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 »  Home  »  Endodontic Articles 8  »  Comparative in-vitro evaluation of three chelator pastes
Comparative in-vitro evaluation of three chelator pastes
Introduction.



M. Hulsmann, M. Heckendorff & F. Schafers
Department of Operative Dentistry, Preventive Dentistry and Periodontology, University of Gottingen, Gottingen, Germany.

Introduction.
It has been shown in numerous investigations that mechanical instrumentation of the root canal does not result in perfectly cleaned canal walls as it leaves behind uninstrumented areas as well as debris and a smear layer of organic and inorganic material (McComb & Smith 1975, Se n et al.1995). In order to enhance the degree of cleanliness copious irrigation of the canal with a wide variety of irrigants has been proposed, including chelating agents (Harrison1984). Chelating agents act on calcified tissue by substituting sodium ions which combine with dentine to give soluble salts for the calcium ions that are bound in a less soluble combination (Weine 1982). The most popular of the chelating agents is EDTA, introduced by Nygaard-Ostby (Nygaard-Ostby 1957). EDTA is a liquid solution of the sodium salt of ethylenediamine tetraacetic acid with a pH of 7.3. Ina normal concentration it removes 10.6 g of calcium from 100 g of calcium (Nicholson et al.1968).
Although introduced into endodontics with the aim to facilitate preparation of calcified and narrow root canals by softening root-canal dentine, it also has been suggested as a useful irrigant owing to its capacity to remove the smear layer. Vonder Fehr&Nygaard-Ostby (1963) presented a combination of Cetavlon and EDTA, and this modification has been known and commercially distributed as EDTAC. The action of this solution has been described to be self-limiting and not exceeding a depth of 50 mm after 48-h exposure (Von der Fehr & Nygaard-Ostby1963).
Stewart et al. (1969) added urea peroxide to EDTA. In contact to sodium hypochlorite, this combination produces foam which lifts debris out of the root canal. A commercial product using this mixture has been known as RC-Prep (Premier-Dental, Norristown, PA, USA). Although EDTA has a relatively low surface tension (Tasman et al.2000) surfactants and disinfectants have been added to the ETDA solution (Brannstrom 1984) to enhance the removal of the superficial smear layer so that the antiseptic components can penetrate the dentinal tubules. This product has been marketed as Tubulicid (Dental Therapeutics, Nacka, Sweden).
Studies on the softening effect of EDTA gave controversial results. Von der Fehr & Nygaard-Ostby (1963) described a depth of demineralization of 20-30 mmafter 5-minworking time of EDTAC. Patterson (1963) reported that a 10% EDTA solution was able to lower the Knoophardness of dentine significantly from 42 to 7. Ameasurable softening effect of EDTA on dentine was confirmed by the studies of Fromme et al. (1970) and Pawlicka (1982).
Controversially, Fraser (1974) came to the conclusion that a softening effect of three different chelators, amongst these RC-Prep, could be found only in the coronal and middle third of the root canal but not in the apical part. These findings were confirmed by a further study using Largal Ultra (Septodont, St. Maur-des-Fossee- Cedex, France), a liquid chelating agent containing EDTA and cetrimide (Fromme et al. 1970). The latter suggest that the demineralizing effect of EDTA depends on the contact of large volumes of the solution with dentine which may occur in the coronal part of wide root canals but not in the narrow apical third. Wandelt (1965) also questioneda softening effect of EDTA as he could not find any signs of demineralization of root dentine under the microscope. The action of EDTA is self-limiting, the demineralization stops when an equilibrium between the calcium ions in dentine and in the chelating agent has been reached (Nygaard-Ostby1957, Seidberg & Schilder 1974).
Goldberg & Spielberg (1982) demonstrated that the extent of demineralization is related to the time of exposure to EDTA, reaching its maximum after 15 min. Although the first effects of the chelator were observed after 5 min an extended working period has been suggested to increase the cleansing effect (McComb & Smith 1975, Goldberg & Spielberg1982).
EDTA in several investigations has been reported to be effective in cleansing the root-canal walls (McComb & Smith 1975, Goldberg & Abramovich 1977, Ram 1980, Goldman et al.1981, Berg et al. 1986, Ciucchi et al. 1989, Garberoglio & Becce 1994, Stewart 1998, Hottel et al. 1999, O’Connell et al. 2000). Nevertheless, the cleaning ability seems to be better in the middle and coronal parts of the root canal (Goldman et al. 1981, O’Connell et al. 2000). The effect of liquid chelators has been shown to be confined to prepared root-canal surfaces whereas no effect on organic tissues in uninstrumented root canals could be detected (Koskinen et al.1980).The combination of EDTA and sodiumhypochlorite (0.5-5.25%) has been shown to be even more effective in smear layer removal than the use of these two solutions alone (Baumgartner &Mader1987) as well as in antibacterial efficacy (Bystroem & Sundqvist 1985). The combined use of EDTA and ultrasound did not enhance the dissolving capability of EDTA (Ciucchi et al.1989).
Heling et al. (1999) and Buck et al. (1999) described a limited antibacterial activity of RC-Prep dependent on the type of bacteria. Patterson (1963) also reported on a limited antibacterial activity and only slight inflammatory reactions in contact with vital tissue. By addition of Cetavlonthe antibacterial as well as the inflammatory potential of EDTA is increased (Weine 1982), probably owing to a lower surface tension and thus deeper penetration of the liquid into dentine (Von der Fehr & Nygaard-Ostby1963). The antibacterial effect and intratubular disinfection of EDTA have been questioned (Orstavik & Haapasalo1990). Recently, the use of EDTA has been shown in vitro to inhibit the substrate-adherence capacity of macrophages when leaking into the periapical tissues thus reducing both periapical inflammatory reactions and periapical healing (Segura et al. 1997).
The ability of EDTA to remove the smear layer has been demonstrated to result in a higher permeability of dentine (Cohen et al. 1970, Brannstrom 1984), a reduced leakage of the definite root-canal filling (Cergneux et al. 1987, Petschelt et al. 1987,Wennberg & Orstavik 1990, Behrend et al.1996), and a larger number of filled lateral canals (Goldberg et al. 1986). In SEM studies it has been shownthat the use of EDTAresulted inwideningof dentinal tubules (Goldberg & Abramovich 1977, Hottel et al. 1999).
As the majority of experimental studies on chelating agents has focused on liquid chelators (EDTA, EDTAC) or one single paste chelator (RC-Prep), it was the aim of the present investigation to compare three chelating pastes with different compositions. The parameters investigated were changes in dentine microhardness, weight loss and cleaning ability.