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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 6  »  Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile - PART 1
Efficiency of rotary nickel-titanium FlexMaster instruments compared with stainless steel hand K-Flexofile - PART 1
Discussion - References.



Discussion.
The purpose of this study was to compare the relative efficiency and shaping ability of rotary FlexMaster nickel- titanium instruments with stainless steel hand K-Flexofiles. K-Flexofiles were chosen as controls, because it is well-known that out of all hand instruments used in a rotary motion, these instruments displayed the greatest cutting efficiency (Tepel et al.1995) and most ideal shape (Al-Omari et al.1992, Schafer et al. 1995). Moreover, like the FlexMaster instruments (Fig. 2) the K-Flexofiles also possess a non-cutting tip without transition angle (Scha- fer et al.1995, Bishop & Dummer1997). Because there is no evidence in the literature to suggest that K-Flexofiles are better used in a linear or rotational working motion (Bishop & Dummer 1997), these instruments were used ina reaming motionas the present K-filehas a triangular cross-section. Indeed, several authors have pointed out that the K-files used in a reaming working motion were more efficient and their use resulted in less canal transportation compared to the K-type instruments in a filing motion (Jungmann et al.1975, Roane et al.1985).
The present study described the shaping abilities of the instruments under strictly controlled laboratory conditions, using clear resin blocks. The use of simulated canals in resin blocks does not re£ect the action of the instruments in root canals of real teeth. However, resin blocks allow a direct comparison of the shaping ability of different instruments (Schafer et al. 1995). A major draw back off using rotary instruments in resin blocks is the heat generated, which may soften the resin material (Kum et al. 2000) and lead to binding of cutting blades, and separation of the instrument (Thompson&Dummer 1997c, Baumann&Roth1999).Thus, owing to the nature of the resin, care should be exercised in the extrapolation of the present results on failure of the use of the FlexMaster instruments in real root canals, where dentine is involved (Thompson & Dummer1997c).
In comparison with the stainless steel K-Flexofiles, rotary FlexMaster instruments achieved better canal geometry, showed less canal transportation and straightening (Figs 4 and 5), and created fewer canal aberrations (Table 4), both in canals with 288 and 358 curves. The ability of rotary nickel-titanium instruments to maintain the original shape of curved canals has been confirmed by several studies (Thompson & Dummer 1997a,b,c,d, Baumann & Roth 1999, Kum et al. 2000). However, similar to other rotary nickel-titanium instruments the FlexMaster instruments created a slight canal transportation toward the outer aspect of the curvature in the apical region of the canals, especially in those having 358 curves (Thompson &Dummer1997d,Thompson & Dummer 1998, Baumann & Roth 1999, Thompson & Dummer 2000b). This canal transportation may be owing to root-canal preparation with instruments of greater taper, because these are stiler compared with those of ISO taper (Kum et al. 2000, Thompson & Dummer 2000b). In contrast, canals enlarged manually with K-Flexofiles showed a more marked transportation toward the outer aspect of the curves and, although not statistically significant (Table 4), a higher incidence of canal aberrations (Al-Omari et al. 1992, Schafer et al. 1995, Bishop & Dummer1997, Kum et al. 2000).
In several studies, the shaping ability of different rotary nickel-titanium instruments and £flexible stainless steel hand K-files have been compared, using either simulated canals in resin blocks or extracted human teeth. Kosa et al. (1999) compared canal transportation in moderately curved mesial roots of mandibular molars using rotary ProFile Series 29 instruments and stainless steel Flex-R files in a contra-angle handpiece.According to their results, the re was no difference in the magnitude of absolute transportation between these systems. Luiten et al. (1995) and Esposito & Cunningham (1995) found no significant differences between NiTiMatic rotary nickel-titanium instruments and stainless steel K-Flex hand files. However, the results of two more recently published studies (Schafer & Fritzenschaft 1999, Kum et al. 2000) corroborate the fifindings of the present investigation, in that in severely curved simulated canals the use of rotary nickel-titanium instruments resulted in less canal transportation, fewer canal aberrations, less instrumentation time and better maintenance of working distance compared with stainless steel K-Flexofiles.
In the present study, none of the canals became blocked with resin shavings and none of the canals showed over-extension of preparation. Thus, the only changes of working length was a decrease of working distance. In general, it was possible with both types of instruments to control the working distance adequately (Table 3). This finding is in agreement with the observations of several other studies, in which only small mean changes in working distance occurred with rotary nickel- titanium instruments (Kum et al. 2000, Thompson & Dummer 2000a). On the whole, it is questionable whether the small changes of working length observed in the present study may have any clinical significance. These changes may be owing to minor canal straightening during canal enlargement or the lacko f length control by the operator (Thompson & Dummer 2000a).
The mean time for the canal preparation was recorded and instrument changes within the described instrumentation sequences were included. Both, in the 288- and 358-curved canals, the FlexMaster instruments were significantly faster than the hand preparation with K-Flexofiles (Table 2).This is in agreement with the fifindings of several authors that instrumentation times with rotary nickel-titanium instruments are substantially faster than with stainless steel hand instruments (Thompson & Dummer 1997a,b,c, Kum et al. 2000, Thompson & Dummer 2000a).
During the present study, no fractures occurred with K-Flexofiles, whereas two FlexMaster instruments separated, both in canals with 358 curves. It is worth emphasizing, that these both were 0.04 taper size 20 instruments and were used for the instrumentation of the second canal. To date, no data are available on the torsional properties of the FlexMaster instruments, therefore, no explanation can be given why this particular instrument was susceptible to separation. Related to the total number of FlexMaster instruments used a fracture rate of approximately1% (2 out of168 the Flex- Master instruments used when all instruments were used to enlarge two canals) resulted. This separation rate is in agreement with previously reported fracture rates of newer rotary nickel-titanium instruments (Thompson & Dummer 1997a, Baumann & Roth 1999, Kum et al. 2000,Thompson & Dummer 2000a).

References.

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