Effect of various polymerization protocols on the cytotoxicity of conventional and self-adhesive resin-based luting cements

Toxicity of resin-matrix cements in contact with fibroblast or mesenchymal cells

The main aim of this study was to perform an integrative review on the toxic effects of resin-matrix cements and their products in contact with fibroblasts or mesenchymal cells. A bibliographic search was performed on PubMed using the following search terms: "cytotoxicity" AND "fibroblast" OR "epithelial" OR "mesenchymal" AND "polymerization" OR "degree of conversion" OR "methacrylate" OR "monomer" AND "resin cement" OR "resin-based cement". The initial search in the available database yielded a total of 277 articles of which 21 articles were included in this review. A decrease in the viability of mouse fibroblasts ranged between 13 and 15% that was recorded for different resin-matrix cements after light curing exposure for 20 s. The viability of human fibroblasts was recorded at 83.11% after light curing for 20 s that increased up to 90.9% after light curing exposure for 40 s. Most of the studies linked the highest toxicity levels when the cells were in contact with Bis-GMA followed by UDMA, TEGDMA and HEMA. Resin-matrix cements cause a cytotoxic reaction when in contact with fibroblasts or mesenchymal cells due to the release of monomers from the polymeric matrix. The amount of monomers released from the resin matrix and their cytotoxicity depends on the polymerization parameters.

Characterization of Contemporary Conventional, Bulk-fill, and Self-adhesive Resin Composite Materials

OBJECTIVE

To evaluate the physical and biological properties of different types of flowable resin composites and their bonding ability to dentin, comparing the performance of self-adhesive and bulk-fill materials with a conventional control.

METHODS AND MATERIALS

Four flowable resin composites were tested: two self-adhesive (Y-flow [SA_YF]; and Dyad Flow [SA_DF]); one bulk-fill (Filtek Bulk Fill Flow [BF]); and one conventional composite (Opallis Flow [OF]). The microshear bond strength (μSBS) to dentin (bovine samples) was investigated at 24 hours and 6 months of storage. The materials were also characterized by degree of conversion, cross-link density, water contact angle, color stability, and cell viability (ISO 10993-5/2009) analyses. Data were analyzed using Analysis of Variance and Tukey tests (α=0.05).

RESULTS

The μSBS values were higher for control specimens at 24 hours, whereas the resin-dentin bonds were similarly distributed among the groups after aging. Adhesive failure was the most frequent pattern observed at both time intervals. SA_YF was the only material that increased the bond strength over time. Degree of conversion increased in the following order: SA_YF (28.6±1.4%) < BF (49.7±0.8%) < OF (60.0±2.0%) = SA_DF (63.6±2.3%). Cross-link density was similar among all materials. The self-adhesive composites were more hydrophilic than the other types, with BF showing the lowest water contact angle and the greatest color alteration. All resin composites had a biocompatible behavior.

CONCLUSION

Chemical composition appeared to be an influential factor affecting the physicomechanical and biological behavior of the materials tested.

In-vitro cytocompatibility of self-adhesive dual-curing resin cements on human mesenchymal stem cells (hMSC) and periodontal ligament cells (PDL-hTERT)

OBJECTIVES

Self-adhesive dual cured resin cements provide easier clinical application than conventional resin cements but release higher amounts of unreacted monomers, potentially affecting their biocompatibility. This study aimed to compare the cytotoxic effects of self-adhesive dual cured resin cements with two conventional resin cements.

METHODS

Samples of four resin cements, two self-adhesive dual cured cements (group A: RelyX Unicem, group B: SmartCem), and two conventional resin cements (group C: Panavia 2.0, group D: Variolink Esthetic DC) were prepared with a similar dimension under standardized polymerization conditions and stored in water. For each material 18 samples were used and cell cultures of human mesenchymal stem cells (hMSCs) or periodontal ligament cells (PDL-hTERT) were added under appropriate conditions. One experimental group (group E) was left untreated as control. A cell viability WST test, was performed in each experimental group at day 1, 7, 14 and 21. Moreover, microscopic examination of cells was performed using cell viability staining.

RESULTS

Viability of both cell types as determined by WST test was significantly impaired at all time periods by the four different cement materials compared to the untreated control. Comparison between the four materials revealed different inhibition of the viability of both, PDL-hTERT and hMSC cells (group C > group B > group A > group D; p < 0.0001).

SIGNIFICANCE

All resin-based cements caused significant impairment of cell viability, reflecting considerable cytotoxicity. Variolink caused significantly smaller changes of viability than the other tested materials.

Influence of dual-cure and self-cure abutment cements for crown implants on human gingival fibroblasts biological properties

AIMS

To analyze the biological effects of the cements Relyx Unicem 2, Panavia V5, Multilink Hybrid Abutment and SoloCem on human gingival fibroblast cells (HGFs).

MATERIALS AND METHODS

HGFs were exposed to different eluates (n = 40) of the studied resin-based cements. Their cytotoxic effects and influence on cell migration were assessed using MTT and wound-healing assays, respectively. Level of HGF attachment, cell morphology and F-actin cytoskeleton content after exposition to the different eluates were analyzed by scanning electron microscopy (SEM) and confocal microscopy analysis, respectively. The levels of intracellular reactive oxygen species (ROS) produced by the eluates of the different cements were also determined by flow cytometry. Data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey´s test.

