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 »  Home  »  Endodontic Articles 6  »  Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile - PART 2
Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile - PART 2
Discussion - References.

One of the most important objectives during root-canal instrumentation is the removal of vital pulp tissue, residual necrotic material, infected dentine, and debris in order to eliminate most of the microorganisms from the root-canal system (European Society of Endodontology 1994, American Association of Endodontists 1998). The ability to achieve these objectives was examined in the present investigation on severely curved root canals, involving FlexMaster rotary nickel-titanium instruments and stainless steel hand K-Flexofiles.
The debris were defined as dentine chips, and residual vital or necrotic pulp tissue attached to the root-canal wall, which in most cases, is infected (Hulsmann et al. 1997). Thus, the debris might prevent the efficient removal of microorganisms from the root-canal system. The smear layer is a surface ¢lm of a thickness of approximately 1-2 mm which remains on the root-canal wall after instrumentation (American Association of Endodontists 1998). No smear layer is found on areas which are not instrumented (West et al.1994).The smear layer contains dentine particles, residual vital or necrotic pulp tissue, bacterial components as well as retained irrigants, and it blocks the openings of the dentinal tubules (West et al.1994). In this way, a thick and heterogeneous smear layer can prevent the efficient elimination of intracanal microorganisms, and compromise the complete sealing of the root canal (Petschelt et al.1987,West et al. 1994).
Although it is recommended to use antibacterial irrigants in combination with chelating agents in order to remove debris as well as the inorganic/organic smear layer (West et al.1994, Hulsmann et al.1997, Gambarini 1999), sodium hypochlorite alone was used as an irrigant, in the present study. Certainly, this solution is still the best available canal irrigant owing to its antibacterial and organic tissue-dissolving properties (SpOngberg et al. 1973, Turkun & Cengiz 1997), but it is not possible to remove the smear layer with NaOCl (Yamada et al. 1983). Nevertheless, considering the major objective of the present investigation (to solely to compare the cleaning effectiveness of the two instrumentation techniques under identical conditions), a simple irrigation technique was used, avoiding any associations of different irrigation solutions. Thus, it has to be taken into consideration that the cleaning efficiency of the two instrumentation techniques might be further improved using a combination of NaOCl and EDTA solutions.
In the present study, the cleaning efficacy of two instrumentation methods was examined on the basis of a separate numerical evaluation scheme for debris and smear layer, by means of an SEM evaluation of the coronal, the middle, and the apical portions of the canals (Mizrahi et al.1975, Bolanos & Jensen1980,Haikel&Allemann1988, Hulsmann et al.1997). In both instrumentation techniques, partially uninstrumented areas with remaining debris were found in all canal sections. Similar ¢finding has also been described by other authors (Bolanos & Jensen 1980, Schwarze & Geurtsen 1996, Hulsmann et al.1997).Moreover, the present results indicate that on averaget he apical third of the canals was less clean than the middle and coronal thirds regardless of the instrument used. This observation is also in agreement with other studies (Wu & Wesselink1 995, Hulsmann et al.1997, Schafer & Zapke 2000).
In general, the use of stainless steel K-Flexofiles resulted in significantly less remaining debris (Table 2) and a thinner and more homogenous smear layer (Table 3) compared to canal shaping with rotary nickel-titanium FlexMaster instruments. Whilst, these results corroborate a previous report, in which stainless steel hand instruments proved to be superior to ProFile rotary nickel-titanium instruments as far as cleaning efficacy is concerned (Schafer & Zapke 2000), in other studies, no significant differences between the cleaning efficacy of stainless steel hand and rotary nickel-titanium instruments were observed (Bechelli et al. 1999, Hulsmann 2000).
Nevertheless, examination of the scores for remaining debris and smear layer after instrumentation with the two instruments revealed no statistically significant differences between the instruments in the apical third of the canals (Tables 2 and 3). Clinically, this ¢finding may be more important than the significant differences between the two instruments in the amount of debris remaining in the coronal and middle portions of the canals, because the microorganisms which remain in the apical portion of the root canal have been considered the main cause of failure (Nair et al. 1990). Moreover, compared with the results obtained in a previous study under nearly identical conditions, FlexMaster instruments displayed a clearly better debris removal efficiency than the rotary ProFile instruments (Schafer & Zapke 2000). Obviously, even different rotary nickel-titanium instruments vary in their debris removal efficiency, possibly owing to their £flute design (Gambarini1999, Hulsmann et al. 2000). ProFile instruments have radial lands in contrast to the FlexMaster instruments and may be unable to cut dentine so effectively. This might explain the differences in the cleaning efficiency of these two rotary nickel-titanium instruments. Summarizing these aspects, it is therefore, open to question, whether the differences in the cleaning effectiveness of FlexMaster instruments and K-Flexofile observed in the present study has any clinical significance in term of successful canal debridement, particularly as the ability of Flex- Master instruments to maintain the original canal curvature was significantly superior compared with that of K-Flexofiles.
The teeth in all experimental groups were balanced with respect to the apical diameter of the root canal. Furthermore, based on the initial radiograph the teeth were also balanced with respect to the angle and the radius of canal curvature. To achieve this a computerized digital image processing system was used to determine both the angle and the radius of curvature (Schafer et al. in press). The homogeneity of the two groups with respect to the defined constraints was examined using a t-test. According to the P-values obtained (Table 1), the groups were well-balanced. The curvatures of all root canals ranged between 258 and 358 and the radii ranged between 4.3 mm and 8.5 mm (Table 1). Thus, the curvatures of the human root canals were comparable to those of the simulated canals in resin blocks used in the ¢first part of this two-part report (curvatures: 288 and 358; radii: 6.5 and 7.5 mm), allowing a comparison of the results obtained in simulated and in human root canals (Schafer & Lohmann 2002).
The results of the present study using extracted human teeth confirm the ¢findings obtained in the part 1 of this two-part report after preparation of simulated canals, in which the use of FlexMaster instruments resulted in significantly less canal transportation than K-Flexofiles. In simulated canals, Flex- Master instruments were significantly faster than K-Flexofiles. Certainly, FlexMaster instruments needed less time to prepare the root canals of real teeth than K-Flexofiles, but this differences was not significant, in contrast to the results obtained in simulated canals.


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