Release of monomers from four different composite materials after halogen and LED curing

PURPOSE

To evaluate the release of monomers from four different composite materials (Ceram X, Filtek Supreme XT, Tetric Flow, Tetric EvoCeram), polymerized using either halogen or LED unit.

METHODS

Ten specimens were made for each material/unit combination. Each specimen was stored in 1 ml 75% ethanol. The storage medium was renewed after 1, 7 and 28 days. Aliquots of this medium were analyzed by LC-MS/MS.

RESULTS

The effect of the curing unit on monomers' release differed significantly among the materials (P < 0.0001). The amount of BisGMA and TEGDMA released from Ceram X was not influenced by the unit used (P > 0.05). Curing with LED reduced the amount of Bisphenol A released from Ceram X compared to halogen. For Filtek Supreme XT, the type of unit exerted a significant effect on the elution of BisGMA (P < or = 0.05). LED curing resulted in a higher release of TEGDMA and UDMA compared to halogen (P < or = 0.05). For Tetric Flow, LED curing resulted in lower monomer release (P < 0.0001). For Tetric EvoCeram, the amounts of BisGMA, UDMA and Bisphenol A were higher when polymerizing with LED compared to halogen. The release of substances was more material dependent and less influenced by the curing unit used.

Elution of residual monomers from dental composite materials

AIM

This study was designed to determine the type and amount of the monomers leached from the different particle sizes of the composite materials.

MATERIALS AND METHODS

Three different disk sizes (2, 4, 6 mm) prepared for each material group (Filtek Flow, Filtek A110, Filtek P60 and Filtek Supreme) were polymerised by LED and halogen light; the specimens were then placed in artificial saliva. The monomer release in 30 min and 24 hrs from the specimens was analyzed in HPLC calibrated for the monomer extracts before.

RESULTS

TEGDMA release was detected in all material groups after 30 min and after 24 hrs. BisGMA and BisEMA were not determined in any groups and UDMA was detected only in Filtek Supreme. Significant differences in release of TEGDMA and UDMA were obtained between the different sizes of discs. Significantly high amount of TEGDMA and UDMA monomer release was obtained in LED than Halogen groups. Lower amount of monomer release was obtained in species of 30 min than 24 hrs.

CONCLUSION

Data has revealed that the monomer release could be detected significantly high from the composite materials polymerized by a lower output curing light device; and higher elution of monomers was determined as the composite thickness has increased. Therefore, the clinical applications of composite materials and the type of curing units have very important effects on the success of restorations and in the decrease of potential side effects.

Quantitative analysis of adhesive resin in the hybrid layer using Raman spectroscopy

The objective was to determine absolute molar concentration of adhesive resin components in the hybrid layer by establishing methods based on Raman spectroscopy fundamentals. The hybrid layer was treated as a three-component system consisting of collagen and an adhesive resin containing two monomers. Adhesive standard specimens and Raman peak area ratios obtained with a 785 nm excitation wavelength were used to construct separate calibration curves for comonomer relative molar concentration and Bis-GMA absolute molar concentration. As collagen and water had no measurable peaks in the fingerprint region, a dilution coefficient K(j) was defined to describe their impact on Raman peak area and to calculate HEMA absolute molar concentration. Methodology was validated using an analogous system containing acetone/ethanol/water. The absolute molar concentration of Bis-GMA and HEMA decreased 87% and 83%, respectively, from the top quarter to the middle of the hybrid layer. Additionally, less Bis-GMA penetrated the hybrid layer than HEMA, as indicated by the approximately 20% decrease in comonomer molar concentration ratio between the adhesive resin layer and the top half of the hybrid layer. Lack of complete monomer infiltration will further challenge dentin-adhesive bond longevity. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Analysis of the degradation of a model dental composite

Dental composites undergo material property changes during exposure to the oral environment and may release compounds of potential toxicity, such as bisphenol A. Degradation of dental composites was studied in a simplified overlayer model in which bisphenol A diglycidyl methacrylate (BisGMA) was covalently bound to a porous silicon oxide surface. It was hypothesized that the chemical structure of this overlayer would allow release of bisphenol A, BisGMA, and the decomposition products thereof, upon exposure to water for an extended period. Liquid chromatography mass spectrometry found leaching of intact BisGMA and several degradation products that contained the bisphenol A moiety from the overlayer into distilled water after 2 wks of aging. The absence of bisphenol A release from the overlayer reduces concerns regarding its potential health risk in dental composites. Nevertheless, health concerns might arise with respect to BisGMA and the leached degradation products, since they all contain the bisphenol A moiety.

ABBREVIATIONS

BisGMA, bisphenol A diglycidyl methacrylate; HPLC, high-performance liquid chromatography; LCMS, liquid chromatography mass spectrometry; MA, methacrylic acid; MPS, 3-(trimethoxysilyl) propyl methacrylate; m/z, mass-to-charge ratio; and TIC, total ion chromatogram.

Elution of monomers from two conventional dental composite materials

OBJECTIVE

The aim of this study was to determine the elution of monomers of two conventional resin composite materials after different polymerization and storage times.

METHODS

Two resin composites (a hybrid and a flowable) were used. Four groups (n=10, diameter: 4.5mm, thickness: 2mm) of each material were fabricated, one for each polymerization time of: 0s, 20s, 40s, and 80s. The samples were stored in 1ml of 75% ethanol at room temperature, and the storage medium was renewed after 24h, 7 days, and 28 days. From the storage medium that was removed, samples were prepared and evaluated, with LC-MS/MS.

