Quantification of Conversion Degree and Monomer Elution from Dental Composite Using HPLC and Micro-Raman Spectroscopy

Does Preheating Influence the Cytotoxic Potential of Dental Resin Composites?

Resin-based dental composites (RBC) release cytotoxic components, however the extent of the elution from preheated RBCs is barely investigated. The aim was therefore to determine the cytotoxic effect of preheated conventional, bulk, and thermoviscous RBCs of clinically relevant sizes using different cell viability methods in a contact-free model. Samples (6 × 4 mm) were prepared from conventional [Estelite Sigma Quick (ESQ), Filtek Z250 (FZ)] and bulk-filled [Filtek One BulkFill Restorative (FOB), SDR Plus Bulk Flow (SDR), VisCalor Bulk (VCB)] RBCs. The pre-polymerization temperature was set to room temperature (RT) and 55/65 °C. Pulp cells were cultured, followed by a 2-day exposure to monomers released from solid RBC specimens suspended in the culture medium. Cytotoxicity was assessed using a WST-1, MTT, and LDH colorimetric viability assays. Data were analyzed using one-way ANOVA, Tukey's post hoc test, multivariate analysis, and independent t-test. The effect size (ƞp2) of material and temperature factors was also assessed. All the RBCs demonstrated cytotoxic effect upon exposure to pulp cells, but to a varying extent (ESQ >> VCB > FZ = FOB = SDR). The effect of pre-polymerization temperature was insignificant (ƞp2 < 0.03), except for the thermoviscous RBC, which showed inconsistent findings when subjected to distinct viability tests. Cell viability was predominantly dependent on the type of material used (p < 0.001) which showed a large effect size (ƞp2 > 0.90). Irrespective of the pre-polymerization temperature, RBC samples in a clinically relevant size can release monomers to such an extent, which can substantially decrease the cytocompatibility.

Release of Monomers from Dental Composite Materials into Saliva and the Possibility of Reducing the Toxic Risk for the Patient

Background and Objectives: The objective of this study was (1) to measure the amount of monomers released into the saliva depending on the time elapsed after the hardening of the composite and on the type of monomer used; and (2) with the prolongation of the light-curing procedure, to publish information on whether it would be possible to influence the level of leached monomers. Materials and Methods: HPLC technique was used to monitor the levels of the unpolymerized monomers Bis-GMA, Bis/EMA, TEGDMA, and UDMA from the four commonly used composite materials, released into the saliva of a volunteer with intact dentition. The levels were monitored in 3 time periods during 24 h after composite hardening. From every composite material, 4 samples were formed and cured with an LED lamp for 10 s, 20 s, 40 s, and 60 s. After the light curing, the same polishing procedure was used and the samples were leached in blank saliva samples. Results: We observed that every monitored composite material eluted monomers into the saliva after its application. The amount of monomers depended on the time elapsed after the curing of the composite and on the type of composite used. A 40 s LED curing procedure can reduce the amount of leached monomers in comparison with the standard 20 s procedure, especially for monomers of higher molecular weight. Conclusions: Our study confirmed the hypothesis that the release of monomers gradually decreases with increasing time after the hardening of the composite filling.

Degree of conversion and residual monomer elution of 3D-printed, milled and self-cured resin-based composite materials for temporary dental crowns and bridges

The aim of this work was to investigate the elution of residual monomers as a function of the manufacturing process, which are CAD/CAM manufacturing, self-curing and 3D printing. The experimental materials used consisted of the base monomers TEGDMA, Bis-GMA and Bis-EMA and 50 wt.% fillers. Additionally, a 3D printing resin without fillers was tested. The elution of the base monomers into the different media (water, ethanol and ethanol/water (75/25 vol. %)) at 37 °C over a period of up to 120 d as well as the degree of conversion (DC) by FTIR were investigated. No monomer elution could be detected in water. Most residual monomers in both other media were released from the self-curing material whereas the 3D printing composite released relatively little. The CAD/CAM blanks released hardly any quantitatively detectable amounts of monomers. Relative to the base composition, TEGDMA eluted less than Bis-GMA and Bis-EMA. DC did not correlate with residual monomer release; thus, leaching was determined not only by the amount of residual monomers present but by further factors as possibly network density and structure. The CAD/CAM blanks and the 3D printing composite showed similar high DC but lower residual monomer release from the CAD/CAM blank, likewise the self-curing composite and the 3D printing resin exhibited similar DC but different monomer elution. In terms of residual monomer elution and DC, the 3D printing composite seems promising as a new material class for the use as temporary dental crowns and bridges.

