In vitro comparison of the cytotoxicity of twelve endodontic materials using a new technique

Optimization of makerspace microfabrication techniques and materials for the realization of planar, 3D printed microelectrode arrays in under four days

Conventional two-dimensional microelectrode arrays (2D MEAs) in the market involve long manufacturing timeframes, have cleanroom requirements, and need to be assembled from multiple parts to obtain the final packaged device. For MEAs to be “used and tossed”, manufacturing has to be moved from the cleanroom to makerspaces. In order to enable makerspace fabricated MEAs comparable to conventional MEAs, the microfabrication processes must be optimized to have similar electrical properties along with biocompatibility and number of recording sites. This work presents a makerspace microfabricated 2D MEA having electrode densities up to a commercially popular 8 × 8 array, all fabricated under four days. Additive manufacturing-based realization of the MEA devices provides immense flexibility in terms of meeting distinct design requirements. A unique non-planar MEA having meso-scale electrodes on the top side of a chip transitioning to traces onto the bottom side through electrical vias is presented in this work. This allows for (a) monolithic integration of a culture well for devices having up to a 6 × 6 MEA array, (b) selective electroplating of the meso-scale electrodes (500 μm diameter) defined by silver ink casting followed by pulsed electroplating of gold or platinum without any masking procedure, (c) casting of a uniform and planar insulation layer via a novel process of confined precision spin coating (CPSC) of SU-8 which acts as a biocompatible insulation atop the meso-scale electrodes; and (d) selective laser micromachining to define the 50 μm × 50 μm microelectrodes. For an 8 × 8 array, the culture well and MEA chip framework are 3D printed as two separate parts and sealed together with a biocompatible epoxy as in commercially available MEAs. The fabricated MEAs have an average 1 kHz impedance of 36.8 kΩ/16 kΩ with a double layer capacitance of 400 nF cm⁻²/520 nF cm⁻² for nano-porous platinum/nano-gold which is comparable to the state-of-art commercially available 2D MEAs. Additionally, it was found out that our 3D printing-based process compares very favorably with traditional glass MEAs in terms of design to device while representing a dramatic reduction in cost, timeline for fabrication, reduction in the number of steps and the need for sophisticated microfabrication and packaging equipment.

“Makerspace microfabrication” with the use of simple tools and materials is used to demonstrate the realization of 2D microelectrode arrays (MEAs) having a density of up to 8 × 8 MEAs in under four days which are comparable to conventional MEAs.

The effects of restorative composite resins on the cytotoxicity of dentine bonding agents

During restoration of damaged teeth in dental clinics, dentin bonding agents are usually overlaid with restorative resin composites. The purpose of this study was to investigate the effects of restorative resin composites on cytotoxicity of dentin bonding agents. Dentin bonding agents were placed on glass discs, pre-cured and uncured resin composite discs. Bonding agents on the glass discs and composite resins discs were light cured and used for agar overlay cytotoxicity testing. Dentin bonding agents on composite resin discs exhibited far less cytotoxicity than that on glass discs. The polymerization of resin composite increased the surface hardness and decreased the cytotoxicity of bonding agents. In conclusion, composite resins in dental restorations are expected to enhance the polymerization of dentin bonding agents and reduce the elution of resin monomers, resulting in the decrease of cytotoxicity.

Histological evaluation of bone response to pediatric endodontic pastes: an experimental study in guinea pig

This study aimed to evaluate by the intra-osseous implant technique the most commonly used materials for pulp therapy in pediatric dentistry: calcium hydroxide (CH), Guedes Pinto paste and CTZ paste, according to FDI (1980) and ANSI/ADA (1982) recommendations. Thirty guinea pigs, 10 for each material, divided into experimental periods of 4 and 12 weeks received one implant on each side of the lower jaw symphysis. The external lateral tube wall served as control for the technique. At the end of the observation periods, the animals were euthanized and specimens were prepared for routine histological examination. It was observed that CH and CTZ paste induced severe inflammation, a large amount of necrotic tissue, lymphocytes, foreign body cells and bone resorption, while Guedes Pinto Paste induced little or no inflammation in the 4-week observation period. After 12 weeks, the reactions to CH and Guedes Pinto paste were also absent/mild, presenting a general pattern of replacement by recently formed bone tissue while a moderate to severe inflammatory response was observed with CTZ paste. Guedes Pinto paste presented acceptable biocompatibility levels in both analyzed periods; CH only showed acceptable biocompatibility in the 12-week period while CTZ paste showed no biocompatibility in both periods. Among the tested materials, only Guedes Pinto paste presented an acceptable biocompatibility.