RESULTS

Bisphenol A and UDMA were not detected in the samples. Regardless of the polymerization time, the material or the storage time, a higher amount of BisGMA was eluted compared to TEGDMA. The amount of monomer that was released from the polymerized samples of the hybrid resin composite (Tetric Ceram) was significantly higher (p<0.0001) compared to the flowable (Tetric Flow). No significant difference was found between samples polymerized for 20s compared to 40s concerning the elution of monomers. Only a polymerization time of 80s resulted in a decreased release of monomers. The release of TEGDMA decreased after 28 days; however, the elution of BisGMA remained at high levels.

SIGNIFICANCE

The release of monomers remains at a high level for a long time (7-28 days) after polymerization. The 40s that are usually used for the polymerization of resin composites seems insufficient in order to prevent a high release of monomers.

HPLC analysis of components released from dental composites with different resin compositions using different extraction media

Components released from dental composite resins are essential factors in the assessment of biocompatibility of these materials. The effect of different extraction media on monomer release from composite resins based on different monomer types was evaluated. Three types of visible light cured composite resins were formulated based on the following monomers: triethylene glycol dimethacrylate (TEGDMA), bisphenol A glycerolate dimethacrylate (BisGMA), and urethane dimethacrylate (UDMA). Seventy-five composite resin discs were fabricated and light cured for 1 min in the absence of oxygen. Extraction media used were: distilled water, saline solution, artificial saliva, serum-free culture medium, and culture medium with 10% fetal calf serum. The analysis of extracts from the composite resins was carried out by High Performance Liquid Chromatography (HPLC). Quantifiable amounts of TEGDMA were released into the aqueous media. However, BisGMA and UDMA were not detectable in any of the extracts from the composite resins. Statistical analysis by one-way ANOVA followed by Tukey's test showed that there was a significant difference in TEGDMA release between culture media and other media (p < 0.05). From the results of this experiment it can be concluded that TEGDMA-based composite resins can release a high quantity of monomer into aqueous environments. The type of extraction medium may have a significant effect on monomer release from composite resins.

Development of high-viscosity, two-paste bioactive bone cements

Self-curing two-paste bone cements have been developed using methacrylate monomers with a view to formulate cements with low polymerization exotherm, low shrinkage, better mechanical properties, and improved adhesion to bone and implant surfaces. The monomers include bis-phenol A glycidyl dimethacrylate (bis-GMA), urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) as a viscosity modifier. Two-paste systems were formulated containing 60% by weight of a bioactive ceramic, hydroxyapatite. A methacroyloxy silane (A174) was used as a coupling agent due to its higher water stability in comparison to other aminosilanes to silanate the hydroxyapatite particles prior to composite formulation. A comparison of the FT-infrared spectrum of hydroxyapatite and silanated hydroxyapatite showed the presence of the carbonyl groups ( approximately 1720 cm(-1)), -C=C-( approximately 1630 cm(-1)) and Si-O- (1300-1250 cm(-1)) which indicated the availability of silane groups on the filler surface. Two methods of mixing were effected to form the bone cement: firstly by mixing in an open bowl and secondly by extruding the two pastes by an auto-mixing tip using a gun to dispense the pastes. Both types of cements yielded low polymerization exotherms with good mechanical properties; however, the lower viscosity of UDMA allowed better extrusion and handling properties. A biologically active apatite layer formed on the bone cement surface within a short period after its immersion in simulated body fluid, demonstrating in vitro bioactivity of the composite. This preliminary data thus suggests that UDMA is a viable alternative to bis-GMA as a polymerizable matrix in the formation of bone cements.

Light-cured or chemically cured orthodontic adhesive resins? A selection based on the degree of cure, monomer leaching, and cytotoxicity

PURPOSE

The purpose of this study was to estimate the degree of cure and monomer leaching of a light-cured and a chemically cured (no-mix) adhesive and to assess their biologic properties.

MATERIAL

The degree of cure of adhesive specimens prepared with a procedure identical to the clinical bonding process was assessed by infrared spectroscopy. The adhesives were then immersed in normal saline solution for 2 months, and the residual monomer leached from the adhesives was quantitatively and qualitatively analyzed by liquid chromatography. The effect of the immersion media on human gingival fibroblasts' viability and proliferation was also evaluated with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and deoxyribonucleic acid (DNA) synthesis assays, respectively. The results were analyzed by analysis of variance and Tukey test (alpha = .05).

RESULTS

No difference was found between the 2 adhesives with respect to their degree of cure and the amount of triethylene glycol dimethacrylate released; no diglycidyl dimethacrylate monomer was detected in the eluent. However, significant qualitative changes in the composition of the substances eluted from the 2 adhesives were observed.

CONCLUSIONS

Whereas no cytotoxic effect was shown for either immersion media, a moderate reduction in the DNA synthesis was obtained by both adhesives, implying a minor cytostatic effect. Further research is required to assess the long-term biologic properties of adhesives, including potential estrogenic action.

