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).

The aim of this study was to evaluate the ability of newly marketed NRT instruments to maintain the original root canal configuration and curvature during preparation in comparison with the three existing instruments in simulated root canals.

Simulated canals in resin blocks were prepared with ProFile, K3, ProTaper, and NRT instrument (n = 10 canals in each case). Pre- and post-operative images were recorded, and assessment of canal shape was completed with a computer image analysis program. The data were analyzed statistically using the One-way ANOVA followed by Duncan's test.

The ability of instruments to remain centered in prepared canals at 1-, 2-mm levels was significantly better in ProFile groups than in other groups (p < 0.05). The change of centering ratio in NRT groups at 5-mm level was significantly greater than ProFile group and at 6- and 7-mm level than all other groups (p < 0.05).

Although the NRT system was comparable to other systems in regards to its ability to maintain the canal configuration of apical portion, this system was more influenced by the mid-root curvature due to its stainless-steel files for coronal preflaring.

The purpose of this study was to investigate influence of each file step of ProTaper® system on canal transportation.

Twenty simulated canals were prepared with either engine-driven ProTaper® or manual ProTaper®. Group R-resin blocks were instrumented with rotary ProTaper® and group M-resin blocks were instrumented with manual ProTaper®. Pre-operative resin blocks and post-operative resin blocks after each file step preparation were scanned. Original canal image and the image after using each file step were superimposed for calculation of centering ratio. The image after using each file step and image after using previous file step were superimposed for calculation of the amount of deviation. Measurements were taken horizontally at five different levels (1, 2, 3, 4 and 5 mm) from the level of apical foramen.

In rotary ProTaper® instrumentation group, centering ratio and the amount of deviation of each step at all levels were not significantly different (p > 0.05). In manual ProTaper® instrumentation group, centering ratio and the amount of deviation of each step at all levels except of 1 mm were not significantly different (p > 0.05). At the level of 1 mm, F2 file step had significantly large centering ratio and the amount of deviation (p < 0.05).

Under the condition of this study, F2 file step of manual ProTaper® tended to transport the apical part of the canals than that of rotary ProTaper®.

The purpose of this study was to compare the shaping ability of the two different Ni-Ti file systems and the two different engine systems in simulated canals.

A total of four groups of each 10 were tested. Each group was instrumented with HeroShaper®and Endo-Mate2® (Group HE), HeroShaper® and Tecnika® (Group HT), ProFile® and Endo-Mate2® (Group PE), and ProFile® and Tecnika® (Group PT).

Canal preparation time was recorded. The images of pre- and post-instrumented root canals were scanned and superimposed. The amounts of increased width and centering ratio were measured and calculated at apical 1, 3 and 5 mm levels.

These data were statistically analyzed with one-way ANOVA and Duncan's multiple range test

The results of this study were as follows;

1. Canal preparation time of HT group was the shortest (p < 0.05).

2. The amount of increased canal width in HE group was significantly larger than PT group at apical 1 mm level (p < 0.05). At apical 3 mm level, PT group was significantly smaller than other groups (p < 0.05). At apical 5 mm level, PE group was significantly larger than PT group (p < 0.05).

3. The amount of centering ratio in HE group was significantly larger than other groups (p < 0.05). At apical 5 mm level, HT group was significantly larger than PE group and PT group (p < 0.05).

Under the condition of this study, torque-controlled endodontic motor is safer than no torque controlled motor, especially when the active file is used.

The purpose of this study was to compare the shaping ability of the three ProTaper® instrumentation techniques in simulated canals.

Thirty resin blocks were divided into 3 groups with 10 canals each. Each group was instrumented with manual ProTaper® (Group M), rotary ProTaper® (Group R), and hybrid technique (Group H). Canal preparation time was recorded. The images of pre- and post-instrumented root canals were scanned and superimposed. The amounts of canal deviation, total canal width, inner canal width, outer canal width and centering ratio were measured at apical 1, 2, 3, 4, 5 and 6 mm levels.

1. Canal preparation time was the shortest in R group (p < 0.05).

2. The amounts of total canal width in R group was generally larger than the other groups, but no significant differences were observed except at the 1, 3 mm levels (p > 0.05).

3. The amounts of inner canal width in R group was larger than M group at the 1 mm level and H group was larger than R group at the 6 mm level (p < 0.05). The amounts of outer canal width in R group was larger than H group only at the 1 mm level (p < 0.05).

4. The direction of canal deviation in H, R group at the 1, 2, 3 mm levels was outward and that in M group at the 1, 2 mm levels was inward. The amounts of canal deviation in H group was larger than R group at the 6 mm level (p < 0.05).

5. The amounts of centering ratio in H group was larger than R group at the 6 mm level (p < 0.05).

The purpose of this study was to compare and evaluate the shaping ability of the three different Ni-Ti file systems used by undergraduate students.

Fifty undergraduate students prepared 150 simulated curved root canals in resin blocks with three Ni-Ti file systems - ProFile® (PF), Manual ProTaper® (MPT), Rotary ProTape® (RPT). Every student prepared 3 simulated root canals with each system respectively. After root canal preparation, the Ni-Ti files were evaluated for distortion or breakage. Assessments were made according to the presence of various types of canal aberrations. The pre- and post-instrumented canal images were attained and superimposed. The instrumented root canal width were measured and calculated for the net transportation (deviation) and the centering ratio.

Under the condition of this study, both ProTaper® systems allowed significantly more removal of root canal wall than the ProFile® system. In the important other aspects such as the centering ratio, there was no significant differences between the systems. Novice dental students were able to prepare curved root canals with any kinds of Ni-Ti file systems with little aberration and great conservation of tooth structure. Students want to learn effective methods and at the same time simple rotary procedures. The rotary ProTaper® systems were one of the most compatible to these students from the point of view of cutting ability. The ProFile® system was also compatible in safe and gentle shaping.