Monomer Penetration Research Articles

Enhancing dentin bonding quality through Acetone wet-bonding technique: a promising approach.

Objective: This paper aimed to assess the impact of the acetone wet-bonding (AWB) technique on dentin bonding and to investigate its potential underlying mechanisms. Materials and Methods: Caries-free third molars were sliced, ground, etched, water-rinsed. Then the specimens were randomly allocated to four groups according to the following pretreatments: 1. water wet-bonding (WWB); 2. ethanol wet-bonding (EWB); 3. 50% (v/v) acetone aqueous solution (50%AWB); 4. 100% acetone solution (AWB). Singlebond universal adhesive was then applied and composite buildups were constructed. The microtensile bond strength (MTBS), failure modes and interface nanoleakage were respectively evaluated after 24h of water storage, 10,000 times of thermocycling or 1-month collagenase ageing. In situ zymography and contact angle were also investigated. Results: Acetone pretreatment preserved MTBS after thermocycling or collagenase ageing (p < 0.05) without affecting the immediate MTBS (p > 0.05). Furthermore, AWB group manifested fewer nanoleakage than WWB group. More importantly, the contact angle of the dentin surfaces decreased significantly and collagenolytic activities within the hybrid layer were suppressed in AWB group. Conclusion: This study suggested that the AWB technique was effective in enhancing the dentin bond durability by increasing the wettability of dentin surface to dental adhesives, removing residual water in the hybrid layer, improving the penetration of adhesive monomer, and inhibiting the collagenolytic activities. Clinical significance: The lifespan of adhesive restorations would be increased by utilization of acetone wet-bonding technique.

Effectiveness of Phytic Acid as an Etchant in Dentistry: A Systematic Review

AbstractThe aim of this study was to assess the effect of phytic acid and to compare it with the phosphoric acid etching through a systematic review. systematic search was carried out using PubMed/MEDLINE, Cochrane library, Indmed, Scopus, and Liliacs databases conducted upto January 2022. In vitro studies comparing phytic acid and phosphoric acid as an etchant on tooth surfaces that performed bond strength, smear layer removal, collagen degradation and monomer penetration were included. The risk of bias was assessed considering Checklist for Reporting In-vitro Studies guidelines. Five studies were chosen for full-text assessment out of 830 that were potentially eligible. The studies found that phytic acid improved bond strength, collagen degradation, smear layer removal, and monomer penetration. Every study had a moderate-to-high risk of bias. Phytic acid enhanced the etch and rinse adhesive's binding strength to dentin, effectively eradicated the smear layer, protected dentin collagen from degradation, and had better resin infiltration and minimal effect on pulpal cells.

Degradation and Stabilization of Resin-Dentine Interfaces in Polymeric Dental Adhesives: An Updated Review

Instability of the dentine-resin interface is owed to the partial/incomplete penetration of the resin adhesives in the collagen fibrils. However, interfacial hydrolysis of the resin-matrix hybrid layer complex activates the collagenolytic and esterase enzymes that cause the degradation of the hybrid layer. Adequate hybridization is often prevented due to the water trapped between the interfibrillar spaces of the collagen network. Cyclic fatigue rupture and denaturation of the exposed collagen fibrils have been observed on repeated application of masticatory forces. To prevent interfacial microstructure, various approaches have been explored. Techniques that stabilize the resin–dentine bond have utilized endogenous proteases inhibitors, cross linking agents’ incorporation in the exposed collagen fibrils, an adhesive system free of water, and methods to increase the monomer penetration into the adhesives interface. Therefore, it is important to discover and analyze the causes of interfacial degradation and discover methods to stabilize the hybrid layer to execute new technique and materials. To achieve a predictable and durable adhesive resin, restoration is a solution to the many clinical problems arising due to microleakage, loss of integrity of the restoration, secondary caries, and postoperative sensitivity. To enhance the longevity of the resin-dentine bond strength, several experimental strategies have been carried out to improve the resistance to enzymatic degradation by inhibiting intrinsic collagenolytic activity. In addition, biomimetic remineralization research has advanced considerably to contemporary approaches of both intrafibrillar and extrafibrillar remineralization of dental hard tissues. Thus, in the presence of biomimetic analog complete remineralization of collagen, fibers are identified.

