Bond strength of resin to acid-etched dentin studied by 13C NMR: interaction between N-methacryloyl-omega-amino acid primer and dentinal collagen

Stability of the Dentin-Bonded Interface Using Self-Etching Adhesive Containing Diacrylamide after Bacterial Challenge

Purpose/Aim: Acrylamides are hydrolytically stable at pH lower than 2, and were shown to preserve bonded interface integrity with two-step, total etch adhesives. The objective of this study was to leverage those two characteristics in self-etching primers containing the acidic monomer 10-MDP and test the microtensile bond strength before and after incubation with S. mutans incubation. Materials and Methods: Acidic primers (10 wt % 10-methacryloyloxydecyl dihydrogen phosphate─10-MDP; 45 wt % N,N-diethyl-1,3-bis(acrylamido)propane─DEBAAP, or 2-hydroxyethyl methacrylate─HEMA; 45 wt %, glycerol-dimethacrylate─GDMA) and adhesives (DEBAAP or HEMA/10-MDP/UDMA 45/10/45 wt %) were made polymerizable by the addition of 0.2 wt % camphorquinone, 0.8 wt % ethyl-4-dimethylaminobenzoate, 0.4 wt % diphenyliodonium hexafluorophosphate, and 0.1 wt % butylhydroxytoluene. Nonsolvated materials were characterized for flexural strength (FS), modulus (E), toughness, water sorption/solubility (WS/SL), contact angle, and vinyl conversion (DC). Viscosity was evaluated after adding 20 and 40 vol % ethanol to the primer and adhesive, respectively. The experimental materials or Clearfil SE Bond (CC─commercial control) were used to bond a commercial composite (Filtek Supreme) to the flat surface of human dentin. Microtensile bond strength (MTBS) was tested in 1 mm2 sticks for the 5 primer/bond combinations: CC (Clearfil Bond Primer and Bond), HH (HEMA/HEMA), DD (DEBAAP/DEBAAP), HD (HEMA/DEBAAP), and DH (DEBAAP/HEMA). Prior to testing, sticks were stored in water or biofilm-inducing culture medium with S. mutans for 1 week. Confocal images and FTIR-ATR evaluation evaluated the hybrid layer of the adhesives. Results were analyzed using Student's t-test (WS, SL, DC, contact angle, FS, E, toughness), one-way ANOVA/Tukey's test for viscosity, and two-way ANOVA/Tukey's test for MTBS (95%). Results: HEMA-based materials had lower contact angle (p = 0.004), higher WS (p < 0.001), and similar SL values compared to DEBAAP (p = 0.126). FS (p = 0.171) and E (p = 0.065) dry values were similar, but after one week of water storage, FS/E dropped more significantly for HEMA materials. Dry and wet toughness was greater for DEBAAP (p < 0.001), but it also had the greatest drop (46%). Clearfil bonds had the highest viscosity, followed by DEBAAP and HEMA, respectively (p = 0.002). For the primers, HEMA had the lowest viscosity (p = 0.003). As far as MTBS, all groups tested in water were statistically different when compared with HH (p < 0.001). After storage in biofilm, DH had the highest MTBS value, being statistically different from HH (p = 0.002), CC (p = 0.015), and DD (p = 0.027). Conclusions: The addition of a diacrylamide and its association with HEMA in self-etching adhesive systems provided greater bonding stability after bacterial challenge.

Novel hydrolytic resistant antibacterial monomers for dental resin adhesive

OBJECTIVES

To evaluate the properties of novel hydrolytic resistant antibacterial monomers and to determine the properties of resin adhesives containing these monomers.

METHODS

Methacrylamide-based QAC (Quaternary Ammonium Compound) monomers, 1-(11-Methacryla-midoundecyl)pyridine-1-ium bromide (MAUPB) and 1-(12-Methacryl-amidododecyl)pyridine-1-ium bromide (MADPB), and their methacrylate-derivatives, N-(1-Methacryloylundecanyl)pyridinium bromide (MUPB) and N-(1-Methacryloyldodecanyl)pyridinium bromide (MDPB), were synthesized and characterized. The minimum inhibitory (MIC) and bactericidal (MBC) concentrations were determined against S.mutans and E.faecalis. Cytotoxicity of unpolymerized monomers were evaluated using L-929 and MDPC-23. Each monomer was incorporated into experimental resins (BisGMA/TEGDMA/CQ/EDMAB or BisGMA/HEMA/CQ/EDMAB) at 10wt%. FTIR Spectra were collected for degree of conversion (DC%) measurement. Bacterial attachment on resin disks were determined by fluorescent microscope. Mechanical properties of experimental resins were evaluated by flexural strength & modulus and shear bond strength testing.