Development of highly reactive mono-(meth)acrylates as reactive diluents for dimethacrylate-based dental resin systems

Reactive diluents such as triethyleneglycol-dimethacrylate (TEGDMA) have been widely used with bisphenol-A-glycidyl-dimethacrylate (Bis-GMA) to achieve restorative resins with appropriate viscosity and higher conversion. However, additional water sorption and polymerization shrinkage were also introduced. The aim of this work is to investigate whether the cure and material properties can be improved in dental resins containing novel mono-(meth)acrylates as reactive diluents so that these Bis-GMA-based copolymers have reduced polymerization shrinkage but higher overall double bond conversion. Several ultra-high-reactivity mono-(meth)acrylates that contain secondary functionalities have been synthesized and investigated. The polymerization rate and double bond conversion were monitored using photo-FTIR. Polymerization shrinkage, dynamic mechanical analysis, and flexural strength were characterized. Compared with the Bis-GMA/TEGDMA control, the Bis-GMA/mono-methacrylate systems studied showed higher final conversions, faster curing rates, and decreased polymerization shrinkage. Our optimum system Bis-GMA/morpholine carbamate methacrylate achieved 86% final conversion (vs. 65%), a polymerization rate 3.5 times faster, and a 30% reduction in polymerization volumetric shrinkage. These results indicate that certain highly reactive, novel mono-(meth)acrylates possess very promising potential to replace TEGDMA as reactive diluents and can readily be applied to develop superior dental resins.

Elution of leachable components from composites after LED and halogen light irradiation

This study investigated the influence of curing lights and modes on the elution of leachable components from dental composites. Four LED/halogen curing lights (LED-Elipar Freelight [FL], 3M-ESPE and GC e-light [EL], GC; high intensity halogen-Elipar Trilight [TL], 3M-ESPE; very high intensity halogen-Astralis 10 [AS], Ivoclar Vivadent) were selected for this study. Pulse (EL1), continuous (FL1, EL2, TL1), turbo (EL3, AS) and soft-start (FL2, EL4, TL2) curing modes of the various lights were examined. A conventional continuous cure halogen light (Max [MX], Dentsply-Caulk) was used for comparison. Three composite (Z100, 3M-ESPE) specimens (6.5 mm in diameter and 1-mm thick) were made for each curing light-mode combination. After polymerization, the specimens were stored in air at 37 degrees C for 24 hours and incubated in acetonitrile at 37 degrees C for 24 hours. BisGMA and TEGDMA extracts were isolated by high performance liquid chromatography (HPLC). Data were subjected to analysis using one-way ANOVA/Scheffe's post-hoc test and Independent Samples t-test at significance level 0.05. The total monomer (BisGMA and TEGDMA) eluted ranged from 8.75 to 27.97 ppm for FL1 and AS, respectively. Significantly more unreacted monomers were leached from composites cured with all modes of EL and AS when compared to MX. No significant difference in the total monomer eluted was observed between the two modes of FL/TL and MX Although composites cured with EL2 released significantly less monomer than EL1, 3 and 4, no significant difference in the total monomer eluted was observed between the continuous and soft-start modes of FL and TL. The elution of leachable components from composites appears to be curing light specific rather than light source (LED or halogen) and curing mode specific.

Stress analysis of an upper central incisor restored with different posts

The effect of different anatomic shapes and materials of posts in the stress distribution on an endodontically treated incisor was evaluated in this work. This study compared three post shapes (tapered, cylindrical and two-stage cylindrical) made of three different materials (stainless steel, titanium and carbon fibre on Bisphenol A-Glycidyl Methacrylate (Bis-GMA) matrix). Two-dimensional stress analysis was performed using the Finite Element Method. A static load of 100N was applied at 45 degrees inclination with respect to the incisor's edge. The stress concentrations did not significantly affect the region adjacent to the alveolar bone crest at the palatine portion of the tooth, regardless of the post shape or material. However, stress concentrations on the post/dentin interface on the palatine side of the tooth root presented significant variations for different post shapes and materials. Post shapes had relatively small impact on the stress concentrations while post materials introduced higher variations on them. Stainless steel posts presented the highest level of stress concentration, followed by titanium and carbon/Bis-GMA posts.

Depth of cure efficacy of high-power curing devices vs traditional halogen lamps

PURPOSE

To determine the depth of cure resulting from three different curing devices in a photoactivated microhybrid composite through high-performance liquid chromatography (HPLC) analysis of leachable monomers.

MATERIALS AND METHODS

Three different curing units, a halogen lamp (Heliolux, Vivadent), a xenon lamp (Kreative Kuring, Allyn Welch), and a plasma-arc lamp (Apollo 95, DMDS) were investigated using a universal microhybrid composite (P 60, 3M) as the test material. To assess the effect of curing device variation, a flexural strength test was performed. In addition, samples of composite were prepared and cured "in contact" (0 mm between the sample surface and light-guide tip) and through a specific thickness of composite (1, 2, or 3 mm). The monomers (bis-GMA and UDMA) eluted from the samples were detected by HPLC.

RESULTS

No significant differences were found in the mechanical properties of composite cured with different light sources. In contrast, the concentration of eluted monomers (bis-GMA, UDMA) at a depth of 2 mm and more was significantly higher for the specimens cured with the high-power curing devices than those cured with the traditional halogen lamp.

CONCLUSION

Under these experimental conditions, high-power curing devices were shown to be inferior in the deep polymerization of resin composite when compared to a traditional halogen lamp.

