The shaping effects of three rotary Nickel-Titanium systems in simulated curved canals

الملخص EN

Background: The purpose of this study is to compare three rotary endodontic nickel-titanium systems (ProFile, GT and ProTaper) with stainless steel hand K-flexofile in simulated curved canals at different levels, this includes: Incidence of canal aberrations (apical zipping associated with elbow, ledge and perforation), Changes of working length, Preparation time for each system and Breakage and permanent deformation of instruments.

Materials and method: Eighty simulated curved canals made of clear polyester resin were used to assess instrumentation.

The acrylic blocks were divided into four groups, 20 simulated canals for each group were enlarged from #10 to # 25.

In the first three groups all NiTi rotary instruments were set into a permanent rotation with a 16:1 reduction hand piece powered by a torque-limited electric motor set at 300 rpm.

All the instruments were used in a crown down manner using a gentle in-and-out (pecking) motion.

In the fourth group the simulated canals were instrumented with stainless steel K-flexo-files by using balanced force technique.

Each simulated canal was filled with a drawing ink using to increase the color contrast for photographic documentation.

Photographs of the unprepared canals were taken by the aid of stereomicroscope and digital camera at magnification of 40 times.

When instrumentation of the canals was completed, the canals were injected again with the drawing ink and the image procedure is repeated.

Preand postoperative digital photographs of the resin blocks were accomplished using Adobe Photoshop CS2 software program.

At this stage the amount of resin removed i.e.

the difference between the canal configuration before and after instrumentation was determined for both the inner and the outer side of the curvature at five reference points.

Assessments were made under the stereomicroscope according to the presence of different types of canal aberrations (apical zip associated with elbow, ledge and perforation).

The changes of working length were determined by subtracting the length of master apical file from the original length (16mm).

The time taken to prepare each canal was recorded in minutes with the aid of a stop timer.

Throughout the study a record was kept of the numbers and sizes of instruments that fractured or became permanently deformed during use.

Results: there were significant differences among the groups, even though more zips and ledge were created with K-flexofile followed by ProTaper.

NiTi instruments caused a significantly greater loss of working length than K-flexofile; while there was no significant difference among NiTi groups.

The shortest mean of preparation time was recorded when ProTaper were used; while the longest time was documented for GT.

No permanent deformation occurred with NiTi groups.

None of the stainless steel K-flexofile was separated.

Conclusion: K-flexofiles created significantly more aberration than NiTi systems.

ProTaper caused more morphological changes compared with ProFile and GT systems.

Small mean changes in working length occurring with rotary NiTi instruments.

The preparation time of ProTaper was faster than with other groups.

NiTi instruments may be more susceptible to separation than stainless-steel instruments.

Most failures of the hand stainless-steel files were deformations rather than fractures.

Fracture rate was approximately 30% for ProTaper, 16.6% for GT and 8.3% for Profiles.