Monomer elution from nanohybrid and ormocer-based composites cured with different light sources

An organotypic model of oral mucosa cells for the biological assessment of 3D printed resins for interim restorations

STATEMENT OF PROBLEM

Three-dimensionally (3D) printed resins have become popular as a new class of materials for making interim restorations. However, little is known about how the fabrication parameters can influence biological compatibility with oral tissues.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of the postpolymerization time on the cytotoxicity of resins for printing interim restorations by using a 3D organotypic model of the oral mucosa.

MATERIAL AND METHODS

Cylindrical specimens were prepared with conventional acrylic resin (AR), computer-aided design and computer-aided manufacture (CAD-CAM) resin (CC), composite resin (CR), and 2 resins for 3D printing (3DP) marketed as being biocompatible. The 3DPs were submitted to postpolymerization in an ultraviolet (UV) light chamber for 1, 10, or 20 minutes (90 W, 405 nm). Standard specimens of the materials were incubated for 1, 3, and 7 days in close contact with an organotypic model of keratinocytes (NOK-Si) in coculture with gingival fibroblasts (HGF) in a 3D collagen matrix, or directly with 3D HGF cultures. Then, the viability (Live/Dead n=2) and metabolism (Alamar Blue n=6) of the cells were assessed. Spectral scanning of the culture medium was performed to detect released components (n=6) and assessed statistically with ANOVA and the Tukey post hoc test (α=.05).

RESULTS

Severe reduction of metabolism (>70%) and viability of keratinocytes occurred for 3DP resin postpolymerized for 1 minute in all periods of analysis in a time-dependent manner. The decrease in cell metabolism and viability was moderate for the 3D culture of HGFs in both experimental models, correlated with the intense presence of resin components in the culture medium. The resins postpolymerized for 10 and 20 minutes promoted a mild-moderate cytotoxic effect in the period of 1 day, similar to AR. However, recovery of cell viability occurred at the 7-day incubation period. The 3DP resins submitted to postpolymerization for 20 minutes showed a pattern similar to that of CR and CC at the end of the experiment.

CONCLUSIONS

The cytotoxic potential of the tested 3DP resins on oral mucosa cells was influenced by postprinting processing, which seemed to have been related with the quantity of residual components leached.

Cytotoxicity effects and differentiation potential of ormocer-based and nanohybrid composite resins on human dental pulp stem cells

OBJECTIVE

to compare conventional nanohybrid (Ceram.x Spectra) and ormocer-based (Admira fusion) dental composite resins effects on human dental pulp stem cells (hDPSCs) in terms of cytotoxicity, self-renewal, migration and osteogenic differentiation.

METHODS

hDPSCs were cultured in presence of different dilutions (undiluted, form 1:2 to 1:100) of CeramX (CX) and Admira fusion (AD) eluates and viability assay in standard or osteogenic conditions were performed. Samples and eluates were prepared according to ISO 10993-12. In addition, apoptosis, self-renewal and migration activity evaluations were carried out. Osteogenic differentiation potential was tested by Alkaline Phosphatase Activity, alizarin red staining and gene expression of specific markers (ALP, RUNX2, OCN, OPN and COL1α1). Statistical analysis was performed by means of a One-way analysis of variance (One-way ANOVA) followed by a Tukey's test for multiple comparison; results were presented as mean ± standard error of mean (SEM).

RESULTS

Admira Fusion demonstrated to be highly biocompatible and showed positive effects on hDPSCs proliferation and differentiation; on the contrary, conventional nanohybrid composite showed to be more cytotoxic and without any notable effect on stem cells differentiation. Moreover, the obtained results were further corroborated by a significant upregulation of osteogenic differentiation markers obtained in presence of ormocer-based composite resin eluate. Specifically, in AD 1:50 group expression levels of ALP, Runx2, Col1α1 were double than control (ALP, p = 0.045; Runx2, p = 0.003; Col1α1, p = 0.001) and CX 1:50 (ALP, p = 0.006; RUNX2, p = 0.029; Col1α1, p = 0.005). Moreover, in the same group, OPN and OCN resulted about 5 times more expressed as compared to control (OPN, p = 0.009; OCN, p = 0.0005) and CX 1:50 (OPN, p = 0.012; OCN, p = 0.0006).

SIGNIFICANCE

The less cytotoxicity obtained by AD than conventional nanohybrid composite may be attributed to a reduced monomers release in the oral environment, supporting the hypothesis of limited adverse effect and enhanced healing potential, mainly when the material is positioned in close contact with pulp tissue.

Repairability of aged dimethacrylate-free ORMOCER-based dental composite resins with different surface roughening methods and intermediate materials

STATEMENT OF PROBLEM

The repair of damaged composite resin restorations has been recommended as a conservative treatment option. However, a reliable protocol for repairing ORMOCER-based restorations is lacking.

PURPOSE

The purpose of this in vitro study was to investigate the effect of different surface roughening methods, repair composite resins, and intermediate materials on the repair bond strength of a dimethacrylate-free ORMOCER-based composite resin.

MATERIAL AND METHODS

Cylindrical composite resin specimens (Admira Fusion) were roughened by using hydrofluoric acid (HF) or a diamond rotary instrument. In both groups, 4 types of intermediate materials were used (Monobond-S, Clearfil SE bond [second bottle], Clearfil Universal bond, GC Composite Primer), and then half of the specimens were repaired with a similar composite resin, and the other half with dimethacrylate composite resin (Clearfil-APX). The specimens (n=20) were then subjected to repair bond strength and failure mode evaluation. The data were analyzed by using the Weibull test, 3-way and 1-way ANOVA, and the Tukey honestly significant difference (HSD) test (α=.05).

RESULTS

All variables, including the surface roughening method, intermediate material, and repair composite resin, had a significant effect on repair bond strength (P<.001). The lowest repair bond strength values were obtained in the group roughened with HF, prepared with Monobond-S, and repaired with Admira Fusion, and the highest values were obtained in the group roughened with a rotary instrument, prepared with GC Composite Primer, and repaired with Clearfil APX (P<.05). All experimental groups had a lower bond strength than the cohesive and control groups (P<.05). In all experimental groups, the predominant failure modes were adhesive and mixed.