RESULTS

Eluates of SoloCem significantly reduces the viability of HGFs (69% reduction compared to control at 48 h). Cell migration of HGFs in presence of undiluted SoloCem eluates was significantly lower than in the control (88% open wound area at 24 h). Contrarily, migration speed with Multilynk eluates was similar to that of the control group at all periods of time and all dilutions studied. SEM analysis showed very few cells in SoloCem group, and a moderate cell growth in Multilink, Panavia and Relyx groups were detected. Finally, ROS levels detected in HGFs treated with the more concentrated SoloCem and Relyx dilutions were significantly enhanced compared with that in the control cells or the other groups (44% and 11% ROS positive cells, respectively).

CONCLUSIONS

The results obtained in the present work suggest that Multilink hybrid abutment has better biological properties and lower cytotoxicity for cementing implant crowns on abutments.

Effect of the photoinitiator system on the polymerization of secondary methacrylamides of systematically varied structure for dental adhesive applications

OBJECTIVE

The aim of this study was to investigate the influence of the photoinitiator system on the polymerization kinetics of methacrylamide-based monomers as alternatives to methacrylates in adhesives dental-based materials.

METHODS

In total, 16 groups were tested. Monofunctional monomers (2-hydroxyethyl methacrylate) - HEMA; (2-hydroxy-1-ethyl methacrylate) -2EMATE, (2-hydroxyethyl methacrylamide) - HEMAM; and (N-(1-hydroxybutan-2-yl) methacrylamide) -2EM; were combined with bifunctional monomers containing the same polymerizing moieties as the monofunctional counterparts (HEMA-BDI; 2EMATE-BDI; HEMAM-BDI; and 2EM-BDI) at 50/50 M ratios. BHT was used as inhibitor (0.1 wt%) and the photoinitiators used were: CQ + EDMAB (0.2/0.8), BAPO (0.2), IVOCERIN (0.2), and DMPA (0.2), in wt%. The polymerization kinetics were monitored using Near-IR spectroscopy (∼6165 cm-1) in real-time while the specimens were photoactivated with a mercury arc lamp (Acticure 2; 320-500 nm, 300 mW/cm2) for 5 min, and maximum rate of polymerization (Rpmax, in %.s-̄1), degree of conversion at Rpmax (DC@Rpmax, in %), and the final degree of conversion (Final DC, in %) were calculated (n = 3). Initial viscosity was measured with an oscillating rheometer (n = 3). Data were analyzed using Two-way ANOVA for the polymerization kinetics and one-way ANOVA for the viscosity. Multiple comparisons were made using the Tukey's test (∝ = 0.05).

RESULTS

There was statistically significant interaction between monomer and photoinitiator (p < 0.001). For the methacrylates groups, the highest Rpmax was observed for HEMA + DMPA and 2EMATE + BAPO. For methacrylamides groups, the highest Rpmax were observed for HEMAM and 2EM, both with DMPA. Final DC was higher for the methacrylate groups, in comparison with methacrylamide groups, independent of the photoinitiators. However, for the methacrylamide groups, the association with BAPO led to the lowest values of DC. In terms of DC@Rpmax, methacrylate-based systems showed significantly higher values than methacrylamide formulations. DMPA and Ivocerin led to higher values than CQ/EDMAB and BAPO in methacrylamide-based compounds. BAPO systems showed de lowest values for both HEMA and HEMAM formulations. For the viscosity (Pa.s), only 2EM had higher values (1.60 ± 0.15) in comparison with all monomers. In conclusion, polymerization kinetics was affected by the photoinitiators for both monomers. Viscosity was significantly increased with the use of secondary methacrylamide.

SIGNIFICANCE

this work demonstrated the feasibility of using newly-synthesized methacrylamide monomers in conjunction with a series of initiator systems already used in commercial materials.

Influence of the degree of conversion and Bis-GMA residues of bulk fill resins on tissue toxicity in an subcutaneous model in rats

AIM

To analyse the influence of the degree of conversion (DC) and light curing residues of different bulk fills (BFs) composites on the inflammatory profile in the subcutaneous tissue of rats.

MATERIALS AND METHODS

Resin disks of BF-resins and their active conventional resins (CR; 3M®, Ivoclar®, and Kerr®) were light-cured at 2 mm (BF-superficial) and 4 mm (BF-deep) thicknesses and analyzed by infrared spectroscopy (FTIR; n = 3/group; DC and light curing residues). Then, the disks were implanted in four quadrants in the subcutaneous tissue of Wistar rats (sham, CR, BF-superficial and RF-deep), and after 7, 14, and 28 days, the animals (n = 6/day) were euthanized for histological analysis of the intensity of the inflammatory process (scores 0-3). Kruskal-Wallis/Dunn and ANOVA/Bonferroni tests were used (p < 0.05, Graph Pad Prism 5.0).

RESULTS

The DC of CR 3M® did not differ significantly compared to BF-superficial and BF-deep resins (p = 0.235). The Ivoclar® and Kerr® resins showed a higher DC with CR and BF-superficial compared to the BF-deep (p = 0.005 and p = 0.011, rctively). Kerr® resins showed a higher Bis-GMA/UDMA ratio, especially in BF-deep resin (p < 0.05). 3M® and Ivoclar resins did not show high inflammation scores, but for Kerr® BF resins (superficial and deep), the inflammatory process was significantly higher than that in the CR and sham quadrants (p = 0.031).

CONCLUSION

The tissue inflammatory response after resin inoculation depends on the DC and light curing residues of Bis-GMA.