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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 5  »  Dynamic torque and apical forces of ProFile .04 rotary instruments during preparation of curved canals
Dynamic torque and apical forces of ProFile .04 rotary instruments during preparation of curved canals
Results.



Regular calibration of the torque and force transducers before each series of measurements showed a linear and stable relationship between torque and force scores and the voltage (Fig. 4). The identical torque-measuring set-up was used for both the static and dynamic tests.

Figure 4. Example of a calibration graph indicating a linear relationship between torque (M) and voltage (U) with M 0.026 + 4.926 U.

Example of a calibration graph indicating a linear relationship between torque

Figure 5. Line diagram of a 'load to fracture' run of a size 60 ProFile .04 performed according to the ISO 3630-1 test, indicating biphasic elastic deformation, yield and plastic deformation characteristics of nickel-titanium alloy.

Line diagram of a load to fracture run of a size 60 ProFile

Table 1. Load to fracture and angular deflection for selected ProFile .04 rotary instruments carried out according to the ISO 3630-1 test (n = 8).

Load to fracture and angular deflection for selected ProFile
a. Significantly different torque scores (ANOVA, P < 0.0001).
b. No significant differences in rotational angles.

Table 2. Number of rotations to failure in a cyclic fatigue test carried out using a stainless steel phantom with 90 and 5 mm radius.

Number of rotations to failure in a cyclic fatigue test carried out using a stainless steel phantom with 90  and 5 mm radius
A, static instrument position;
B, oscillating movement with 0.5 Hz and 2 mm width.
a. Significantly different to sizes 30.04 and 45.04 (P < 0.01).
b. Significantly different to size 15.04 in test A (P < 0.01).

Experiment a.
Load to failure was determined for sizes 20, 35 and 60 ProFile .04 instruments and findings for a size 60 instrument are shown as an example (Fig. 5). This example also details the deformation phases typical for nickel– titanium alloys. Means for torsional strain and rotational angle at failure are listed in Table 1. Torque values were significantly different between the file sizes investigated ( P < 0.0001), whilst the angles were not.
Results of the cyclic fatigue tests for size 15, 30 and 45 ProFile instruments, expressed as numbers of rotations to failure, are listed in Table 2. In general, fatal cyclic fatigue occurred at 400 rotations or greater. Significantly higher scores were recorded for the size 15 instruments, whilst ProFile sizes 30 and 45 had similar scores. The only significant difference noted between the static and the oscillating movements of the instruments, mimicking the clinically used pecking motion, was that recorded for the size 15 ProFile instrument ( P < 0.01, Table 2) which fractured after 798 194 and 581 74 cycles with and without oscillations, respectively.

Experiment b.
A total of 356 preparation cycles in plastic blocks or extracted teeth were analysed. Torque values during simulated canal preparation differed widely with respect to canal types and instrument sizes and mean maximum scores are listed in Figure 6. Two significantly different ( P < 0.01) groups of instruments were identified by virtue of their torque scores. First, the smaller ProFile instruments, sizes 20–30, in which torque values did not exceed 6 Nmm whilst secondly, the larger instruments, sizes 35–60, generated mean torque scores of up to 25 Nmm. Furthermore, within each instrument size, the highest torque scores were recorded in plastic blocks with straight simulated canals, whilst canals in natural teeth had the lowest torque scores. In most of the larger instrument sizes, this difference was statistically significant (Fig. 6).
Comparing the three preparation stages, size 60–20 instruments used in the crown-down phase generated maximum mean torques from 22 to 4 Nmm. In contrast, during apical preparation to a size 40, torque scores of 30 Nmm and greater developed. Similarly high torque scores were also recorded during the step-back phase. A two-way anova indicated a highly significant effect of both canal type and instrumentation phase ( P < 0.0001) on the torques generated, whilst a combination of both factors had no effect ( P > 0.05, Table 3).

Figure 6. Bar diagrams detailing torque scores generated whilst preparing various canal types using ProFile .04 rotary instruments. Significant differences within one instrument size are indicated by horizontal bars (P < 0.05 or 0.01).

Bar diagrams detailing torque scores generated whilst preparing various canal types using ProFile .04 rotary instruments

Table 3. Two-way analyses of variance carried out separately for torque, force and rotations during simulated rotary root canal preparation (n = 356).

Two-way analyses of variance carried out separately for torque, force and rotations during simulated rotary root canal preparation

Figure 7. Bar diagrams detailing apical forces exerted whilst preparing various canal types using ProFile .04 rotary instruments. Significant differences within one instrument size are indicated by horizontal bars (P < 0.05 or 0.01).

Bar diagrams detailing apical forces exerted whilst preparing various canal types using ProFile rotary instruments

Figure 8. Line diagram of a typical recording during apical preparation of a curved canal in a plastic block using a size 40 ProFile .04 instrument. The number of revolutions counting from the entrance of the canal totalled 22, whilst only 13 revolutions generated torque (black bars) above the minimum torque threshold (0.8 Nmm, marked by dotted line).

Line diagram of a typical recording during apical preparation of a curved canal in a plastic block using a size 40 ProFile

Similarly, the results of the apically directed forces were also grouped by instrument size and canal type (Fig. 7). In extracted teeth, the mean forces generated ranged from 3.5 and 5.5 N, but did not differ significantly between instruments. In contrast, for plastic blocks, forces decreased with decreasing instrument size. Generally, forces were high for curved canals in plastic blocks (maximum 7.3 N for ProFile no. 40) and low for straight canals in plastic blocks (4.9 N for ProFile no. 40).
When grouped into preparation phases, sizes 35 and 40 were used with significantly higher forces during crown-down (6 N and 7.5 N, respectively) than during the apical preparation (3.5 N and 6 N, respectively). These results were statistically significant ( P < 0.01 and P < 0.05, respectively). A two-way anova indicated that the apically directed forces were significantly affected by both canal type and preparation stage ( P < 0.0001), as well as by a combined effect ( P < 0.0001, Table 3).
The number of working rotations during preparation was determined accepting a torque threshold of 0.8 Nmm (Fig. 8). Repeatedly, the instruments’ working times determined in this way made up only 50% of the total preparation times (Fig. 8). The mean number of revolutions required to complete the crown-down, apical preparation and step-back phases of canal preparation varied from 41.3 (size 40 in curved canals in plastic blocks) to 18.3 rotations (size 25 in straight canals in plastic blocks). Grouped by instrument size, the numbers of rotations were generally highest in curved canals in plastic blocks whilst canals in natural teeth yielded the lowest scores (Fig. 9). A two-way anova indicated highly significant effects of canal type and preparation phases, as well as a combined effect on numbers of working rotations ( P < 0.001, Table 3).
Figures 6, 7 and 9 detail the scores for the size 4 Gates- Glidden burs recorded for torque, force and number of rotations, respectively. Similar scores were found for torque and number of rotations with Gates-Glidden burs compared to those recorded for the size 60 ProFile instruments, except that a higher force directed apically was recorded for Gates-Glidden burs.