CONCLUSIONS

The use of a diamond rotary instrument was a more reliable method of creating roughness, and different intermediate materials based on the clinical situation can be used to repair dimethacrylate-free ORMOCER-based composite resin with similar or different composite resins. However, in general, the highest repair bond strengths were achieved with Clearfil APX-repaired specimens.

Dental Resin-Based Luting Materials-Review

As cementation represents the last stage of the work involved in making various indirect restorations (metal ceramic crowns and bridges, full ceramic crowns and bridges, inlays, onlays, and fiber posts), its quality significantly contributes to the clinical success of the therapy performed. In the last two decades, the demand for ceramic indirect restorations in everyday dental practice has considerably increased primarily due to the growing significance of esthetics among patients, but also as a result of hypersensitivity reactions to dental alloys in some individuals. In this context, it is essential to ensure a permanent and reliable adhesive bond between the indirect restoration and the tooth structure, as this is the key to the success of aesthetic restorations. Resin-based luting materials benefit from excellent optical (aesthetic) and mechanical properties, as well as from providing a strong and durable adhesive bond between the restoration and the tooth. For this reason, resin cements are a reliable choice of material for cementing polycrystalline ceramic restorations. The current dental material market offers a wide range of resin cement with diverse and continually advancing properties. In response, we wish to note that the interest in the properties of resin-based cements among clinicians has existed for many years. Yet, despite extensive research on the subject and the resulting continued improvements in the quality of these materials, there is still no ideal resin-based cement on the market. The manuscript authors were guided by this fact when writing the article content, as the aim was to provide a concise overview of the composition, properties, and current trends, as well as some future guidelines for research in this field that would be beneficial for dental practitioners as well as the scientific community. It is extremely important to provide reliable and succinct information and guidelines for resin luting materials for dental dental practitioners.

Effect of varying functional monomers in experimental self-adhesive composites: polymerization kinetics, cell metabolism influence and sealing ability

The aim was to evaluate the effects of adding different functional monomers to experimental self-adhesive composites (SACs) on polymerization kinetics, cell metabolic activity, and sealing ability. SACs were formulated using urethane dimethacrylate as the base monomer and triethylene glycol dimethacrylate. Additionally, 10 wt.% of distinct functional monomers were added - 10-methacryloyloxydecyl dihydrogen phosphate, glycerol phosphate dimethacrylate (GPDM), 2-hydroxyethyl methacrylate (HEMA) or hydroxyethyl acrylamide (HEAA). ATR-FTIR was used to determine real-time polymerization kinetics (20 min,n= 3). The final extrapolated conversion and polymerization rates were determined (DC,max;Rp,max). TheDC,maxvalues were employed to calculate volumetric shrinkage. The MTT assay was performed on MDPC-23 cells using disc extracts at different concentrations (n= 8). Class V cavities were prepared in 60 sound human molars, assigned to six groups (n= 10), depending on the composite used and aging type (T0 or TC, if thermocycled for 10 000 cycles). One-way ANOVA, two-way, andKruskal-Wallistests were employed to treat the data (ɑ= 0.05). Varying the functional monomers had a large impact on DC,max, as confirmed by one-way ANOVA (p<0.001). The highest was obtained for HEMA (64 ± 3%). The HEMA and HEAA formulations were found to be significantly more toxic at concentrations below 100%. For microleakage, having a functional monomer or not did not show any improvement, irrespective of margin or aging period (Mann-Whitney U,p> 0.05). Larger functional monomers MDP and GPDM affected polymerization properties. Conversely, their acidity did not seem to be detrimental to cell metabolic activity. Regarding sealing ability, it seems that the functional monomers did not bring an advantage to the composites. Varying the functional monomer in SACs had a clear impact on the polymerization kinetics as well as on their cytotoxic potential. However, it did not confer better microleakage and sealing. Claiming self-adhesiveness based only on functional monomers seems dubious.

N-acetyl cysteine inhibits IL-1α release from murine keratinocytes induced by 2-hydroxyethyl methacrylate

The hydrophilic compound 2-hydroxyethyl methacrylate (HEMA) is a major component of dental bonding materials, and it enhances the binding of resin-composites to biomolecules. However, HEMA is a well-known contact sensitizer. We reported previously that intradermal injection of HEMA induces the production of IL-1 locally in the skin. Keratinocytes are the first barrier against chemical insults and constitutively express IL-1α. In this study, we analyzed whether HEMA induces the production of inflammatory cytokines from murine keratinocyte cell line Pam212 cells. We demonstrated that HEMA induced the release of 17-kDa mature IL-1α and caused cytotoxicity. The activity of calpain, an IL-1α processing enzyme, was significantly higher in HEMA-treated cells. The thiol-containing antioxidant N-acetyl cysteine (NAC) inhibited HEMA-induced IL-1α release but not cytotoxicity. NAC inhibited intracellular calpain activity and reactive oxygen species (ROS) production induced by HEMA. NAC post-treatment also inhibited IL-1α release and intracellular ROS production induced by HEMA. Furthermore, HEMA-induced in vivo inflammation also inhibited by NAC. NAC inhibited polymerization of HEMA through adduct formation via sulfide bonds between the thiol group of NAC and the reactive double bond of HEMA. HEMA-induced IL-1α release and cytotoxicity were also inhibited if HEMA and NAC were pre-incubated before adding to the cells. These results suggested that NAC inhibited IL-1α release through decreases in intracellular ROS and the adduct formation with HEMA. We concluded that HEMA induces IL-1α release from skin keratinocytes, and NAC may be a promising candidate as a therapeutic agent against inflammation induced by HEMA.

A Pilot Study on Monomer and Bisphenol A (BPA) Release from UDMA-Based and Conventional Indirect Veneering Composites

This study aimed to investigate the release of common monomers from conventional (Dialog Vario, Enamel Plus HFO) and UDMA-based indirect veneering composites (VITA VM LC, GC Gradia). Ten cylindrical samples of each material were prepared (n = 40), immersed in HPLC grade water, and incubated for 24 h in an incubation shaker at 37 °C and 112 rpm. Extraction was performed following ISO 10993-12 and monomers were detected and quantified by HPLC-MS/MS. In all the samples, urethane dimethacrylate (UDMA) and bisphenol A (BPA) were quantifiable. Compared to water blanks, BPA levels were only elevated in the eluates from conventional composites. In all other samples, concentrations were in the range of extraneous BPA and were therefore clinically irrelevant. Low concentrations of Bisphenol A-glycidyl methacrylate (BisGMA) were found in one BPA-free composite and in both conventional materials. Statistical analyses showed that BPA-free materials released significantly less BisGMA and no BPA, while UDMA elution was comparable to elution from conventional materials. All measured concentrations were below reported effective cytotoxic concentrations. Considering these results, the substitution of BPA-derivatives with UDMA might be beneficial since BPA-associated adverse effects are ruled out. Further studies should be enrolled to test the biocompatibility of UDMA on cells of the oral environment.

