1H-NMR studies of the interaction of dental adhesive monomer, 4-META with calcium

Varying 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) level improves polymerisation kinetics and flexural strength in self-adhesive, remineralising composites

OBJECTIVES

To assess the influence of systematically varying concentrations of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) versus 3% 4-META on the polymerisation kinetics and shrinkage, biaxial flexural strength (BFS) and modulus of remineralising composites.

METHODS

Composites were prepared by adding poly(propylene glycol) dimethacrylate (24 wt%), camphorquinone (1 wt%) and MDP (0%, 5%, 10%, 15% and 20 wt%) or 4-META (3%) to urethane dimethacrylate. These were mixed with glass fillers containing 8 wt% monocalcium phosphate and 4 wt% polylysine (powder-liquid ratio of 3:1). Continuous spectral changes, following 20 s light exposure (37 °C), were assessed with an ATR-FTIR to monitor polymerisation kinetics (n = 3). Final extrapolated conversions (D_C,max) were employed to calculate polymerisation shrinkage. BFS and modulus of 24-h dry stored disc specimens (10 × 1 mm; n = 10) were determined using a ball-on-ring jig setup.

RESULTS

Maximum rate of polymerisation and D_C,max increased linearly from 2.5 to 3.5% s^-1 and 67 to 83%, respectively, upon increasing MDP from 0 to 20 wt%. Values with 3% 4-META were 2.6% s^-1 and 78%. Shrinkage was 3.8 ± 0.3% for all formulations. Raising 4-META or MDP from 0 to 3 versus 5%, respectively, increased strength from 106 to 145 versus 136 MPa. A decreasing trend with higher MDP concentrations was noted. Elastic modulus showed no specific trend upon MDP increase.

SIGNIFICANCE

Whilst final conversion levels were enhanced by 3% 4-META or >5% MDP, trends did not correlate with strength. Peak strengths with 3% 4-META or 5% MDP may therefore be due to acidic monomers providing linkage between the hydrophilic, non-silane treated particles and the polymer matrix.

Effect of fluoride-releasing 4-META/MMA-TBB resin on enamel demineralization around orthodontic brackets: An in vitro µCT analysis

This study aimed to evaluate the impact of fluoride-releasing 4-META/MMA-TBB resin on the degree of enamel demineralization typically detected around orthodontic brackets using μCT. Enamel-dentin blocks were prepared from bovine teeth. Brackets were attached with either 4-META/MMA-TBB resin (SBC), fluoride-releasing 4-META/MMA-TBB resin (SBF), or fluoride-releasing RMGIC (FLC). The specimens were subjected to demineralization (pH 4.5, 21 days) and scanned by μCT (0, 7, and 21 days). Fluoride ion release under the experimental conditions was measured. The degree of demineralization detected in SBF and FLC was significantly lower than that in SBC; there were no significant differences in the degree of demineralization detected in SBF and FLC. The level of fluoride ion detected in FLC was significantly higher than that detected in SBC. Fluoride-releasing 4-META/MMA-TBB resin protected against enamel demineralization around orthodontic brackets when compared to the results from the fluoride-free resin.

Effect of a self-etching primer containing 4-META and sodium sulfite after phosphoric acid etching on bonding strength of MMA-TBB resin to human enamel

PURPOSE

The aim of this study was to evaluate the shear bond strength and durability of MMA-TBB resin to human enamel applied a self-etching primer with phosphoric acid etching.

METHODS

A self-etching primer (Teeth primer, TP) containing 4-methacryloyloxyethyl trimellitate anhydride (4-META) and sodium sulfite and two etchants having different phosphoric acid concentrations (K-etchant gel, KE, 35-45%: Red gel, RG, 20-25%) were used as treatment agent, and MMA-TBB resin was used as luting agent. Enamel surfaces were treated with six methods which were as follow: KE, RG, TP, KE+TP, and RG+TP. After enamel specimens were bonded with MMA-TBB resin and stored in distilled water for 24h, the shear bond strength test was done at 0 thermocycling or 20,000 thermocycling. These results were statistically verified with Steel-Dwass multiple comparisons and Man-Whitney U test.