Logistic Regression Analysis of LC-MS/MS Data of Monomers Eluted from Aged Dental Composites: A Supervised Machine-Learning Approach

Compound identification by database searching that matches experimental with library mass spectra is commonly used in mass spectrometric (MS) data analysis. Vendor software often outputs scores that represent the quality of each spectral match for the identified compounds. However, software-generated identification results can differ drastically depending on the initial search parameters. Machine learning is applied here to provide a statistical evaluation of software-generated compound identification results from experimental tandem MS data. This task was accomplished using the logistic regression algorithm to assign an identification probability value to each identified compound. Logistic regression is usually used for classification, but here it is used to generate identification probabilities without setting a threshold for classification. Liquid chromatography coupled with quadrupole-time-of-flight tandem MS was used to analyze the organic monomers leached from resin-based dental composites in a simulated oral environment. The collected tandem MS data were processed with vendor software, followed by statistical evaluation of these results using logistic regression. The assigned identification probability to each compound provides more confidence in identification beyond solely by database matching. A total of 21 distinct monomers were identified among all samples, including five intact monomers and chemical degradation products of bisphenol A glycidyl methacrylate (BisGMA), oligomers of bisphenol-A ethoxylate methacrylate (BisEMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA). The logistic regression model can be used to evaluate any database-matched liquid chromatography-tandem MS result by training a new model using analytical standards of compounds present in a chosen database and then generating identification probabilities for candidates from unknown data using the new model.

The effect of high-irradiance rapid polymerization on degree of conversion, monomer elution, polymerization shrinkage and porosity of bulk-fill resin composites

OBJECTIVE

The purpose was to compare the degree of conversion (DC), monomer elution (ME), polymerization shrinkage (PS) and porosity of two addition-fragmentation chain transfer (AFCT) modified resin-based composites (RBC) light-cured with rapid- (RP), turbo- (TP) or conventional polymerization (CP) settings.

METHODS

Cylindrical samples (6-mm wide, 4-mm thick) were prepared from Tetric PowerFill (TPF) and Filtek One Bulk (FOB). Four groups were established according to the polymerization settings: 3s-RP, 5s-TP, 10s-CP and 20s-CP. Samples in 1 mm thickness with 20s-CP settings served as controls. The DC at the top and bottom surfaces was measured with micro-Raman spectroscopy. ME was detected with high-performance liquid chromatography. PS and porosity were analyzed by micro-computed tomography. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).

RESULTS

FOB showed higher DC values (61.5-77.5 %) at the top compared to TPF (43.5-67.8 %). At the bottom TPF samples achieved higher DCs (39.9-58.5 %) than FOB (18.21-66.18 %). Extending the curing time increased DC (except the top of FOB) and decreased ME. BisGMA release was the highest among the detected monomers from both RBCs. The amount was three-fold more from TPF. The factor Material and Exposure significantly influenced DC and ME. PS (1.8-2.5 %) did not differ among the groups and RBCs except for the lowest value of TPF cured with the 3s_RP setting (p = 0.03). FOB showed 4.5-fold lower porosity (p < 0.001). Significantly higher pore volume was detected after polymerization in 3s_RP (p < 0.001).

SIGNIFICANCE

High-irradiance rapid 3-s curing of AFCT modified RBCs resulted in inferior results for some important material properties. A longer exposure time is recommended in a clinical situation.

Effect of Pre-Heating on the Monomer Elution and Porosity of Conventional and Bulk-Fill Resin-Based Dental Composites

The pre-heating of dental resin-based composites (RBCs) improves adaptability to cavity walls, reducing microleakages. However, the rapid cooling of the pre-heated RBC may change the polymerization kinetics, and thus the final network configuration of the RBC. It is well known that unreacted monomers remaining in the set RBC can leach into the oral cavity. However, it is still not clear how the pre-heating and cooling of RBCs alter monomer elution (ME). Thus, the purpose was to determine the ME from room-temperature and pre-heated RBCs, in addition to determining the closed porosity (CP) volume. Bulk-filled RBCs and layered conventional RBC samples were prepared. The pre-polymerization temperature was set at 24 °C and 55/65 °C. The ME from RBC samples was assessed with high-performance liquid chromatography using standard monomers. CP was measured with micro-computed tomography. ME decreased significantly from bulk fills and increased from layered samples as a result of pre-heating. Pre-heating was unfavorable in terms of CP in most RBCs. Based on the effect size analysis, ME and CP were greatly influenced by both material composition, pre-polymerization temperature, and their interaction. While the pre-heating of high-viscosity bulk-fill RBCs is advantageous from a clinical aspect regarding biocompatibility, it increases CP, which is undesirable from a mechanical point of view.

Comparative chemical properties, bioactivity, and cytotoxicity of resin-modified calcium silicate-based pulp capping materials on human dental pulp stem cells

OBJECTIVES

This study investigated the cytotoxicity, the residual monomer release, degree of conversion (DC), calcium ion (Ca²⁺) release, and crystal structure of TheraCal PT (ThPT) by comparison with TheraCal LC (ThLC) and mineral trioxide aggregate (MTA).

MATERIALS AND METHODS

The cytotoxicity of the cured materials was evaluated on human dental pulp stem cells (hDPSCs) isolated from third molars by the water-soluble tetrazolium salt (WST-1) method. The monomer release and DC of the resin-containing materials were analyzed by high-performance liquid chromatography (HPLC) and Fourier transform infrared (FTIR), respectively. The chemical composition and Ca²⁺ release of the materials were determined by scanning electronic microscopy-energy-dispersive spectroscopy (SEM-EDS), X-ray diffractometry (XRD), and inductively coupled plasma-optical emission spectroscopy (ICP-OES), respectively. Statistical differences were evaluated with one-way ANOVA, repeated measure ANOVA, and the Tukey test (p < 0.05).

