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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 5  »  Reduction in intracanal bacteria during root canal preparation with and without apical enlargement
Reduction in intracanal bacteria during root canal preparation with and without apical enlargement
Discussion - References.

The methodology used in this study was similar to those used by Orstavik & Haapasalo (1990), Dalton et al. (1998) and Siqueira et al. (1999). However the use of a chemomechanical preparation technique meant that it was unique when compared to these other studies. Dalton et al. (1998) and Siqueira et al. (1999) omitted the use of an antimicrobial irrigant, on the grounds that only the mechanical effects of instrumentation and irrigation were to be assessed. A bacteriological assessment was chosen for the present study because of the importance of canal disinfection in the successful treatment of apical periodontitis. Root sections were used instead of whole teeth because it was thought that sample retrieval would be more convenient. Palatal roots were chosen because they are usually long and contain relatively gently curving root canals. The decision to select roots with canals of this configuration was made because curved canals are associated with a more complicated curvature determination and distribution process (Schneider 1971) and with an increased risk of intracanal procedural accidents such as zipping, ledging and root perforation (Roane et al. 1985). No canal possessed a curvature greater than five degrees as assessed using the Schneider model (Schneider 1971).
Enterococcus faecalis was chosen as the bacteriological marker in the study. It is a non-fastidious, easy-to-grow aerobic bacterium of significant clinical importance, that could be used in a study applying a bacteriological assessment method. Other bacteria commonly associated with endodontic infections may require symbiotic support from other bacteria, but E. faecalis has been reported to survive and successfully thrive alone (Dahlen & Haapasalo 1998). The SEM evaluation used in the present study confirmed that the specimens were successfully reinfected with the organism (Fig. 1).
An empirical method was used to establish the working length of each specimen. This method has also been used by a number of other workers (Al-Omari & Dummer 1995, Wu & Wesselink 1995, Siqueira et al. 1997). The point at which the file just emerged from the canal (visualized under magnification for improved accuracy) was considered to be the apical foramen and the point 1 mm short of the latter was designated the apical constriction. The latter is the ideal biological limit of root canal instrumentation and obturation (Ricucci & Langeland 1998). In the study, apical enlargement at the working length referred to the sequential widening of the apical region of the root canal at the apical constriction, without its destruction.
The results of the present study demonstrated that both chemomechanical preparation techniques (experimental groups A and B) were more effective at eliminating E. faecalis from the root canals when compared to the technique which only employed the antimicrobial irrigation regimen (control group C). Siqueira et al. (1999) showed that instrumentation and irrigation could remove more than 90% of bacterial cells from root canals. However, they used 0.85% saline solution as the irrigant (which had no antimicrobial effect on the E. faecalis used). Dalton et al. (1998) compared two preparation techniques in vivo using different instruments, but they also used a saline irrigant. Although they obtained considerable bacterial reduction after preparation, none of the test subjects were rendered free of bacteria. Yared & Bou Dagher (1994) also obtained sizeable bacterial reductions after chemomechanical root canal preparation in vivo. However, none of their subjects was rendered free of bacteria after chemomechanical preparation.
The difference between the two experimental techniques used in the present study was in the way the apical portion of the root canal was prepared. This part of the root canal is important, as it is the region most likely to harbour intraradicular bacteria associated with root canal treatment failure (Nair et al. 1990). The basis for apical enlargement was in its potential ability to directly or indirectly eliminate bacteria in this area of the root canal system. By widening the canal apically, infected dentine can be removed physically. A wider canal may also mean that the needle delivering the antimicrobial irrigant could penetrate deeper into the root canal, thereby providing a more effective flushing action (Chow 1983).
Buchanan (1993a,b,c, 1998) described the use of the preparation technique applied to the specimens in group B. In his description he referred to the regimen as ‘the tapered preparation’. Buchanan’s concepts on cleaning and shaping of the root canal were based on descriptions by Schilder (1974) and Weine et al. (1975). The proposed tapered preparation, with serial step-back, was designed to prevent unwanted effects such as zipping, gouging and perforation. Therefore, a tapered preparation would result in a more ideally shaped root canal with minimal iatrogenic damage. Buchanan (1998) incorporated coronal flaring in his technique and so delivery of the antimicrobial irrigant was thought to be sufficient. He indicated that a tapered preparation would facilitate a better root canal filling and any remaining bacteria would be entombed, and eventually starved, within the root canal system. Interestingly, Buchanan did not provide any evidence to support this claim but Peters et al. (1995), in a review article, expressed a similar opinion regarding the fate of microorganisms in the root canal.
The use of Ni–Ti rotary instruments means there is no need to compromise on canal disinfection and a reliance on the root filling to ‘seal-in’ any remaining bacteria, because larger instruments can now be used safely to carefully enlarge the canal and so directly eliminate more infected dentine. The concept of a weakened root subsequent to apical enlargement still remains a valid concern and so indiscriminate use of root canal widening should be avoided.
Another key reason given by Buchanan (1993c) justifying the serial step-back technique was that it is a safeguard against changes to the working length during preparation. Schilder (1974) reported that as the root canal is widened, a straightening effect was produced that eventually shortened the distance between the coronal reference point and the apical limit of preparation. If the same working length (which was usually determined early, before any canal preparation was done) was consistently used, overpreparation of the canal may result. Application of a step-back method compensated for this relative decrease in canal length. Modern endodontics however, advocates that the working length be determined at a later stage during preparation (Saunders & Saunders 1997). It is advised that the coronal two-thirds of the canal be flared before the working length is established. Thus, any further apical preparation after the working length is found would produce little or no change to the latter.
It is possible to extrapolate the results of the present study to the clinical setting but the latter is significantly more complex. First, only a few instances of failed root canal treatment are associated with a single species bacterial infection (Dahlen & Haapasalo 1998) and the vast majority of endodontic infections resulting in apical periodontitis are associated with a polymicrobial flora (Stashenko et al. 1998). Secondly, whereas the present study used straight or only slightly curved root sections, narrow and curved canals are frequently encountered clinically and are more difficult to clean and shape (Walton 1976, Siqueira et al. 1997). The consequence that the latter could have on the results of a study was exemplified in the study by Yared & Bou Dagher (1994), where chemomechanical preparation failed to completely disinfect the canals in clinical test subjects. However, coronal flaring was not undertaken in the same controlled way as with the Ni–Ti instruments used in the present study.


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