In vitro genotoxicity of root canal sealers

AIM

To evaluate the effect of leakage on differences in genotoxicity of root canal sealers ex vivo according to their main components using two different cytogenetic assays.

METHODOLOGY

Six materials of different composition (GuttaFlow, Epiphany, Diaket, IRM, SuperEBA and Hermetic) were tested on human peripheral blood lymphocytes using the comet assay and chromosomal aberration analysis. Prepared materials were eluted in physiological solution for 1 h, 1 day, 5 and 30 days. Thereafter cultures were treated with 8 microg, 4 microg and 2 microg of each sealer. Frequencies of chromatide and chromosome breaks and accentric fragments were determined. Comet assay was used to evaluate primary DNA damage by measuring tail length and tail intensity. Chi-square, Fisher's PLSD (Protected Least Significant Difference) and Kruskall-Wallis non parametric tests were used for statistical analysis.

RESULTS

After 1-h elution only the highest dose of Diaket, Hermetic and SuperEBA significantly (P = 0.035, P = 0.048, P = 0.037 respectively) affected the measured cytogenetic parameters. The migration ability of DNA was more strongly affected than induction of chromosomal aberrations. After elutions longer than 24 h none of the tested sealers exhibited a genotoxic effect.

CONCLUSION

Under the conditions used in the study all sealers had acceptable biocompatibility in terms of genotoxicity.

Calcium hydroxide-based root canal sealers: a review

The aim of this review was to consider laboratory experiments and clinical studies of calcium hydroxide-based root canal sealers. An extensive search of the endodontic literature was made to identify publications related to calcium hydroxide-based root canal sealers. The articles were assessed for the outcome of laboratory and clinical studies on their biological properties and physical characteristics. Comparative studies with other sealers were also considered. Several studies were evaluated covering different properties of calcium hydroxide-based sealers including physical properties, biocompatibility, leakage, adhesion, solubility, antibacterial properties, and periapical healing effect. Calcium hydroxide-based root canal sealers have a variety of physical and biological properties. Comparative studies reveal their mild cytotoxicity, but their antibacterial effects are variable. Further research is required to establish the tissue healing properties of calcium hydroxide in root canal sealers.

The Properties of Endocal 10 and Its Potential Impact on the Structural Integrity of the Root

The purpose of this research was to determine if the use of Endocal 10 (previously called Biocalex 6.9) is associated with root fracture and to assess its sealability. Thirty-six freshly extracted, single canal human mandibular incisors were instrumented and randomly divided into two equal groups (n = 15). Canals in group A were obturated with vertically compacted gutta-percha and Sealapex, and those in group B were filled with Endocal 10 placed with a #25 Lentulo spiral per manufacturer's instructions. Two blinded investigators evaluated the teeth for fractures using transillumination and an operating microscope at 12 x magnification. Three of the fifteen samples filled with Endocal 10 had vertically fractured in half, whereas none of the teeth filled with gutta-percha had any evident fracture lines. The remaining teeth were tested for leakage via a fluid filtration model at 1 wk and 30 days postobturation. No leakage was found among any of the samples whether filled with gutta-percha or with Endocal 10 at either time interval. Statistical analyses were completed using Fisher's exact test (p = 0.023), which showed that there was a significant increase in chance of fracture when using Endocal 10 versus gutta-percha. The results indicate that, although Endocal 10 is able to seal the tooth as well as gutta-percha and sealer, there is a significant potential risk of root fracture.

In vitro evaluation of the cytocompatibility of a glass-lonomer cement sealer

The purpose of this study was to evaluate the cytocompatibility of two different types of root canal sealers in cell culture. Human periodontal ligament cells were cultured with set materials from an experimental glass-ionomer cement sealer (KT-308) and a commercially available zinc oxide-eugenol-based sealer (Canals) for 1, 3, and 7 days. Cytotoxic effects were evaluated from the morphological changes under a light microscope. Canals induced severe degenerative alteration of human periodontal ligament cells. In contrast, human periodontal ligament cells adjacent to KT-308 showed normal morphology and growth during the culture period. These results suggest that the glass-ionomer cement sealer, KT-308, is cytocompatible and has good potential as a root canal sealer.

Biocompatibility of dental materials used in contemporary endodontic therapy: a review. Part 2. Root-canal-filling materials

Root-canal-filling materials are either placed directly onto vital periapical tissues or may leach through dentine. The tissue response to these materials therefore becomes important and may influence the outcome of endodontic treatment. This paper is a review of the biocompatibility of contemporary orthograde and retrograde root-canal-filling materials.