Influence of composition on rate of polymerization contraction of light-curing resin composites

A slow contraction may result in reduced gap formation when a restorative resin polymerizes in a dental cavity. It was the aim in the present work to investigate the rate of contraction in relation to composition of experimental light-curing resin composites. The monomer of the resin composites consisted of mixtures of BisGMA, TEGDMA, and in one series HEMA. The resins contained varying amounts of initiators, co-initiators, and inhibitor, and were made composite by adding a silanized glass filler to a content of 74% by weight of the composite paste. The polymerization contraction up to 120 sec was determined by means of the bonded-disk method. Within the ranges studied, the concentration of initiator and co-initiator in the monomer mixture had only an insignificant influence on rate of polymerization. In comparison to camphorquinone, the initiators 1-phenyl-1,2-propanedione and benzil reduced the rate of polymerization without affecting the final contraction. In comparison to N,N-dimethyl-p-aminobenzoic acid ethyl ester, N,N-cyanoethyl methylaniline was as effective, while N,N-diethanol-p-toluidine was less effective as co-initiator. A relatively high content of the inhibitor methoxyhydroquinone reduced the initial rate but not the final polymerization contraction. The rate of polymerization increased with the level of HEMA and TEGDMA in the monomer mixture. It was concluded that intrinsic slow cure may be obtained with certain compositions of resin composites without impairing the final extent of polymerization.

Water sorption and solubility of dental composites and identification of monomers released in an aqueous environment

Water sorption and solubility of six proprietary composite resin materials were assessed, and monomers eluted from the organic matrix during water storage identified. Water sorption and solubility tests were carried out with the following storage times: 4 h, 24 h and 7, 60 and 180 days. After storage, water sorption and solubility were determined. Eluted monomers were analysed by high performance liquid chromatography (HPLC). Correlation between the retention time of the registered peak and the reference peak was observed, and UV-spectra confirmed the identity. The results showed an increase in water sorption until equilibrium for all materials with one exception. The solubility behaviour of the composite resin materials tested revealed variations, with both mass decrease and increase. The resin composition influences the water sorption and solubility behaviour of composite resin materials. The HPLC analysis of eluted components revealed that triethyleneglycol dimethacrylate (TEGDMA) was the main monomer released. Maximal monomer concentration in the eluate was observed after 7 days. During the test period, quantifiable quantities of urethanedimethacrylate (UEDMA) monomer were observed, whereas 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane (Bis-GMA) was only found in detectable quantities. No detectable quantities of bisphenol-A were observed during the test period.

Filler particle leachability of experimental dental composites

We studied the effect of matrix selection, filler composition, and filler silanization on filler leachability after storage in distilled water or artificial saliva. We evaluated 2 matrix systems, 2 filler systems and 2 silane treatment procedures, combined into 8 different dental composite materials. A total of 128 batches were made, and 2 specimens per batch were prepared. Of these 2 specimens per batch, one was stored in distilled water and the other in artificial saliva, both at 37 degrees C. We transferred the specimens each 30th day during a 3-yr period to new vials containing either freshly distilled water or newly mixed artificial saliva and analyzed the solutions the specimens had been stored in regarding Si, Ba and Al concentrations. The analyses revealed that storage solution, filler composition, and total time in the storage solution had strong effects on leachability. The average monthly leakage of the three elements was linear with time and higher in the artificial saliva. The Ba-containing filler leached Si faster in artificial saliva than in distilled water, and roughly twice as much as the quartz filler. The storage effect approached an order of magnitude, while the filler effect was roughly a factor of two. Filler leaching was linear over time.

Estrogenicity of fissure sealants and adhesive resins determined by reporter gene assay

It is controversial whether the dental resinous materials containing 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (Bis-GMA), which is synthesized from the estrogenic compound bisphenol A (BPA), include unreacted BPA and/or can mimic the effects of natural steroid hormones. In the present study, the estrogenic activities of 3 fissure sealants and 5 adhesive resins, which were all unpolymerized, were determined by means of a reporter gene assay, and the relevance of the components to the estrogenicity was investigated. Two commercially available sealants were confirmed to have estrogenic activity, although none of the tested materials contained BPA. In contrast, hydrophobic monomer bisphenol A dimethacrylate (BPA-DMA), which is also estrogenic, was found to be included in these estrogenic sealants in an amount greater than the minimum concentration to show estrogenicity. This suggests that the estrogenicity of the two proprietary sealants was associated with BPA-DMA rather than with BPA.

Migration of bisphenol-A diglycidyl ether (BADGE) and its reaction products in canned foods

Bisphenol-A diglycidyl ether (BADGE) is used as an additive or starting agent in coatings for cans. The presence of hydrochloric acid in the organosol (PVC-based) lacquers results in formation of chlorohydroxy compounds of BADGE. These compounds, as well as BADGE itself, are potential migrants into the preserved food and are of toxicological concern. In the present investigation the presence of BADGE and the chlorohydroxy compounds (BADGE.HCl and BADGE.2HCl) in various kinds of canned foods from 30 brands have been determined by HPLC with fluorescence detection. BADGE was found in levels up to 5.1 mg/kg in the food and only in food from cans containing BADGE.HCl and BADGE.2HCl in the lacquers. BADGE was found both in fish in oil and in fish in tomato sauce, however, the highest amounts were found in the fatty foodstuffs. BADGE.HCl and BADGE.2HCl were found in concentrations up to 2.4 mg/kg and 8.3 mg/kg, respectively. Unlike BADGE, BADGE.2HCl was found in similar concentrations in fish in oil and in fish in tomato sauce. In aqueous and acidic foodstuffs BADGE readily hydrolyses into mono- and dihydrolysed products (BADGE.H2O and BADGE.2H2O). In this study BADGE.H2O was not found in any food sample, whereas BADGE.2H2O was found in levels up to 2.6 mg/kg. The Scientific Committee for Food (SCF) of the European Commission has proposed that a limit of restriction of 1 mg/kg food shall include BADGE itself and BADGE.H2O, BADGE.HCl, BADGE.2HCl and BADGE.HCL.H2O. The present results indicate that the migration of BADGE.HCl and BADGE.2HCl, compounds with almost no data on toxicity, implies a greater problem than BADGE.H2O and BADGE.2H2O.

