Cytotoxicity of resin composites as a function of interface area

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.

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.

In situ photochemical crosslinking of hydrogel membrane for Guided Tissue Regeneration

OBJECTIVE

Periodontitis is an inflammatory disease that destroys the tooth-supporting attachment apparatus. Guided tissue regeneration (GTR) is a technique based on a barrier membrane designed to prevent wound space colonization by gingival cells. This study examined a new formulation composed of two polymers that could be photochemically cross-linked in situ into an interpenetrated polymer network (IPN) forming a hydrogel membrane.

METHODS

We synthetized and characterized silanized hydroxypropyl methylcellulose (Si-HPMC) for its cell barrier properties and methacrylated carboxymethyl chitosan (MA-CMCS) for its degradable backbone to use in IPN. Hydrogel membranes were cross-linked using riboflavin photoinitiator and a dentistry visible light lamp. The biomaterial's physicochemical and mechanical properties were determined. Hydrogel membrane degradation was evaluated in lysozyme. Cytocompatibility was estimated by neutral red uptake. The cell barrier property was studied culturing human primary gingival fibroblasts or human gingival explants on membrane and analyzed with confocal microscopy and histological staining.

RESULTS

The IPN hydrogel membrane was obtained after 120s of irradiation. The IPN showed a synergistic increase in Young moduli compared with the single networks. The CMCS addition in IPN allows a progressive weight loss compared to each polymer network. Cytocompatibility was confirmed by neutral red assay. Human cell invasion was prevented by hydrogel membranes and histological sections revealed that the biomaterial exhibited a barrier effect in contact with soft gingival tissue.

SIGNIFICANCE

We demonstrated the ability of an innovative polymer formulation to form in situ, using a dentist's lamp, an IPN hydrogel membrane, which could be an easy-to-use biomaterial for GTR therapy.

Evaluation of residual monomer release and toxicity of self-adhesive resin cements

The aim of this study was to evaluate the amount of leached residual monomers from self-adhesive resin cements and evaluate their toxicity in-vitro. A total of 60 disk-shaped specimens (5 mm in diameter and 0.5 mm in thickness) were prepared from each cement (RelyX U200, SpeedCEM, G-Cem) (n=20). Specimens were immersed in artificial saliva and the amount of released monomers [urethane dimethacrylate (UDMA) and triethyleneglycol dimethacrylate (TEGDMA)] was identified. Then, the cytotoxicity and genotoxicity effect on cells were evaluated using the defined amounts of released monomers from cements. The highest monomer release was detected in G-Cem (p<0.05). The highest cytotoxicity value was identified from SpeedCEM (p<0.01) and the highest genotoxicity values were calculated from RelyX U200 (p<0.05). Released UDMA and TEGDMA from self-adhesive resin cements induced cytotoxicity and genotoxicity effect on cells.

Cytotoxicity of glass ionomer cements containing silver nanoparticles

BACKGROUND

Some studies have investigated the possibility of incorporating silver nanoparticles (NAg) into dental materials to improve their antibacterial properties. However, the potential toxic effect of this material on pulp cells should be investigated in order to avoid additional damage to the pulp tissue. This study evaluated the cytotoxicity of conventional and resin-modified glass ionomer cements (GIC) with and without addition of NAg.

MATERIAL AND METHODS

NAg were added to the materials at two different concentrations by weight: 0.1% and 0.2%. Specimens with standardized dimensions were prepared, immersed in 400 µL of culture medium and incubated at 37°C and 5% CO2 for 48 h to prepare GIC liquid extracts, which were then incubated in contact with cells for 48 h. Culture medium and 0.78% NAg solution were used as negative and positive controls, respectively. Cell viability was determined by MTT and Trypan Blue assays. ANOVA and the Tukey test (α=0.05) were used for statistical analyses.