RESULTS

MTA showed significantly lower cytotoxicity than either ThLC or ThPT after 1, 3, and 7 days (p < 0.05). TEGDMA release of ThPT is significantly higher than ThLC (p < 0.05). All materials showed calcium Ca²⁺ release, with MTA significantly higher than the others (p < 0.05).

CONCLUSIONS

MTA showed low cytotoxicity and high Ca²⁺ release compared to ThLC and ThPT.

CLINICAL RELEVANCE

The cytotoxicity and residual monomer release of ThLC and ThPT may raise concerns about the viability of hDPSCs. Further investigations with the use of in vivo research models are required to validate in vitro bioactivity properties and the potential adverse biological effects of ThLC and ThPT on hDPSCs.

Analysis of Monomer Release from Different Composite Resins after Bleaching by HPLC

(1) Background: This study aimed to examine the effect of bleaching agents on the release of triethylenae glycol dimethacrylate, 2-hydroxyethyl methacrylate, bisphenol A, urethane dimethacrylate, and bisphenol A-glycidyl methacrylate monomers, which are released from different composite resins, using the high-performance liquid chromatography (HPLC) method. (2) Methods: Ninety disc-shaped specimens were produced and immersed in artificial saliva. After different bleaching applications [office type bleaching (OB) and home type bleaching (HB)], the specimens were immersed in a 75 wt% ethanol/water solution, and the released monomers were analyzed by HPLC at predefined time intervals: 1, 7, and 28 days. The Kruskal−Wallis and Mann−Whitney U tests were conducted for statistical analysis (p = 0.05). (3) Results: The monomers were released at all times from all composite specimens. The monomer release was increased over time. The highest monomer release was detected on day 28. Bleaching applications affected monomer release. No statistical difference was found between OB and HB applications (p > 0.05). The most released monomer was Bisphenol-A in all composites. (4) Conclusion: Given that a residual monomer release from composite resins has a toxic effect and that bleaching treatments increase this release, a treatment protocol should be made in accordance with the manufacturer’s instructions.

Influence of curing modes on monomer elution, sorption and solubility of dual-cure resin-cements

OBJECTIVE

To explore the effect of two curing modes, for dual-cure resin cements, on their monomer elution, water sorption and solubility after 30 d water storage and 30 d dry reconditioning.

METHODS

Eight dual-cure resin-cements were investigated (Bifix SE, Nexus Third Generation, PANAVIA SA, PANAVIA V5, RelyX Ultimate Universal, RelyX Unicem 2, RelyX Universal and SpeedCEM Plus). Six disk-shaped specimens were made per curing mode: light-cure (LC) versus self-cure (SC) to measure amounts of eluted monomers after 30 d of water storage at 37 °C. Ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC MS/MS) was performed to identify and quantify three eluted monomers (Bis-GMA, UDMA and TEGDMA). Water sorption/ solubility specimens were prepared according to ISO 4049. Specimens from each curing mode (LC/SC) were immersed separately in distilled water for 30 d and then reconditioned for 30 d; all at 37 °C. Mass change was measured at different time intervals. Data were analyzed via one-way ANOVA, Tukey post-hoc tests and independent sample t-tests (α = 0.05).

RESULTS

After 30 d of water storage, the three monomers Bis-GMA, UDMA and TEGDMA were detected in water. All monomers showed a variable extent of elution into water and were significantly higher (p < 0.0001) with SC compared to LC curing modes. BSE had the highest quantity of eluted monomers. After 30 d of water sorption (μg/mm³), all rein-cements showed significantly higher sorption (p < 0.05) of SC compared to LC curing modes except for PV5, RXU and CEM (p > 0.05). After 30 d of water solubility (μg/mm³), all resin-cements showed significantly higher solubility (p < 0.0001) of SC compared to LC curing mode. BSE had the highest water sorption and solubility. The total amounts of eluted monomers correlated positively with solubility: r² = 0.95 for LC and r² = 0.93 for SC.

SIGNIFICANCE

Whenever light access is possible, light curing remains beneficial to reduce the extent of resin degradation and related properties of dual-cure resin cements. BSE showed statistically the highest extent of eluted monomers, sorption and solubility.