The effect of post-cure heating on residual, unreacted monomer in a commercial resin composite

OBJECTIVES

This paper examined the influence of post-cure temperature on the amount of unreacted monomer remaining in a commercial light-cured resin composite restoration following initial light-curing and subsequent post-cure heating.

METHODS

Discs of composite were light-cured and then subjected to immediate post-cure heating (50, 75, 100, or 125 degrees C for 7 min) or were left unheated (control). They were then placed in a solvent for two weeks at 37 degrees C to extract the unreacted monomer. HPLC analysis was used to determine the amounts of TEGDMA, BIS-GMA, and ethoxylated BIS-GMA remaining after the different treatments. The amounts of each monomer leaching were compared using ANOVA with respect to the different curing treatments.

RESULTS

Even the lowest post-cure heat treatment (50 degrees C) resulted in 80% reduction in remaining, unreacted TEGDMA, 75% reduction in BIS-GMA, and 77% lower ethoxylated BIS-GMA than the light-cured only control. Post-cure heating at 75 degrees C and above resulted in the lowest amount of each type monomer remaining uncured in the polymer and did not significantly decrease with an increase in post-cure temperature for the most part.

SIGNIFICANCE

One of the main benefits of post-cure heating of resin composite restorations could be the enhancement of biocompatibility of these restorations as a result of the significant decrease in potentially leachable, unreacted monomer.

Extractable free monomers from self-cured dental sealants resulting from dispensing errors

High performance liquid chromatography (HPLC) experiments were performed on a series of commercially available self-curing dental sealant materials that were deliberately mismixed. The goal of the experiments was to measure the amount of extractable sealant under conditions of nonideal processing as might happen clinically. The stoichiometry of the two component resins ranged from a 2/1 to a 1/2 catalyst to base mixture using a commercially available self-cure sealant that was to be mixed 1/1 based on the manufacturer's recommendations. Following fabrication the samples were immersed in an ethanol/water mixture as an extraction fluid that was then analyzed using HPLC. Values other than the 1-1 stoichiometry led to a statistically larger extractable content of bis-glycidyl methacrylate relative to the control. The extractable fraction of triethylene glycol dimethacrylate also increased with mismixing, although statistical differences varied somewhat more. Given the increased concerns about the effects of extractable monomers on the endocrine system, there may be an increased need to maintain proper stoichiometry in a clinical setting.

Detection of bisphenol-A in dental materials by gas chromatography-mass spectrometry

The xenoestrogenic substance bisphenol-A is widely used as a synthetic precursor of resin monomers, such as bisphenol-A diglycidyl methacrylate. Reports describing the release of bisphenol-A from polymerized resin into saliva have aroused considerable concern regarding exposure to xenoestrogen by dental treatment. The purpose of the present study was to demonstrate a reliable methodology of detecting the trace amounts of bisphenol-A in dental materials. Bisphenol-A was separable from bisphenol-A diglycidyl methacrylate, which is often employed as the principal dimethacrylate monomer, by selective extraction with a Sep-Pak C18 cartridge. Using this extraction method in combination with a gas-chromatography mass-spectrometry, we have obtained evidence that all unpolymerized materials used in this study were contaminated with bisphenol-A. Quantitative analysis using a deuterium-labeled compound as an internal standard revealed bisphenol-A contents in commercial dental materials ranging from < 1 microgram/g material to about 20 micrograms/g material. The polymerized dental materials released up to 91.4 ng bisphenol-A/g material into phosphate buffered saline during 24-h incubation. These results indicate that bisphenol-A can be released from dental materials, however the leachable amount would be less than 1/1000 of the reported dose (2 micrograms/kg body weight/day) required for xenoestrogenisity in vivo.

High pressure liquid chromatography of dentin primers and bonding agents

OBJECTIVE

The purpose of this study was to analyse the composition of representative dentin primers and bonding agents, and to investigate the relationship between chromatographic retention times and partition coefficient (log P) values.

METHODS

Dentin bonding systems (DBS) were analysed with reversed phase high-performance liquid chromatography (HPLC). The log P values were obtained computationally with the advanced chemistry development software.

RESULTS

The DBS were analysed and the monomers were identified. The log P values were calculated and the relationship between log P and retention times for the monomers was described by the equation: log P = 2.436R(t) - 3.636, with a correlation value (r) of r = 0.9095.

SIGNIFICANCE

The components of the DBS were successfully resolved and identified, thus illustrating the analytical power of HPLC regarding those systems. Also the log P values correlated with the retention times of monomers. Thus, they can be used as a prediction tool in future analysis. These findings are important for a mechanistic understanding of Primer and Adhesive actions in the bonding to the dentin.

Pharmacokinetics of bisphenol A released from a dental sealant

BACKGROUND

Limited information is available regarding potentially estrogenic bisphenol A, or BPA, released from dental sealants. This study determined the rate- and time-course of BPA released from a dental sealant (Delton Opaque Light-cure Pit and Fissure Sealant, Preventive Care/Dentsply) when applied at a dosage of 8 milligrams (one tooth) or 32 mg (8 mg on each of four teeth) to 40 healthy adults.

