increased dramatically with decreased pH for both phosphoric and citric acids, but were higher for citric acid than for phosphoric acid. Significance The AFM allowed quantification of changes during etching of wet dentin. Peritubular dentin etching rates increased with decreasing pH, as expected, but changes were not linear and were different for the two acids studied over a similar pH range. Intertubular dentin surface recession was small and plateaued for low concentrations. The peritubular etching rate and intertubular dentin recession did not depend on dentin depth.

Interaction of citric acid with hydroxyapatite: surface exchange of ions and precipitation of calcium citrate.

The use of citric acid is efficacious and distinctive in the demineralization of dentinal root surfaces for periodontal regeneration and in the etching and conditioning of enamel or dentin for bonding restorative resins. To decipher the role of citric acid in these applications, it is important that one have a basic understanding of its interaction with synthetic hydroxyapatite. The uptake or removal of citrate ions from aqueous solutions of citric acid (4 to 100 mmol/L, 10 mL) by hydroxyapatite (1 g) was studied at 22 degrees C after a given reaction period (from 3 hr to 11 days) by immediate spectrophotometric monitoring of the concentrations of the filtrates (214 nm). The concentrations of calcium, phosphate, and hydrogen ions were also determined in the same solutions. The interaction: (i) is a time-independent ionic-exchange process with the substrate when the initial acid concentrations are dilute (4 to 12.5 mmol/L), and (ii) is a reactive process that is time-dependent for higher acid concentrations. The exchange process shows an adsorption of about one citrate ion per (100) face of the unit cell of hydroxyapatite for a maximally exchanged surface. The curves representing the reactive process may be quantitatively or qualitatively explained on the basis of the supersaturation of the solutions with respect to calcium citrate and its slow precipitation. The physico-chemical analysis of the needle-shaped birefringent crystals of the precipitate from the supersaturated solutions confirms the precipitate to be Ca3(citrate)2.4H2O.

SEM Evaluation of the Resin-Dentin Interface with Proprietary Bonding Agents in Human Subjects

Laboratory studies on dentin bonding do not replicate physiological reality. This study examined with SEM the attachment produced in vivo under clinical conditions. Forty-four cavities were prepared in buccal/lingual surfaces of 16 premolar teeth scheduled for extraction and assigned randomly for treatment with: All-Bond 2 (Bisco) (A) with and (B) without dentin etch, (C) Scotchbond 2 (3M), (D) Scotchbond Multi-Purpose (3M), and (E) controls, using Enamel Bond (Kulzer) with dentin etch. After atraumatic extraction, restorations were split transversely by freeze-fracture and acid-treated. SEM examination of A revealed significant areas of gap-free attachment, with evidence of an acid-resistant hybrid layer (5-8 microns), often with resin tags of various lengths. Resin-reinforced collagen fibers were seen. Gap formation was coincident with lack of bonding resin layer over primed dentin. Attachment with B was less effective; a hybrid layer was infrequently seen and few resin tags. Pooled bonding resin at internal line angles appeared to favor an effective bond. Treatment C resulted in large areas of detachment, leaving an adherent primed dentin layer with short resin tags. Treatment D revealed significant areas of gap-free attachment and evidence of a hybrid layer. Controls (E) showed total bond failure. Attachment with A and D was secure, restorations remaining in situ even after freeze-fracture. This study confirmed that brief acid pre-treatment of dentin, allowing diffusion of resin-dentin primers, appeared conductive to development of an effective bond in vivo, similar to that reported in vitro.

Improving Bond Strength Through Acid Etching of Dentin and Bonding to Wet Dentin Surfaces

A bonding system using moisture on the tooth surface can be an enormous benefit as obtaining dentin dryness in the mouth is nearly impossible. The author describes a system that bonds to both wet and dry surfaces.

Total Etch—The Rational Dentin Bonding Protocol

Phosphoric acid etching of dentin is critically reexamined in view of current adhesive resin development. Research and clinical experience both suggest that "total etch," the simultaneous etching of dentin and enamel, is a rational protocol with many modern adhesive resins.

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The penetration by bacteria through dentinal tubules was studied using a device that included portion of bovine anterior teeth. Strains of 4 genera, Streptococcus mutans, Lactobacillus casei, Staphylococcus aureus and Escherichia coli, were used for the experiment, and the effects of acid etching of dentin on the penetration of bacteria through the dentin was examined. The time required for penetration through dentinal tubules of acid-etched samples was shorter than that of unetched samples. The minimum time required for half the samples to become positive for bacterial penetration through dentin MPT50 was 4 hours for all strains chosen when the acid-etched dentin was the target. In non-acid etched samples, the MPT50 varied among the genera and ranged from 20 hours to 48 hours; the speed of penetration was Sta. aureus = L. casei greater than Str. mutans greater than E. coli. Observation under the scanning electron microscope indicated that the smeared layer was completely coated on the surface of the prepared cavity, and when bacterial penetration occurred, a portion of the smear layer on the dentin disappeared. In longitudinal sections, the penetration by the bacteria into the tubules was visible. From these results, it is suggested that the smeared layer have an important effects on bacterial penetration through these tubules.

A Scanning Electron Microscopic Investigation of Bonding of Methacryloyloxyalkyl Hydrogen Maleate to Etched Dentin

Three types of methacryloyloxyalkyl hydrogen maleates--2-(methacryloyloxy)ethyl hydrogen maleate (2MEM), 1-(methacryloyloxy-methyl)ethyl hydrogen maleate (MMEM), and 1-(methacryloyloxymethyl)propyl hydrogen maleate (MMPM)--were prepared for use as bonding agents. The relationships between the thickness of an acid-proof dentin layer and the bond strength and chemical structure of the synthesized monomers were investigated. The bond strengths of 2MEM/composite system to dentin treated with either 37% phosphoric acid solution or 10% citric acid-3% ferric chloride solution (10-3 solution) were superior to those of the others. The acid-proof dentin layer for all bonding agents containing the synthesized monomers at the resin-dentin interface was clearly visible in a scanning electron microscope, regardless of the types of dentin etching agents used. After treatment of the dentin with the phosphoric acid solution, the layers of 2MEM, MMEM, and MMPM were 5-6 micron, 3-4 micron, and 2-3 micron thick, respectively. When the dentin was treated with the 10-3 solution, the layer for each bonding agent was approximately 1 micron thick.