Intraosseous implantation for biological evaluation of endodontic materials

A critical analysis of research methods and experimental models to study biocompatibility of endodontic materials

Materials used for endodontics and with direct contact to tissues have a wide range of indications, from vital pulpal treatments to root filling materials and those used in endodontic surgery. In principle, interaction with dental materials may result in damage to tissues locally or systemically. Thus, a great variety of test methods are applied to evaluate a materials' potential risk of adverse biological effects to ensure their biocompatibility before commercialization. However, the results of biocompatibility evaluations are dependent on not only the tested materials but also the test methods due to the diversity of these effects and numerous variables involved. In addition, diverse biological effects require equally diverse assessments on a structured and planned approach. Such a structured assessment of the materials consists of four phases: general toxicity, local tissue irritation, pre‐clinical tests and clinical evaluations. Various types of screening assays are available; it is imperative to understand their advantages and limitations to recognize their appropriateness and for an accurate interpretation of their results. Recent scientific advances are rapidly introducing new materials to endodontics including nanomaterials, gene therapy and tissue engineering biomaterials. These new modalities open a new era to restore and regenerate dental tissues; however, all these new technologies can also present new hazards to patients. Before any clinical usage, new materials must be proven to be safe and not hazardous to health. Certain international standards exist for safety evaluation of dental materials (ISO 10993 series, ISO 7405 and ISO 14155‐1), but researchers often fail to follow these standards due to lack of access to standards, limitation of the guidelines and complexity of new experimental methods, which may cause technical errors. Moreover, many laboratories have developed their testing strategy for biocompatibility, which makes any comparison between findings more difficult. The purpose of this review was to discuss the concept of biocompatibility, structured test programmes and international standards for testing the biocompatibility of endodontic material biocompatibility. The text will further detail current test methods for evaluating the biocompatibility of endodontic materials, and their advantages and limitations.

Bioactivity of Photoactivated Functionalized Nanoparticles Assessed in Lipopolysaccharide-contaminated Root Canals In Vivo

INTRODUCTION

The persistence of dentin-bound lipopolysaccharides (LPS) in disinfected root canals impedes treatment outcomes of endodontic procedures. This study assessed the effects of photoactivated rose bengal-functionalized chitosan nanoparticles (CSRBnps) on LPS-contaminated root dentin in vivo using an intraosseous implantation model and neotissue formation as a marker.

METHODS

Fifty human, 3-mm-long root segments with a 1.2-mm canal lumen were divided into 5 groups (n = 10): group 1, canals not contaminated; group 2, canals contaminated with Pseudomonas aeruginosa LPS; group 3, canals contaminated and disinfected with sodium hypochlorite (NaOCl); group 4, canals contaminated and disinfected with NaOCl and calcium hydroxide; and group 5, canals contaminated and disinfected with NaOCl and CSRBnps (300 μg/mL) with photoactivation (λ = 540 nm, 40 J/cm²). Specimens were implanted into mandibles of guinea pigs, block dissected after 4 weeks, and the canal content evaluated histologically and immunohistochemically. The ingrown neotissue interface (50 μm) with dentin was characterized for fibroblasts, osteoclasts, inflammatory markers, dentin resorption, mineralization, and angiogenesis and dichotomized as type 1 (no inflammation and resorption, indicative of LPS inactivation) or type 2 (inflammation and resorption). The frequency of the observed parameters was analyzed using the Fisher exact test.

RESULTS

The outcome was categorized as type 1 in groups 1 and 5, type 2 in group 2, and mixed type 1 and 2 in groups 3 and 4. The outcomes in groups 1 and 5 (P > .05) differed significantly (P < .05) from those in groups 2, 3, and 4.

CONCLUSIONS

Disinfection of LPS-contaminated root canals with photoactivated CSRBnps in vivo supported ingrowth of neotissue without signs of inflammation or resorption, suggestive of effective inactivation of dentin-bound LPS.

