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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 4  »  A comparison of the shaping characteristics of two nickel–titanium endodontic hand instruments
A comparison of the shaping characteristics of two nickel–titanium endodontic hand instruments
Discussion - References.



Discussion.
Comparison of the amount of removed dentine in conjunction with the preparation time represents the efficiency of an instrument. The S-files removed more dentine than the K-type files (Stenman & Spångberg 1990), possibly because the rake angle of the S-file is positive compared to the K-file (Schafer 1997). In this study, the preparation times tended to be shorter for Ni–Ti K-files compared to Ni–Ti S-files in all groups (Table 1). An explanation for this finding is the fact that the Ni–Ti S-files removed significantly more dentine at the most coronal level compared to the Ni–Ti K-files. The circumferential instrumentation of unflared canals requires substantial dentine removal at this level and the more effective the instrument the more dentine is removed at the most coronal level. This dentine removal resulted in a longer preparation time and increased fatigue for the operator.
Procedural accidents such as zip and elbow formation were observed in straight root canals. This surprising result may be explained by the morphology of human root canals. Roots grouped as ‘straight’ do actually have slightly curved canals (Dobo-Nagy et al. 1995). Our conception concerning the relatively high prevalence of procedural accidents in straight canals is discussed in our previous paper (Dobo-Nagy et al. 1997b). In the present study no significant differences were observed between the two instruments in terms of procedural accidents. However, semiquantitative methods for observing the prevalence of perforations, blockage or zip and elbow formation are not adequate for determining fine differences between instruments.
The preparation asymmetry measurement (Dobo- Nagy et al. 1997a,b) is a sensitive quantitative method for determining the transportation of root canals. Using this method the Ni–Ti S-file produced greater transportation at the apical as well as at the danger zone in J-form canals. The differences in transportation between the two instruments in the J-form canal group may be explained by the different designs of the two instruments. The positive rake angle combined with unbalanced preparation of Ni–Ti S-files delivered an increased hour-glass shape in abrupt curvatures. This implies that the Ni–Ti K-files should be chosen for abrupt curvatures in preference to Ni–Ti S-files. Comparison of transportation values according to root canal forms revealed a statistically significant difference between J- and C-form canals prepared with Ni–Ti S-files. This observation may be explained by the increased effectiveness of the Ni–Ti S-files in the coronal part of the canal. This simplified root canal form modified by the instrument itself delivered significantly better results in the C-form canal group prepared with Ni–Ti S-files.

References.

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