The influence of dimethyl sulfoxide on resin–dentin bonding: A systematic review

This article aims to systematically review published literature about the influence of dimethyl sulfoxide (DMSO) on resin–dentin bonding. Online databases (Medline (PubMed), Embase, Web of Science, and the Cochrane Library) were searched on this topic. Gray literature was searched using Google Scholar. Published works until December 2020 were collected, and pertinent articles were selected in accordance with the eligibility criteria. Quality assessment was conducted via the modified Consolidated Standards of Reporting Trials (CONSORT) checklist and the modified Cochrane risk of bias tool. Thirty-eight studies were identified, twelve of which satisfied the eligibility criteria were included in this review. Micro tensile bond strength (MTBS) was set as the main outcome. Secondary outcomes include nanoleakage evaluation, the effect of DMSO on dentin collagen fibrils, and protease inhibition. Several studies proved the promotion of DMSO on long-term dentin bond strength of etch-and-rinse adhesives. However, evidence about its effect on bond strength of self-etch adhesives was insufficient. Different concentrations of DMSO solution also cause diverse impact on dentin bonds. Based on the included studies, DMSO considerably affects resin–dentin bonds by dissociating demineralized dentin matrix, inhibiting matrix metalloproteinases (MMPs), and enhancing penetration of resin monomers. The influence of DMSO on dentin bonding may offer inspirations for dental clinical practice to optimize resin–dentin bonds. • DMSO is beneficial for improving the long-term dentin bond strength of etch-and-rinse adhesives. • The influence of DMSO on self-etch adhesives remains controversial and needs more validation. • DMSO can dissociate demineralized dentin matrix, inhibit matrix metalloproteinases, and enhance resin monomer penetration. • DMSO may enlighten the concept of “wet bonding” technique from surface moisture to bio-modification of dentin. • DMSO offers inspiration for dental clinical practice to optimize resin–dentin bonds.

Surfactant Penetration into Human Skin from Sodium Dodecyl Sulfate and Lauramidopropyl Betaine Mixtures.

Surfactant mixtures are used in a variety of personal care and cosmetic applications but are known to be harsh on the skin. The purpose of this study was to examine anionic surfactant penetration into human skin from nonideal surfactant mixtures under short-time exposure conditions that are relevant to realistic exposure scenarios. This was done by measuring the penetration of a radiolabeled probe (14C-SDS) into human cadaver skin in Franz diffusion cells in vitro from the mixtures of sodium dodecyl sulfate (SDS) and lauramidopropyl betaine (LAPB). Monomer and micelle concentrations in the SDS/LAPB/14C-SDS mixtures were predicted using a regular solution theory approximation. We confirmed that the mixtures of SDS and LAPB exhibit nonideal behavior with a net attraction between the two surfactants. Penetration of 14C-SDS into excised human skin from the mixtures of SDS and LAPB was found to decrease in a log-linear manner with increasing mole fraction of LAPB in the bulk solution (R2 = 0.97, p < 0.001). Additionally, the penetration of 14C-SDS into excised human skin from the mixtures of SDS and LAPB was found to correlate linearly and strongly with the predicted values of 14C-SDS monomer concentration in SDS/LAPB/14C-SDS mixtures (R2 = 0.95, p < 0.01). 14C-SDS penetration from the mixed surfactant composition could be quantitatively reconciled with that from an SDS-only composition by postulating a secondary, positive contribution from LAPB related to its own penetration and binding to skin components that increased SDS penetration at low concentrations. This research therefore supports a monomer penetration theory of surfactant penetration into the skin, combined with a measurable impact of favorable surfactant interactions within the tissue.

Parametric study of a yellow birch surface impregnation process

Wood is a renewable resource that has been used as a material in appearance products for years. Despite its acceptable mechanical resistance, different modification processes were developed to enhance wood’s hardness and make it an even more durable material. Impregnating wood pores with monomers under vacuum-pressure cycle is a common method for that purpose. However, most implemented processes are long and mostly submerge wood into a monomer formulation (Bethell’s full-cell process). For that, they can be considered wasteful on the quantity of materials used, energy consumed and on process duration. The objective of this paper was to evaluate the parameters that influence the penetration of monomers into the tangential surface of Yellow birch (Betula alleghaniensis Brit.) samples. The analyzed factors were the monomer formulation’s viscosity, the surface temperature, the vacuum level applied to the process, the anatomy of samples, and the absorption time. After impregnation, the weight gain of the samples was calculated. Monomer penetration depth was calculated and visualized using density profiles and micro X-ray tomography imaging. Results showed that using a low viscosity monomer formulation allied to a certain level of vacuum and absorption time can considerably increase the impregnation into the wood.