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.

Stain Susceptibility of Composite Resins: Pigment Penetration Analysis

Composite resins are considered the material of choice for esthetic direct restorations, considering both their satisfying esthetic and mechanical properties. The success of composite resin restorations depends highly on their color stability. Discoloration causes color mismatch, consequent patient dissatisfaction, and eventually additional costs for correction/replacement of the restoration. The purpose of this study was to evaluate the degree of pigment penetration within the composite resins, in order to understand how discoloration can be treated properly. Two different commercially available composite resins were compared in the study: a nano-filled composite resin and a non-homogeneous micro-hybrid composite resin. A coffee solution was used to induce staining of the materials. Subsequently, the penetration of the pigments was measured by analyzing the color from the outside to the inside of the specimen. 14 levels were analyzed starting from 0.1 mm to 3.0 mm in depth. The ANOVA test demonstrated a statistically significant difference (p < 0.0001) between test and control groups up to a depth of 1.0 mm for the nano-filled composite and up to a depth of 2.0 mm for the non-homogeneous micro-hybrid composite. The two composite resin materials, subjected to pigmenting treatment, underwent a color variation with different patterns.

Analytical Methods for Determination of BPA Released from Dental Resin Composites and Related Materials: A Systematic Review

Knowing the impacts of bisphenol A (BPA) on human health, this systematic review aimed to gather the analytical methods for the quantification of BPA release of BPA in dental materials in in vitro and in vivo (biological fluids) studies. A brief critical discussion of the impacts of BPA on human health and the possible association with BPA in dental materials was also presented. The research was carried out by three independent researchers, (according to PRISMA guidelines) in PUBMED and SCOPUS databases, by searching for specific keywords and articles published between January 2011 and February 2022. Seventeen articles met the eligibility criteria and were included in this systematic review: 10 in vitro and 7 in vivo. In in vitro studies, the highest amounts of BPA released were from flowable to conventional resins, followed by resin-modified glass ionomer. In contrast, the smallest amount was released from "BPA-free" composites and CAD-CAM blocks. Regarding in vivo studies, a higher concentration of BPA were found in saliva than urine or blood. The best analytical method for trace quantifying BPA is LC-MS/MS (Liquid Chromatography with Tandem Mass Spectrometry) due to its selectivity, low quantification limits, and the unequivocal identification. However, further studies are required to develop faster and more sensitive methods, in order to obtain more reliable results.

Evaluation of residual monomer release after polymerization of different restorative materials used in pediatric dentistry

BACKGROUND

The choice of the restorative resin material to be used in pediatric dentistry is of a great importance due to the cytotoxic effects caused by residual monomers. In this study, it was aimed to investigate the amount of residual monomer released over time from different resin-based restorative materials, which are widely used in pediatric dentistry, by using high performance liquid chromatography with photodiode array detector (HPLC-PDA).

METHODS

The compomers in all colors (Twinky Star and Glasiositte A₂), two composites with different hybrid properties (Arabesk-GrandioSO), and RMGIC (Ionolux) samples with 2 × 5 mm diameters were prepared. The samples were polymerized with an LED light unit (CELALUX 2, VOCO, Cuxhaven, Germany) and then finishing-polishing procedures were applied. A total of 156 samples were obtained, 13 samples in each of the 12 groups. The amount of residual monomer (BIS-GMA; HEMA, TEGDMA, UDMA) (µg/mL) released into the 75% ethanol solution was determined at different times, (1st hour, 1st, 7th, 14th, and 21st day) by using HPLC-PDA.

RESULTS

The residual monomer release continued on day 21 and BIS-GMA was the most released monomer in all groups. HEMA release showed a maximum increase in all the materials at day 7. The highest amount of residual monomer was detected in the gold-colored compomer. HEMA and BIS-GMA release from RMGIC was less than others in all time frames.

CONCLUSIONS

The color and composition of resin-based restorative materials affect the amount of residual monomer. Pediatric dentists should prefer gold-colored compomers less than others as a restorative material, especially in deep cavities. More studies are needed about the subject.

Resin-based composite materials: elution and pollution

Pollution arises from all human activity and the provision of oral healthcare using resin-based composite restorative materials (RBCs) should be considered. This paper aims to provide a comprehensive review of the potential pollutant risk to the environment from the chemical compounds found in resin-based restorative materials, by including: 1) the principal pollutant compounds present in the resin matrix; 2) the degradation process of RBCs and its consequences; 3) the methods used for the detection and quantification of monomer elution and RBC microparticles; and 4) a review of the release mechanisms of eluates and RBC microparticles into the environment.RBCs are pollutants by virtue of the compounds created during the degradation processes. These are in the form of the constituent eluted monomers and microparticles. Their impact on the environment and biodiversity is unknown. These materials are currently one of the main direct-placement restorative materials and their success is unquestionable when used and maintained correctly. Mitigation strategies for reducing the impact of pollution on the environment should be considered and implemented by all stakeholders and processes in the supply chain, from manufacturing, clinical use and waste management.

Monomer Release from Dental Resins: The Current Status on Study Setup, Detection and Quantification for In Vitro Testing

Improvements in mechanical properties and a shift of focus towards esthetic dentistry led to the application of dental resins in various areas of dentistry. However, dental resins are not inert in the oral environment and may release monomers and other substances such as Bisphenol-A (BPA) due to incomplete polymerization and intraoral degradation. Current research shows that various monomers present cytotoxic, genotoxic, proinflammatory, and even mutagenic effects. Of these eluting substances, the elution of BPA in the oral environment is of particular interest due to its role as an endocrine disruptor. For this reason, the release of residual monomers and especially BPA from dental resins has been a cause for public concern. The assessment of patient exposure and potential health risks of dental monomers require a reliable experimental and analytical setup. However, the heterogeneous study design applied in current research hinders biocompatibility testing by impeding comparative analysis of different studies and transfer to the clinical situation. Therefore, this review aims to provide information on each step of a robust experimental and analytical in vitro setup that allows the collection of clinically relevant data and future meta-analytical evaluations.