RESULTS

The antibacterial activity of MDPB≥MUPB>MADPB>MAUPB. The TC50 of MAUPB> MADPB>MUPB >MDPB. Incorporation of MAUPB in BisGMA/TEGDMA-based resin, had no significant effect on DC%, while significantly increase DC% in BisGMA/HEMA-based Resin. MUPB and MAUPB containing resins showed less viable bacterial attachment than pure resins. After 3-month storage, resins containing MAUPB illustrated higher flexural strength than their corresponding resins containing MUPB. BisGMA/HEMA-based resin containing MAUPB illustrated significantly higher resin-dentin shear bond strength than that of MUPB and pure resin.

CONCLUSIONS

Methacrylamide monomer containing QAC, MAUPB, possessed antibacterial properties and superior physical and mechanical properties when incorporated in resin adhesives as compared to their corresponding methacrylate monomer, MUPB.

CLINICAL SIGNIFICANCE

Methacrylamide-based QAC monomers are potentially used to formulate antibacterial hydrolytic resistant resin adhesives and enhance resin-dentin bond strength.

Synthesis of di- and triacrylamides with tertiary amine cores and their evaluation as monomers in dental adhesive interfaces

PURPOSE/AIM

In an attempt to increase the service life of dental adhesive interfaces, more hydrolytically and enzymatically-stable methacrylate alternatives, such as methacrylamides, have been proposed. The aim of this study was to investigate polymerization behavior, as well as mechanical and biological properties of experimental adhesives containing multi-functional acrylamides.

MATERIALS AND METHODS

Multi-functional acrylamides (N,N-Bis[(3-methylaminoacryl)propyl]methylamine - BMAAPMA, Tris[(2-methylaminoacryl)ethyl]amine - TMAAEA, N,N'-bis(acrylamido) 1,4-diazepane - BAADA, N,N-Diethyl-1,3-bis(acrylamido)propane - DEBAAP) or HEMA (2-Hydroxyethyl methacrylate - control) were added at 40 wt% to UDMA. 0.2 wt% DMPA and 0.4 wt% DPI-PF6 were used as initiators. Polymerization kinetics was followed in real-time in near-IR during photoactivation (320-500 nm, at 630 mW/cm²). Water sorption/solubility and flexural strength/modulus were measured according to ISO 4049. ¹H NMR was used to assess monomer degradation kinetics. MTT assay was used to assess cytotoxicity against OD-21 and DPSC cells. Biofilm formation and adhesion were assessed by Luciferase Assay and Impingement technique, respectively. Solvated adhesives (40 vol% ethanol) were used to test interfacial adhesion strength. The results were analyzed by ANOVA/Tukey's test (α = 0.05).

RESULTS

In general, the pure methacrylate mixture had higher rate of polymerization (Rp_max), degree of conversion (DC) at Rp_max, and final DC than the acrylamides. Flexural properties after water storage decreased between 11 and 65%, more markedly for acrylamides. Interfacial bond strength was greater and more stable long-term for the newly synthesized acrylamide formulations (less than 4% reduction at 6 months) compared to the methacrylate experimental control (42% reduction at 6 months). HEMA degraded by almost 90%, while the acrylamides showed no degradation in acidic conditions. Cytotoxicity and biofilm formation, in general, were similar for all groups.

CONCLUSIONS

Despite demonstrating high water sorption, the acrylamide-containing materials had similar mechanical and biological properties and enhanced interfacial bond strength stability compared to the methacrylate control.

Use of (meth)acrylamides as alternative monomers in dental adhesive systems

OBJECTIVES

Methacrylamides are proposed as components for dental adhesive systems with enhanced resistance to hydrolytic and enzymatic degradation. The specific objective of this study was to evaluate the polymerization kinetics, water sorption and solubility, pH-derived degradation and microtensile bond strength of various monofunctional acrylamides and meth(acrylamides) when copolymerized with dimethacrylates.