Chemical surface densification of hardwood through lateral monomer impregnation and in situ electron beam polymerization, Part I: density profile and surface hardness of three hardwood species

Filling wood cells with polymeric materials offers great opportunities to improve wood strength. Some applications, such as flooring, may require densification on one side of the material only. Yellow birch (Betula alleghaniensis Britt.), sugar maple (Acer saccharum Marsh.) and red oak (Quercus rubra L.) were surface densified through lateral chemical impregnation of monomers under vacuum followed by in situ electron beam polymerization. Lateral impregnation led to low mean chemical retention of 4% for sugar maple, 11% for red oak and 12% for yellow birch. X-ray densitometry and microtomography revealed an asymmetric density profile comparable to mechanically surface densified wood due to polymer-filled vessels. Scanning electron microscopy images showed presence of polymer-filled fibers beneath the surface. Brinell hardness of all species increased significantly compared to untreated wood. Low chemical retention significantly improved hardness due to localized polymer beneath the surface. Density profile characteristics were extracted from densitometry curves and correlated to hardness. Deep monomer penetration was more favorable to hardness than high surface density peak.

TENSILE STRENGTH OF BONDING MATERIAL TO DENTINE USING WATER-WET AND ETHANOL-WET TECHNIQUES

Background: Composite resins have hydrophobic properties so it cannot attach to dentine. Moist dentin is a normal condition caused by the presence of fluid in dentinal tubules. Therefore bonding material is required to bond dentine with composite. Water-wet technique is a technique in which dentine surface is rinsed after etching by using water and allowing it to be moist and prevent the collapse of dentine collagen fibrils. This technique is commonly used today, but excess water disturbs the effectiveness of dentine and bonding material attachment. Ethanol-wet technique is a technique in which ethanol is used to replace water before bonding to reduce excess water in dentine surface. This technique will initiate monomer penetration into interfibrillar space of dentine. It will affect the result of tensile strength test. Purpose: The purpose of this study was to compare tensile strength of bonding material to dentine using water-wet and ethanol-wet techniques. Method: 12 samples of bovine incisors teeth were randomly divided into 2 group. Each group consists of six samples. Group 1 was treated with water-wet technique and group 2 was treated with ethanol-wet technique. Autograph was used as a tensile strength test instrument. Result : The average of tensile strength using water-wet technique was 2,16067 MPa and ethanol-wet technique was 4,21900 MPa. Conclusion: Ethanol-wet technique have higher value of tensile strength than water-wet technique.

Influence of polar solvents on permeability, stiffness and collagen dissociation of demineralized dentin

The purpose of this in vitro study was to evaluate and compare the effect of dimethyl sulfoxide (DMSO) or ethanol on the permeability, stiffness and collagen dissociation of demineralized dentin.Dentin cubes (2 × 2 × 2 mm) were demineralized in EDTA and incubated in DMSO or ethanol (0.01, 0.1, 1, 5, 10, 20, 50 and 100%) (n= 10/group) for 30 s, followed by 100% HEMA incubation. Extracted HEMA was quantified. For elastic modulus (E), demineralized dentin beams (6 × 2 × 1 mm) were incubated in DMSO or ethanol (1, 10, 20, 50 and 100%) for 10, 30 or 60 min at 3-point bending. Additional demineralized dentin discs (1 mm) were incubated in DMSO (1, 10, 50 and 100%) for 10, 30 and 60 min and the optical clearing effect was observed. The data were analyzed using ANOVA and Tukey's test (α=0.05) using SigmaPlot (Systat Software Inc., San Jose, CA).Compared to controls, HEMA uptake was significantly higher with all DMSO concentrations, and with 0.1% or higher ethanol concentrations (p<0.05). HEMA uptake in DMSO-incubated specimens (0.01, 5 and 10%) was significantly higher than with the ethanol incubation. Significant increase in elastic moduli was observed with 50–100% DMSO- and only with 100% ethanol after 10 min incubation. The optical clearing effect of 50–100% DMSO-incubated dentin disks was observed starting from 10 min.The pretreatment of dentin surfaces with low concentrations of DMSO resulted in significant improvement of the penetration of monomers to demineralized dentin matrices. Increase in penetration of monomers combined with a reversible stiffening of dentin collagenous matrix may explain the previously shown increase in durability of wet- or dry-bonded adhesive interfaces with DMSO treatment.

