Cutting efficiency of four different rotary nickel: Titanium instruments.

AIM: The aim of this study was to evaluate the cutting efficiency of rotary nickel-titanium (NiTi) instruments K3, NiTi Tee, Profile, and Quantec with taper size 04/25.
MATERIALS AND METHODS: The number of samples was 10 for each group (n = 10). The cutting efficiency was measured by the mass loss from each acrylic resin block after instrumentation of a simulated canal using the Crown-down technique.
RESULTS: The analysis of variance (ANOVA) showed that there was a statistically significant difference among the studied groups. The Tukey's test showed that the acrylic resin blocks prepared with instruments K3 (0.00369 ± 0.00022), NiTi Tee (0.00368 ± 0.00023), and Profile (0.00351 ± 0.00026) presented the greatest mass loss, showing no statistically significant difference among them (P < 0.05). The lowest mass loss was found in the blocks prepared with Quantec instruments (0.00311 ± 0.0003) (P < 0.05).
CONCLUSIONS: It could be concluded that the K3, NiTi Tee, and Profile instruments presented a greater cutting efficiency than the Quantec instruments.

INTRODUCTION

Root canal preparation is performed with the use of endodontic instruments and auxiliary chemical substances, seeking to achieve cleaning, shaping, and disinfection, in order to fill the root canal later.[1]

The use of rotary nickel–titanium (NiTi) instruments has increased considerably due to their safe use, when used in accordance with the recommendations of their manufacturers, enabling the canal to be prepared more quickly, when compared with manual instruments, and even with better quality, in case of canals with severe curvatures.[23]

Cutting dentin is an important step during root canal preparation, as it is necessary to remove contaminated dentin and shape the canal to create conditions for it to be filled.[4] Due to elasticity, one could suppose that the cutting efficiency of NiTi instruments would be lower than that of steel instruments, because they undergo deflection or bend during contact with the dentinal surface.[5] However, studies have shown that NiTi instruments have a more efficient cutting capacity when compared with steel instruments.[67]

Although there have been significant advancements in rotary instrumentation, the influence of the rotary cutting instrument blade design is still controversial, with respect to the efficiency of their cleaning capacity.[89] Their cutting capacity results from a complex inter-relationship between different parameters, such as, the sectional design of the instrument, radial lands or active cutting blades, metallurgical properties,[9-11] and treatment of instrument surfaces with the incorporation of ions.[1213]

The aim of this study is to evaluate the cutting efficiency of different rotary NiTi instruments; that is, K3, NiTi Tee, Profile, and Quantec.

MATERIALS AND METHODS

Instruments

Forty instruments with taper size .04/25 were tested and divided into groups according to their brands (n = 10): K3 (Sybron-Endo, Orange County, CA, USA), NiTi Tee (Sjöding Sendoline, Kista, Sweden), Profile (Dentsply Maillefer, Ballaigues, Switzerland), and Quantec (Analytic Endodontics, Mexico). The characteristic of each instrument is shown in Table 1.

Table 1

Different instrument designs

Cutting efficiency

Forty acrylic resin blocks (Dentsply Maillefer, Petrópolis, RJ, Brazil), with simulated canals were used in this study, and for each block, a rotary instrument was used. The canals initially had a diameter of a caliber 10 instrument, having been manually prepared in this manner, up to a caliber 20 instrument, to their full extent, using the Crown-down technique, under irrigation with 5 ml distilled and deionized water, at every change of instrument.

Before any intervention, the blocks were washed in an ultrasonic vat, with distilled water and detergent solution, in the proportion of 10 : 1 for 20 minutes, dried with air jets, and placed in an oven at 60°C for 48 hours. The blocks were then weighed, to determine the Initial Weight (IW).

Instrumentation of each block with the analyzed instruments was performed by the same operator using a TC 3.000 engine (Nouvag, TCM Endo, Goldach, Switzerland) at a constant speed of 300 rpm. The instruments were introduced into the canal, inundated with 5 ml distilled and deionized water, until the working length was reached, which was 0.5 mm short of the total working length of the simulated canal. Each instrument remained at the working length for 5 seconds, and was then removed, while it was still running. The procedure of washing and drying the acrylic resin blocks was performed before the instruments were used, was repeated after instrumentation, to determine the Final Weight (FW), and also performed before the use of 04/25 instruments.

The cutting efficiency of each instrument was measured by means of measuring the acrylic resin block mass before and after using the .04/25 instruments (FW - IW), with the aid of a precision digital analytic balance (Bel Engineering, Italy), which was due to the quantity of material removed by instrumentation.