Biocompatibility of dental materials used in contemporary endodontic therapy: a review. Part 1. Intracanal drugs and substances

Irrigation solutions and intracanal medicaments are used within the root canal to clean and aid in disinfecting the dentinal walls. Although these materials are intended to be contained within the root canal, they invariably contact the periapical tissues, either through inadvertent extrusion through the apex or leaching. This paper is a review on the methodology involved in biocompatibility testing followed by a discussion on biocompatibility of contemporary intracanal drugs and substances used in endodontics.

Biocompatibility of root canal filling materials

Results of in vitro and in vivo studies clearly indicate that some endodontic sealers may cause local and systemic adverse effects. Though occasionally contradictory data has been reported from various authors, it may be concluded that zinc-oxide-eugenol sealers possess a marked cytotoxic and tissue-irritating potency. Most Ca(OH)2-based materials, however, were biocompatible. Genotoxic effects have been observed with sealers releasing paraformaldehyde or containing mutagenic substances, such as bisphenol-A-diglycidyl-ether or its derivatives. It cannot be excluded that these materials may pose a systemic risk because formaldehyde is rapidly distributed systemically following its application into the pulp cavity. Furthermore an increasing number of cases with an aspergillosis of the maxillary sinus have been observed which were mainly caused by zinc-releasing endodontic sealers. Overall, it is recommended that for endodontic practice, sealers that have been found to be biocompatible in a "mixed bag" of various in vitro and in vivo tests, be selected. From this point of view, ZnOE-sealers should no longer be used for root canal fillings. This recommendation applies also to sealers containing paraformaldehyde or generating this substance during their setting reaction. More experimental and clinical studies are necessary to elucidate whether new materials, such as mineral trioxide aggregate (MTA) or calcium phosphate cement, will be biocompatible alternatives in the future.

Resistance of experimental glass ionomer cement sealers to bacterial penetration in vitro

This study evaluated penetration of Enterococcus faecalis in canals filled with glass ionomer cement sealers. Canals of 40 extracted teeth in four equal experimental groups were prepared and filled with KT-308 (experimental sealer) and a single gutta-percha cone (SC), ZUT (KT-308 with an antibacterial agent) and SC, Kerr sealer and vertically compacted gutta-percha (VC), or Kerr sealer with the antibacterial agent and VC. Eight additional teeth served as positive controls and four as negative controls. Pulp chambers were inoculated with E. faecalis, and bacterial penetration through the filled canals was assessed over a period of 90 days. Incidence of bacterial penetration was significantly higher for ZUT/SC than for Kerr sealer/VC (p < 0.05). KT-308/SC did not differ significantly from any other material. The positive controls showed significantly faster penetration than all the other groups (p < 0.05). It was concluded that KT-308 effectively prevented penetration of E. faecalis, whereas ZUT required further development.

Evaluation of the cytocompatibility of three endodontic materials

The goal of this in vitro study was to evaluate the relative cytocompatibility of three endodontic materials: calcium hydroxide, a calcium oxide-based compound, and a zinc oxide-eugenol-based sealer. The evaluation was conducted 24, 72, and 168 h after contact with the compounds and involved three complementary techniques: a colorimetric cytotoxicity test, scanning electron microscopy, and flow cytometry. The results we obtained confirmed the initial cytotoxicity of the zinc oxide-eugenol-based sealer and showed that the calcium oxide-based compound had the same relative cytocompatibility as calcium hydroxide.

Cytotoxic and mutagenic potencies of various root canal filling materials in eukaryotic and prokaryotic cells in vitro

Cytotoxic and mutagenic effects of root canal filling cements of various chemical composition were determined in vitro. Materials set for 24 h and 1 wk were eluted for 24 h in cell culture medium (cytotoxicity testing) and dimethyl sulfoxide or physiological saline (mutagenicity testing). The differences between cytotoxic potencies of eluates of the endodontic materials on L-929 cells were quantified colorimetrically (MTT test). Eluates of Traitement SPAD were about 5- to 30-fold more toxic than silver-free AH26, Tubli-Seal, CRCS, and Endomethsone N. The rank order of the toxic effects depended on the setting time of mixed materials. Dimethyl sulfoxide and saline eluates of Traitement SPAD, Tubli-Seal, Endomethasone N, CRCS, and Ketac-Endo were not mutagenic in the Ames test. Both eluates of silver-free AH26 set for 24 h were weakly mutagenic in Salmonella typhimurium TA100. Weak mutagenicity of saline eluates of the material was also observed in TA97a and TA102. These results point to the possibility that mixed silver-free AH26 might contain small amounts of two mutagenic substances: bisphenol A diglycidyl ether and formaldehyde.

