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Azerbaycan Saytlari

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

Since the introduction of EDTA solutions into endodontics by Nygaard-Ostby (1957) their benefits have been debated. Initially, liquid chelators such as EDTA solutions in different concentrations or with different additional detergents and surfactants were used in order to soften dentine and thus facilitate root-canal enlargement. Recently, the use of paste-type chelating agents has been proposed with the primary aim to serve as gliding agents for rotary nickel-titanium files. Until now comparative studies on the properties of chelating pastes have not been published. Therefore, it was the aim of the present study to compare the changes in weight and microhardness and the degree of root-canal cleanliness after application of three chelator pastes in vitro. Three separate evaluations were undertaken using dentine disks or instrumented root canals. Great care was taken to achieve standardized working times and standardized amounts of the respective chelators. As the dimensions (diameter, thickness, preoperative weight) of the dentine slices could not be standardized the results for weight loss and changes in microhardness were presented as relative changes in percentage and analysed statistically. Cleaning ability was investigated using the SEM with a four-score index for the degree of remaining smear layer. Cleanliness was rated separately for the coronal, middle and apical parts of the root canals.

The existence of a smear layer after endodontic procedures in the root-canal system was described first by McComb & Smith (1975). Brannstrom & Nyborg (1973) could demonstrate that bacteria were able to survive and multiply in the smear layer. As it consists of organic and inorganic compounds it may be dissolved by irrigants suchas citric acid or EDTA, whereas the most commonly used root-canal irrigant sodium hypochlorite is not able to remove the smear layer unless it is used in combination with ultrasonics (Lester & Boyde 1977, Cameron1983).The removal of smear layer seems desirable as it increases dentine permeability (Pashley et al. 1981) thus allowing better disinfection of deeper layers of the infected root-canal dentine (Orstavik &Haapasalo 1990). Additionally, it has been shown in several invitro studies that adaptation and adhesion of root-canal filling materials to the root-canal wall may be increased and thus leakage of the root-canal filling be decreased by removal of the smear layer (Cergneux et al. 1987, Petschelt et al.1987,Wennberg & Orstavik1990, Behrend et al.1996).
Nevertheless, some authors seriously question whether the smear layer really should be dissolved and removed completely (Sen et al. 1995, Perez et al. 1996, Peters et al. 2000). They argue that bacteria might reinvade the cleaned root canal from the dentinal tubules, which might be prevented by leaving the smear layer at least inside the entrances of the dentinal tubules. With regard to removal of the smear layer and cleanliness of the root-canal walls the present study confirmed the results from several recent investigations (McComb & Smith 1975, Ram 1980, Goldman et al. 1981, Berg et al. 1986, Abbott et al.1991, Garberoglio & Becce1994, Stewart1998, Calt & Serper 2000, O’Connell et al.2000).None of the canals investigated under the SEM were completely cleaned, but no superficial debris could be found and the majority of the dentinal tubules were opened in the middle and coronal part of the root canals. Many of the specimens under the SEM showed widening of the dentinal tubules as described by several investigators (Goldberg & Abramovich 1977, Hottel et al. 1999) for liquid EDTA preparations. This effect was more pronounced in the coronal and middle thirds than in the apical parts of the root canals where no significant differences to the control group existed. This probably is owing to the fact that more of the chelating pastes gets in contact to the canal walls coronally than apically. Similar results have been reported by Goldman et al. (1981), Ciucchi et al. (1989) and O’Connell et al. (2000) for the liquid chelators REDTA and EDTA in different concentrations (15 and 25%, respectively). On the other hand, these authors could demonstrate that EDTA alone did not have any effect on uninstrumented canal walls. As it does not affect soft tissues, the pulp tissue remnants and predentine remained in these areas (Goldman et al. 1981, O’Connell et al. 2000). Cleaning efficacy of EDTA could be enhanced by alternate irrigation with sodium hypochlorite (Baumgartner & Mader 1987, O’Connell et al.2000). Goldberg&Spielberg (1982) reported on a significant influence of the working time of EDTA on the canal wall cleanliness with a maximum effect after 15 min. This has not been evaluated in the present study for cleaningabilityof the chelating pastes, but for weight loss and changes in microhardness. In a recent evaluation using Glyde-File during rotary instrumentation of root canals Ahn & Yu (2000) found no influence of this chelator on the smear layer and a significantly superior performance of liquid EDTA. This finding could not be confirmed by the present investigation showing good results regarding the cleaning ability of Glyde-File at least for the coronal and middle part of the root canal.
The results for root-canal cleanliness are partly contradicting the results of two previous studies on rootcanal preparation with different rotary Ni-Ti instruments (Hulsmann et al. 2001, Versumer et al. 2002). Despite the use of a chelator paste (RC-Prep) root-canal cleanliness showed no satisfying results with smear layer covering large parts of the root-canal walls. This may be due to the fact that less paste was used than in the present investigation and that instrumentation was performed in severely curved root canals. In straight root canals, distribution of the chelator paste over the rootcanal walls may be easier to control than in curved canals. On the other hand, it could be confirmed that debris was removed nearly completely and only smear layer remained on the canal walls and that the degree of cleanliness decreased from the coronal to the apical part of the root canals.