Effect of Volume and Renewal of the Storage Media on the Release of Monomer from Dental Composites

This study evaluated the effect of the volume and renewing of storage media on monomer leachability from dental composite. Samples of two dental composites (BEAUTIFIL II Gingiva (BG) and Filtek Bulk-Fill Flowable (FBF)) were stored after polymerization in 1 and 3 milt storage media (ethanol/water 75%) for seven days. Refreshing of storage media was done in half of the samples of each group. The amounts of releasing monomers (UDMA, BisGMA, TEGDMA) in storage media were measured by high-performance liquid chromatography (HPLC). Data was analyzed using two-way ANOVA and t-test (α = 0.05). Elution of TEGDMA and UDMA from both composites was significantly higher in 3 mL storage media. In groups with refreshing of storage media, BisGMA had higher amounts of release. Saturation makes the storage media volume important factor in monomer elution. Refreshing of storage media had significant effect on monomer release before the elution of 50% of total released monomer.

Meta-analytical analysis on components released from resin-based dental materials

OBJECTIVES

Resin-based materials are applied in every branch of dentistry. Due to their tendency to release substances in the oral environment, doubts have been raised about their actual safety. This review aims to provide a comprehensive analysis of the last decade literature regarding the concentrations of elutable substances released from dental resin-based materials in different type of solvents.

MATERIALS AND METHODS

All the literature published on dental journals between January 2010 and April 2022 was searched using international databases (PubMed, Scopus, Web of Science). Due to strict inclusion criteria, only 23 papers out of 877 were considered eligible. The concentration of eluted substances related to surface and volume of the sample was analyzed, considering data at 24 h as a reference. The total cumulative release was examined as well.

RESULTS

The most eluted substances were HEMA, TEGDMA, and BPA, while the less eluted were Bis-GMA and UDMA. Organic solvents caused significantly higher release of substances than water-based ones. A statistically significant inverse correlation between the release of molecules and their molecular mass was observed. A statistically significant positive correlation between the amount of released molecule and the specimen surface area was detected, as well as a weak positive correlation between the release and the specimen volume.

CONCLUSIONS

Type of solvent, molecular mass of eluates, and specimen surface and volume affect substances release from materials.

CLINICAL RELEVANCE

It could be advisable to rely on materials based on monomers with a reduced elution tendency for clinical procedures.

Effects of Monomer Composition of Urethane Methacrylate Based Resins on the C=C Degree of Conversion, Residual Monomer Content and Mechanical Properties

(1) Background: This study investigated the influence of Bis-GMA, TEGDMA, UDMA, and two different polyethylene glycol (PEG)-containing, UDMO-based co-monomers on the Young’s modulus and flexural strength, degree of methacrylate C=C double bond conversion and residual monomer elution of experimental dental resins. (2) Methods: Urethane methacrylate-based monomer was synthesised via a radical chain growth polymerization mechanism using PEG in order to improve the mechanical properties. Dental resins were formulated using Bis-GMA, UDMA, or UDMO as base monomers combined with TEGDMA as a dilution monomer and DMAEM + CQ as the photo-initiator system. Degree of conversion (DC), mechanical properties, and residual monomer content of light-activated methacrylate resin formulations were evaluated and statistically analysed by ANOVA and a Tukey’s test. (3) Results: PEG-containing UDMO resins had lower Young’s modulus and elastic strength than UDMA-derived resin for all irradiation times. The highest DC (67,418%) was observed for the PEG-containing UDMO-based resin formulation when light cured for 40 s. For all samples, DC increased with the photo-polymerization time. The amount of residual monomer decreased after increasing the light-curing period from 20 to 40 s, resin with UDMO content 0.01 mol of PEG having the smallest amount of free eluted monomer. (4) Conclusions: A strong structure–property relationship exists in photo-cured dimethacrylate-based dental resins. The time and quantity of the photochemical initiation system can influence the physical–mechanical properties of the resins but also the monomers in their composition.

Evaluation of Monomer Elution and Surface Roughness of a Polymer-Infiltrated Ceramic Network CAD-CAM Material After Er,Cr:YSGG Laser-assisted Tooth Bleaching

PURPOSE

The aim of this in vitro study was to examine the effect of Er,Cr:YSGG laser-assisted tooth bleaching treatment on the elution of monomers and surface roughness of a hybrid computer-aided design-computer-aided manufacturing (CAD-CAM) material, and to compare it with a resin composite for direct restorations.

METHODS AND MATERIALS

Forty specimens of a hybrid CAD-CAM material (Enamic) and forty of a conventional resin composite (Tetric) were fabricated and randomly divided into four groups (n=10). Half of the specimens of each material were stored in distilled water and the other half in artificial saliva for 7 days. At the end of this period, the storage medium was analyzed by high-performance liquid chromatography (HPLC), and the surface roughness parameters of the specimens were evaluated by optical imaging noncontact interferometric profilometry. Afterwards, half of the specimens of each tested material received a conventional in-office tooth bleaching treatment and the other half an Er,Cr:YSGG laser-assisted bleaching treatment, and then they were again incubated in distilled water and artificial saliva for an additional 7-day time period. At the end of this period, the effect of the bleaching treatments on elution of monomers and surface roughness of the tested materials was evaluated.

RESULTS

Bisphenol A (BPA), urethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA), and bisphenol A-glycidyl dimethacrylate (BisGMA) were eluted from the conventional resin composite into both the solutions tested. Only TEGDMA was eluted from the hybrid CAD-CAM material. However, no statistically significant differences were found among the surface roughness parameters of both materials. Both the conventional and Er,Cr:YSGG laser-assisted tooth bleaching treatments affected the monomer elution from the composite resin. However, there were no statistically significant differences (p<0.05) between the treatments.

CONCLUSIONS

According to the results of this study, tooth bleaching with Er,Cr:YSGG laser or conventional technique is safe, even if the bleaching agent comes in contact with hybrid CAD-CAM restorations.