METHODS

Base monomers were added at 60 wt%, and included either BisGMA or UDMA. Monofunctional monomers were added at 40 wt%, including one (meth)acrylate as the control, two secondary methacrylamides and two tertiary acrylamides. DMPA (0.2 wt%) and DPI-PF6 (0.4 wt%)/BHT (0.1 wt%) were added as initiators/inhibitor. Polymerization kinetics wwere followed with near-IR spectroscopy in real time. Water sorption (WS) and solubility (SL) were measured following ISO 4049. Monomer degradation at different pH levels was assessed with 1H NMR. Microtensile bond strength (MTBS) was assessed in caries-free human third molars 48 h and 3 weeks after restorations were placed using solvated BisGMA-based adhesives (40 vol% ethanol). Data were analyzed with one-way ANOVA/Tukey's test (α = 0.05).

RESULTS

As expected, rate of polymerization and final degree of conversion (DC) were higher for the acryl versions of each monomer, and decreased with increasing steric hindrance around the vinyl group for each molecule. In general, UDMA copolymerizations were more rapid and extensive than for BisGMA, but this was dependent upon the specific monofunctional monomer added. WS/SL were in general higher for the (meth)acrylamides compared to the (meth)acrylates, except for the tertiary acrylamide, which showed the lowest values. One of the secondary methacrylamides was significantly more stable than the methacrylate control, but the alpha substitutions decreased stability to degradation in acid pH. MTBS in general was higher for the (meth)acrylates. While for all materials the MTBS values at 3 weeks decreased in relation to the 24 h results, the tertiary acrylamide showed no reduction in bond strength.

SIGNIFICANCE

This study highlights the importance of considering steric and electronic factors when designing monomers for applications where rapid polymerizations are needed, especially when co-polymerizations with other base monomers are required to balance mechanical properties, as is the case with dental adhesives. The results of this investigation will be used to design fully formulated adhesives to be tested in clinically-relevant conditions.

Intrafibrillar mineralization of polyacrylic acid-bound collagen fibrils using a two-dimensional collagen model and Portland cement-based resins

The biomimetic remineralization of apatite-depleted dentin is a potential method for enhancing the durability of resin-dentin bonding. To advance this strategy from its initial proof-of-concept design, we sought to investigate the characteristics of polyacrylic acid (PAA) adsorption to desorption from type I collagen and to test the mineralization ability of PAA-bound collagen. Portland cement and β-tricalcium phosphate (β-TCP) were homogenized with a hydrophilic resin blend to produce experimental resins. The collagen fibrils reconstituted on nickel (Ni) grids were mineralized using different methods: (i) group I consisted of collagen treated with Portland cement-based resin in simulated body fluid (SBF); (ii) group II consisted of PAA-bound collagen treated with Portland cement-based resin in SBF; and (iii) group III consisted of PAA-bound collagen treated with β-TCP-doped Portland cement-based resin in deionized water. Intrafibrillar mineralization was evaluated using transmission electron microscopy. We found that a carbonyl-associated peak at pH 3.0 increased as adsorption time increased, whereas a hydrogen bond-associated peak increased as desorption time increased. The experimental resins maintained an alkaline pH and the continuous release of calcium ions. Apatite was detected within PAA-bound collagen in groups II and III. Our results suggest that PAA-bound type I collagen fibrils can be mineralized using Portland cement-based resins.

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.

Role of 2-hydroxyethyl methacrylate in the interaction of dental monomers with collagen studied by saturation transfer difference NMR

OBJECTIONS

Functional adhesive monomers are formulated with solvents and hydrophilic resin monomers, such as 2-hydroxyethyl methacrylate (HEMA). In theory, exposed collagen fibrils should be covered and protected by the resin matrix. We examined if the atomic- and molecular-level interaction of monomers with collagen would be affected when the monomers are blended with HEMA.