Evaluation of the biocompatibility of resin-based root canal sealers in rat periapical tissue

We evaluated the biocompatibility of resin-based root canal sealers (RCSs) in the periapical tissues of rats. Wistar rats underwent tooth replantation for reproducing the response of periapical tissue with RCSs. The resin-based Epipany SE, AH Plus Jet, the eugenol-based sealer (Canals) and a control group were employed. The upper right first molar was extracted and applied with RCSs on apices, and then the tooth was repositioned. Histological evaluation demonstrated that mild inflammation occurred in the periapical tissue with Epiphany and AH Plus Jet sealers on day 7, whereas Canals induced severe-to-moderate inflammation. The statistical analyses demonstrated that the significant differences were observed between Canals and the other groups on day 7 regarding inflammatory response. On day 14, the lesions induced by all sealers were healed and replaced predominantly by fibrous connective tissue. Our results suggest that Epiphany SE and AH Plus Jet are good biocompatible materials.

Properties and applications of calcium hydroxide in endodontics and dental traumatology

Calcium hydroxide has been included within several materials and antimicrobial formulations that are used in a number of treatment modalities in endodontics. These include, inter-appointment intracanal medicaments, pulp-capping agents and root canal sealers. Calcium hydroxide formulations are also used during treatment of root perforations, root fractures and root resorption and have a role in dental traumatology, for example, following tooth avulsion and luxation injuries. The purpose of this paper is to review the properties and clinical applications of calcium hydroxide in endodontics and dental traumatology including its antibacterial activity, antifungal activity, effect on bacterial biofilms, the synergism between calcium hydroxide and other agents, its effects on the properties of dentine, the diffusion of hydroxyl ions through dentine and its toxicity. Pure calcium hydroxide paste has a high pH (approximately 12.5-12.8) and is classified chemically as a strong base. Its main actions are achieved through the ionic dissociation of Ca(2+) and OH(-) ions and their effect on vital tissues, the induction of hard-tissue deposition and the antibacterial properties. The lethal effects of calcium hydroxide on bacterial cells are probably due to protein denaturation and damage to DNA and cytoplasmic membranes. It has a wide range of antimicrobial activity against common endodontic pathogens but is less effective against Enterococcus faecalis and Candida albicans. Calcium hydroxide is also an effective anti-endotoxin agent. However, its effect on microbial biofilms is controversial.

A biocompatible model for evaluation of the responses of rat periapical tissue to a new zinc oxide-eugenol sealer

We aimed to establish an experimental animal model to evaluate materials for endodontic therapy. We focused on the biocompatibility of new paste-type zinc oxide-eugenol (ZOE) sealer. The results of this sealer were compared with those of conventional powder/liquid ZOE and eugenol-free sealers. The molars of Wistar rats were extracted and repositioned in the original socket after application of the sealers on the root apices. Mild inflammation occurred in the periapical tissue of the replanted teeth with both ZOE sealers on day 7, whereas the eugenol-free sealer induced severe inflammation. On day 14, the lesions induced by all types of sealers were healed and replaced predominantly by fibrous connective tissue. Thus, all endodontic materials showed high biocompatibility, although the extent of inflammatory reactions during the early stages varied depending on the types of materials. We demonstrated that our animal model was useful for the assessment of the biocompatibility of endodontic materials.

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.

Halothane affects focal adhesion proteins in the A 549 cells

Halothane is a volatile anaesthetic, which is known to induce alterations in cellular plasma membranes, modulating the physical state of the membrane lipids and/or interacting directly with membrane-bound proteins, such as integrin receptors. Integrin-mediated cell adhesion is a general property of eukaryotic cells, which is closely related to cell viability. Our previous investigations showed that halothane is toxic for A 549 lung carcinoma cells when applied at physiologically relevant concentrations and causes inhibition of adhesion to collagen IV. The present study is focused on the mechanisms underlying halothane toxicity. Our results imply that physiologically relevant concentrations of halothane disrupt focal adhesion contacts in A 549 cells, which is accompanied with suppression of focal adhesion kinase activity and paxillin phosphorylation, and not with proteolytic changes or inhibition of vinculin and paxillin expression.We suggest that at least one of the toxic effects of halothane is due to a decreased phosphorylation of the focal contact proteins.