Cytotoxicity of three resin-based root canal sealers: an in vitro evaluation

The cytotoxicity of three resin-based root canal sealers (AH26, AH-Plus, Topseal) was evaluated in vitro. The experiments included two cell lines, L929 mouse skin fibroblasts and RPC-C2A rat pulp cells. The cytotoxicity was assessed by sulforodamine B (SRB) colorimetric assay and hemocytometer viable cell counting after 24- and 48-h exposure. AH26 had a severe cytotoxic effect whilst Topseal and AH-Plus showed a markedly lower toxic influence on the cells during the experimental period.

Lateral condensation in treatment of pulpitis and pulp gangrene: studies on dog canine teeth

The clinical investigation, carried out in dogs, comprises selected cases of chronic pulpitis and pulpal gangrene of canine teeth resulting from injuries. A group of 20 teeth (group 1) underwent extirpation of pulp, as well as elaboration of a root canal and its filling with Endomethasone paste, under general anaesthesia during a one-stage procedure. The second group of 20 teeth differed from the first in an additional concentration of the paste, due to an introduction of gutta-percha points (lateral condensation). This sealing modification proved to diminish the risk of leaving empty spaces after pulp removal in the pulpitis state. However, in teeth where gangrenous pulp extirpation was performed, lateral condensation was endangered by pushing the paste through beyond the apex. Both anomalies were likely to predispose to the development of apical periodontitis.

Endodontic treatment including apexification in a chow chow with a necrotic immature mandibular canine tooth

A necrotic immature mandibular, canine tooth in a two year-old, male, intact Chow Chow was endodontically treated. This tooth had an open apex, wide root canal, thin dentinal walls, and there was periapical bone resorption. An apexification procedure was used to induce apical closure by calcified tissue formation, with resolution of the periapical inflammation.

In vitro evaluation of the cytotoxicity of calcium hydroxide-based root canal sealers

The cytotoxicity of three calcium hydroxide-containing root canal sealers (Sealapex, CRCS and Apexit) was tested by using L929 and BHK 21/C13 cells. After setting for 24 h, the sealers were covered with cell suspension. Cytotoxicity was determined by a quantitative technique at 24 h, 48 h and 72 h. All the sealers were found to be cytotoxic. Sealapex showed the highest cytotoxicity, causing a significant decrease in cell density. CRCS was less toxic than Sealapex and more toxic than Apexit. Apexit proved to be the least toxic material.

Endodontic cements induce alterations in the cell cycle of in vitro cultured osteoblasts

The effects of endodontic cements on the cell cycle of MG63 osteoblasts cultured in vitro have been examined. Three groups of compounds were tested. Group I encompassed zinc oxide- and eugenol-based cements (Tubliseal, Argoseal, N2), group II consisted of cements with a phenol group other than eugenol (AH26, Forfenan, Methode R/R), and group III included CaOH-based cements (Biocalex, Endocalex). The cell cycle of MG63 cells was analyzed by flow cytometry; the DNA content was evaluated by means of the propidium iodide uptake method, whereas the proportion of cells in the S phase was defined by the incorporation of bromodeoxyuridine later revealed by a specific antibody. The results showed that some root canal sealers could hamper the periapex healing processes by inhibiting the cell proliferation through a selective action on different phases of the cell cycle.

Cytotoxicity of some modified root canal sealers and their leachable components

The toxic effects of modified endodontic sealers, Fillcanal, N-Rickert, FS, and Sealer 26, were assessed. The material toxicity was measured through radiochromium release method that uses direct and indirect contact methods. The sealers were evaluated freshly mixed and after various setting times. L929 mouse and periodontal ligament fibroblast cells were used as target cells. Fillcanal, N-Rickert, and FS showed high toxicity. Fillcanal leaches toxic material when fresh and after setting time. Sealer 26 was the least toxic.

Toxicity of Pulpispad using four different cell types

The cytotoxic effect of a zinc oxide-eugenol-based paste (Pulpispad) was evaluated in vitro after setting for 1 day and 1 week. Target cells were L929 cells, gingival, periodontal ligament and pulpal fibroblasts. The material was incubated with the cells for 4 and 24 hours, and its toxicity was evaluated with the 51Cr-release method. Pulpispad was highly cytotoxic to all cell lines even after setting for 1 week. The use of Pulpispad is not recommended for future clinical application. The various responses among the four cell lines indicated that diploid cell lines can, under certain circumstances, be less sensitive than aneuploid cell lines. It is therefore suggested that in the evaluation of biomaterials the choice of cell lines should be carefully considered, as they can display varying sensitivities.