Development of New Experimental Dental Enamel Resin Infiltrants-Synthesis and Characterization

The aim of the present study was to obtain experimental infiltration materials, intended for the treatment of dental white spots, and to investigate them. Two series of infiltrants (P1–P6)/(P1F–P6F) were obtained, based on different monomer mixtures, without/with glass filler (with fluoride release ability). Each infiltrant from the second series contained the same amount of glass powder, and each infiltrant from the (P–PF) group contained the same resin composition. The characteristics of the experimental infiltrants were investigated by degree of conversion (DC), mechanical strength, water sorption (WS), and fluoride release, in addition to residual monomer for (P1F–P6F) infiltrants. The results were compared with those obtained for commercial Icon infiltrant. For the experimental infiltrants, without/with filler, the recorded DC was in the range of 58.27–89.70%/60.62–89.99%, compared with Icon (46.94%) 24 h after polymerization. The release of fluoride depends on the permeability of the polymer matrix, with respect to the water sorption, which may help to diffuse ions in the storage medium but which can also influence the release of residual monomers. The highest flexural strengths were recorded for the (TEGDMA/HEMA/Bis-GMA) infiltrants (133.94 ± 16.389 MPa/146.31 ± 7.032 MPa). The best experimental infiltrants were P2 and P2F (Bis-GMA/HEMA/TEGDMA).

Influence of curing modes on conversion and shrinkage of dual-cure resin-cements

OBJECTIVE

To explore the effect of curing modes of dual-cure resin cements on their degree of conversion (DC) and polymerization shrinkage (PS) over specific post-activation periods.

METHODS

Five self-adhesive (PANAVIA SA, RelyX Universal Resin, RelyX Unicem 2, Bifix SE, and SpeedCEM Plus) and three conventional (PANAVIA V5, Nexus Third Generation, and RelyX Ultimate Universal) dual-cure resin cements were studied. Four specimens (n = 4) were made per curing mode (light/self-cure) to measure either DC or PS. FTIR was utilized to measure real-time DC (%) over 24 h. The Bonded Disk method was used to measure shrinkage at 23 °C over 1 h. The data were analyzed using one-way ANOVA, Tukey post-hoc tests and independent/ paired sample t-tests (a = 0.05).

RESULTS

After 1 h post-activation, the DC of light-cured (LC) specimens ranged between 66.6% and 77.4%, whereas for self-cured (SC) specimens DC ranged between 44.4% and 73.2%. After 24 h, the DC of LC specimens ranged between 74.8% and 82.4% and between 62.7% and 81.7% for SC specimens. After 24 h, the DC of three cements (BSE, PV5, and RXU) were comparable between their curing modes (p > 0.05), whereas five cements (CEM, NX3, PSA, RXU2, RXL) had significantly lower DC for SC compared to LC specimens (p < 0.05). After 1 h post-activation, shrinkage ranged between 5.9% and 8.5% for LC and between 4.9% and 8.3% for SC specimens. Most cements were not significantly different between curing modes. However, light-cured PAS, RXL and RXU2 had significantly higher shrinkage (p < 0.05). After 1 h post-activation, a strong positive correlation existed between conversion and shrinkage (LC: r² = 0.95 and SC: r² = 0.93).

SIGNIFICANCE

Whenever light access is possible, light-curing of resin-cements remains beneficial to the overall efficacy of their conversion and thus all factors that depend on that. Conversion and shrinkage behavior are intrinsically important factors in clinical selection of resin-cement products.

Characteristics of Dental Resin-Based Composites in Leukemia Saliva: An In Vitro Analysis

BACKGROUND

The aim was to analyze, in vitro, four resin based composite systems (RBCs) immersed in saliva of leukemia patients before starting chemotherapy regiments.

MATERIAL AND METHODS

Saliva was collected from 20 patients (4 healthy patients, 16 leukemia patients). Resin disks were made for each RBC and were immersed in the acute leukemia (acute lymphocytic (ALL), acute myeloid (AML)), chronic leukemia (chronic lymphocytic (CLL), chronic myeloid (CML)), Artificial saliva and Control environment, and maintained for seven days. At the end of the experiment, the characteristics and the effective response of saliva from the studied salivas' on RBCs was assessed using water sorption, water solubility, residual monomer and scanning electron microscopy (SEM). Data analysis was performed and a p-value under 0.05 was considered statistically significant.

RESULTS

The behaviour of RBCs in different immersion environments varies according to the characteristics of the RBCs. RBCs with a higher filler ratio have a lower water sorption. The solubility is also deteriorated by the types of organic matrix and filler; the results of solubility being inversely proportional on the scale of negative values compared to sorption values. Chromatograms of residual monomers showed the highest amount of unreacted monomers in ALL and AML, and the Control and artificial saliva environments had the smallest residual monomer peaks. Because of the low number of differences between the experimental conditions, we further considered that there were no important statistical differences between experimental conditions and analysed them as a single group.

CONCLUSION

The influence of saliva on RBCs depends on the type of leukemia; acute leukemia influenced the most RBCs by changing their properties compared to chronic leukemia.

