Restorative Dentistry & Endodontics

Effect of internal stress on cyclic fatigue failure in K3: Jun-Young Kim, Jin-Woo Kim, Kyung-Mo Cho, Se-Hee Park; Restor Dent Endod 2012;37(2):74-78. Published online May 18, 2012; DOI: https://doi.org/10.5395/rde.2012.37.2.74

Abstract PDF PubReader ePub: Objectives
This study aimed to evaluate the relationship between the cyclic fatigue of a K3 file and internal stress intentionally induced until the activation of the auto-stop function of the torque-controlled motor.
Materials and Methods
K3 (Sybron Endo) .04 and .06 taper, size 25, 30, 35, 40 and 45 were used in this study. To give the internal stress, the K3 files were put into the .02 taper Endo-Training-Bloc (Dentsply Maillefer) until the activation of the auto-stop function of the torque-controlled motor. The rotation speed was 300 rpm and torque value was 1.0 N·cm. K3 were grouped by the number of induced internal stress and randomly distributed to 4 experimental groups (n = 10, Stress 0 [control], Stress 1, Stress 2 and Stress 3). For measuring the cyclic fatigue failure, the K3 files were worked against a sloped glass block and time for file separation was recorded. Data was statistically analyzed Statistical analyses were performed using two-way ANOVA and Duncan post-hoc test at p < 0.05 level.
Results
Except .04 taper size 30 in Stress 1 group, there were statistically significant differences in time for file separation between control and all experimental groups. K3 with .04 taper showed higher cyclic fatigue resistance than those of .06 taper.
Conclusion
In the limitation of this study, the cyclic fatigue of the K3 file was influenced by the accumulated internal stress from use until the auto-stop function was activated by the torque-controlled motor. Therefore, clinicians should avoid the reuse of the K3 file that has undergone auto-stops.

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Comparison of apical transportation and change of working length in K3, NRT AND PROFILE rotary instruments using transparent resin block: Min-Jung Yoon, Min-Ju Song, Su-Jung Shin, Euiseong Kim; J Korean Acad Conserv Dent 2011;36(1):59-65. Published online January 31, 2011; DOI: https://doi.org/10.5395/JKACD.2011.36.1.59

Abstract PDF PubReader ePub: Objectives
The purpose of this study is to compare the apical transportation and working length change in curved root canals created in resin blocks, using 3 geometrically different types of Ni-Ti files, K3, NRT, and Profile.
Materials and Methods
The curvature of 30 resin blocks was measured by Schneider technique and each groups of Ni-Ti files were allocated with 10 resin blocks at random. The canals were shaped with Ni-Ti files by Crown-down technique. It was analyzed by Double radiograph superimposition method (Backman CA 1992), and for the accuracy and consistency, specially designed jig, digital X-ray, and CAD/CAM software for measurement of apical transportation were used. The amount of apical transportation was measured at 0, 1, 3, 5 mm from 'apical foramen - 0.5 mm' area, and the alteration of the working length before and after canal shaping was also measured. For statistics, Kruskal-Wallis One Way Analysis was used.
Results
There was no significant difference between the groups in the amount of working length change and apical transportation at 0, 1, and 3 mm area (p = 0.027), however, the amount of apical transportation at 5 mm area showed significant difference between K3 and Profile system (p = 0.924).
Conclusions
As a result of this study, the 3 geometrically different Ni-Ti files showed no significant difference in apical transportation and working length change and maintained the original root canal shape.

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A study on transportation of apical foramen after overinstrumentation by ProFile®, ProTaper™ and K^3TM in simulated canals with different curvatures: Hyun Yang, In-Seok Yang, Yun-Chann Hwang, In-Nam Hwang, Suk-Ja Yoon, Won-Jae Kim, Won-Mann Oh; J Korean Acad Conserv Dent 2007;32(2):87-94. Published online March 31, 2007; DOI: https://doi.org/10.5395/JKACD.2007.32.2.087

This study was done to evaluate transportation of the apical foramen after 0.5 mm overinstrumentation by ProFile, ProTaper and K³ in simulated resin root canal.