METHODS

The authors recruited 40 healthy subjects (18 men and 22 women, 20-55 years of age) who did not have histories of pit and fissure sealant placement or composite resin restorations. The authors collected saliva (30 milliliters) and blood (7 mL) specimens from all subjects immediately before sealant placement (baseline) and at one hour, three hours, one day, three days and five days after sealant placement. They used high-pressure liquid chromatography to determine BPA (detection sensitivity 5 parts per billion, or ppb) in all specimens.

RESULTS

The authors detected BPA in some saliva specimens (5.8-105.6 ppb) collected at one hour and three hours. The BPA, however, was not detectable beyond three hours or in any of the serum specimens. For the one- and three-hour saliva samples, the BPA concentration in the high-dose (32 mg) group was significantly greater than in the low-dose (8 mg) group (P < .05, Wilcoxon signed rank test). In the high-dose group, there was a significant decrease in saliva BPA concentrations from one hour to three hours (P < .01, Wilcoxon signed rank test).

CONCLUSION

This study showed that BPA released orally from a dental sealant may not be absorbed or may be present in nondetectable amounts in systemic circulation. The concern about potential estrogenicity of sealant may be unfounded.

Elution parameters and HPLC-detection of single components from resin composite

The toxic effects of mercury derived from amalgam fillings have been a focus of controversy in Germany during the last 25 years. As alternatives to amalgam, composites are used widely to restore anterior and posterior permanent teeth. This study quantifies the amount of TEGDMA and methacrylic acid that can be derived from a polymerized commercial hybrid composite material. Different specimens were made with different curing methods with and without an oxygen inhibition layer. To simulate the removal of composite fillings, some samples were pulverized. The specimens were eluted in distilled water at 37 degrees C for different time intervals. To check the influence of acid conditions, pulverized material was incubated in 6 M HCl. The separation of the eluted chemical resin components was done by HPLC. A defined mixture of pure components was used as an external standard for the identification and quantification of the eluted components. The results focus on the release of triethylengly-coldimethacrylate (TEGDMA) and methacrylic acid. Concerning the different incubation methods, the results showed higher TEGDMA elution with oxygen inhibited surface layer and with the pulverized samples. Within acid conditions, the amount of TEGDMA found was low, but the amount of methacrylic acid increased. Small resin monomers like TEGDMA are primarily eluted from composite in aqueous solutions. Within acid conditions a hydrolytic disintegration of the ester bonding of the monomers could be observed. Methacrylic acid--a substance with allergenic potential--could be detected.

Identification and characterization of estrogen-like components in commercial resin-based dental restorative materials

Recently, resin-based dental restorative materials have been targeted as potential sources of xenoestrogens, specifically bisphenol A (BPA) and bisphenol A dimethacrylate (BAD), which could contribute to overall estrogen load and result in deleterious side effects. The present study used high-pressure liquid chromatography (HPLC) to analyze twenty-eight different commercially available dental resins for the presence of BPA and/or BAD. In addition, sublines of the MCF-7 human breast tumor cell line were cultured in the presence of eluates from eleven of the dental resins and assessed for proliferative responses using the sulforhodamine B assay. Only one resin, Delton II, had detectable levels of BPA or BAD that could be verified by Fourier transform infrared spectrometry. Likewise, eluates from Delton II were the only samples that elicited a significant proliferative response in two of the MCF-7 sublines tested. Therefore, we conclude that dental resins in general do not represent a significant source of BPA or BAD exposure.

Determination of leachable components from four commercial dental composites by gas and liquid chromatography/mass spectrometry

OBJECTIVES

The purpose of our study was to determine the quality and quantity of leachable residual (co)monomers and additives eluted from various commercial dental composite resins after polymerization.

METHODS

Polymerized specimens from four universal hybrid-type composite resins were eluted for 3 days with methanol resp, water. Then all extracts were analysed by gas chromatography/mass spectrometry or liquid chromatography/mass spectrometry using a particle beam interface.

RESULTS

In all polymerized composite resin specimens, (co)monomers and various additives as well as contaminants from manufacturing processes were identified. Almost every compound detected in the unpolymerized resins could also be identified in the methanol extracts, but only a few of them were found in the water extracts. From these the co-monomer TEGDMA was extracted in quantities higher than those reported to be cytotoxic in primary human oral fibroblast cultures.

CONCLUSIONS

From our results we conclude that the extractable quantities of composite resin components should be minimized, either by reducing the mobility of leachable substances within the set material or by applying less water-soluble components. Furthermore, all ingredients of a dental composite should be declared by the manufacturers, in order to identify those substances in a product which may cause adverse side effects in patients and dental personnel.

High-pressure infrared and FT-Raman investigation of a dental composite

Composite resins are often used as filling materials on load-bearing surfaces of teeth. As masticatory stresses can be high, here, we study the effect of pressure on the behaviour of a dental composite. Using a polymerized wafer, the IR and FT-Raman spectra of a zirconia-containing proprietary composite (Z100, 3M, Minneapolis, MN, USA) were recorded. The high-pressure IR spectra were also recorded. Band assignments were made for the main peaks of both organic and inorganic components. Breaks in the pressure dependences (dv/dP) of the organic components were found at 22 kbar. Different pressure dependences for different vibrational modes of inorganic components were also observed. These data suggest that the network structure of the composite is compacted under high pressure and that both the atomic distance and bonding angles in the network are altered.

