The aim of this study was to compare the effects of anticurvature filing with stainless steel k-file versus nickel-titanium ProFile in the shaping of mesial root canals of extracted mandibular molars.

A total of 60 canals from 30 mesial roots of mandibular molar teeth were randomly assigned to three groups with n=20 each. They were prepared with different instruments and methods: The first group with stainless steel k-file and circumferential filing, the second with precurved stainless steel k-file and anticurvature filing and the third with ProFile (.06 taper) and anticurvature filing. Using a micro-computed tomography system (skyscan-1076, SKYSCAN, Antwerpen, Belgium), pre-and post-operative specimens were scanned. Subsequently, canal images were superimposed and changes in root dentin thickness were measured at distal side (danger zone) of the canal. The data was analyzed using a one-way ANOVA and the comparison of means was conducted using a post hoc multiple comparison Tukey test.

There were significant differences in the change of root dentin thickness at the 7.5~8.5mm level between group 1 and 2, 3.5~6mm level between group 1 and 3 and 3.5~6mm level between group 2 and 3(n=20, P<0.05).

This study investigated the effect of anticurvature filing method on preparation of the curved root canal using ProFile.

Thirty six resin blocks were divided equally into three groups by instrumentation motions: anticurvature filing motion, circumferential filing motion and straight up-and-down motion. Each resin block was sectioned at 8 mm level from the apex and at the greatest curvature of the canal and reassembled in metal mold by a modified Bramante technique. All groups were instrumented with the ProFile system. At each levels, image of sectioned surface were taken using CCD camera under a stereomicroscope at ×40 magnification and stored. Distances of transportation at the inner and outer area of curvature and the centering ratio were determined and compared by statistical analysis, along with the assessment of the increase of root canal cross-sectional area.

The results were as follows;

1. In all groups, there was no statistical difference in the mean increase of root canal cross-sectional area, the centering ratio, and the mean distances of transportation at the inner area of curvature at each level.

2. At 8 mm level from the apex, the mean distances of transportation at the outer area of curvature decreases in following order anticurvature filing motion, circumferential filing motion, straight up-and-down motion but, no significant difference at the greatest curvature of the canal among three groups.

Effect of anticurvature filing motion using ProFile does not seem to be different from other instrumentation motions at the inner area of curvature in curved root canal.

The aim of this study was to evaluate the shaping abilities of four different rotary nickel-titanium instruments with anticurvature motion to prepare root canal at danger zone by measuring the change of dentin thickness in order to have techniques of safe preparation of canals with nickel-titanium files.

Mesiobuccal and mesiolingual canals of forty mesial roots of extracted human lower molars were instrumented using the crown-down technique with ProFile, GT™ Rotary file, Quantec file and ProTaper™. In each root, one canal was prepared with a straight up-and-down motion and the other canal was with an anticurvature motion. Canals were instrumented until apical foramens were up to size of 30 by one operator. The muffle system was used to evaluate the root canal preparation. After superimposing the pre- and post-instrumentation canal, change in root dentin thickness was measured at the inner and outer sides of the canal at 1, 3, and 5 mm levels from the furcation. Data were analyzed using two-way ANOVA.

Root dentin thickness at danger zone was significantly thinner than that at safe zone at all levels (p < 0.05).

There was no significant difference in the change of root dentin thickness between the straight up-and-down and the anticurvature motions at both danger and safe zones in all groups (p > 0.05).

ProTaper removed significantly more dentin than other files especially at furcal 3 mm level of danger and safe zones (p < 0.05)

Therefore, it was concluded that anticurvature motion with nickel-titanium rotary instruments does not seem to be effective in danger zone of lower molars.