Effect of Polymerization Time on Residual Monomer Release in Dental Composite: In Vitro Study

Light activated resin-based composites are the most accepted and used materials among clinicians. The aim of this study is to determine the amount of residual monomer released from nanofiller composite resins for different polymerization times and storage periods in vitro. To this purpose, Tetric Ceram (Ivoclar, Liechtenstein), Clearfil Majesty Posterior (Kuraray, Japan), Grandio (VOCO, Germany), and Filtek Ultimate Universal (3M, USA) were used as nanofiller resin composites samples. Four groups ( $n=40$ , diameter: 5 mm, thickness: 2 mm) of each material were fabricated, and each group was exposed to three different polymerization time (10, 20 and 40 sec). High-performance liquid chromatography (HPLC) was used to measure the amount of monomers released over 1, 15, and 30 days. The highest amount of monomer release was seen in Tetric EvoCream composite, while the least monomer release was seen in Clearfil Majesty composite. Regardless of the polymerization time, material, or storage period, the highest amount of eluted monomer was Bis-GMA. It is observed that there is no statistically significant difference between various polymerization times. Monomer release reached its highest level on the 15th day and decreased on the 30th day for all composites. Polymerization time did not affect the monomer release from the composites, but the type of the monomers and concentration of the filler used in the composites affected the amount of released monomers. The use of TEGDMA (co)monomer reduced the monomer release.

Cytotoxicity of Different Composite Resins on Human Gingival Fibroblast Cell Lines

The aim of the present study was to evaluate and compare the cytotoxic effects of eight composite resins on immortalized human gingival fibroblasts. Composite resins were eluted in cell culture medium for 48 or 72 h at 37 °C. Immortalized human gingival fibroblast-1 (HGF-1) cell lines were seeded in 96-well (1 × 10⁴) plates and incubated for 24 h at 37 °C with the obtained extraction medium. The percentage of viable cells in each well (MTT test) was calculated relative to control cells, which were set to 100%. Data observed were not normally distributed, and nonparametric statistical methods were used for statistical analysis. The Wilcoxon test was used for intragroup comparison, and the Kruskal–Wallis test was used for intergroup multiple comparisons. Significance value was set as p < 0.05. All materials tested showed cytotoxic effects on gingival fibroblasts, recordable as noncytotoxic, mildly cytotoxic or severely cytotoxic, depending on the percentage of cell viability. The Wilcoxon test for intragroup comparison showed that the percentage of viable cells decreased significantly for extracts, for all composite resins tested. The composite resins contained monomers that displayed cytotoxic properties. BisGMA, TEGDMA and UDMA had inhibitory effects and induced apoptotic proteins in pulp fibroblast. Composite resins that contained lower percentages of unbound free monomers—and that released less ions—possessed superior biocompatibility in vitro.

Correlation of the mechanical and biological response in light-cured RBCs to receiving a range of radiant exposures: Effect of violet light

OBJECTIVE

This study correlates the mechanical and biological response of commercially available resin-based composites (RBCs) to clinically relevant light-curing conditions.

METHODS

Two RBCs (Venus and Venus Pearl; Kulzer) that use different monomer and photo-initiator systems, but have a similar filler volume and shade, were exposed to either just blue light, or violet and blue light from two different LCUs (Translux Wave and Translux 2Wave; Kulzer). Distance and exposure times were adjusted so that both LCUs delivered 5 similar levels of radiant exposures (RE) between 1.5 J/cm²-25 J/cm² in the blue wavelength range. Thus, the violet light was additional light. The top and bottom of 2-mm thick specimens were subjected to a depth-sensing indentation test (Martens hardness/HM, Vickers hardness/HV, indentation modulus/Y_HU, mechanical work/W_total, plastic deformation work/W_plas, creep/Cr). The viability of human gingival fibroblasts was assessed after three days of exposure to RBC eluates. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), t-test and a Spearman correlation analysis were used.

RESULTS

As the RE increased, the mechanical properties increased at a greater rate at the top compared to the bottom of the RBCs. Values measured at the bottom of 2-mm increments approached the values measured at the top only when RE > 25 J/cm² of blue light was delivered. Toxicity decreased with RE and elution cycles and was lower for Venus Pearl. Within one RE level, addition of violet light resulted in significantly improved properties (in 131 out of 150 comparisons, p < 0.05). This effect was stronger for Venus Pearl. There was a good correlation between mechanical and biological parameters. This correlation decreased as the number of eluates increased.

CLINICAL SIGNIFICANCE

The mechanical and biological response to variation in RE is interrelated. The addition of violet light has a positive effect, particularly at low RE.

The effect of pre-heating on monomer elution from bulk-fill resin composites

Background

The present study was aimed to evaluate the effect of pre-heating of bulk -fill resin composites on monomer elution from them.

Material and Methods

Three different types of resin composites were used including Tetric N-Ceram Bulk Fill, X-tra Fill and X-tra Base. 10 cylindrical samples were prepared from each resin composites. Before light curing, 5 samples were pre-heated until reaching 68˚C, then 5 other samples were polymerized at room temperature. After 24 hours, release of UDMA, TEGDMA and BIS-GMA monomers were measured by High-Performance Liquid Chromatography analysis. Data analysis was performed by two-way ANOVA test, Games-Howell and Sidak post hoc tests.

Results

Pre-heating did not have any statistically significant effect on the mean values of UDMA, TEGDMA and Bis-GMA elution (p>0.05). The greatest amount of released Bis-GMA and UDMA was obtained from Tetric N-Ceram Bulk-fill composite. The greatest amount of released TEGDMA was obtained from X-tra Fill composite. X-tra Base composite showed the lowest amount of monomer release (P<0.001).

Conclusions

Pre-heating did not have any effect on monomer release from bulk-fill resin composites. Moreover, the amount and the type of monomers released from various bulk-fill resin composites were not similar.

Key words:Bulk fill composite resin, elution, HPLC, residual monomer, temperature.

Monomer release from surgical guide resins manufactured with different 3D printing devices

OBJECTIVES

The aim of this study was to assess the post curing monomer release of resins applicable for 3D printing of surgical implant guides in dependency of printing technique and storing media using high performance liquidchromatography.