Bone Tissue Response to a Methacrylate-Based Endodontic Sealer: A Histological and Histometric Study

Biocompatibility of endodontic sealers is a prime requisite for successful endodontic therapy. The purpose of this study was to evaluate the reaction of bone to a methacrylate-based endodontic sealer. Silicone tubes, filled with a methacrylate-based sealer and silicone rods used as controls, were implanted in the tibias of white male Wistar rats. Ten and 60 days after implantation the reaction of the bone was analyzed by means of histological and histometric methods. After 10 days the amount of reactionary bone in contact with the methacrylate-based sealer was significantly lower than that observed for the controls (p < 0.05). Cell counts demonstrated that the number of inflammatory cells that were in contact with the sealer were significantly higher (p < 0.05). After 60 days, no significant differences were observed in the amount of reactionary bone that was in contact with either material. The initial inflammatory reaction observed for the methacrylate-based sealer was resolved. Furthermore the cell counts demonstrated no statistically significant differences (p > 0.05) between the methacrylate based sealer and control.

Effect of MTAD on Postoperative Discomfort: A Randomized Clinical Trial

The purpose of this study was to compare levels of postoperative discomfort after cleaning and shaping of root canals using two protocols for removal of smear layer. Seventy-three consecutive patients requiring root canal treatment were included. At random, canals were cleaned and shaped with one of the following protocols. In group 1, 5.25% sodium hypochlorite was used as the root canal irrigant. The smear layer was removed by placing 17% EDTA in the canal(s) for 1 min followed by a 5-ml rinse with 5.25% NaOCl. In group 2, canals were irrigated with 1.3% NaOCl; the smear layer was removed by placing MTAD in the canal(s) for 5 min. Access cavities were closed with a sterile cotton pellet and Cavit. The patients recorded degree of discomfort at various time intervals after cleaning and shaping on a visual analogue scale for 1 wk. No significant statistical difference was found in the degree of discomfort between the two groups (p = 0.58).

Effect of halothane on lung carcinoma cells A 549

The halogenated hydrocarbons, such as halothane, are widely used as anesthetics in clinical practice; however their application is often accompanied with metabolic, cardiovascular and respiratory complications. One of the possible factors for this negative outcome might be the severe toxicity of these agents. In this paper, we investigate in vitro effects of halothane on human lung carcinoma A 549 cells, namely on their cytotoxicity, adhesive properties and metabolic activity. The cytotoxicity response of lung carcinoma A 549 cells to halothane was determined by lactate dehydrogenase (LDH) assay (for cytotoxicity), by detachment assay after adhesion to type IV collagen (for cell adhesive properties) and by surface tension measurements of culture medium (for cell metabolic activity). Regarding the cytotoxicity, the determined maximal non-toxic concentration of halothane on A 549 cells, given here as volume percentages (vol.%) was 0.7 vol.% expressed as aqueous concentration in the culture medium. Direct measurement of the actual halothane concentration in the culture medium showed that 0.7 vol.% corresponds to 1.05 mM and 5.25 aqueous-phase minimum alveolar concentration (MAC). Concentrations equal or higher than 1.4 vol.% (2.1 mM; 10.5 MAC) of halothane provoked complete detachment (cell death), or reduction of initial adhesion to collagen IV in half of the cell population. Surfactant production of A 549 cells, registered up to 48 h after halothane treatment, was inhibited by halothane concentrations as low as 0.6 vol.% (0.9 mM; 4.5 MAC). Our results demonstrate that sub toxic halothane concentrations of 0.6 vol.% inhibits surfactant production; concentrations in the range 0.8-1.4 vol.% induce membrane damages and concentrations equal and higher than 1.4 vol.%--cell death of approximately 50% of the cells.

