Biological evaluation of root canal sealers using in vitro and in vivo methods

Hazards of Improper Dispensary: Literature Review and Report of an Accidental Chloroform Injection

Several clear, transparent solutions are used in endodontics. Inappropriate dispensing methods can lead to accidental injection or accidental irrigation. These accidents can cause permanent tissue damage including damage to the bone, periodontium, nerves, and vasculature. This article reports on the consequences of an accidental chloroform injection. Nonsurgical retreatment of tooth #8 was planned as part of a restorative treatment plan in a 69-year-old woman. The dentist accidentally injected chloroform instead of local anesthesia because chloroform was loaded into the anesthetic syringe. The patient experienced severe pain and swelling and soft tissue necrosis and suffered permanent sensory and motor nerve damage. A review of the literature was performed on accidents caused by improper dispensary, namely accidental injections and accidental irrigations. The data were extracted and summarized. Sodium hypochlorite, chlorhexidine, formalin, formocresol, 1:1000 adrenaline, benzalkonium chloride, and lighter fuel were accidentally injected as an intraoral nerve block or as infiltration injections. Bone and soft tissue necrosis, tooth loss, and sensory nerve damage (anesthesia and paresthesia) were the most common consequences reported. Such disastrous events can be prevented by appropriate labeling and separate dispensing methods for each solution. There is a need for disseminating information on toxicity and biocompatibility of materials/solutions used in endodontics. The authors recommend training dental students and endodontic residents on immediate and long-term therapeutic management of patients when an accidental injection or accidental irrigation occurs.

Physicochemical Properties of Epoxy Resin-Based and Bioceramic-Based Root Canal Sealers

Three bioceramic sealers (EndoSequence BC sealer, EndoSeal MTA, and MTA Fillapex) and three epoxy resin-based sealers (AH-Plus, AD Seal, and Radic-Sealer) were tested to evaluate the physicochemical properties: flow, final setting time, radiopacity, dimensional stability, and pH change. The one-way ANOVA and Tukey's post hoc test were used to analyze the data (P = 0.05). The MTA Fillapex sealer had a highest flow and the BC Sealer presented a flow significantly lower than the others (P < 0.05). The BC Sealer and MTA Fillapex samples were not set in humid incubator condition even after one month. EndoSeal MTA had the longest setting time among the measurable materials and Radic-Sealer and AD Seal showed shorter setting time than the AH-Plus (P < 0.05). AH-Plus and EndoSeal MTA showed statistically higher values and MTA Fillapex showed statistically lower radiopacity (P < 0.05). BC Sealer showed the highest alkaline pH in all evaluation periods. Set samples of 3 epoxy resin-based sealers and EndoSeal MTA presented a significant increase of pH over experimental time for 4 weeks. In conclusion, the bioceramic sealer and epoxy resin-based sealers showed clinical acceptable physicochemical properties, but BC Sealer and MTA Fillapex were not set completely.

The hemolytic and cytotoxic properties of a zeolite-containing root filling material in vitro

OBJECTIVE

This in vitro study characterized the hemolysis and cytotoxicity of ZUT, an experimental glass ionomer cement (GIC) sealer with an added antimicrobial-containing zeolite (0.2% Zeomic w/w).

STUDY DESIGN

ZUT, Ketac-Cem (GIC component of ZUT), Ketac-Endo, and two AH 26 sealer formulations were tested at various times after mixing. Hemolysis produced by standardized specimens was determined spectrophotometrically (n = 6/material). Cytotoxicity was assessed by using a Millipore Filter test with a HeLa cell monolayer (n = 10/material). Tests were repeated, and results were analyzed with a one-way analysis of variance (alpha = .05).

RESULTS

Disks of AH 26 containing silver produced the most hemolysis of all test groups (P < .0001). Compared to controls, GICs and AH 26 formulations were noncytotoxic at 1 and 6 hours after mixing, respectively (P > .05). Addition of Zeomic did not increase the cytotoxic and hemolytic activity of Ketac-Cem (P > .05).

CONCLUSION

Overall results suggest ZUT is less cytotoxic than AH 26 and possesses characteristics similar to the other GIC formulations tested.

A comparison of the effectiveness of chloroform and eucalyptus oil in dissolving root canal sealers

OBJECTIVE

The solubility of 8 different root canal sealers in chloroform and in eucalyptus oil was compared.

STUDY DESIGN

For standardized samples (n=12), ring molds were filled with mixed sealers based on epoxy resin, silicone, calcium hydroxide, zinc oxide-eugenol, glass ionomer, and polyketone. These samples were immersed in chloroform or eucalyptus oil for 30 seconds, 1 minute, 2 minutes, 5 minutes, 10 minutes, and 20 minutes. Then, the mean weight loss was determined and statistically analyzed.

RESULTS

With the exception of the silicone, all the sealers showed significantly higher solubilities (P <.05) in chloroform than in eucalyptus oil. Epoxy resin was the most soluble sealer in chloroform. In eucalyptus oil, calcium hydroxide, and zinc oxide-eugenol showed the highest solubility.