RESULTS

Both tests revealed a significant decrease in cell viability in all groups of resin modified cements (p<0.001). There were no statistically significant differences between groups with and without NAg (p>0.05). The differences in cell viability between any group of conventional GIC and the negative control were not statistically significant (p>0.05).

CONCLUSIONS

NAg did not affect the cytotoxicity of the GIC under evaluation.

KEY WORDS

Glass ionomer cements, totoxicity, cell culture techniques, nanotechnology, metal nanoparticles.

Mechanical and biological properties of acrylic resins manipulated and polished by different methods

This study evaluated the influence of the manipulation technique and polishing method on the flexural strength and cytotoxicity of acrylic resins. Two manipulation techniques and three polishing methods were used in the fabrication of acrylic plates that were divided into 6 groups (n=10). Groups MM, MC and MW: mass technique with mechanical polishing, chemical polishing and without polishing, respectively; and Groups SM, SC and SW: Saturation technique with mechanical polishing, chemical polishing and without polishing, respectively). Flexural strength was tested in a universal testing machine and the cytotoxicity assay used cell cultures (L-929) for periods of 24 h to 168 h. Flexural strength and cytotoxicity data were assessed using two-way and three-way ANOVA, respectively (α=0.05), followed by post hoc Bonferroni test for multiple comparisons. The effect of combinations of manipulation techniques and polishing methods on flexural strength showed significant differences only between Group SC and Groups MW, MM and MC (p<0.01). Cell viability ranged from 51% (3.9%) to 87,6% (3.2) in the 24-h time interval, and from 87.8% (5.0) to 95.7% (3.1%) in the 168-h time interval. With the increase of cell viability, from the third day (72 h), there was no significant difference among the groups, except between MM and SC (p<0.01) at 72 h. In conclusion, the manipulation technique and polishing method had more influence on the cytotoxicity than on flexural strength.

Resin-composite cytotoxicity varies with shade and irradiance

OBJECTIVES

The study was aimed at investigating the cytotoxicity of different composites as a function of composite shade and the light curing unit (LCU) employed.

METHODS

Non-polymerized and polymerized samples of the composites Grandio(®) (VOCO, Cuxhaven), Solitaire(®) (Heraeus Kulzer, Hanau) and Filtek Z 250(®) (3M/Espe, Seefeld) in two markedly differing shades (A2, C2) were prepared. Polymerization was performed with two LCUs: Heliolux II (Ivoclar/Vivadent, Ellwangen) and Swiss Master Light (EMS, Nyon, Switzerland). To obtain composite extracts, the samples were immersed in cell culture medium (DMEM--Dulbecco's Modified Eagle Medium), which was replaced daily up to the 7th day of the experiment, and then on the 14th, 21st and 28th day. After incubation of human gingival fibroblasts (HGF) with the extracts obtained, cytotoxicity was determined using the MTT test.

RESULTS

With the non-polymerized samples, essentially no influence of the composite shades investigated on HGF viability was detected, with the exception of the Solitaire material, where a higher cytotoxicity of the shade C2 in the non-polymerized state was found at the end of the observation period. After polymerization of the different composites, the cytotoxic reaction observed for the extracts of shade C2 was stronger than that observed for A2. After polymerization with the Heliolux II (HLX) LCU, the extracts of composites Grandio and Solitaire C2 were significantly more toxic than those of the A2 shade (p<0.01). Polymerization with the Swiss Master Light (SML) reduces this cytotoxic effect. The extracts of the Grandio composite showed the least cytotoxic effect throughout the observation period, irrespective of the LCU used. For the extracts of the Z250 specimens, the cytotoxicity observed was generally higher.

SIGNIFICANCE

The results show that the shade of the composite has an influence on its cytotoxicity and that this cytotoxicity is also influenced by the light curing unit used. It was observed that composites of the darker shade (C2) had a higher cytotoxicity, which varied with the LCU employed.

The influence of pH levels on mechanical and biological properties of nonlatex and latex elastics

OBJECTIVE

To evaluate the influence of pH levels on interarch elastics with regard to force decay and cytotoxicity.