RESULTS

The shear bond strength of TP group, KE+TP group, and RG+TP group were significantly higher than KE group and RG group in pre-thermocycling. KE+TP group and RG+TP group were significantly higher than other groups in post-thermocycling.

CONCLUSIONS

Applying TP with phosphoric acid etching can increased shear bond durability despite difference of phosphoric acid concentrations (35-45% or 20-25%).

The improvement of biocompatibility of adhesives : The effects of resveratrol on biocompatibility and dentin micro-tensile bond strengths of self-etch adhesives

OBJECTIVE

The aim of this in vitro study is to evaluate the effects of resveratrol (RES) addition on the cytotoxicity and microtensile bond strength (μTBS) of different adhesives.

MATERIALS AND METHODS

Five self-etching adhesives (G-aenial Bond-GC, Optibond All in One-Kerr, Gluma Self Etch-Kulzer, Clearfil S³ Bond-Kuraray, and Nova Compo-B Plus-Imicryl) were tested. They were applied to L-929 cell culture by the extract method. In the test groups, 0.5 μM RES (Sigma-Aldrich) was added into the medium. Cell viability was assessed by MTT assay after 24 h. Human extracted third molars were used for μTBS test (n = 7). The adhesives with or without 0.5 μM RES addition were applied on dentin surfaces. A composite build-up was constructed. Then, the specimens were sectioned into multiple beams with the non-trimming version of the microtensile test and subjected to microtensile forces. Statistical analysis was performed using ANOVA and post hoc Tukey test (p ˂ 0.05).

RESULTS

The extracts of all adhesives decreased the cell viability. However, RES addition increased the cell viability in all groups (p ˂ 0.05). RES addition did not cause any decrease in μTBS values of the adhesives compared to baseline. Optibond All in One showed the highest μTBS after RES addition. It was followed by Clerafil S³ Bond and Nova Compo-B Plus. No difference was determined between the Optibond All in One and Clearfil S³ Bond. There was difference between Optibond All in One and Nova Compo-B Plus (p ˂ 0.05).

CONCLUSION

RES addition may improve the biocompatibility without causing negative influence on μTBS of the adhesives.

CLINICAL RELEVANCE

RES addition has clinical applicable potential to overcome the adverse biocompatibility of adhesives.

Effect of sodium sulfite, carboxylic monomer, and phosphoric acid etching on bonding of tri-n-butylborane initiated resin to human enamel

The purpose of the present study is evaluation of bonding durability of tri-n-butylborane (TBB) initiated resin without 4-methacryloyloxyethyl trimellitate anhydride (4-META) joined to human enamel. Ground human enamel was bonded with TBB resin under six surface conditions: 1) as ground, 2) primed with Teeth Primer, 3) sodium sulfite solution, 4) 4-META solution, 5) acetone-water, and 6) phosphoric acid etching. Pre- and post-thermocycling bond strengths and change in strength after thermocycling were compared. Etching enamel with 35-45% phosphoric acid enhanced bonding durability between enamel and TBB-initiated resin. Priming with Teeth Primer or 4-META solution improved bond strength between enamel and TBB-initiated resin. Sodium sulfite had little effect on enamel bonding in the present bonding systems.