In vitro elution of leachable components from dental sealants

Recent concerns have been raised about the possibility that estrogenic chemicals, in particular bisphenol-A, or BPA, might be leached out of dental sealants. This study aimed to identify and quantify BPA and other components released from seven light-cured fissure sealants in vitro. None of the tested sealants was shown to have released BPA; however, the investigators identified other eluted components that should be investigated for their biological effects.

The effect of comonomer composition, silane heating, and filler type on aqueous TEGDMA leachability in model resin composites

Experimental composites using either bisGMA/TEGDMA or UEDMA/ TEGDMA matrices, quartz or barium glass fillers, and 2 different filler silanization methods were evaluated regarding monomer leachability in distilled water. The leached amount was detected and quantified using gas chromatography. The results showed that twice as much TEGDMA is leached from a bisGMA/TEGDMA based composite than from an UEDMA/ TEGDMA based composite, when both contain 50 wt% TEGDMA. The hypothesis suggested that the higher degree of cure of UEDMA/TEGDMA based composites would be reflected in a lower monomer leaching value, and this hypothesis was supported by the findings. Whether such a correlation exists within groups of UEDMA/TEGDMA based matrices having different degrees of cure was not determined and needs to be investigated in future studies. Variables such as filler composition and silane treatment did not affect the leaching values of TEGDMA in water. That finding suggests that future studies should target differences in matrices, and that the need for considering effects of filler composition and silane treatment methods should not receive the same priority.

How different curing methods affect mechanical properties of composites for inlays when tested in dry and wet conditions

The purpose of this investigation was to evaluate the differences in the mechanical properties of 3 composite materials in relationship to the intraoral and extraoral curing techniques of direct and indirect (inlay) restorations, and how the mechanical properties are affected by water sorption. Creep characteristics in compression as well as the stress-strain relationship at a constant loading rate both in compression and flexure, were determined. A secondary aim was to investigate the influence of filler content and monomer composition on the mechanical properties. The results are presented as creep curves and as values for elastic moduli, ultimate strength, and ultimate strain. The materials were cured with 2 curing methods. Method A was light curing with a handheld curing unit, and method B was curing in light curing ovens. Water sorption increased the creep values for all types of specimens. Curing in light ovens (method B) gave significantly lower creep values at high stresses than curing with a handheld curing unit (method A). Water sorption decreased the modulus and ultimate strength values for specimens cured with method A. The ultimate strength values also differed for dry and wet specimens cured with method B. There were no general differences in compressive and flexural stress-strain properties between specimens cured according to the methods A and B.

Fluoride release of restorative materials exposed to a fluoridated dentifrice

The purpose of this study was to examine the effect that brushing with a fluoridated dentifrice (Crest--Procter and Gamble) has on the fluoride release of restorative materials. Thirty standardized discs were fabricated; 10 were P-50 (3M) nonfluoridated composite resin (control), ten were Heliomolar Radiopaque (Ivoclar/Vivadent) fluoride releasing composite resin, and ten were Ketac Fil (ESPE) glass ionomer cement. Specimens were placed into separate containers of 10 mL deionized water. Half the specimens from each group were brushed with fluoridated dentifrice for two minutes twice per day and rinsed. The fluoride level of each specimen was evaluated for thirty days, using a fluoride specific ion analyzer. An analysis of variance (ANOVA) and Duncan's test (p < 0.05) indicated significant differences in fluoride release. The brushed glass ionomer was significantly higher than all other groups and the glass ionomer not brushed was significantly higher than all composite groups. Glass Ionomer Cement-brushed > Glass Ionomer Cement > Fluoridated Composite Resin-brushed = Fluoridated Composite Resin = Composite Resin-brushed = Composite Resin. Brushed glass ionomer appears to release the highest fluoride level, acting as a fluoride reservoir from the dentifrice for subsequent fluoride release.

A study of component release from resin pit and fissure sealants in vitro

OBJECTIVE

A recent study reported that an estrogenic chemical, bisphenol-A, was released from a fissure sealant. The aim of this study was to identify and quantify the major (or detectable) components released from any of seven commercially-available, light-cured pit and fissure sealants in vitro.

METHODS

The fissure systems of ten extracted, third molar teeth were filled with sealant, light-activated and immersed in separate containers of distilled water. Separate, cylindrical stainless steel molds were filled with sealant which was then light-activated and immersed. Each mold or tooth with sealant was moved to a new container of water at defined times and each remaining water sample (eluate) then analyzed by high performance liquid chromatography (HPLC).

RESULTS

Triethylene glycol dimethacrylate (TEGDMA) was present in all eluates from each of the sealants tested. 2,2-bis[4'-(2'-hydroxy-3'-methacryloyloxy)phenyl]propane (BisGMA) was detected at much lower levels (about one thousand-fold less) in eluates from one sealant only. Bisphenol-A was not detected in any eluates. The rates of TEGDMA and BisGMA release were highest on first immersion and decreased thereafter. The total amount of TEGDMA released was on the order of 0.25 mg per tooth. Most release occurred during the first day.

SIGNIFICANCE

Because bisphenol-A release could not be detected from any of the seven sealants tested, these results call into question earlier concerns expressed about possible adverse effects of bisphenol-A released from resin sealants.