MATERIALS AND METHODS

One nonlatex (NLAO) group and one latex (LAO) group were tested (n  =  10). Elastics were stretched to 25 mm and were held for 1, 6, 12, and 24 hours in artificial saliva solutions with pH levels of 5.0, 6.0, and 7.5. Force magnitudes were measured at 25 mm of activation. The cytotoxicity assay was performed using cell cultures (L929 mouse fibroblast cell line), which were subjected to the cell viability test with neutral red ("dye-uptake"). Force decay and cytotoxicity were assessed using analysis of variance, the Sidak method, and a Tukey's test.

RESULTS

The interactions between group, pH, and time showed no statistically significant differences (P  =  .29). When pH per time (P  =  .032) and group per time (P  =  .0009) were considered, these interactions showed statistically significant differences (P < .05). The pH did not interfere directly in the degradation results of the tested elastics. The cytotoxicity test showed that group LAO presented lower cell viability when compared with group NLAO over the course of the entire experiment. There was a gradual reduction in cell viability from 1 hour to 24 hours. A significant difference (P < .05) was found between the interactions group pH and the control group of cells, except between group NLAO at the time point of 1 hour at different pH values and at the time points of 6 and 12 hours with pH 5 (P > .05).

CONCLUSIONS

No significant correlation between pH, force decay, and cytotoxicity was observed.

Effect of reduced exposure times on the cytotoxicity of resin luting cements cured by high-power led

Objective

Applications of resin luting agents and high-power light-emitting diodes (LED) light-curing units (LCUs) have increased considerably over the last few years. However, it is not clear whether the effect of reduced exposure time on cytotoxicity of such products have adequate biocompatibility to meet clinical success. This study aimed at assessing the effect of reduced curing time of five resin luting cements (RLCs) polymerized by high-power LED curing unit on the viability of a cell of L-929 fibroblast cells.

Material and Methods

Disc-shaped samples were prepared in polytetrafluoroethylene moulds with cylindrical cavities. The samples were irradiated from the top through the ceramic discs and acetate strips using LED LCU for 20 s (50% of the manufacturer's recommended exposure time) and 40 s (100% exposure time). After curing, the samples were transferred into a culture medium for 24 h. The eluates were obtained and pipetted onto L-929 fibroblast cultures (3x10⁴ per well) and incubated for evaluating after 24 h. Measurements were performed by dimethylthiazol diphenyltetrazolium assay. Statistical significance was determined by two-way ANOVA and two independent samples were compared by t-test.

Results

Results showed that eluates of most of the materials polymerized for 20 s (except Rely X Unicem and Illusion) reduced to a higher extent cell viability compared to samples of the same materials polymerized for 40 s. Illusion exhibited the least cytotoxicity for 20 s exposure time compared to the control (culture without samples) followed by Rely X Unicem and Rely X ARC (90.81%, 88.90%, and 83.11%, respectively). For Rely X ARC, Duolink and Lute-It 40 s exposure time was better (t=-1.262 p=0,276; t=-9.399 p=0.001; and t=-20.418 p<0.001, respectively).

Conclusion

The results of this study suggest that reduction of curing time significantly enhances the cytotoxicity of the studied resin cement materials, therefore compromising their clinical performance.

A selective laser melted Co-Cr alloy used for the rapid manufacture of removable partial denture frameworks: Initial screening of biocompatibility

The aim of this study was to determine the cytotoxicity of a Co-Cr alloy used for the rapid manufacture of removable partial denture frameworks using murine fibroblasts L929 cell lines and three test methods: the MTT assay, the agar diffusion test (ADT) and the dye exclusion test (DET). Two groups of disc specimens (5 mm diameter, 1 mm thick) were fabricated. The first group was cast using a conventional method (CM) in a Nautilus CC casting. The second group was fabricated using selective laser melting (SLM) in SLM Realiser The total cell number and viability of cells pre-incubated with CM and SLM alloys were comparable to the control sample. Differences between the growth inhibitory effects of the CM and SLM alloys in the MTT assay were below 30 %. Results of two independent agar diffusion tests with CM and SLM alloys showed neither detectable discoloration around or under the discs nor a detectable difference in staining intensity. As the cell response for both CM and SLM alloys was 0/0, the discs can be rated as noncytotoxic. The results suggested that the F75 Co-Cr alloy used for the SLM process did not release harmful material that could cause acute effects against L929 cells under the given experimental conditions.