Peptide-Lipid Interaction Sites Affect Vesicles’ Responses to Antimicrobial Peptides

This article presents coarse-grained molecular dynamics simulations of pore-forming antimicrobial peptide melittin and its interactions with vesicles composed of a mixture of zwitterionic and anionic phospholipids. Besides creating holes in the membrane, the adsorption of melittin also induces vesicle budding, which can develop into vesiculation at high peptide concentrations, as well as vesicle invagination, which can eventually result in a corrugated membrane surface. These rich morphology changes are mediated by the curvature of the vesicles and the peptide concentration. Highly curved vesicles favor the recruitment of melittins with a higher density of binding sites. The peptides mainly penetrate into the membrane surface in monomers via hydrophobic interaction. Lowly curved vesicles recruit melittins with a low density of binding sites. Surplus peptides are prone to form oligomers and shallowly adsorb on the surface of membrane via electrostatic interaction. The penetration of monomers induces membrane pore formation and positive membrane curvature, which promote vesicle budding. The adsorption of oligomers induces negative membrane curvature, which promotes vesicle invagination. This work demonstrates that antimicrobial peptides adopt multiple actions to destroy bacterial membranes.

STUDIES OF MONOMER IMPREGNATION AND POLYMERIZED “IN-SITU” IN WOOD USING DYNAMIC MECHANICAL THERMAL ANALYZER (DMTA)

Some tropical hardwoods (acacia mangium, madhuca utilis, dacrydium spp., dipterocarpus spp.,dyera costulata, shorea spp., shorea gibbosa, shorea macrophylla, endospermum diadenum, cratoxylum arborescens) are selected and impregnated with methyl methacrylate (MMA) and polymerized “in-situ” by using catalyst-heat technique. Treatability of the wood as determinedfrom the fractional volumetric retentions of monomer i.e. fraction of voids filled by the impregnant showed that the mean retention range from 15.03% (acacia mangium) to 56.59% (cratoxylum arborescens). The penetration of monomer evaluated using ultrasonic wave showed that the treated wood had higher velocities which indicate significant increase in density. This paper deals with the viscoelastic relaxation of polymerized treated wood. The efficiency of monomer as a plasticizer is studied through the temperature dependence of the storage modulus (E´) and loss tangent (tan d) of treated and untreated wood by dynamic mechanical thermal analysis (DMTA) over a temperature of -100 to 200ºC. E´ decrease with temperature, and as the maximum mechanical damping develop, the glass transition temperature (Tg) of plasticized wood decrease with the plasticizer content.

Effect of phytic acid etchant on resin–dentin bonding: Monomer penetration and stability of dentin collagen

PurposePhytic acid (IP6) works well as an etchant in dentin bonding to remove the smear layer due to its acidity and chelating effect. This study compared the etching effect of IP6 with phosphoric acid (PA) and ethylenediaminetetraacetic acid (EDTA) on resin–dentin bond strength, micromorphology of the etched dentin surface and nanoleakage formation along resin–dentin interfaces and compared the protecting effect against collagen degradation. MethodsDentin disks and flat dentin surfaces were obtained from extracted human teeth. Specimens were etched with 35% PA (15s), 0.5M EDTA (30s) or 1% IP6 (30s). The surfaces and longitudinal sections of the etched dentin disks were observed using field emission scanning electron microscope (FE-SEM). An etch-and-rinse adhesive was used to create composite build up-specimens for microtensile bond strength (μTBS) testing and nanoleakage observation. To evaluate the effect on collagen degradation, demineralized bovine root dentin blocks were challenged with bacterial collagenase and then observed under light microscope. ResultsPA- and EDTA- treated groups showed significantly lower μTBS when compared to IP6-treated group. PA showed distinct nanoleakage and severe collagen degradation. Only slight nanoleakage was detected in IP6 group. IP6 showed better effect than EDTA in preventing collagen degradation induced by bacterial collagenase. ConclusionsIP6 effectively removed the smear layer and etched dentin, providing high bond strength values and causing minimal nanoleakage and slight collagen degradation.

Solvent type influences bond strength to air or blot-dried dentin.