Effect of propanal and diacetyl on quantity of remaining double bonds of chemically cured BisGMA/TEGDMA resins

The aim of the present study was to determine the effect of propanal and diacetyl addition on the quantity of remaining double bonds of chemically cured dental resins. Propanal (propionaldehyde) or diacetyl (2,3-butanedione) was added to monomer mixtures, which were then made chemically curable. The monomer mixtures were varied with respect to content of propanal or diacetyl. Addition of propanal or diacetyl to chemically curable resins resulted in a decrease in the quantity of remaining double bonds from 19.6% to 1.9% and from 19.6% to 11.4%, respectively. A negative correlation of statistical significance was found between content of propanal and quantity of remaining double bonds, while the relationship between content of diacetyl and quantity of remaining double bonds was found not to be linear. Propanal was equally effective in reducing the quantity of remaining double bonds in chemically cured and in the light cured resins studied previously. As regards diacetyl, a more pronounced effect on quantity of remaining double bonds was noted for light cured resins as compared with chemically cured resins. The most likely common reaction mechanism of propanal and diacetyl seemed to be that of chain transfer reactions. Furthermore, analysis of the data indicated a possible additional photoinitiating function of diacetyl.

Laboratory evaluation of three visible light-cured resinous liners

OBJECTIVES

The aim of the present study was to evaluate the composition and the laboratory performance of three visible light-cured resinous liners (Cavalite, Ionoseal and Timeline).

METHODS

Monomers were separated from fillers and were analysed by HPLC. Set pastes were analysed by FTIR spectroscopy and diametral strengths and water solubility were measured.

RESULTS

The monomers identified in the liners were BisEMA/2-HEMA (Cavalite), BisDMA/BisGMA (Ionoseal) and UEDMA (Timeline). Significant variations were found in the filler content but the mechanical response as assessed by the diametral tensile strength showed no statistical differences. The curing efficiency ranged from 24.2 to 31.0% (top surfaces) to 26.0-54.0% (bottom surfaces) of remaining C = C bonds. No positive correlations were found between curing efficiency and optical properties. The bond strength of the liners to dentine was negligible compared with that to composite. All the liners demonstrated extensive gap formation and debonding at the liner-dentine interfaces in marginal adaptation testing. Statistical differences were noticed in the water absorption and water solubility values of the products. Ionoseal showed extensive hydrolytic degradation compared with the other liners. No evidence of acid-base reaction was found in the set products.

Residual monomer leaching from chemically cured and visible light-cured orthodontic adhesives

The objective of this study was to quantify the amount of residual monomer leached from chemically cured and visible light-cured orthodontic adhesives based on Bis-GMA/TEGDMA monomers, when bonded to ceramic and stainless steel brackets. The residual TEGDMA and Bis-GMA monomer concentrations were determined by high performance liquid chromatographic (HPLC) analysis of the extracts after specimen immersion in ethanol/water solution for 15 days at 37 +/- 1 degree C. According to the results the highest monomer concentrations eluted were obtained from the chemically cured adhesive. Direct (through the bracket) irradiation of stainless steel brackets bonded to the visible light-cured adhesive showed high monomer elution as well. A polycarbonate base ceramic bracket manifested significantly greater amount of monomer release compared with ceramic brackets when combined with the visible light-cured adhesive. Indirect (from the incisal and cervical edges of the bracket) irradiation of the visible light-cured adhesive bonded to the stainless steel brackets resulted in lower residual monomer elution compared to that of directly (through the bracket) irradiated metallic brackets. No statistical difference was found between direct or indirect irradiation of the ceramic brackets tested, with respect to monomer elution from the light-cured adhesive.

Movement of resin cement components through acid-treated dentin during crown cementation in vitro

This study examined the hypothesis that components of crown cements may be forced through acid-treated dentin during cementation. Freshly extracted, human third molar teeth were prepared to accept full crowns. Roots were removed to allow irrigation of the pulp chamber with saline before, during, and after crown placement with resin dentin bond and resin composite cement. Saline samples were collected and analyzed by high performance liquid chromatography to identify and quantify resin components arriving in the pulp space. Two components of the bond-cement system used were identified in the pulp space samples immediately after crown cementation. These were 2-hydroxyethylmethacrylate and 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane. The amounts of these components in the pulp space decreased when the bonding agent was cured prior to crown placement. The results of this study supported the hypothesis that crown cementing components may flow through acid-treated dentin during crown cementation.

Effect of different glass ionomers on the acid production and electrolyte metabolism of Streptococcus mutans Ingbritt

In order to study the effects of different glass ionomers on the metabolism of Streptococcus mutans, test slabs of freshly mixed conventional glass ionomer (Fuji), silver glass ionomer (Ketac-Silver), composite (Silux), and 2-week-old Fuji were fitted into the bottom of a test tube. A plaque-like layer of S. mutans strain Ingbritt was centrifuged onto the test slabs, and the samples were incubated for 20 h in 1.7% (w/v) sucrose solution. For freshly mixed Fuji and Ketac-Silver, the pH fall was significantly smaller than for old Fuji and composite. These materials also released the largest amount of fluoride into the fluid phase. Incubation with glass ionomer materials led to an increase in the cellular concentration of fluoride in bacteria, but intracellular fluoride did not correlate with the fall in pH. The lowest pH was associated with the lowest cellular magnesium content. Ketac-Silver released large amounts of calcium in the fluid phase, and the cellular calcium content was doubled in this group. The results show that freshly mixed glass ionomers affect acid production and electrolyte metabolism of S. mutans in vitro. The effect of conventional glass ionomer, however, seems to disappear after a few weeks. The effects of calcium and silver released by cermet glass ionomer deserve further study.