METHODS

We performed saturation transfer difference (STD) NMR spectroscopy to investigate the binding interaction of two functional monomers, 4-methacryloyloxyethyl trimellitic acid (4-MET) and 10-methacryloyloxydecyl dihydrogen phosphate (MDP), with atelocollagen as a triple-helical peptide model. The STD NMR measurement was performed by adding 4-MET or MDP to the atelocollagen solution.

RESULTS

When the atelocollagen was saturated, the STD signals were detected in the MDP spectrum for the protons in the aliphatic chain when MDP was dissolved in DMSO. However, the STD signals disappeared when MDP was mixed with HEMA. No STD signal was visible for the 4-MET ligand samples in either DMSO or for the HEMA blend sample.

DISCUSSION

The interaction of MDP with atelocollagen is hydrophobic; however, the MDP-HEMA blend may form an aggregate in the atelocollagen solution, which would suppress the hydrophobicity of MDP. The formation of the MDP-HEMA aggregate may compromise the MDP-collagen interaction, and leave the collagen fibrils unprotected by MDP and HEMA. Unstable chemical interaction of the monomers with the exposed collagen may deteriorate hybrid layer integrity and strong dentine bonding.

Monomer-Collagen Interactions Studied by Saturation Transfer Difference NMR

Functional monomers in dentin adhesives are involved in wetting dental substrates, demineralization, and the formation of calcium salts. However, the interaction of these monomers with collagen is not understood at a molecular/atomic level. We performed saturation transfer difference (STD) NMR spectroscopy to investigate the binding interaction of 2 functional monomers, 4-methacryloyloxyethyl trimellitate anhydride (4-META) and 10-methacryloyloxydecyl dihydrogenphosphate (MDP), with atelocollagen as a triple-helical peptide model. High STD intensities were detected on the protons in the aliphatic region in MDP, whereas they were not detected for 4-META. The STD results imply that MDP has a relatively stable interaction with the collagen, because of the hydrophobic interactions between the hydrophobic MDP moieties and the hydrophobic collagen surface. This finding indicates that MDP-collagen complexation accounts for stable dentin bonding.

Evaluation of intermolecular interactions of self-etch dentin adhesive primer molecules with type 1 collagen: computer modeling and in vitro binding analysis

The objective of this investigation was to study adhesion of self-etch primer systems to dentin by computer-modeled docking simulations and in vitro binding assay methods. Computer modeling employed analysis of docking simulations of a self-etch primer molecule 10-methacryloxydecamethylene phosphoric acid (MDP) and its calcium salt (MDPCa) as ligands. Typical type 1 collagen segments were selected as targets to reflect potential differences in the amino acid residues in dentinal type 1 collagen triple helix motif. The binding assay involved immunochemical analysis of the modification of anti-collagen binding to collagen by prior exposure of the demineralized dentin to MDP. The estimated mean docking energy values ranged between -4.5 and -8.9kcalmol(-1). The results revealed significant differences in the docking energy estimates as a function of ligand and target structures (p<0.01). Van der Waals and electrostatic contributions were also significantly influenced by ligand selection and collagen structure. Both MDP and MDPCa appear to be important in the overall interactions. Binding assay studies also lend evidence of collagen-ligand intermolecular interactions. It is suggested that the ability of self-etch dentin primer systems to bond effectively to dentin is not limited to the interaction of the primer with the hydroxyapatite of dentin, but also due to the ability to prime dentin efficiently through intermolecular interactions between the primer and its calcium salt with the collagen matrix. Virtual screening methods may be very valuable to select primer molecules for dentin bonding.

Systematic review of the chemical composition of contemporary dental adhesives

Dental adhesives are designed to bond composite resins to enamel and dentin. Their chemical formulation determines to a large extent their adhesive performance in clinic. Irrespective of the number of bottles, an adhesive system typically contains resin monomers, curing initiators, inhibitors or stabilizers, solvents and sometimes inorganic filler. Each one of these components has a specific function. The aim of this article is to systematically review the ingredients commonly used in current dental adhesives as well as the properties of these ingredients. This paper includes an extensive table with the chemical formulation of contemporary dental adhesives.

Chemical analysis and bonding reaction of RelyX Unicem and Bifix composites—A comparative study

OBJECTIVES

The chemical and physical properties of the dual curing luting composites RelyX Unicem (3M ESPE) and Bifix (VOCO) were analyzed with regard to their elemental composition, surface morphology and polymerization reaction. The bonding of both materials to hydroxyapatite (HAp) was studied.