Pre-Heating Effect on Monomer Elution and Degree of Conversion of Contemporary and Thermoviscous Bulk-Fill Resin-Based Dental Composites

Detection of unreacted monomers from pre-heated resin-based dental composites (RBC) is not a well-investigated topic so far. The objectives were to determine the temperature changes during the application and polymerization, the degree of conversion (DC) and unreacted monomer elution of room temperature (RT), and pre-heated thermoviscous [VisCalor Bulk(VCB)] and high-viscosity full-body contemporary [Filtek One Bulk(FOB)] bulk-fill RBCs. The RBCs' temperatures during the sample preparation were recorded with a K-type thermocouple. The DC at the top and bottom was measured with micro-Raman spectroscopy and the amounts of eluted BisGMA, UDMA, DDMA, and TEGDMA were assessed with High-Performance Liquid Chromatography. The temperatures of the pre-heated RBCs decreased rapidly during the manipulation phase. The temperature rise during photopolymerization reflects the bottom DCs. The differences in DC% between the top and the bottom were significant. RT VCB had a lower DC% compared to FOB. Pre-heating did not influence the DC, except on the bottom surface of FOB where a significant decrease was measured. Pre-heating significantly decreased the elution of BisGMA, UDMA, DDMA in the case of FOB, meanwhile, it had no effect on monomer release from VCB, except TEGDMA, which elution was decreased. In comparison, RBC composition had a stronger influence on DC and monomer elution, than pre-cure temperature.

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.

Degree of conversion and in vitro temperature rise of pulp chamber during polymerization of flowable and sculptable conventional, bulk-fill and short-fibre reinforced resin composites

OBJECTIVE

Determine the degree of conversion (DC) and in vitro pulpal temperature (PT) rise of low-viscosity (LV) and high-viscosity (HV) conventional resin-based composites (RBC), bulk-fill and short-fibre reinforced composites (SFRC).

METHODS

The occlusal surface of a mandibular molar was removed to obtain dentine thickness of 2 mm above the roof of the pulp chamber. LV and HV conventional (2 mm), bulk-fill RBCs (2-4 mm) and SFRCs (2-4 mm) were applied in a mold (6 mm inner diameter) placed on the occlusal surface. PT changes during the photo-polymerization were recorded with a thermocouple positioned in the pulp chamber. The DC at the top and bottom of the samples was measured with micro-Raman spectroscopy. ANOVA and Tukey's post-hoc test, multivariate analysis and partial eta-squared statistics were used to analyze the data (p < 0.05).

RESULTS

The PT changes ranged between 5.5-11.2 °C. All LV and 4 mm RBCs exhibited higher temperature changes. Higher DC were measured at the top (63-76%) of the samples as compared to the bottom (52-72.6%) in the 2 mm HV conventional and bulk-fill RBCs and in each 4 mm LV and HV materials. The SFRCs showed higher temperature changes and DC% as compared to the other investigated RBCs. The temperature and DC were influenced by the composition of the material followed by the thickness.

SIGNIFICANCE

Exothermic temperature rise and DC are mainly material dependent. Higher DC values are associated with a significant increase in PT. LV RBCs, 4 mm bulk-fills and SFRCs exhibited higher PTs. Bulk-fills and SFRCs applied in 4 mm showed lower DCs at the bottom.

TEGDMA (Triethylene Glycol Dimethacrylate) Induces Both Caspase-Dependent and Caspase-Independent Apoptotic Pathways in Pulp Cells

Monomers leached from resin-based composites (RBCs) may reach intrapulpal concentrations of the millimolar (mM) range, which could contribute to inflammation. The aim of this investigation was to assess the cytotoxicity of triethylene glycol dimethacrylate (TEGDMA) monomers on pulp cells as well as to identify molecular mechanisms leading to apoptosis. Pulp cells were harvested from molars extracted for orthodontic reasons and cultured through an explant method. To assess cytotoxicity, cells underwent a 5-day exposure to 0.75, 1.5, and 3 mM TEGDMA and were subject to cell counting and WST-1 staining. Based on the findings, cells were subsequently exposed to 0.1, 0.2, 0.75, 1.5, and 3 mM TEGDMA for 24 h to uncover the details of apoptosis. Changes in the production or cleavage of the apoptosis-specific proteins caspase-8, caspase-9, caspase-3, caspase-12, and Apoptosis-Inducing Factor (AIF) were measured by Western blot. The 5-day study showed concentration- and time-dependent cytotoxicity. Significant cell death was detected after 24 h with TEGDMA concentrations of 1.5 and 3 mM. One-day exposure to TEGDMA led to the activation of caspase-8, -9, -3, and -12 and an increased AIF production. Results suggest that relevant concentrations of TEGDMA monomers, leached from RBCs, induce apoptosis in pulp cells through both caspase-dependent as well as caspase-independent mechanisms. Endoplasmic reticulum stress and the activation of caspase-independent apoptotic pathways may be further mechanisms by which monomers induce apoptosis in pulp cells.

Influence of curing duration and mixing techniques of bulk fill resin composites on bi-axial flexural strength and degree of conversion

OBJECTIVES

The aim was to assess the influence of polymerization duration, method and resin manipulation techniques on the biaxial flexural strength (BFS) and degree of conversion (DC) of bulk fill resin composites (BFRC).