CONCLUSION

Under the conditions of this study, chloroform was a far more effective solvent of root canal sealers than eucalyptus oil. Because of the potential hazards of chloroform, further studies on the dissolution of root canal sealers in different solvents seem to be necessary.

Cytotoxicity of halothane on human gingival fibroblast cultures in vitro

Recently halothane has been reported to be the most suitable alternative to chloroform in dissolving gutta-percha. Periapical tissue toxicity of halothane is not completely known. In this study gutta-percha dissolved by halothane was evaluated with the almar blue dye assay using human gingival fibroblast cultures. The cytotoxic effects of halothane on human gingival fibroblasts depended on the exposure dose, frequency, and duration. A reduced concentration and smaller amount of gutta-percha solvents may minimize the cytotoxic effects on host tissues.

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.

Tissue reaction to gutta-percha particles of various sizes when implanted subcutaneously in guinea pigs

Tissue reaction to gutta-percha was studied using subcutaneously implanted Teflon cages in guinea pigs. Gutta-percha was tested in three forms: (i) as large particles prepared by dividing gutta-percha cones into pieces, (ii) as fine particles prepared by ball-milling of gutta-percha, and (iii) as particles produced by dissolving gutta-percha in rosin-chloroform. Gutta-percha evoked two distinct types of tissue response. The large pieces were well encapsulated and the surrounding tissue was free of inflammation. The fine particles evoked an intense, localized tissue response, characterized by the presence of macrophages and multinucleated giant cells. The rosin-chloroform treated gutta-percha induced a similar tissue reaction to that observed with the fine particles of gutta-percha. In addition, cell remnants were present in association with the material, which indicates an initial toxicity to rosin-chloroform treated gutta-percha. These results show that the size and surface character of gutta-percha can determine the type of tissue reaction to the material. The accumulation of macrophages around gutta-percha may be an important factor in the impairment of healing of periapical lesions when teeth are root filled with excess material.

Cytotoxicity evaluation of six root canal sealers

Cell cultures of human gingival fibroblasts obtained from healthy patients were used to evaluate the toxicity of six different endodontic cements: AH-26, Pulp Canal Sealer, Rocanal-R2, Rocanal-R3, Bioseal, and Endomethasone. The toxicity was determined by measuring spectrophotometrically at 405 nm the colorimetric reaction of N-acetyl-beta-hexosaminidase, an endogenous enzyme, with the chromogenic substrate [p-nitrophenol-N-acetyl-beta-D-glucosamide (NAG)]. Severe cytotoxicity was observed in the 1- and 2-wk test solutions of AH-26. Pulp Canal Sealer and Endomethasone showed low cytotoxicity in the 1- and 2-wk test solutions at 24, 48, and 72 h. Moderate cytotoxicity was observed in the 1- and 2-wk test solutions of Bioseal, except at 48 and 72 h of 1-wk test solutions. Rocanal-R2 showed severe cytotoxicity in the 1-wk test solutions at 48 and 72 h, and in the 2-wk test solutions at 24, 48, and 72 h. Moderate cytotoxicity was seen in the 1- and 2-wk test solutions of Rocanal-R3 only at 24 h.

In vitro evaluation of dental materials

Biocompatibility has been described as the ability of a material to perform with an appropriate host response in a specific application. Appropriate host response means no (or a tolerable) adverse reaction of a living system to the presence of such a material. An adverse reaction may be due to the toxicity of a dental material. Therefore toxicity may be regarded as one reason for nonbiocompatibility of a dental material. The toxicity of a dental material can be evaluated by in vitro tests, animal experiments and clinical trials. There exists a variety of different in vitro test methods. The most widely used biological systems for toxicity screening of dental materials are cell cultures. Cell cultures for toxicity screening of dental materials are valuable tools for understanding their biological behavior, if the limitations of the methods are taken into consideration, especially concerning the interpretation of the results. Further research should concentrate on better simulations of the in vivo situation in cell cultures. In this review the applications of various cell culture methods to evaluate the cytotoxicity of a wide range of dental materials, e.g. metals, alloys, polymers and cements, are described.

Toxic effects of various retrograde root filling materials on gingival fibroblasts and rat sarcoma cells

The aim of this in vitro study was to evaluate the effect of amalgam, glass ionomer, composite and titanium on the growth of gingival fibroblasts (GF) and rat sarcoma cells (UMR) in vitro. The cells were either obtained from gingival biopsies taken during deliberation of unerupted canines (GF) or were of commercial origin (UMR). Equal numbers of cells were placed on culture dishes and incubated for a period of two weeks with the freshly prepared test materials. The cultures were photographed through a light microscope after 7 days incubation and finally counted after 14 days. It was shown that the proliferation of gingival fibroblasts was less disturbed by titanium, being approximately 96% of the control value (cell cultures without test particles), followed by composite, amalgam and glass ionomer (61%, 49% and 35% of the control value respectively). The number of UMR cells after 14 days incubation with the various materials was 76% of the control value with titanium, 12% with composite and 5% with both amalgam and glass ionomer. Inhibition of cell growth (UMR) around the test particles was most prominent around amalgam and glass ionomer, followed by composite and titanium. These effects were noted only with freshly prepared components however, so that the toxic reaction was less pronounced or minimal in a second incubation using the same particles sterilized in between. The results demonstrated that potential retrograde root filling materials have a variable toxic effect on gingival fibroblasts and rat sarcoma cells. The fact that the influence on proliferation disappeared when the test was performed with materials already tested once may be of clinical importance when estimating the biocompatibility in vivo.