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.

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.

Comparison of two implantation sites for testing intraosseous biocompatibility

The purpose of this study was to compare two implantation sites--the mandible and the femur of the rabbit--for testing in vivo intraosseous biocompatility. Twenty-two new Zealand rabbits were anesthetized, and the mandibular and femur bones were exposed. A hybrid glass ionomer cement or zinc oxide eugenol cement was loaded into silicone carriers and inserted into the two bones after drilling the two cortical plates. Eleven rabbits were killed 4 wk after implantation, and 11 rabbits were killed after 12 wk. The mandibles and femurs were prepared using standard histological procedures; tissue reactions were graded from none to severe. At 4 wk, no statistically significant difference was found between the two implantation sites. After 12 weeks, bone healing was statistically better in the mandible than in the femur. The mandible seems to be a better implantation site in the case of intraosseous implantation tests. The intraosseous biocompatibility of Vitremer was similar at 4 wk and superior at 12 wk to that of Super-EBA.

Comparison of the intraosseous biocompatibility of Vitremer and super EBA by implantation into the mandible of rabbits

OBJECTIVES

This study compared the intraosseous biocompatibility of Vitremer, a new hydrophilic glass-ionomer cement, to that of Super EBA.

STUDY DESIGN

Twenty-two New Zealand rabbits were anesthetized, the mandibular bone exposed, and two holes were drilled through the cortical plate. The materials were loaded into silicone carriers and inserted into the mandibles. Eleven rabbits were killed 4 weeks after implantation, 11 animals after 12 weeks. The mandibles were prepared with standard histologic procedures; the tissue reactions were graded from none to very severe.

RESULTS

At 4 weeks Vitremer implants showed very slight to slight reactions, and the Super EBA implants showed slight reactions and one moderate reaction with no significant difference between the two materials. At 12 weeks, bone healing had occurred, despite the persistence of some fibrous tissue interposition. The reactions were classified as none to very slight for Vitremer and very slight to slight for EBA. Statistical analysis showed better results for Vitremer at 12 weeks.

CONCLUSION

The intraosseous biocompatibility of Vitremer was similar at 4 weeks and superior at 12 weeks to that of Super EBA. Its other properties should be evaluated before considering its use in clinical practice.

Comparison of the intraosseous biocompatibility of Dyract and Super EBA

The purpose of this study was to compare the intraosseous biocompatibility of Dyract, a new hydrophilic glass-ionomer cement, to that of Super EBA. Twenty-four New Zealand rabbits were anesthetized, one leg was shaved, the femur exposed, and two holes were drilled through the cortical plate. The materials were loaded into silicone carriers and inserted into the femur. Half of the rabbits were killed 4 weeks after implantation and the other half at 12 weeks and the femurs were prepared using standard histological procedures. The tissue reactions were graded from none to severe. At 4 weeks both materials showed slight to moderate reactions, characterized by the presence of fibrous tissue interposition and inflammatory cells. At 12 weeks, bone healing had occurred, despite the persistence of some fibrous tissue interposition, and the reactions were classified as slight. At both observation periods, statistical analysis failed to show any difference between the two materials indicating that Dyract and Super EBA had similar intraosseous biocompatibility.

Root end filling materials: a review

When non-surgical attempts prove unsuccessful or are contraindicated, surgical endodontic therapy is needed to save the tooth. The procedure usually consists of exposure of the involved area, root end resection, root end preparation and insertion of a root end filling material. Numerous materials have been suggested as root end filling materials. This article is a review of the literature on the suitability of various root end filling materials based on their leakage assessment, marginal adaptation, cytotoxicity, and usage test in experimental animals and humans.