Cytotoxicity of latex and non-latex orthodontic elastomeric ligatures on L929 mouse fibroblasts

This study investigated the cytotoxicity exists between latex and non-latex Orthodontic elastomeric ligatures. Six elastomeric ligatures (1 latex, 2 latex-free and 3 polyurethane) from different manufacturers were divided into 6 groups of 15 elastics each: A (Latex-free, American Orthodontics), M (Polyurethane, Morelli), G (Polyurethane,GAC International), Te (Polyurethane, Tecnident), TP (Natural latex,TP Orthodontics) and U (Latex-free,3M Unitek). The cytotoxicity assay was performed using cell cultures (L929 mouse fibroblast cell line), which were subjected to the cell viability test with neutral red ("dye-uptake") at 1, 2, 3, 7 and 28 days. Data were analyzed statistically by ANOVA and Tukey's test (α=0.05). No statistically significant differences (p>0.05) were observed between Groups M and Te in all experimental periods, except at 2 days. No significant differences (p>0.05) in cell viability were found either among Groups A, G, TP and U or between Groups M and Te at 24 h or among Groups CC, A, G, TP and U at 2 and 28 days. It may be concluded that latex-free elastomeric ligatures from American Orthodontics and Unitek trademarks induced less cell lysis compared to latex and polyurethane ligatures.

Cytotoxic effects of dental bonding substances as a function of degree of conversion

OBJECTIVES

Recently, we found that dental bonding substances tested alone or in combination with composites are far more cytotoxic than composite materials alone. These data are in line with several cytotoxicity reports but contradict in vivo studies showing the beneficial effects of bonding materials. The aims of the present study were to develop a preparation method for composite specimens modelling conditions in the oral cavity and to analyse the influence of bonding substances on the cytotoxicity of six different composite materials.

METHODS

Cylindrical composite specimens were prepared in polyethylene blocks containing 5 mm diameter cylindrical holes (cylinder height 2 mm), covered with a polyethylene foil and light cured from one end for 40 s. In a second series of experiments, composite specimens were combined with bonding materials. Bonding was applied onto the polyethylene foil in one or two layers and light cured according to the manufacturers' instructions. Subsequently, polyethylene moulds were placed on top of the bonding materials and composites prepared as described above. After unilateral light curing from the top of the cylindrical holes, visual confirmation of adherence at the base was obtained. Specimens were added to the cultures immediately after production or after preincubation for 7 days under cell culture conditions. Specimens were incubated with L-929 fibroblasts for 72 h and cell numbers determined by flow cytometry. To evaluate the degree of conversion (DC) of bonding materials cured with and without air inhibition a third series of experiments was performed. FTIR spectroscopic measurements were made on thin-films of dentin-bonding agents, cured under both an-aerobic and aerobic conditions, to determine degree of conversion.

RESULTS

Cytotoxicities of all six tested composites were significantly different (p<0.0001) and diminished after 7 days of preincubation (p<0.0001). Bonding substances had no statistically significant influence on the cytotoxicity of composite materials (p=0.159). A highly significant statistical reduction in the degree of conversion for each resin cured under air inhibition conditions was documented (p<0.01).

SIGNIFICANCE

Our study demonstrates that cell culture toxicity data are highly model dependent and that internationally standardized test protocols for toxicity screening of dental materials in line with the existing standards are clearly needed to obtain comparable results.