METHODS

The main components were analyzed by XPS and EDX. The minor components were identified with ICP-OES. Moreover, the morphology was examined by SEM and the polymerization reaction products were investigated using GPC. XPS was also applied to study the bonding mechanisms to HAp.

RESULTS

The inorganic product particles consist of an Al-Si-Na-glass network, which incorporates radiopaque strontium and barium for Bifix and strontium and lanthanum for RelyX Unicem. RelyX Unicem contains about 10% fluoride and 2% Ca(OH)(2), whereas Bifix comprises 2% fluoride. After polymerization, reaction products of 10(5)-10(6)g/mol were identified with RelyX Unicem. Both products contain mono- and oligomeric compounds. The reaction with HAp generates calcium atoms with a reduced binding energy. They act as an electron acceptor and show chemical interaction between the composite and HAp. With RelyX Unicem 86% of the calcium atoms reacted, compared to 65% with Bifix.

SIGNIFICANCE

The intense chemical interaction of RelyX Unicem with HAp seems to be relevant to clinical aspects and explains the mechanical product properties. After setting, a polymer was found with RelyX Unicem but only monomeric/oligomeric products were identified at the surface of Bifix.

Effect of HEMA adsorption on the stability of native and denatured type I tendon collagen

Adsorption behavior and stabilization/destabilization effects of 2-hydroxyethyl methacrylate (HEMA) on a bovine tendon collagen (BTC) (type I), either native (N) or thermally denatured (D), were studied by IR spectroscopy and differential scanning calorimetry (DSC). The amount of HEMA adsorbed was larger on BTC(D) than on BTC(N), because BTC(D) had a larger specific surface area (SSA) as revealed from SSA measurement. Denaturation temperature (Td) of BTC(N), measured by DSC in aqueous HEMA solution, decreased from 63 degrees C to 40 degrees C with increasing HEMA concentration (CHEMA) up to 20 wt%. This destabilization might be caused by the loss of hydrophobic stabilization of the helix structure as CHEMA was increased. At CHEMA > 20 wt%, the structure of collagen was restabilized presumably due to the dehydration effect conferred by HEMA at higher concentration. BTC(D) with little helix content, however, showed only a weak endothermic peak in the DSC measurement and the Td at 40 degrees C was independent of CHEMA.

Development of Bonding System for Resin Core Construction by M.OMEGA.A Adhesive

We designed self-etching primers consisting of a series of four N-methacryloyl-omega-amino acids, MomegaA, of different methylene chain numbers for resin core construction. The interacted amount of MomegaA's carboxylic acid with root or crown dentin apatite was determined, and its effects on dentin bond durability examined. The addition of both dentin particles to the MomegaA solutions caused the carbonyl carbon peak of carboxylic acid in MomegaA to shift to a lower field, chiefly because of an acid-base interaction between carboxylic acid and calcium. Then, as the pKa value of MomegaA's carboxylic acid increased, the amount of carboxylic acid that interacted with calcium decreased. In terms of dentin bonding durability, the four tested MomegaA adhesives provided noticeably higher bond strengths of resin to root or crown dentin than ED Primer II. Therefore, from the perspective of restoring pulpless teeth with minimal intervention, carboxylated MomegaA adhesives seemed to be very useful as functional monomers for self-etching primers.

Efficacy of varying the NMEP concentrations in the NMGly–NMEP self-etching primer on the resin-tooth bonding

It is well understood that the application of a self-etching primer enhances the bonding at the resin-teeth interface. In this study, we designed a self-etching primer consisting of N-methacryloyl glycine (NMGly) and N-methacryloyl-2-aminoethyl phosphonic acid (NMEP). The demineralization effects on the hydroxyapatite or dentin by the carboxylic acid in the NMGly and by the phosphonic acid in the NMEP and their effects on the bond strength of the resin to the tooth were examined. The application of the NMGly-NMEP solution to the enamel resulted in an increase in the bond strength when additional amounts of NMEP were added to the NMGly aqueous solution. This increase was due to the phosphonic acid in the NMEP demineralizing the enamel. Conversely, the addition of the NMEP to the NMGly solution resulted in a decrease in the bond strength to the dentin. The optimal concentration of the NMEP in the NMGly-NMEP solution resulted in bond strengths of over 20 MPa for both the enamel and dentin.