After obtaining the results, a statistical analysis was performed using the GraphPad Prism 4 (GraphPad Software Inc. 1992 – 2003) program. Having verified the normality of the sample, the analysis of variance (P < 0.05) was performed. The Tukey test was later used for multiple comparisons among the groups.

RESULTS

The means and standard deviations of mass loss from the acrylic resin blocks during instrumentation are shown in Table 2.

Table 2

Mean of acrylic resin mass removed from blocks during instrumentation. Given in grams

The results test showed that the acrylic resin blocks prepared with K3, NiTi Tee, and Profile instruments presented the greatest mass loss, showing no statistically significant difference among them (P < 0.05). The lowest mass loss was found in the blocks prepared with Quantec instruments (P < 0.05).

DISCUSSION

Biomechanical techniques for preparing root canals have evolved from manual methods to rotary techniques employing nickel-titanium instruments. Using NiTi rotary instruments for root canal instrumentation has enabled clinicians to create consistently tapered preparations more predictably and efficiently, while minimizing procedural mishaps, especially in curved canals.[14]

The greater cutting capacity of K3 instruments, as compared to Quantec, is possibly due to the unique cross-section design of K3, which has a positive angle of inclination for greater cutting efficiencies and ample radial lands and relief at the posterior extremity of the blade, to reduce friction.[15] Unlike Quantec, which has two cutting blades, K3 has a third radial land to help prevent entanglement.[16] Thus, the K3 instruments present excellent cutting capacity, as the debris resulting from its cutting action is easily displaced from the working area, and removed by the unique helical angle of this file.[17] Schafer and Florek[16] conducted a study in which they compared the efficiency of the K3 system and K-Flexofile files for smear layer removal. The authors obtained excellent results with the K3 system, although complete root canal cleaning had not been obtained.

The NiTi Tee instruments showed a cutting efficiency similar to that of the K3 and Profile instruments, and superior to that of the Quantec instruments. These instruments had a rounded, non-cutting tip and a positive cutting angle, without the presence of radial land. In addition, they had two 90° cutting blades that caused grooves (scratches) on the canal wall, which allowed the removal (drainage) of dentin scrapings and other debris resulting from instrumentation.[18] Jodway and Hülsmann,[18] comparing K3 and NiTi Tee instruments, observed that they were safe as regards their use, and had similar root canal cleaning and shaping capacities.

The good cutting capacity of Profile instruments could be attributed to the U-shaped, cross-sectional design, with radial lands and central parallel core. With a neutral and negative angle of inclination, this configuration allows widening action and dentin removal instead of cutting.[15] Thus, the debris is transported up to the coronal portion and effectively removed from the root canals.[19] Some studies have indicated that the positive cutting angle improves the cutting efficiency of the instrument.[517] Nevertheless, this is not the only determining factor for the cutting capacity of instruments,[15] as the Profile instruments, which have a negative cutting angle, presented the same efficiency as the K3 and NiTi Tee instruments and greater efficiency than the Quantec instruments, fitted with a positive cutting angle.

Quantec instruments have two cutting blades and a helical angle combined with spaces created in the instrument, which progressively increase as they withdraw from the cutting edge, creating a larger area of escape and allowing rapid debris removal from the canal. Thus, when activated, the instrument does not make a thread; therefore it does not stick to the canal walls, diminishing the risk of instrument fracture, because it has a less aggressive cut,[20] which possibly reduces its cutting power, as it presents the lowest cutting efficiency among the studied instruments.

The cutting capacity of endodontic instruments is an important factor to evaluate, as the preparation of dentinal walls, by eliminating contamination and shaping endodontic space, is an important step in successful endodontic therapy.[4] However, after debridement, in some oval and flattened root canals, the walls may not be prepared, irrespective of the debridement technique, leaving a smear layer, debris, and unprepared root canal walls.[2122] This complex anatomy may be considered as one of the main challenges in controlling the root canal infection, because the pulp tissue as well as the root dentin may conceal toxins and microorganisms, compromising the final result of endodontic treatment.[23] The use of endodontic irrigant solutions and ultrasound agitation,[24] or even the association of endodontic instruments[25] are ways that may improve the cleaning of roots that have a complex anatomy.

CONCLUSIONS

From the results of the present study it can be concluded that K3, NiTi Tee, and Profile instruments present a better cutting efficiency than the Quantec instruments.