MATERIAL AND METHODS

Specimens of Nextdent SG, Freeprint Splint, Fotodent Guide, 3Delta Guide, and V-print SG (n = 4) were additively manufactured with the corresponding DLP/SLA printing devices (Rapidshape D20II, Form2, Solflex350). Postprocessing was done according to the manufacturer's specifications. Subsequently, samples were eluted in methanol and water for 3 days and analyzed with gas chromatography/mass spectrometry (GC/MS).

RESULTS

A total of twelve different substances released from the tested resin materials. The highest eluted concentration for MMA in methanol was 20.27 ± 8.60 μg/mL followed by 12.66 ± 3.38 μg/mL of HPMA. HEMA was found at concentration of 11.17 ± 2.43 μg/mL in methanol and 1.15 ± 0.11 μg/mL in water. TPGDA and TEGDMA reached maximum concentration in methanol of 4.29 ± 0.54 μg/mL and 5.07 ± 0.93 μg/mL and in water of 0.79 ± 0.19 μg/mL and 0.36 ± 0.14 μg/mL, respectively. Significant difference was found for the material Nextdent SG manufactured on SLA and DLP printing device for THFMA (p = 0.041), TEGDMA (p = 0.026), TPGDA (p = 0.05) and EGDMA (p = 0.06). The amount of monomers released into water did not reach the detection threshold for V-print SG.

SIGNIFICANCE

The study revealed significant influence of the printing technique and resin material on the elution of monomers. The elution in methanol and water was significantly different. While the relative amount of eluted monomers from 3D printed guides is comparable to conventional direct composites and below toxic relevant concentrations, the absolute amount of monomer can rise in a clinic situation due to the size of the guides.

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.

Evaluation of Two Resin Composites Having Different Matrix Compositions

This study compared two resin composites with similar filler systems and different matrix compositions. The depth of cure (DoC), polymerization shrinkage, and marginal leakage were evaluated. A Filtek Bulk Fill resin composite (FB) and a Filtek Supreme resin composite (FS) were used. For the DoC and polymerization shrinkage, cylindrical specimens with different thicknesses were prepared. The DoC was attributed to the bottom/top ratios of Vickers microhardness numbers. For polymerization shrinkage, each specimen was firstly scanned using micro-computed tomography (µCT) then cured for 20 s, then for 10 s, and then for 10 s, and they were rescanned between each curing time. Data were processed using the Mimics software. For marginal leakage, standardized 5 mm cavities were prepared in 90 molars. After etching and bonding, materials were packed according to groups: FB-bulk, FB-incremental, and FS-incremental, which were cured for 20, 30, and 40 s, respectively. After thermo-cycling, teeth were stored in 1% methylene blue dye for 24 h and then sectioned and observed for dye penetration. The results showed insignificant differences in the shrinkage and leakage between the different packing techniques and curing times of both materials. In conclusion, the introduction of a novel matrix into resin composite composition enabled bulk-filling in one layer up to 5 mm deep while keeping a tolerable polymerization shrinkage.

Effect of preheating on the cytotoxicity of bulk-fill composite resins

Background. Due to the effect of pre-heating on the degree of conversion of composite resins and the possible effect on cytotoxicity, the effect of pre-heating of bulk-fill composite resins was investigated on cytotoxicity in this study. Methods. In this study, three different types of composite resin were used, including Tetric N-Ceram Bulk-Fil, Xtrafil, and Xtrabase. From each composite resin, 10 cylindrical samples (5 mm in diameter and 4 mm in height) were prepared, with five samples preheated to 68°C, and the other five samples polymerized at room temperature (25°C). Twenty-four hours after polymerization, cytotoxicity was assessed by MTT assay on human fibroblasts. Statistical analysis of data was carried out with two-way ANOVA and Sidak Post-Hoc. The significance level of the test was determined at 0.05. Results. There was no statistically significant difference between the mean percentage of cytotoxicity in terms of pre-heating (P>0.05), but the cytotoxicity of the studied composite resins was significantly different (P<0.001). The cytotoxicity of Tetric N-Ceram Bulk-fil composite resin was higher than that of the two other composite resins. Conclusion. Pre-heating of bulk-fill composite resin did not affect their cytotoxicity. In addition, the cytotoxicity of different bulk-fill composite resins was not the same.

Cytotoxicity of Different Nano Composite Resins on Human Gingival and Periodontal Ligament Fibroblast Cell Lines: An In Vitro Study

The aim of this study is to determine the cytotoxicity of three different nano composite resins (CRs) on human gingival fibroblast (hGF) and periodontal ligament fibroblast (hPDLF) cell lines. These CRs selected were nanohybrid organic monomer-based Admira Fusion (AF), nanohybrid Bis-(acryloyloxymethyl) tricyclo [5.2.1.0.sup.2,6] decane-based Charisma Topaz (CT), and supra nano filled resin-based Estelite Quick Sigma (EQS). MTT assay was performed to assess the cytotoxicity of CRs at 24 h and one week. AF and EQS applied on hGF cells at 24 h and one week demonstrated similar cytotoxic outcomes. Cytotoxicity of CT on hGF cells at one week was higher than 24 h (p = 0.04). Cytotoxicity of CT on hGF cells was higher at 24 h (p = 0.002) and one week (p = 0.009) compared to control. All composites showed higher cytotoxicity on hPDLF cells at one week than the 24 h (AF; p = 0.02, CT; p = 0.02, EQS; p = 0.04). AF and EQS demonstrated lower cytotoxicity on hPDLF cells than the control group at 24 h (AF; p = 0.01, EQS; p = 0.001). CT was found more cytotoxic on hPDLF cells than the control (p = 0.01) and EQS group (p = 0.008) at one week. The cytotoxicity of CRs on hGF and hPDLF cells vary, according to the type of composites, cell types, and exposure time.

Influence of diazonium and surfactant modification of the mesoporous material on its adsorption properties

We describe a new and direct route to obtain Al-SBA-15-modified materials with different groups on their surface using diazonium salts. For comparison, modification using surfactants was also used. In the present study, we decided to examine the applicability of these materials in the adsorption of compounds released from dental fillings. The effectiveness of modification was proved by results of Fourier transform infrared spectroscopy and energy-dispersive spectrometry. The results indicate the formation of characteristic groups on the surface of the materials. The materials after modification are characterized by smaller surface area and pore volume, which is result of covering the surface with an aryl or surfactant layer. The adsorption properties change after modification and depend on the used modifier. Diazonium modification has a positive effect on sorptive properties when hydroxyl and dimethylamine groups are obtained. The methods of material modification presented in this work may in the future lead to the improvement in the properties of sorbents used in solid-phase extraction.