BackgroundAir-drying of etched and rinsed dentin surface may force the exposed collagen fibrils to collapse. Blot-drying is an alternative method to wipe the excess water from the dentin surface without compromising the monomer penetration. Contemporary total etch adhesives contain ethanol/water or acetone as solvent in which resin monomers are dissolved. Solvent type of the adhesive system has an important role in bonding to dentin. An adhesive containing tertiary butanol as an alternative solvent has been in the market. Purpose of this study is to determine the shear bond strengths of three total-etch adhesives with different solvents (acetone, ethanol or tertiary butanol) applied to air or blot dried moist dentin.MethodsSixty extracted non-carious human third molars were divided into three main groups according to solvent content of the adhesives [acetone based - One Step (OS, Bisco, IL, USA); ethanol/water based - Optibond Solo Plus (OB, Kerr, CA, USA); and tertiary butanol based - XP Bond (XP, Caulk/Dentsply, DE, USA)]. Each main group was divided into two groups according to drying methods (blot or air) (n = 10). Shear bond strengths (SBS) were measured. Data were analyzed by Student’s t test and Tukey HSD test (p < 0,05).ResultsXP showed highest SBS values in both drying methods applied (p < 0.05). Drying method did not influence the SBS in OS and OB (p > 0.05). XP-blot produced significantly higher SBS than XP-air (p < 0.05).ConclusionsTertiary butanol based adhesive showed higher bond strength values than ethanol or acetone based adhesives. Blot drying of dentin improved the bond strength values of tertiary butanol based adhesive. Further research is necessary to determine in vivo and in vitro performance of tertiary butanol based adhesives.

Permeation of intrinsic water into ethanol- and water-saturated, monomer-infiltrated dentin bond interfaces

ObjectivesThe aim of this study was to evaluate the formation of dentin bonding interfaces using the water-wet and the ethanol-wet techniques under simulated pulpal pressure, and to assess the effect of adhesive solvent and thermomechanical loading. MethodsFlat dentin surfaces were restored under 20mm-simulated pulpal pressure following two bonding approaches (water-wet and ethanol-wet bonding) in combination with dental adhesives containing ethanol (Single Bond Plus and Scotchbond Multi-Purpose) or acetone (One-Step Plus and All-Bond 2) as solvent. Half of the restorations of each subgroup were subjected to thermocycling followed by cyclic loading (three teeth per group). Bond strength was measured using the microtensile bond strength test and fitted to a Weibull distribution (α=0.05). Ultrastructural analyses of the interface and leakage/nanoleakage evaluation were performed using confocal scanning microscopy (CLSM) and transmission electron microscopy (TEM). ResultsWater permeation through dentin tubules during adhesive application prevented adequate penetration of adhesive monomers into the demineralized collagen matrix in both bonding techniques, but more severely for water-wet bonding. Acetone-solvated adhesives showed worse bonding performance and hybridization than ethanol-based systems when applied in the ethanol-wet mode, both before and after thermomechanical challenge. SignificanceThe ethanol-wet bonding technique helps to compensate for water permeation from dentin tubules during the bonding procedures to form more stable dentin bonds, especially when used in conjunction to ethanol-solvated systems.

Effect of dimethyl sulfoxide wet-bonding technique on hybrid layer quality and dentin bond strength

ObjectivesThis study examined the effect of a dimethyl sulfoxide (DMSO) wet bonding technique on the resin infiltration depths at the bonded interface and dentin bond strength of different adhesive systems. MethodsFlat dentin surfaces of 48 human third molars were treated with 50% DMSO (experimental groups) or with distilled water (controls) before bonding using an etch-and-rinse (SBMP: Scotchbond Multi-Purpose, 3M ESPE) or a self-etch (Clearfil: Clearfil SE Bond, Kuraray) adhesive system. The restored crown segments (n=12/group) were stored in distilled water (24h) and sectioned for interfacial analysis of exposed collagen using Masson's Trichrome staining and for microtensile bond strength testing. The extent of exposed collagen was measured using light microscopy and a histometric analysis software. Failure modes were examined by SEM. Data was analyzed by two-way ANOVA followed by Tukey Test (α=0.05). ResultsThe interaction of bonding protocol and adhesive system had significant effects on the extension of exposed collagen matrix (p<0.0001) and bond strength (p=0.0091). DMSO-wet bonding significantly reduced the extent of exposed collagen matrix for SBMP and Clearfil (p<0.05). Significant increase in dentin bond strength was observed on DMSO-treated specimens bonded with SBMP (p<0.05), while no differences were observed for Clearfil (p>0.05). SignificanceDMSO-wet bonding was effective to improve the quality of resin–dentin bonds of the tested etch-and-rinse adhesives by reducing the extent of exposed collagen matrix at the base of the resin–dentin biopolymer. The improved penetration of adhesive monomers is reflected as an increase in the immediate bond strength when the DMSO-wet bonding technique is used with a water-based etch-and-rinse adhesive.

