The study of different sealers in non human primates provides in vivo evidence of tissue reactions. In this study, four chemically different sealers were tested in 30 root canals of M. mulatta monkeys. Fillings were performed within the canals or roots were perforated and overfilled to compare the direct and indirect tissue reactions initiated by the four sealers. In canals without overfilling with Apexit and Grossman’s sealers, no periapical tissue reactions were detected, which suggests good tissue compatibility of these sealers.
In six root canals filled with Endomethasone, no inflammatory reaction was detected; however, in the other three cases, Endomethasone initiated chronic lymphocytic/ plasmocytic infiltration. The occurrence of periapical inflammatory reactions initiated by Endomethasone in correctly filled root canals has already been demonstrated in nonhuman primates (Crstavik & Mjor1992). Because sealers within the canal have minimal direct contact with the periapical tissue through the apical foramen, the periapical tissue injury may be related to the release of a certain component of the sealer rather than to direct toxicity. Vajrabhaya & Sithisarn (1997) and Leonardo et al. (1999) suggested that the chemical nature of Endomethasone could be responsible for the inflammatory reaction because the paraformaldehyde content of the sealer was relatively high and it released formaldehyde after setting. The tissue reactions initiated by Endomethasone in overfilled root canals were completely different. Endomethasone initiated a foreign body-type granulomatous reaction where giant cells and epitheloid cells were apposed to the surface and encompassed the sealer. Because sealer particles were not present in the macrophages, it seemed that Endomethasone particles were large enough to preclude phagocytosis by a single macrophage and therefore the giant cells demarcated them from the periapical tissue. This finding suggests that Endomethasone is a relatively inert foreign body that initiates granulomatous reaction. From these observations it seems that Endomethasone initiates inflammatory reactions through multiple pathways. It is possible that Endomethasone has a toxic effect based on the paraformaldehyde content and initiates a chronic granulomatous reaction based on the foreign body nature of the sealer.
AH26 also initiated a chronic lymphocytic/plasmocytic inflammatory reaction around two of the seven properly filled root canals, but neither granulomatous nor necrotic tissue reaction was associated with the inflammation. It has been demonstrated that AH26 is a relatively cytotoxic sealer (Gerosa et al. 1995, Osorio et al. 1998, Telli et al.1999,Huanget al.2002) as it contains toxic epoxide bisphenol resin (Gerosa et al.1995) and releases formaldehyde during and after setting (Spangberg et al. 1993, Gerosa et al.1995, Leonardo et al.1999). Similar to Endamethasone, AH26 also initiated periapical chronic inflammatory reactions in the overfilled root canals; however, the lymphocytic infiltration did not contain foreign body giant cells.TheAH26 particles were phagocytosed by macrophages and carried to the periphery of the inflammatory reaction. This finding suggests that in the course of time, macrophages may completely clear the sealer from the overfilled area and periapical tissue may heal eventually; however, in a 3-year follow-up period in nonhuman primates (baboon), periapical tissue inflammatory reactions were still detectable when AH26 was used (Pascon et al.1991).
In root canals filled with Grossman’s sealer with in the canal, no inflammatory reaction was detected. In the overfilled cases, mild to moderate lymphocytic/plasmocytic reaction associated with the direct contact of the sealer with the periapical tissue. The lymphocytic/plasmocytic reaction suggested some irritant effect of the sealer, but did not support the results of previous in vitro and animal studies, where high cytotoxicity of the eugenol and instability of zinc oxide-eugenol-type of sealer were demonstrated (Hume 1984,Tagger & Tagger 1986, Yesilsoy et al.1988, Araki et al.1993).
No periapical tissue reaction was detected in root canals filled with in the canal with Apexit showing good clinical and histological results, but mild inflammation was seen in an overfilled case. The tissue reaction was restricted to mild lymphocytic/plasmocytic infiltration without macrophages and giant cells. Similar to the present study, no foreign body giant cells were detected in the inflamed area around implanted Apexit in mice (Silva et al.1997). In contrast to the results of the present study, Apexit initiated foreign body giant cell inflammatory reaction in overfilled root canals of dogs and subcutaneous tissue of rats (Leonardo et al. 1997, Kolokouris et al.1998).The results of these studies emphasize the differences among tissue reactions initiated by sealers in different animal models. Apexit initiated giant cell reaction in non primate mammals, but this reaction was absent in primates. The absence of giant cells in cases of Apexit suggests a good tissue biocompatibility of the sealer in nonhuman primates.
In some cases, where root canals were filled with in the canal with AH26 and Endomethasone, inflammatory tissue reactions developed, but in others it was not so. This difference in properly filled canals suggests that other factors may also influence the accomplishment of the root canal filling. However, it has been suggested that inflammatory reaction was reduced when dentine chips were placed into the apical opening of the canal, this did not influence the inflammatory reaction in this study because dentine chips were rinsed out from the canal and they were not detected in the histological screening. It is also possible that these differences were related to nondetected bacterial infections. The Gram staining procedure has limitations to detect infections because most of the suspected endodontic pathogens are Gram-negative bacteria (Sundqvist1990).