Evaluation of the biocompatibility of resin composite-based dental materials with gingival mesenchymal stromal cells

Resin composite-based dental materials can leach certain components into the oral environment, causing potentially harmful gingival biological effect. Gingival tissue is a rich source of mesenchymal stem cells (MSCs) that is easily accessible, and can be used as a complementary approach for the investigation of dental material biocompatibility. Using gingival MSCs (gMSCs), the present study aimed to investigate the cytotoxicity of two classes of restorative dental materials (ormocers and resin composites) used to restore class II cavities close to the gingival margin, in addition to analyzing the leached compounds from these resin composite-based materials. Functionality assays (Colony-forming unit, migratory potential, and proliferation assays) and a viability assay (MTT) were employed. Cells' aspect was observed by scanning electron microscopy (SEM). Leached monomers were also quantitated using high-performance liquid chromatography (HPLC). The cytotoxicity of the biomaterials was highlighted by impaired functionality and diminished viability of gMSCs. Despite being variants of the same commercial material, the two ormocers behaved differently one material having a more negative impact on cell functionality than the other. Cells appeared to attach well to all materials. Main monomer molecules were mostly released by the tested materials. For all samples, an increased elution of monomers was recorded in artificial saliva as compared with culture medium. One composite material has released nearly eight times more urethane dimetacrylate in artificial saliva than in culture medium. Significantly lower gMSC viability scores were recorded for all the investigated samples in comparison with the control.

Rapid Antibiofilm Effect of Ag/ZnO Nanocomposites Assisted by Dental LED Curing Light against Facultative Anaerobic Oral Pathogen Streptococcus mutans

The integration of nanomaterials with clinical therapeutic instruments is a promising approach to improve the effects of nanomaterials. We reported an efficient synergistic antibacterial strategy formed through the combination of Ag/ZnO nanocomposites with a light-emitting diode (LED) curing light, which is a commonly used small instrument in dental clinics. The as-designed integration depicted a significantly enhanced bactericidal effect on facultative anaerobic oral pathogen Streptococcus mutans (S. mutans) both in planktonic and biofilm phases over a very short irradiation time (≤5 min). Further study showed that the combination of LED and Ag/ZnO nanocomposites induced more ·OH and ·O₂^- generation, which is responsible for the enhanced antibacterial activity. Moreover, this combination could destroy S. mutans biofilm by killing the bacteria embedded within biofilm, inhibiting exopolysaccharide production and down-regulating the biofilm-related gene expression. Therefore, it is proposed that this combination could be applied in dental clinics to realize dental caries prevention and dental restoration simultaneously.

Simultaneous analysis of bisphenol A based compounds and other monomers leaching from resin-based dental materials by UHPLC-MS/MS

Resin-based dental materials have raised debates concerning their safety and biocompatibility, resulting in a growing necessity of profound knowledge on the quantity of released compounds into the oral cavity. In this context, the aim of this study was to develop a comprehensive and reliable procedure based on liquid chromatography with mass spectrometry for the simultaneous analysis of various leached compounds (including bisphenol A based compounds) in samples from in vitro experiments. Different experiments were performed to determine the optimal analytical parameters, comprising mass spectrometry parameters, chromatographic separation conditions, and sample preparation. Four internal standards were used as follows: deuterated diethyl phthalate and bisphenol A (commercially available), and deuterated analogues of triethylene glycol dimethacrylate and urethane dimethacrylate (custom-made). The optimized method was validated for linearity of the calibration curves and the associated correlation coefficient, lower limit of quantification, higher limit of quantification, and intra- and interassay accuracy and precision. Additionally, the developed liquid chromatography with tandem mass spectrometry method was applied to the analysis of leaching compounds from four resin-based dental materials. The results indicated that this method is suitable for the analysis of different target compounds leaching from dental materials. This method might serve as a valuable basis for quick and accurate quantification of leached compounds from resin-based dental materials in biological samples.

Biological evaluation of subgingivally placed direct resin composite materials

Placement of composite resin restorations in deep subgingival cavities can damage surrounding soft tissues. In addition, commonly used resin-based composites (RBCs) might interfere with wound healing and periodontal health. To clarify cellular interactions with RBCs, we used an MTT assay to investigate adhesion of primary human gingival fibroblasts and human osteoblasts (hFOB 1.19) on five RBC materials with and without surface modifications (alumina blasting with 50- or 110-μm Al₂O₃). In addition, high-performance liquid chromatography (HPLC) was used to determine release of resin monomers from RBCs after 1 h, 1 day, and 7 days. As compared with tissue culture plastics (the control), cellular adhesion was significantly lower (P < 0.001) for human gingival fibroblasts and osteoblasts. Only minor, nonsignificant differences between individual RBCs were identified. HPLC analyses identified the release of three bifunctional methacrylates bisphenol A glycerolate dimethacrylate, triethylene glycol dimethacrylate, and diurethane dimethacrylate from RBCs and showed that monomer release increased between 1 h and 1 day but remained low. The present findings suggest that surface adhesion in the subgingival area is limited for the tested RBCs. Although residual monomer release was low for all tested RBCs, it might be sufficient to adversely affect cell adhesion.

A Comparative Evaluation of Microleakage among Newer Composite Materials: An in vitro Study

Background:

Good adhesive bonding of restorative materials to cavity walls minimizing microleakage is an important criterion for the performance and longevity of a restoration in the oral cavity. The present study is aimed to compare the microleakage among newer composite materials.

Materials and Methods:

Forty-five extracted healthy premolars were collected; standard Class II cavities were prepared. They were randomly divided into three groups of 15 teeth each. The groups were made based on the different composite restorative materials used for restoration. Group A consisted of conventional microfilled composite resin restorations, and Group B was posterior nanocomposite resin. Group C was restored using ORMOCER – Admira. After completion of restorations, all teeth were subjected to thermocycling at 5° C, 37° C, and 55° C for 250 cycles. Later, all samples were immersed into 50% silver nitrate dye group wise for for 4 hours (h), and teeth were sectioned buccolingually. Sectioned teeth were observed under a stereomicroscope for the evaluation of microleakage. ANOVA and unpaired t-tests were used for statistical analysis. The significance level was at set P < 0.001.