Non-thermal atmospheric plasmas in dental restoration: Improved resin adhesive penetration

ObjectiveTo investigate the influence of non-thermal plasma treatment on the penetration of a model dental adhesive into the demineralized dentine. MethodsPrepared dentine surfaces were conditioned with Scotchbond Universal etchant for 15s and sectioned equally perpendicular to the etched surfaces. The separated halves were randomly selected for treatment with an argon plasma brush (input current 6mA, treatment time 30s) or gentle argon air blowing (treatment time 30s, as control). The plasma-treated specimens and control specimens were applied with a model adhesive containing 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane (BisGMA) and 2-hydroxyethyl methacrylate (HEMA) (mass ratio of 30/70), gently air-dried for 5s, and light-cured for 20s. Cross-sectional specimens were characterized using micro-Raman spectral mapping across the dentine, adhesive/dentine interface, and adhesive layer at 1-μm spatial resolution. SEM was also employed to examine the adhesive/dentine interfacial morphology. ResultsThe micro-Raman result disclosed that plasma treatment significantly improved the penetration of the adhesive, evidenced by the apparently higher content of the adhesive at the adhesive/dentine interface as compared to the control. Specifically, the improvement of the adhesive penetration using plasma technique was achieved by dramatically enhancing the penetration of hydrophilic monomer (HEMA), while maintaining the penetration of hydrophobic monomer (BisGMA). Morphological observation at the adhesive/dentine interface using SEM also confirmed the improved adhesive penetration. The results further suggested that plasma treatment could benefit polymerization of the adhesive, especially in the interface region. ConclusionThe significant role of the non-thermal plasma brush in improving the adhesive penetration into demineralized dentine has been demonstrated. The results obtained may offer a better prospect of using plasma in dental restoration to optimize adhesion between tooth substrate and restorative materials.

Quantitative and qualitative evaluation of resin-dentin bond strengths: in vitro effects of surface treatment with metalloproteinase inhibitors

AIM: The objective of this study was to evaluate the use of MMPs inhibitors (chlorhexidine and EDTA) in bond strength and quality of the hybrid layer of adhesive restorations in normal dentin using two ethanol-based total-etch adhesive systems. MATERIAL AND METHODS: Thirty-two extracted human molars were coronally sectioned and randomly divided into 8 groups (n=4), depending on the surface pre-treatment and adhesive system used. The total-etch adhesive systems Single Bond 2 (2-step) and Adper Scotchbond Multi-Purpose Plus (3-step) were used as follows: 1) according to manufacturer's instructions (etching with 37% phosphoric acid (H3PO4) for 15 s); 2) etching with H3PO4 for 15 s, followed by 2% chlorhexidine for 120 s; 3) etching with 0.1 M EDTA for 60 s; 4) etching with 0.1 M EDTA followed by 2% chlorhexidine for 120 s. Teeth were incrementally restored with composite resin (Filtek Z350XT). After water storage for 24 h, teeth were double-sectioned, yielding stick specimens of 1.0 mm² bonded area, and then subjected to microtensile bond strength (MTBS) test at 0.5 mm/min. Additional specimens were gold-sputtered to be analyzed under scanning electron microscopy (SEM). Data (in Mega Pascal) were subjected to Kruskal-Wallis and Dunn (p &lt;0.05) tests. RESULTS: The etching protocol (37% H3PO4 or EDTA) interfered with hybrid layer formation, monomer penetration and the MTBS. Funnel shaped resin tags were observed when dentin was etched with 37% H3PO4. In these specimens, MTBS were also higher. EDTA conditioning produced thin hybrid layers and smaller MTBS, regardless the adhesive system used. Chlorhexidine application after conditioning resulted in no apparent differences between both evaluated techniques (37% H3PO4 or EDTA). CONCLUSION: The use of chlorhexidine as a MMP inhibitor does not alter immediate bond strength values and does not interfere with hybrid layer formation.