The pKa effects of the carboxylic acid in N-methacryloyl-omega-amino acid on the demineralization and bond strengths to the teeth

It is understood that the application of a self-etching primer to the tooth enhances the bonding of the resin to the tooth. In this study, we designed a self-etching primer consisting of a series of three N-methacryloyl-omega-amino acids (NMomegaA) with different methylene chain lengths. The demineralization aspect of the teeth components by the carboxylic acid in the NMomegaA and its effects on the bond strength of the resin to the tooth were examined. The amount of decalcification of the hydroxyapatite or dentin by the carboxylic acid in the NMomegaA was strongly dependent on the carboxylic acid's pKa value in the NMomegaA. However, the bond strength's mean values for both the enamel and dentin were not influenced by the degree of demineralization by the carboxylic acid in the NMomegaA. The greater mean value of the dentin's bond strength than with the enamel's was due to differences in the adhesion mechanism types, since the NMomegaA not only exhibited an etching efficacy but also a priming efficacy to the collagen that had been exposed by the NMomegaA conditioning.

Hydrolytic stability of methacrylamide in acidic aqueous solution

In order to develop a more effective self-etching primer, with a longer lasting shelf life, we designed a self-etching primer comprised of methacrylamide, N-methacryloyl glycine, NMGly. In this study, the hydrolytic stability of the amide portion in the NMGly was examined. The difference in the hydrolytic stability between the methacrylamide and the methacrylate, 2-hydroxyethyl methacrylate, HEMA was then discussed. The addition of an acid to an aqueous solution allows for the hydrolysis of the ester portion in the methacrylate and for the production of methacrylic acid, MA and ethylene glycol, EG. From our study, the data clearly demonstrated that, if the storage duration of a commercially available self-etching primer is prolonged, then the functional methacrylates constituting the self-etching primer will be altered upon use. However, the hydrolytic stability of the amide portion in the methacrylamide, NMGly, designed as an acidic and/or hydrophilic monomer for the self-etching primer, was greater than the results achieved with the methacrylate, HEMA.

Development of self-etching primer comprised of methacrylamide, N-methacryloyl glycine

In order to develop a more effective self-etching primer, it is helpful to understand how a functional monomer conditions the surface of the teeth.In this study, the reactivity by the carboxylic acid in the N-methacryloyl glycine (NMGly) on the calcium phosphate in hydroxyapatite or dentin was studied. The efficacy of the NMGly as a functional monomer for a self-etching primer was then examined. Applying NMGly to both the enamel and dentin resulted in an increase in the bond strength of resin, since the carboxylic acid in the NMGly decalcified the calcium phosphate in the hydroxyapatite and dentin. The bond strength to dentin achieved was higher than with the enamel. This difference was most likely due to different enamel and dentin adhesion mechanisms.

Dissociation states of collagen functional groups and their effects on the priming efficacy of HEMA bonded to collagen

Applying 2-hydroxyethylmethacrylate (HEMA) solution to etched dentin enhances the bonding of resin to dentin. However, the principal adhesion mechanisms have not yet been identified. In this study, we examined the dissociation states of the collagen functional groups of the side-chain amino acid residues and their effects on the bond strength of resin to etched dentin primed by the HEMA solution. The bond strength was strongly dependent upon the dissociation state of the collagen functional groups. Inhibiting the dissociation of the carboxylic acid or the amine of a collagen functional group resulted in increased bond strength of resin to collagen. By understanding the significance of inhibiting the dissociation state, we can better design and develop more effective and efficient primer and bonding agents.

A 13C NMR study on the adsorption characteristics of HEMA to dentinal collagen

To develop a more effective primer, we must understand how 2-hydroxyethylmethacrylate, the HEMA primer, enhances bonding at the resin-dentin interface. In this study, to obtain an insight into the adhesion mechanisms of adhesive resin to etched dentin through HEMA, we examined the adsorption characteristics of HEMA to dentinal collagen by using the 13C NMR technique. The addition of dentinal collagen to the HEMA solution resulted in a decrease in T(1) values of carbons attributed to the HEMA, thus reflecting an interaction between HEMA and collagen. Specifically, a reduction in the T(1) value in the ester carbonyl carbon attributed to HEMA greater than that in the other carbons suggested the formation of a hydrogen bond between the ester carbonyl group in HEMA and the dentinal collagen.