Comparative tissue tolerance of a new endodontic sealer

An experimental radiopaque resin root canal sealer was tested for tissue biocompatibility in rat connective tissue. The controls were four widely used sealers: Sealapex, Kerr's sealer, AH-26, and Roth's sealer. Polyethylene tubes were filled with the sealers and allowed to set for 24 hours in 100% humidity. Each sealer was implanted in the connective tissue of Sprague-Dawley rats and removed after 3, 10, 20, 30, and 60 days, fixed, and histologically prepared for light microscope evaluation. At each time period there was practically no difference in the reaction of all the sealers. By 60 days, the total picture was one of well-tolerated biocompatibility.

Root canal sealer cytotoxicity on human gingival fibroblasts: 2. Silicone- and resin-based sealers

The cytotoxicity of two resin (AH26 and Diaket)- and one silicone (Lee Endo-Fill)-based root canal sealers were tested over a period of 21 days. The incorporation rate of L-[14C]leucine was measured to establish the potential of human gingival fibroblasts to synthesize protein after being in contact with the sealers. The cells were gained from biopsies from healthy patients between 20 and 30 years of age. The sealers were allowed to set for 24 and 48 h before dispensing the fibroblastic suspension into the culture dishes. AH26 showed in the 24-h group a severe cytotoxic reaction during the entire experimental period. Diaket showed a relative severe cytotoxic potential with slight cell recovery after 3 days of culturing. Lee Endo-Fill showed a significantly lower (p less than 0.05) cytotoxic potential during the first 11 days of incubation. However, between the 15th and 21st days of culturing an ascending cytotoxic potential was registered. With Diaket and Lee Endo-Fill a relative lower cytotoxic response was observed in the 48-h group; however, cytotoxic patterns similar to the 24-h group prevailed.

Radiographic evaluation of intraosseous implants of endodontic materials

Following several case reports of cyst development after endodontic treatment of decidous teeth, the osseous response to formaldehyde- or phenol-based materials was evaluated by a standardized radiographic technique. Endodontic medicaments contained in Teflon carriers were implanted between feline deciduous canine and molar teeth and the permanent successional teeth. Persistent radiolucency surrounding formocresol implants and sequestration of Kri-paste implants were noted in contrast to apparent bony healing around the zinc oxide-eugenol controls and those implants containing glutaraldehyde. These results suggest a greater tissue tolerance to glutaraldehyde-containing agents in contrast to the more traditional endodontic agents used in deciduous teeth.

Toxicity of root canal sealers on rat bone cells in primary culture

The cytotoxic effects on cultured rat bone cells of newly-developed root canal sealers and commercially available sealers were compared. Various root canal sealers were applied to cultured bone cells obtained from rat calvaria by the enzyme digestion method. Measurement of [3H]-thymidine incorporation, alkaline phosphatase activity, and calcium release were performed after 24 and 48 h. No significant difference was found in cellular DNA synthesis and alkaline phosphatase activity between cells exposed to New B-1, New B-5 and controls after exposure for 24 and 48 h. Cells in contact with Tubliseal, Diaket and AH-26 demonstrated a significant difference from controls in DNA synthesis and alkaline phosphatase activity. Calcium release at 24 h was significantly different in the cells treated with New B-1 and New B-5 than in controls. No appreciable difference was found, however, between New B-6, Sealapex and controls. At 48 h, cells treated with New B-1, New B-5 and New B-6 showed differed significantly difference from controls, but the cells exposed to Sealapex did not. The newly-developed root canal sealers had lower toxicity in vitro than five types of commercially available root canal sealers.

Biological evaluation of dental restorative materials--a comparison of different test methods

Three restorative materials--two composite resins and zinc oxide-eugenol cement--were subjected to three cytotoxicity tests--chromium release, millipore filter, and agar overlay--one implantation test, and a pulp study. In the cytotoxicity test the materials were evaluated freshly prepared and after storage at 37 degrees C for 24 h. In the implant test polyethylene tubes holding freshly prepared materials were inserted subcutaneously into rats. After 30 and 90 days the tissue response at the end of the tube and at a window site along the side of the tube was assessed. In the pulp study the materials were placed in cavities prepared in newly erupted monkey teeth. After 7 and 78 days the reaction of the pulp tissue was studied. Comparison of the results from the cytotoxicity tests revealed a varying degree of correlation, indicating that the three tests were not interchangeable. When data from the pulp study were compared to those of the cytotoxicity tests and implantation test, the correlation was not as good. This emphasizes that the final biological evaluation of dental restorative materials still has to be carried out as pulp studies.