| Objective To compare the shaping ability of Twisted File (TF) and Protaper rotary nickel-titanium endodontic instruments during the preparation of lightly and severely curved root canals in extracted teeth using Cone-Beam Computed Tomography (CBCT).Methods 60 single distal root canals, which were separated from 41 extracted human mandibular molars, with curvatures ranging between 0° and 35° were selected and divided into two groups of 30 each:lightly curved group(curvatures ranging between 0° and 15°); severely curved group(curvatures ranging between 16° and 35°). The initial root canal curvature was determined using the technique proposed by Schneider(1971). Then each group was divided randomly into two groups of 15 each: TF group and Protaper group. Based on radiographs taken prior to instrumentation, the groups were balanced with respect to the angle and the radius of canal curvature. Before and after instrumentation with Twisted Files and Protaper to to 0.06 taper,0.25 mm (current standards), the diameter was measured using CBCT at 2,4* 6mm from the apex. Using pre-and post-instrumentation radiographs, the degree of canal transportation, in addition to instruments’centering ability, was recorded and determined with an image analysis program. Root curvature、preparation time and fracture of the instruments were also recorded. These data were analyzed statistically using ANOVA and t test.Results 1. Preparation time:instrumentation with TF was significantly faster than with Protaper (P<0.01). The preparation time of TF group was 47.91±7.93s, while the Protaper group was 102.07±9.24s.2. Root curvature:All instruments maintained the original canal curvature well with no significant differences between the two different files. Lightly curved group, The mean and standard deviation of the root canal curvatures before and after instrument-ation in the TF group were 8.70±3.40°、22±3.33°, in the Protaper group, they were 8.02±3.22°、7.52±3.13°. The Student’s/test showed no statistically significant difference in the these variables between the two groups (P>0.05); severely curved group, the mean and standard deviation of the root canal curvatures before and after instrumentation in the TF group were 26.70±5.57°、22.67±5.03°, in the Protaper group, they were 26.12±5.47±> 22.03±4.82°. The Student’s/test showed statistically significant difference in these variables before and after the instrumentation (P<0.05). Intra-group comparison showed no significant difference (P>0.05). There was significant difference in the variations between the lightly curved group and the severely curved group (P<0.05).3. Canal transportation:No canal transportation was found between TF and Protaper (P>0.05). The mean degree of canal transportation instrumented with TF was significantly lower in the lightly curved group than in the severely curved group (P<0.05), while the mean degree of canal transportation instrumented with Protaper was significantly lower in the lightly curved group than in the severely curved group at 2mm and 4mm from the apex (P<0.05).4. Instruments:the total number of TF instruments used was 18, no cyclic flexural fatigue failure was detected, three of them were found screw loose solution, one of them was found thread tighten; the total number of Protaper instruments used was 30, no significant screw loose solution was detected; two of them was found thread tighten; one of them was found flexural fatigue failure. Those all happened in the severely curved group. Conclusion 1 Under the conditions of this study, the two NITI rotary instruments maintained the original canal curvature well and were safe to use. The TF and Protaper system were found to have less canal transportation and better centering ability in the lightly curved group than in the severely curved group; CBCT is a noninvasive and objective method for the evaluation of the instruments’ shaping ability.2 The instruments continuously progress towards the apex of the root canal.3 Instrumentation with TF was significantly faster than with Protaper.4 The flexibility of TF rotary nickel-titanium endodontic instruments was slightly better than Protaper. |
PDF Full Text Request