A mechanistic study of plasma treatment effects on demineralized dentin surfaces for improved adhesive/dentin interface bonding

Our previous work has shown that non-thermal plasma treatment of demineralized dentin significantly (p<0.05) improved adhesive/dentin bonding strength for dental composite restoration as compared with the untreated controls. This study is to achieve mechanistic understanding of the plasma treatment effects on dentin surface through investigating the plasma treated dentin surfaces and their interaction with adhesive monomer, 2-hydroxyethyl methacrylate (HEMA). The plasma treated dentin surfaces from human third molars were evaluated by water contact angle measurements and scanning electron microscopy (SEM). It was found that plasma-treated dentin surface with subsequent HEMA immersion (Plasma/HEMA Treated) had much lower water contact angle compared with only plasma-treated (Plasma Treated) or only HEMA immersed (HEMA Treated) dentin surfaces. With prolong water droplet deposition time, water droplets spread out completely on the Plasma/HEMA Treated dentin surfaces. SEM images of Plasma/HEMA Treated dentin surfaces verified that dentin tubules were opened-up and filled with HEMA monomers. Extracted type I collagen fibrils, which was used as simulation of the exposed dentinal collagen fibrils after acid etching step, were plasma treated and analyzed with Fourier transform infrared spectroscopy (FT-IR) and circular dichroism (CD) spectra. FT-IR spectra of the Plasma/HEMA Treated collage fibrils showed broadened amide I peak at 1660cm−1 and amide II at 1550cm−1, which indicate secondary structure changes of the collagen fibrils. CD spectra indicated that 67.4% collagen helix structures were denatured after plasma treatment. These experimental results demonstrate that non-thermal argon plasma treatment was very effective in loosing collagen structure and enhancing adhesive monomer penetration, which are beneficial to thicker hybrid layer and longer resin tag formation, and consequently enhance adhesive/dentin interface bonding.

Depletion of water molecules during ethanol wet-bonding with etch and rinse dental adhesives

The treatment of demineralized dentin with ethanol has been proposed as a way to improve hydrophobic monomer penetration into otherwise water saturated collagen fibrils. The ethanol rinse is expected to preserve the fibrils from collapsing while optimizing resin constituent infiltration for better long term adhesion. The physico-chemical investigations of demineralized dentin confirmed objectively these working hypotheses. Namely, Differential Scanning Calorimetry (DSC) measurements of the melting point of water molecules pointed to the presence of free and bound water states. Unfreezable water was the main type of water remaining following a rinsing step with absolute ethanol. Two different liquid water phases were also observed by Magic Angle Spinning (MAS) solid state Nuclear magnetic Resonance (NMR) spectroscopy. Infrared spectra of ethanol treated specimens illustrated differences with the fully hydrated specimens concerning the polar carbonyl vibrations. Optical microscopy observations as well as scanning electron microscopy showed an improved dentin-adhesive interface with ethanol wet bonding. The results indicate that water can be confined to strongly bound structural molecules when excess water is removed with ethanol prior to adhesive application. This should preserve collagen from hydrolysis upon aging of the hybrid layer.

Comparison of the kinetic friction of planar neutral and polyelectrolyte polymer brushes using molecular dynamics simulations

We have simulated the relative shear motion of both neutral and polyelectrolyte end-grafted polymer brushes using molecular dynamics. The flexible neutral polymer brush is treated as a bead-spring model, and the polyelectrolyte brush is treated the same way except that each bead is charged and there are counterions present to neutralize the charge. We investigated the friction coefficient, monomer density, and brush penetration for both polyelectrolyte and neutral brushes with both equal grafting density and equal normal force under good solvent conditions. We found that polyelectrolyte brushes had a smaller friction coefficient and monomer penetration than neutral polymer brushes with the identical grafting density and chain length, and the polyelectrolyte brushes supported a much higher normal load than the neutral brushes for the same degree of compression. Charged and neutral brushes with their grafting densities chosen so that they support the same load exhibited approximately the same degree of interpenetration, but the polyelectrolyte brush exhibited a significantly lower friction coefficient. We present evidence that the reason for this is that the extra normal force contribution provided by the counterion osmotic pressure that exists for polyelectrolyte brushes permits them to support the same load as an identical neutral polymer brush of higher grafting density. Because of the resulting lower monomer density for the charged brushes, fewer monomer collisions take place per unit time, resulting in a lower friction coefficient.