METHODS

One hundred and eighty disc specimens were fabricated using MultiCore (MC) and Core-It (CI) bulk fill resin composite. Each material group, specimens were divided into nine subgroups based on curing methods (Light cure for 10 and 20 s; and auto-cure) and mixing techniques (first auto-mix, second automix, and hand mix). BFS was tested with a ball indenter at a crosshead speed of 0.50 mm/min. DC was assessed for MC and CI materials for 10 s and 20 s light cure; and auto cure specimens using Fourier Transform-Infrared Spectroscopy (FTIR). Statistical data comparisons were performed using ANOVA, Bonferroni and Tukey-Kramer tests.

RESULTS

For MC and CI, BFS was highest in 10 s light cure specimens, however comparable to specimens cured for 20 s (p > 0.05). Auto cure specimens showed lower BFS than light cured samples for both materials (p < 0.05). Hand mixed specimens showed significantly compromised BFS compared to automix technique for MC and CI. DC % was comparable for 10 s and 20 s light cure methods for both materials (p > 0.05), which was higher than DC % of auto cure bulk fill resins (p < 0.05). CI showed higher DC % and BFS compared to MC bulk fill resin composite.

CONCLUSION

Photo-polymerization duration of 10 and 20 s showed similar outcomes for BFS and DC %; and BFS for auto-mixed resins (MC and CI) was significantly higher than hand mixed resin. BFS and DC was higher in photopolymerized groups as compared to auto-cured resin regardless of the manipulation technique for both materials (MultiCore and Core it).

The Effect of Irradiance on the Degree of Conversion and Volumetric Polymerization Shrinkage of Different Bulk-Fill Resin-Based Composites: An In Vitro Study

Objective  The influence of different light-emitting diode (LED) curing light intensities on the degree of conversion (DC) and volumetric polymerization shrinkage (VPS) of bulk-fill resin-based composite (RBC) restorative materials was evaluated.

Materials and Methods  Twenty-four specimens of each RBC material (Filtek one bulk-fill posterior, Reveal HD Bulk, Tetric N-Ceram, and Filtek Z350) were prepared. The RBCs were shaped in molds and cured using an LED curing light unit at high-intensity (1,200 mW/cm ² ) for 20 seconds and low-intensity (650 mW/cm ² ) for 40 seconds Fourier-transform infrared (FTIR) spectroscopy was used to determine the DC and microcomputed tomography was used to evaluate VPS. Data were analyzed using one- and two-way ANOVA, independent t -test, and Tukey’s and Scheffe’s post hoc multiple comparison tests.

Results  With high-intensity curing light, Reveal HD showed the highest DC (85.689 ± 6.811%) and Tetric N-Ceram the lowest (52.60 ± 9.38%). There was no statistical difference in VPS when using high- or low-intensity curing light. The highest VPS was observed for Reveal HD (2.834–3.193%); there was no statistical difference ( p > 0.05) among the other RBCs.

Conclusion  Curing light intensities do not significantly influence the VPS of RBC materials. Reveal HD bulk cured with high-intensity light had the highest DC.

Influence of TEGDMA monomer on MMP-2, MMP-8, and MMP-9 production and collagenase activity in pulp cells

Objectives

Resin-based composites may leach monomers such as triethylene-glycol dimethacrylate (TEGDMA), which could contribute to intrapulpal inflammation. The aim of this investigation was to examine whether various concentrations of TEGDMA are able to influence dentally relevant Matrix metalloproteinase (MMP)-2, MMP-8, and MMP-9 production, total collagenase/gelatinase activity in pulp cells, and suggest possible signaling mechanisms.

Materials and methods

Pulp cells were cultured, followed by a 1-day exposure to sublethal TEGDMA concentrations (0.1, 0.2, and 0.75 mM). Total MMP activity was measured by an EnzCheck total collagenase/gelatinase assay, while the production of specific MMPs and the relative changes of phosphorylated, i.e., activated signaling protein levels of extracellular signal-regulated kinase (ERK)1/2, p38, c-Jun N-terminal kinase (JNK) were identified by western blot. Immunocytochemistry image data was also plotted and analyzed to see whether TEGDMA could possibly alter MMP production.

Results

An increase in activated MMP-2, MMP-8, and MMP-9 production as well as total collagenase activity was seen after a 24-h exposure to the abovementioned TEGDMA concentrations. Increase was most substantial at 0.1 (P = 0.002) and 0.2 mM (P = 0.0381). Concurrent p-ERK, p-p38, and p-JNK elevations were also detected.

Conclusions

Results suggest that monomers such as TEGDMA, leached from resin-based restorative materials, activate and induce the production of dentally relevant MMPs in pulp cells. Activation of ERK1/2, p38, or JNK and MMP increase may play a role in and/or can be part of a broader stress response.

Clinical relevance

Induction of MMP production and activity may further be components in the mechanisms of intrapulpal monomer toxicity.

The polymerization efficiency of a bulk-fill composite based on matrix-modification technology

Objectives

To evaluate the polymerization efficiency of a matrix-modified bulk-fill composite, and compare it to a conventional composite which has a similar filler system. The degree of conversion (DC%) and monomer elution were measured over different storage periods. Additionally, fillers' content was examined.

