Comparison of Single and Multi Ni-Ti Systems on Shaping

Objectives: The conventional root canal preparation is accomplished with multi stainless steel hand k-files (SSK). There are single file system and multi file system in Ni-Ti rotary shaping. The purpose of this study was to compare the single Ni-Ti system and multi files preparation system on the resin models.
Methods: Thirty six transparent resin models (Dentsply, USA) which had curved root canals of 30 degrees were used. Reciploc (VDW, Switzerland: RE) were used for single file system, and Twisted File (SybronEndo, USA; TF), ProTaper (Dentsply, USA; PT), and SSK were used under the multi-file system. A dentist shaped the resin models and the forces were measured at 100 ms intervals with a digital force gauge. Methylene blue liquids were injected before and after preparation of canal, and digital photographs were taken. The two photographs were superimposed. The changes after shaping were observed and measured the increment of inside and outside of the curvature at 1mm intervals form apical foramen to 9mm levels. The centering ratios were calculated by absolute value of division by inside and outside length. The data were analyzed by Games-Howell’s method after the one-way ANOVA.
Results: The apical transportations were seen in the 66% of SSK and 0% in Ni-Ti system. The increment of inside diameters of the canals after shaping on RE were greater than inside of other groups. The least changes at apical inside wall were in the SSK group. The increments of outside at 1 to 9mm from apical foramen using Ni-Ti were greater than SSK. The least centering ratios were in SSK. The pushing and pulling forces were greatest in SSK and were smaller RE, PT, in order of TF. The pushing forces indicated the significant differences between all groups, however the pulling forces showed the no significant between TF and PT.
Conclusions: The Ni-Ti rotary files are efficient instruments for shaping of curved canal and need smaller forces than hand stainless files.