Effect of primers containing N-methylolacrylamide or N-methylolmethacrylamide on dentin bond durability of a resin composite after 5 years

OBJECTIVES

The effect of experimental dentin primers containing N-methylolacrylamide (MEAA) or N-methylolmethacrylamide (MEMA) on bond durability of a resin composite (Photo Clearfil A) with a bonding agent (Clearfil Photo Bond) to bovine dentin was investigated.

METHODS

The etching agents were 10% maleic acid (10% MA), 10% phosphoric acid (10% PA) and 10% citric acid-3% ferric chloride (10-3 solution). Water solutions of 35% hydroxyethyl methacrylate (HEMA), 50% MEAA or 30% MEMA were used as dentin primers. The etched dentin was pre-treated with the dentin primers for 30s. The resin composite systems were applied in a Teflon tube positioned onto pre-treated dentin surfaces. After water immersion for 1 day and 5 years, the shear bond strengths were measured. The amounts of calcium dissolved with etching agents were measured using atomic absorption spectrometry. The thicknesses of hybrid layers at the dentin-resin interfaces treated with 6 mol/l HCl and 1% NaOCl were measured using scanning electron microscopy.

RESULTS

The bond strengths of the specimens (Controls) without primers to dentin etched with 10% MA and 10-3 solution significantly decreased after immersion in water for 5 years (p<0.05) while other bond strengths did not decrease. The bond strengths of the composites to MEMA- and MEAA-primed dentin were significantly higher than that of the control after 1 day, regardless of the types of etching agents (p<0.05). The 5 year bond strengths of the composites to HEMA-, MEMA- and MEAA-primed dentin were significantly higher than that of the control, regardless of the types of etching agents (p<0.05). The 1 day and 5 year bond strengths of the composite to MEAA-primed dentin were significantly higher than those of the composites to HEMA-primed dentin, regardless of the types of etching agents (p<0.05). The highest amount (182.3+/-8.0 microg/cm(2)) of dissolved calcium was determined for the pre-treatment with 10% PA, followed by that (152.0+/-6.9 microg/cm(2)) with 10% MA and that (140.1+/-2.8 microg/cm(2)) with 10-3 solution (p<0.05). The hybrid layer thicknesses (approximately 1 microm) for 10-3 solution were thinner than those (approximately 2 microm) for others after HCl immersion. For the controls, the hybrid layers after NaOCl immersion become narrower or disappeared. The main fracture pattern of specimens was a mixture of resin-dentin interface failure and dentin cohesive fracture after the bond test.

CONCLUSIONS

MEAA solution was more effective in improving the bond strength of the controls to etched dentin than was HEMA after 1 day and 5 years. Clearfil Photo Bond created good hybrid dentin layers which could resist NaOCl-attack and showed good dentin bond durability when dentin primers were used, regardless of the type of etching agent.

Adhesion of N-methacryloyl-omega-amino acid primers to collagen analyzed by 13C NMR

Previously, we reported that the strength of the interaction between N-methacryloyl-omega-amino acid (NMomegaA) primers and dentinal collagen exhibited a strong correlation with the bond strength of the resin to etched dentin. To determine the pertinent functional groups of the amino acid residues in the dentinal collagen, to which the amide and/or the carboxylic acid groups of the NMomegaAs are adsorbed, we used 13C NMR techniques--primarily through the observation of spin-lattice relaxation times, Ti--to investigate the adsorption characteristics resulting from the interaction of NMomegaAs with a model oligopeptide for collagen, (PPG)5. The addition of NMomegaAs to a collagenous solution resulted in a decrease in the T1 values of the carbonyl carbons attributed to the carboxylic acid of the C-terminal Gly and to the third amide of the N-terminal Pro residues in the (PPG)5 molecule, thus reflecting the formation of hydrogen-bonded interactions.