Materials and Methods

Cylindrical specimens were prepared, in bulk and incrementally, from Filtek Bulk Fill (B) and Filtek Supreme XTE (S) composites using a Teflon mold, for each test (n = 6). Using attenuated total reflection method of Fourier transformation infrared spectroscopy, DC% was measured after 24 hours, 7 days, and 30 days. Using high-performance liquid chromatography, elution of hydroxyethyl methacrylate, triethylene glycol dimethacrylate, urethane dimethacrylate, and bisphenol-A glycidyl dimethacrylate was measured after 24 hours, 7 days and 30 days. Filler content was examined by scanning electron microscopy (SEM). Data were analyzed using 2-way mixed-model analysis of variance (α = 0.05).

Results

There was no significant difference in DC% over different storage periods between B-bulk and S-incremental. Higher monomer elution was detected significantly from S than B. The elution quantity and rate varied significantly over storage periods and between different monomers. SEM images showed differences in fillers' sizes and agglomeration between both materials.

Conclusions

Matrix-modified bulk-fill composites could be packed and cured in bulk with polymerization efficiency similar to conventional composites.

Validation of a Simple HPLC-UV Method for the Determination of Monomers Released from Dental Resin Composites in Artificial Saliva

Bisphenol-A (BPA), bisphenol A glycerolate dimethacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA) are organic monomers that can be released from dental composites into the oral cavity. Over specific concentrations, they can act as endocrine disruptors or cause toxic effects. The purpose of this work is to develop and validate an analytical method to determine BPA, Bis-GMA, TEGDMA, and UDMA monomers released from synthetic dental resins in artificial saliva. The method was validated before its application to new hybrid ceramic materials used in computer-aided design and computer-aided manufacturing (CAD/CAM) restorations to determine the release of monomers in various time intervals (e.g., 24 h, and 7, 14, 30, and 60 days), both in methanolic solutions, as well as in artificial saliva. Chromatographic analysis was performed isocratically on a Perfect Sil Target ODS-3 analytical column (250 mm × 4.6 mm, 5 µm) with CH₃CN/H₂O, 58/42% v/v as mobile phase within 23 min. The developed method was validated in terms of selectivity, linearity, accuracy, and precision.

Effect of thermocycling on the amount of monomer released from bulk fill composite resins

The goal of this study was to examine the effect of thermal cycling on the amount of monomer released from bulk fill composites. Five bulk fill composite resins were used in the study. Extraction solutions were obtained at the end of the time/thermal cycle periods: 0-1 day/0-1,500, 1-3 days/1,500-4,500 and 3-7 days/4,500-10,000. The monomers in the extractions samples taken at each time point were measured on an HPLC instrument. The obtained data were analyzed by repeated measures of variance analysis and tukey multiple comparison tests (p<0.05). The thermocycling increased the amount of monomer released from all composites at 0-1 day (p<0.05). At 0-1 and 1-3 days, Venus Bulk Fill and Filtek Bulk Fill composite resins were more affected. Polymer networks with high molecular weight monomers such as Bis-GMA and UDMA can be less affected by thermal changes compared to polymers with low molecular weight monomers.

The Influence of Irradiation Time and Layer Thickness on Elution of Triethylene Glycol Dimethacrylate from SDR® Bulk-Fill Composite

Objective. This study aimed to evaluate triethylene glycol dimethacrylate (TEGDMA) elution from SDR bulk-fill composite. Methods. Three groups of samples were prepared, including samples polymerized in a 4 mm layer for 20 s, in a 4 mm layer for 40 s, and in a 2 mm layer for 20 s. Elution of TEGDMA into 100% ethanol, a 75% ethanol/water solution, and distilled water was studied. The TEGDMA concentration was measured using HPLC. Results. The TEGDMA concentration decreased in the following order: 100% ethanol > 75% ethanol > distilled water. Doubling the energy delivered to the 4 mm thick sample caused decrease (p < 0.05) in TEGDMA elution to distilled water. In ethanol solutions, the energy increase had no influence on TEGDMA elution. Decreasing the sample thickness resulted in decrease (p < 0.05) in TEGDMA elution for all the solutions. Conclusions. The concentration of eluted TEGDMA and the elution time were both strongly affected by the hydrophobicity of the solvent. Doubling the energy delivered to the 4 mm thick sample did not decrease the elution of TEGDMA but did decrease the amount of the monomer available to less aggressive solvents. Elution of TEGDMA was also correlated with the exposed sample surface area. Clinical Relevance. Decreasing the SDR layer thickness decreases TEGDMA elution.