Results:

The results of this study showed that Group C (ORMOCER – Admira) presented with the least microleakage followed by Group B (Tetric N-Ceram) followed by Group A (Tetric Ceram).

Conclusions:

Overall ORMOCER – Admira performed better than the other two composite materials with the least microleakage.

Elution of monomer from different bulk fill dental composite resins

OBJECTIVE

The purpose of this study was to evaluate the elution of Bis-GMA, TEGDMA, HEMA, and Bis-EMA monomers from six bulk fill composite resins over four different time periods, using HPLC.

METHODS

Six different composite resin materials were used in the present study: Tetric Evo Ceram Bulk Fill (Ivoclar Vivadent, Amherst, NY), X-tra Fill (VOCO, Cuxhaven, Germany), Sonic Fill (Kerr, Orange, CA, USA), Filtek Bulk Fill (3M ESPE Dental Product, St. Paul, MN), SDR (Dentsply, Konstanz, Germany), EQUIA (GC America INC, Alsip, IL). The samples (4mm thickness, 5mm diameter) were prepared and polymerized for 20s with a light emitted diode unit. After fabrication, each sample was immediately immersed in 75wt% ethanol/water solution used as extraction fluid and stored in the amber colored bottles at room temperature. Ethanol/water samples were taken (0.5mL) at predefined time intervals:10m (T1), 1h (T2), 24h (T3) and 30 days (T4). These samples were analyzed by HPLC. The obtained data were analyzed with one-way ANOVA and Tukey HSD at significance level of p<0.05.

RESULTS

Amount of eluted Bis-EMA and Bis-GMA from Tetric Evo Ceram Bulk Fill and amount of eluted TEGDMA and HEMA from X-tra Fill higher than others composites (p<0.05).

SIGNIFICANCE

Residual monomers were eluted from bulk fill composite resins in all time periods and the amount of eluted monomers was increased with time.

Leaching of monomers from bulk-fill composites: An in vitro study

AIM AND OBJECTIVES

To evaluate the elution of bisphenol A-glycidyl methacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) from two bulk-fill composites at different polymerization times, for different storage periods when cured with quartz-tungsten-halogen (QTH) curing unit.

MATERIALS AND METHODS

Tetric N-Ceram bulk fill and EverX Posterior were analyzed using high-performance liquid chromatography unit. Totally, 68 samples were prepared, two groups (n = 17) from both the composites, one for each tested polymerization time. Each sample was cured with a QTH curing unit, using soft-start curing technique and stored in 2 ml of ethanol for 24 h. Storage medium was renewed and then stored again for 1 week. Data acquired were statistically analyzed.

RESULTS

The elution of BisGMA was significantly higher from Tetric N-Ceram bulk fill and BisGMA and TEGDMA from EverX Posterior composite at the end of 24 h, irrespective of the curing time. In EverX Posterior, a higher amount of TEGDMA was eluted at the end of 24 h, while at the end of 1 week, significantly higher amount of BisGMA was released.

CONCLUSION

A significant amount of the release of BisGMA as well as TEGDMA was seen from both the composites when stored for different time intervals.

Effect of LED-LCU light irradiance distribution on mechanical properties of resin based materials

The objective of this study is to analyze the light power distribution along the tip end of the light guide of three LED-LCUs (Light Curing Units) and to evaluate its effect on the mechanical properties of a polymer based dental composite. Firstly, the light power distribution over the whole area of LED-LCU light guide surface was analyzed by three methods: visual projection observation, spectral measurement and optical spectral analysis (OSA). The light power distribution and the total irradiance were different for the three LEDs used, but the wavelength was within the camphorquinone absorption spectrum. The use of a blank sheet was quite on hand to make a qualitative analysis of a beam, and it is costless. Secondly, specimens of a hybrid composite with approximately 8mm diameter and 2mm thickness were produced and polymerized by 20s exposition time to each LED-LCU. Thirdly, the elastic modulus (E) and hardness (HV) were measured throughout the irradiated area by instrumented micro-indentation test (IIT), allowing to correlate localized power and mechanical properties. Both E and HV showed to be very sensitive to local power and wavelength dependent, but they followed the beam power profile. It was also shown that the mechanical properties could be directly correlated to the curing process. Very steep differences in mechanical properties over very short distances may impair the material performance, since residual stresses can easily be built over it.

Gene expression analysis of conventional and interactive human gingival cell systems exposed to dental composites

OBJECTIVES

The aim of this study was the detection of putative gene expression-related effects of dental composites in conventional and interactive gingival cell systems.

METHODS

Conventional monoculture (MC) and interactive cell systems (ICS) comprising human gingival fibroblast (HGF) and immortalized human gingival keratinocytes (IHGK) were exposed for 24h and 7 days according to ISO10993-12:2012 manufactured eluates of different composites (Ceram X(®), Filtek™ Supreme XT, Filtek™ Silorane, Fusio™ Liquid Dentin, and Vertise™ Flow). qRT-PCR-based mRNA analysis for biomarkers indicating cell proliferation, differentiation, apoptosis, inflammation, and adhesion was performed. Apoptotic cells were quantified by annexin-V labeling.

RESULTS

Due to low RNA amounts, qPCR could not be performed for Vertise™ Flow and Fusio™ Liquid Dentin at day 7. At 24h, flowables yielded increased transcription for biomarkers of inflammation and apoptosis in IHGK, irrespective of the cell system. HGF cultures displayed lower transcription for cell adhesion markers in both cell systems. Filtek™ Supreme XT showed increased differentiation by elevated filaggrin gene expression in both cell systems for IHGK at day 7, while Filtek™ Silorane and Ceram X(®) yielded elevation of inflammation biomarkers in both cell types. Annexin-V labeling revealed high apoptosis rates for both flowables and Filtek™ Supreme XT for IHGK, while low rates were detected for Filtek™ Silorane and Ceram X(®).

SIGNIFICANCE

Among the composites evaluated, exposition of IHGK and HGF in conventional and interactive cell systems demonstrated most pronounced gene expression alterations in response to flowables, coinciding with elevated levels of apoptosis.