Tissue reaction to implanted super-EBA and mineral trioxide aggregate in the mandible of guinea pigs: a preliminary report

In vitro sealing ability and biocompatibility tests on mineral trioxide aggregate (MTA) have shown similar or better properties for this material than for existing root-end filling substances. The purpose of this study was to examine the tissue reaction of implanted Super-EBA and MTA in the mandibles of guinea pigs. After anesthetizing seven guinea pigs, raising a tissue flap and preparing two bony cavities, the test materials were placed in Teflon cups and implanted in the mandibles. Two bony cavities without implanted materials were left to heal and used as negative controls. The presence of inflammation, predominant cell type, and thickness of fibrous connective tissue adjacent to each implant was recorded. The tissue reaction to MTA implantation was slightly than that observed with Super-EBA implantation. Based on these results , it seems that both Super-EBA and MTA are biocompatible.

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.

Osseous reaction to implanted ZOE retrograde filling materials in the tibia of rats

The osseous reaction of IRM and EBA cement were studied utilizing an intraosseous implant technique in rats. Samples of IRM, EBA cement, and amalgam were placed into polyethylene tubes and subsequently introduced surgically into rat tibias. Specimens of each were evaluated histologically after 7, 14, 21, 56, and 100 days. The IRM and amalgam samples demonstrated essentially complete healing at 56 days. The EBA cement samples displayed a slightly greater inflammatory response up to the 56-day interval; however, they also showed complete healing by 100 days. A favorable osseous reaction was seen with both of these zinc oxide-eugenol materials.

Tissue reaction to endodontic materials: methods, criteria, assessment, and observations

The purpose of this study was to develop methods and criteria for the testing of the biocompatibility of endodontic materials. One hundred twenty-one teeth from 12 baboons (Papio anubis) were used to test three sealers: AH26, Kerr pulp canal sealer, and Kloroperka N.O. Gutta-percha cones were used as solid core in all cases. Under disinfected conditions, access preparation was performed, and with working length approximately 1.0 mm short of the foramen, the instrumentation of the root canal was started, using sodium hypochlorite (1%) for irrigation. After the root canals were cleaned and shaped, they were obturated with gutta-percha cones and the sealer, and by lateral condensation technique. Histologic periapical reactions were evaluated at 1, 7, 30, 365, 730, and 1095 days. The methods and criteria used were adequate for ranking of the biocompatibility of the tested materials in the short and long periods. At short observation periods (1 to 7 days) AH26 caused severe reactions, and Kerr pulp canal sealer and Kloroperka N.O., moderate and mild reactions, respectively. At 2- and 3-year observation periods the ranking was AH26, mild; Kerr pulp canal sealer, moderate; and Kloropercha N.O., severe.

An evaluation of the biocompatibility of a glass ionomer-silver cement in rat connective tissue

Pellets of a glass ionomer-silver cement and a zinc oxide-eugenol cement were implanted into the soft tissues and bones of 30 rats. Following experimental periods of 14, 30, and 80 days, the animals were killed and tissue sections were prepared. The responses to each of the materials initially and at 30 days consisted of mild inflammation. No severe inflammatory responses were noted in any of the groups. By 80 days, although mild inflammation persisted, the materials appeared to be well tolerated. Bone apposition occurred in the glass ionomer-silver cement group; the zinc oxide-eugenol group produced fibrosis.

A radiographic, histological, and histometric study of endodontic materials

Silicone tubes filled with CRCS, a calcium hydroxide-based cement, were implanted at two different localizations in the right tibias of white male Wistar rats. A similar number of solid silicone rods were implanted in the left tibias of the same animals and were used as inert controls. Fifteen days after implantation the bone tissue reactions to these materials were evaluated by means of radiographic, histological, and histometric methods. The radiographic and histometric analysis of the tissues around the deep end of the implants showed that the amount of reactional bone formation in contact with CRCS was significantly lower than that observed in contact with the controls (p less than 0.01). Also, the cell counts obtained from the tissues in contact with CRCS were significantly less than those obtained from the controls (p less than 0.01). This methodology appears to be a refined procedure for analyzing the possible toxic effects of endodontic materials in bone tissues. However, we feel that more extensive experiments will be necessary before predicting the long-term results which could be obtained from this experimental model.