Degree of Conversion and BisGMA, TEGDMA, UDMA Elution from Flowable Bulk Fill Composites

The degree of conversion (DC) and the released bisphenol A diglycidyl ether dimethacrylate (BisGMA), triethylene glycol dimethacrylate (TEGDMA) and urethane dimethacrylate (UDMA) monomers of bulk-fill composites compared to that of conventional flowable ones were assessed using micro-Raman spectroscopy and high performance liquid chromatography (HPLC). Four millimeter-thick samples were prepared from SureFil SDR Flow (SDR), X-tra Base (XB), Filtek Bulk Fill (FBF) and two and four millimeter samples from Filtek Ultimate Flow (FUF). They were measured with micro-Raman spectroscopy to determine the DC% of the top and the bottom surfaces. The amount of released monomers in 75% ethanol extraction media was measured with HPLC. The differences between the top and bottom DC% were significant for each material. The mean DC values were in the following order for the bottom surfaces: SDR_4mm_20s > FUF_2mm_20s > XB_4mm_20s > FBF_4mm_20s > XB_4mm_10s > FBF_4mm_10s > FUF_4mm_20s. The highest rate in the amount of released BisGMA and TEGDMA was found from the 4 mm-thick conventional flowable FUF. Among bulk-fills, FBF showed a twenty times higher amount of eluted UDMA and twice more BisGMA; meanwhile, SDR released a significantly higher amount of TEGDMA. SDR bulk-fill showed significantly higher DC%; meanwhile XB, FBF did not reach the same level DC, as that of the 2 mm-thick conventional composite at the bottom surface. Conventional flowable composites showed a higher rate of monomer elution compared to the bulk-fills, except FBF, which showed a high amount of UDMA release.

Conversion, shrinkage, water sorption, flexural strength and modulus of re-mineralizing dental composites

OBJECTIVES

Cure, volumetric changes and mechanical properties were assessed for new dental composites containing chlorhexidine (CHX) and reactive calcium phosphate-containing (CaP) to reduce recurrent caries.

METHODS

20wt.% of light curable urethane dimethacrylate based liquid was mixed with 80wt.% glass filler containing 10wt.% CHX and 0-40wt.% CaP. Conversion versus depth with 20 or 40s light exposure was assessed by FTIR. Solidification depth and polymerization shrinkage were determined using ISO 4049 and 17304, respectively. Subsequent volume expansion and biaxial flexural strength and modulus change upon water immersion were determined over 4 weeks. Hydroxyapatite precipitation in simulated body fluid was assessed at 1 week.

RESULTS

Conversion decreased linearly with both depth and CaP content. Average solidification depths were 4.5, 3.9, 3.3, 2.9 and 5.0 with 0, 10, 20, and 40% CaP and a commercial composite, Z250, respectively. Conversions at these depths were 53±2% for experimental materials but with Z250 only 32%. With Z250 more than 50% conversion was achieved only below 1.1mm. Shrinkage was 3% and 2.5% for experimental materials and Z250, respectively. Early water sorption increased linearly, whilst strength and modulus decreased exponentially to final values when plotted versus square root of time. Maximum volumetric expansion increased linearly with CaP rise and balanced shrinkage at 10-20wt.% CaP. Strength and modulus for Z250 decreased from 191 to 158MPa and 3.2 to 2.5GPa. Experimental composites initial strength and modulus decreased linearly from 169 to 139MPa and 5.8 to 3.8GPa with increasing CaP. Extrapolated final values decreased from 156 to 84MPa and 4.1 to 1.7GPa. All materials containing CaP promoted hydroxyapatite precipitation.

SIGNIFICANCE

The lower surface of composite restorations should both be solid and have greater than 50% conversion. The results, therefore, suggest the experimental composite may be placed in much thicker layers than Z250 and have reduced unbounded cytotoxic monomer. Experimental materials with 10-20wt.% additionally have volumetric expansion to compensate shrinkage, antibacterial and re-mineralizing components and competitive mechanical properties.

Retrospective evaluation of posterior direct composite restorations: 10-year findings

OBJECTIVES

This 10-year retrospective study investigated the differences in the changes and the longevity of Class II restorations using 4 similar microhybrid resin composites (Filtek Z250, Herculite XR, Gradia Direct Posterior, Renew).

METHODS

Data were collected from patient records. Those patients who received posterior restoration between 2001 and 2003, and who still visited the clinical practice for regular check-up visits were selected. A total of 225 adult patients (86 males, 139 females) with 701 restorations were evaluated by 2 operators using the USPHS criteria. Data were analyzed with Fisher's Exact Test, Pearson's Chi-Square Test and Kaplan-Meier analysis (p<0.05).

RESULTS

A failure rate of 2.1% was detected. The reasons of failures included restoration fracture, secondary caries and endodontic treatment. Similar survival rates for Gradia Direct Posterior (91.25%) and Renew (92.19%) were observed; better performance was observed with the Filtek Z250 (99.1%) and Herculite XR (98.64%). There was a higher probability of failure in 3 surface (n=10) than in 2 surface (n=5) restorations (p<0.001), and this rate was similar when molars (n=8) and premolars (n=7) were compared. The most frequent but clinically acceptable deficiency was the marginal discoloration.

SIGNIFICANCE

All four microhybrid resin composites showed acceptable clinical durability in Class II restorations during the 10-year follow-up period, with an overall survival rate of >97.8%. Higher rates of failures and deficiencies were observed with the Renew (fracture) and Gradia Direct Posterior (color match), respectively.