Weight loss.
Regarding weight loss, significant differences between the three pastes were found. Specimens treated with Calcinase- Slide showed higher weight loss than RC-Prep after 6- and 9-min working time, Glyde-File was significantly superior to RC-Prep after 6 min. Seidberg & Schilder (1974) using a gravimetric method demonstrated for EDTA a chelation of a determinable quantity of dentine. They found this process to be self-limiting, the most rapid chelation occurred within the first hour. A measurable weight loss of root dentine after use of liquid EDTA was also reported by Heling et al. (1965).

The demineralizing effect of EDTA solutions has been controversial. The results of the present study indicate a reduction of microhardness of dentine as wellas ameasurable weight loss after treatment with a paste chelating agent. Weight loss as well as changes in microhardness were significantly related to the contact period between the chelator paste and dentine. No differences between the three different chelators could be found, indicating that the addition of carbamide peroxide (Glyde-File and RC-Prep) does not have any significant effect on softening of the dentine. Recently, it has been shown that 10% carbamide peroxide used as a bleaching agent does not significantly change microhardness or the mineral content of enamel (Potocnik et al. 2000).
Numerous investigators have measured the hardness of dentine and reported wide variations along different regions of a tooth. As with previous investigators Pashley et al. (1985) demonstrated a statistically highly significant inverse correlation between dentine microhardness and tubular density. Tubular density increased and microhardness decreased near the pulp chamber, presumably owing to a decrease in the amount of intertubular dentine and an increase in individual tubular diameter. Measurements of changes in microhardness in the present study therefore were performed near the root canal. Pre- and postoperative measurements were undertaken in the same region and the results are presented as relative changes, i.e. weight loss (%) in relation to preoperative values. Significant changes in microhardness have been reported previously in several studies for liquid chelators as EDTA solutions with a maximum after approximately 5 min of working time and no significant further increase after 24 h (Pawlicka 1982).Patterson (1963) even described a maximum demineralization after 5 days, thus proposing the use of such agents as intracanal dressings. The measurements in the present study were undertaken after 2.5, 5 and 10 min which should mimic real working times during instrumentation of root canals. In contrast to Pawlicka (1982), the results show a further statistically significant decrease of microhardness after 5 min. These differences to previous studies presumably are owing to the fact that the penetration ability of paste agents into dentine will be clearly lower than that of liquid EDTA solutions. However, other studies have shown that in narrow canals little, if any demineralization occurred (Patterson 1963, Wandelt 1965, Fraser 1974). Verdelis et al. (1999) also reported the low decalcification efficacy of RC-Prep owing to its low pH.
No significant differences between the three pastes could be found, but decrease in microhardness was significantly related to working time indicating a time dependent demineralization, which is in contrast to the results of previous studies (Patterson 1963, Wandelt 1965). Fraser (1974) described a softening effect of RCP rep to a depth of 30-40 mm from the root-canal border in the coronal third with even smaller values in the middle and apical third, in his study liquid chelators performed better than pastes. In the light of recent observations reported by Mjor et al. (2001) the tubular density and structure of dentine in the apical part of the root canal differ from that in the coronal and middle parts of root canal. There fore, it needs further comparative investigations on the differences between liquid and paste chelating agents in different parts of the root canal.
It remains unclear whether weight loss as well as changes in dentine microhardness really are of any clinical significance. Under the conditions of the present study, a relatively large volume of the chelating agent had intimate contact to a large amount of root dentine which is not comparable to the situation of a narrow and calcified root canal. Whereas it seems questionable if such low changes in microhardness really might affect the ease of preparation of such root canals it should be remembered that chelator pastes act additionally as lubricants thus enhancing the gliding capability of endodontic files (Weine1982).
Further studies are necessary to evaluate whether liquid or paste chelators should be preferred as adjuncts during root-canal preparation.


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