Sixty simulated resin root canal with a curvature of J and S-shape were divided into two groups. Each group consisted of three subgroups with 10 blocks according to the instruments used: ProFile®, ProTaper™, and K^3TM. Simulated resin root canal was prepared by ProFile, ProTaper and K³ with 300 rpm by the crown-down preparation technique. Pre- and post-instrumentation apical foramen images were overlapped and recorded with Image-analyzing microscope 100X (Camcope, Sometech Inc, Korea). The amounts of difference in width and dimension on overlapped images were measured after reference points were determined by Image Analysis program (Image-Pro® Express, Media Cybernetic, USA). Data were analyzed using Kruskal-Wallis and Mann-Whitney U-test.

The results suggest that ProFile showed significantly less canal transportation and maintained original apical foramen shape better than K³ and ProTaper.

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A comparison of canal centering abilities of four root canal instrument systems using X-ray micro-computed tomography: Hye-Suk Ko, Heyon-Mee You, Dong-Sung Park; J Korean Acad Conserv Dent 2007;32(1):61-68. Published online January 31, 2007; DOI: https://doi.org/10.5395/JKACD.2007.32.1.061

Abstract PDF PubReader ePub

The purpose of this study was to compare the centering abilities of four root canal instrument systems and the amounts of dentin removed after root canal shaping using them.

The mesial canals of twenty extracted mandibular first molars having 10 - 20° curvature were scanned using X-ray micro-computed tomography (XMCT)-scanner before root canals were instrumented. They were divided into four groups (n = 10 per group). In Group 1, root canals were instrumented by the step-back technique with stainless steel K-Flexofile after coronal flaring. The remainders were instrumented by the crown-down technique with Profile (Group 2), ProTaper (Group 3) or K3 system (Group 4). All canals were prepared up to size 25 at the end-point of preparation and scanned again. Scanned images were processed to reconstruct three-dimensional images using three-dimensional image software and the changes of total canal volume were measured. Pre- and post-operative cross-sectional images of 1, 3, 5, and 7 mm from the apical foramen were compared. For each level, centering ratio were calculated using Adobe Photoshop 6.0 and image software program.

ProTaper and K3 systems have a tendency to remove more dentin than the other file systems. In all groups, the lowest value of centering ratio at 3 mm level was observed. And except at 3 mm level, ProTaper system made canals less centered than the other systems (p < 0.05).

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Comparison of shaping ability of rotary Ni-Ti file systems used by undergraduates: Mun-Seong Kang, Hyeon-Cheol Kim, Bock Hur, Jeong-Kil Park; J Korean Acad Conserv Dent 2006;31(1):1-10. Published online January 31, 2006; DOI: https://doi.org/10.5395/JKACD.2006.31.1.001

Abstract PDF PubReader ePub

The purpose of this study was to compare the shaping ability of three Ni-Ti file systems used by dental students or the experts and consequently to aid in choosing a proper systems for educational courses of dental students and beginners.

Fifty students and ten dentists who have clinical experience over two years prepared 180 simulated root canals in resin blocks with three Ni-Ti systems; ProFile® (PF), HeroShaper® (HS), K3^TM (K3).

After preparation, the Ni-Ti files were evaluated for distortion and canal preparation time was recorded. The images of pre- and post-instrumented canals were scanned and superimposed. Amounts of increased canal widths, deviation, and centering ratio were calculated at apical 1, 3 and 5 mm levels and statistical analysis was performed.

The results were as follows:

HS showed the shortest preparation time and instrumented canal width in K3 was significantly larger than other groups (P < 0.05).

At 1 and 3 mm levels, all groups had outward deviation. In student group, at the 1 mm level, PF had the least deviation (P < 0.05).

In the centering ratio, the PF had the best centering ability compared to the others at 5 mm level. At 1 and 3 mm levels, HS and PF had better abilities than K3. Student group had better ratio than the expert at 3 mm level with PF (P < 0.05).

Based on the results, it is surmised that the ProFile® is the safest and most ideal instrument for students and beginners.

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