Effect of solvent type on the degradation of 4-MET

This study sought to investigate the degradation mechanism of 4-methacryloyloxy ethyl trimellitic acid, 4-MET, which is commonly used as an acidic monomer in solvated self-etching primers or one-step bonding agents. To this end, we examined the effects of solvent type used--such as ethanol, methanol, and acetone--on the degradation mechanism of 4-MET by using the 13C NMR technique. The degradation mechanism of 4-MET was strongly dependent on the type of solvent used. When an alcohol-based solution was used for 4-MET, the esterification of 1- or 2-carboxylic acid in 4-MET occurred. However, when an acetone solvent was used for 4-MET, the esterification reaction did not occur. Increases in the aging period of 4-MET solvated solutions resulted in the hydrolysis of the benzoyl ester portion in 4-MET. The 2-hydroxyethyl methacrylate, produced as a subproduct, also became hydrolyzed. In addition, methacrylic acid, non-esterified and esterified trimellitic acid, as well as ethylene glycol were produced as subproducts. In particular, the production of trimellitic acid and ethylene glycol affected the bonding efficacy and durability of the resin to the tooth created by self-etching primers or one-step bonding agents that contained the altered 4-MET.

Multinuclear magnetic resonance studies on the chemical interaction of a self-etching adhesive with radicular and coronal human dentin

This study presents evidence at molecular level for the chemical interaction between human dentin from different tooth regions and a monomer with phosphate groups, incorporated in the formulation of a simplified adhesive system. Because dentin was observed as a powder, previous verification was obtained for an eventual collagen denaturation due to the grinding process. The presence of chemical bonds involving coronal (CD) or radicular dentin (RD) was investigated using multinuclear magnetic resonance (MR) techniques. Narrow signals were identified in the carbon magic angle spinning (MAS) spectra of CD and RD treated with the adhesive, which were assigned to methylenic groups in methacryloyloxydecyl dihydrogen phosphate (MDP) bound to hydroxyapatite Ca2+; 1H spectra of the adhesive components and treated dentin, in ethanol, support this conclusion. (31)P MAS spectra obtained from both dentin regions present additional shielding and broadening effects subsequent to application and photopolymerization of the adhesive, which were higher for CD. Multinuclear MR studies provided evidence for the interaction of the adhesive with dentin, which involves hydroxyapatite and is stronger for CD than for RD, but no direct proof was obtained on bonding to collagen.

Hydrolysis of functional monomers in a single-bottle self-etching primer--correlation of 13C NMR and TEM findings

Self-etching primers/adhesives that combine acidic methacrylate monomers with water in a single bottle are hydrolytically unstable and require refrigeration to extend their shelf-lives. This study tested the null hypothesis that one year of intermittent refrigeration of a 4-MET-containing simplified self-etching primer does not result in hydrolytic changes that are identifiable by transmission electron microscopy and (13)C NMR spectroscopy. Human dentin was bonded with UniFil Bond immediately after being unpacked, or after one year of intermittent refrigeration at 4 degrees C. Fresh and aged primers were analyzed by NMR for chemical changes. Ultrastructural observations indicated that there was an augmentation in etching capacity of the aged adhesive that was not accompanied by resin infiltration or effective polymerization. New NMR peaks detected from the aged ethanol-based primer confirmed that degradation occurred initially via esterification with ethanol, followed by hydrolysis of both ester groups in the 4-MET. Hydrolysis of functional methacrylate monomers occurs despite intermittent refrigeration.

13C NMR analysis of the etching efficacy of acidic monomers in self-etching primers

It is well understood that the application of a self-etching primer enhances the bonding of the resin to the tooth. In this study, the demineralisation aspects by the Mega Bond Primer (MB) or the UniFil Bond Primer (UB) on the tooth were investigated by using liquid-state and solid-state 13C NMR techniques. The addition of hydroxyapatite or dentine to MB and the addition of dentine to UB resulted in the decrease in the peak intensity of the 13C NMR peaks attributed to the methacryloxy decyl phosphoric acid, MDP in the MB or 4-methacryloyloxy ethoxy carbonylphthalic acid, 4-MET in the UB. This decrease was because the MDP or 4-MET demineralised the tooth and the calcium salts produced from the MDP or 4-MET were precipitated from the MB or UB solution. The NMR technique is very powerful in evaluating the demineralisation aspects of the tooth by a self-etching primer. However, the calcium salts produced by the MDP or 4-MET on the tooth surface would not facilitate retention in bonding, since these calcium salts were merely deposited on to the surface of the tooth.

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.

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.