Luiz Fernando FARINIUK1
Danilo M. Zanello GUERISOLI2
João Vicente Baroni BARBIZAM2
Jesus Djalma PÉCORA2
Manoel D. SOUSA-NETO1
1Faculty of Dentistry, University of Ribeirão Preto
(UNAERP), Ribeirão Preto, SP, Brazil
2Faculty of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
Correspondence: Prof. Dr. Manoel D. Sousa-Neto, Rua Cav. Torquato Rizzi, 1638, ap. 43, 14020-300 Ribeirão Preto, SP, Brasil. e-mail: email@example.com
Braz Dent J (2001) 12(1): 39-42 ISSN 0103-6440
INTRODUCTION | MATERIAL AND METHODS | RESULTS | DISCUSSION | RESUMO | REFERENCES
With the development of rotary nickel-titanium files and their applications in Endodontics, the concepts of root canal preparation have changed. The objective of this research is to evaluate the transportation of simulated root canals caused by stainless steel ENDOflash rotary files compared to nickel-titanium ProFile files (.04, .06 and Orifice Shapers). Twenty-four simulated root canals with a 30o curvature were randomly divided into 2 groups and prepared with ENDOflash or ProFile files according to manufacturers' instructions. Comparison between the simulated root canals before and after instrumentation showed significant differences (p<0.001) between the groups, with greater transportation observed with ENDOflash files. One case of deformation was observed with a ProFile instrument (#20 / .04) and there were no fractures.
Key Words: root canal preparation, nickel-titanium files, ENDOflash, ProFile.
The innovative spirit of researchers has not been able to modify the Endodontic paradigm, based on cleaning, disinfecting and sealing of the root canal system. Schilder (1) described the concepts of cleaning and shaping associated with tridimensional obturation, where the appropriate form of the root canal for sealing with gutta-percha is "telescopic". Technique refinements, development of new instruments and materials represent undeniable progress, but the basic concepts that rule Endodontics have been the same for centuries. One of the greatest challenges today is still the instrumentation of curved root canals with minimum alteration of their original path.
Stainless steel files are the most popular, mainly used in manual techniques. Nickel-titanium files, that show special characteristics of flexibility, are slowly conquering more territory in Endodontics.
The constant search for automation of root canal shaping seeks to reduce patient and clinician stress, as well as to preserve the essential characteristics of the canal shape. Many attempts in this direction have failed, because the mechanization of instrumentation often results in loss of instrument control within the root canal, leading to deformation. However, with the rotary nickel-titanium files, a new phase for automation of root canal shaping has begun, due to the characteristics of the metallic alloy. These instruments assure a safe, adequate and quick shaping of the root canal system, with greater control for the clinician. With the techniques proposed for reverse enlargement of the root canal, such as the crown-down (2) and step-down (3) techniques, the risk of accidents during endodontic therapy decreased. The ProFile System (Maillefer, Ballaigues, Switzerland), with a "U" shaped cross-section, three radial lands and 4% or 6% taper, focuses on this principle. The files are operated with high torque, low-speed electric motor, with a constant rate of 150 to 350 rpm.
Recently, a new concept of mechanical modeling of the root canal has arisen, the KaVo ENDOflash (KaVo, Biberach, Germany), that generates a limited torque rotation transmitted to "high grade steel" files that, according to the manufacturer, prevents fractures during root canal shaping.
The objective of this research is to evaluate transportation, in simulated root canals, caused by stainless steel ENDOflash files compared to nickel-titanium ProFile files.
MATERIAL AND METHODS
Simulated Canal Construction
Twenty-four simulated root canals in resin blocks were constructed following the technique described by Dummer et al. (4), with modifications. On a large shallow tray, 20 mm of agar-agar was poured and let to solidify. The tips of long anesthesia needles were removed, pre-curved in 30o and placed perpendicularly inside the agar layer, with the tip end facing up. A disposable, 1-cm sided square spectrophotometer cuvette (LIP Equipment Ltd., West Yorkshire, UK) had its bottom end removed and placed on the agar layer, with the needle inside it. A new agar layer was poured to seal the base of the cuvette. Epoxy resin (Stycast 1266, Hitek Electronic Materials Ltd., North Lincolnshire, UK) was poured inside the cuvette, immersing the needle into it. After 24 h, they were pulled from inside the resin and the cuvette was removed from the body of the simulated canal.
After polishing both ends of the resin block, a Peeso bur activated by a low speed motor was used to prepare the first 8 mm of the simulated canal, with abundant irrigation with water to remove debris. The artificial canals were then filled with India ink, scanned with a table scanner (Genius, Taiwan) and the image stored in a computer. After instrumentation, canals were again scanned and the images superimposed.
ENDOflash files are made from "high grade steel" stainless steel, being classified as K-type files with a non-cutting tip and available in sizes 15 to 80, and 21, 25 and 31 mm in length.
ProFile files used in this experiment were from the ProFile .04/.06 & Orifice Shapers set. These instruments are made of nickel-titanium alloy, having a non-cutting tip and "U" shaped cross section with 3 radial lands that keep the instrument centered in the root canal.
Root Canal Instrumentation
Preparation of the 24 simulated root canals, randomly separated into 2 groups, was performed by a single operator.
Group 1 was instrumented with ENDOflash files, activated by an ENDOflash LUX3 3640L handpiece (KaVo, Biberach, Germany) with a 40 times reduction factor, coupled to an electric TC 3000 motor (Nouvag, Goldach, Switzerland). The final rotation speed obtained was 250 rpm.
An initial flush of 1 ml of distilled water was followed by exploration of the simulated canal with a #10 file. Then, using the ENDOflash files, a crown-down technique was performed, starting with a #55 file up to a #35 file, which reached the working length. The apical stop was enlarged to a #40 file. Irrigation with 1 ml distilled water was performed at each instrument change.
Group 2 was shaped with ProFile files, activated by a 975 AE handpiece (W&H, Salzburg, Austria) with a 20 times reduction, coupled to the same electric motor as group 1. After irrigation with distilled water and exploration of the simulated canal, the operator followed the manufacturer's technique for narrow and curved canals, in the following sequence: Orifice Shapers #3 and #2, ProFile files .06/25, .06/20, .04/25 and .04/20.
Irrigation with 1 ml distilled water was performed at each instrument change.
The initial and final images of the root canals were superimposed. Measurements at 2, 4, 6, and 8 mm from the apex at the inner and outer aspects of the curve were performed, and analysis performed using the free UTHSCSA ImageTool program version 1.27 (developed at the University of Texas Health Science Center at San Antonio, TX; available from the Internet by anonymous FTP from ftp://maxrad6.uthscsa.edu). Figure 1 illustrates how the measurements were made.
Recording, Storage and Data Analysis
Measurements at the different lengths from the apex, at the inner and outer aspects of the curve, were recorded and submitted to statistical analysis (Mann-Whitney U test). Time spent to shape the canals, deformations and fractures of the instruments and loss of working length were also recorded.
Data analysis of the outer aspect of the curve showed significant differences (p<0.001) between the files. Stainless steel ENDOflash files caused more deformation of the simulated canal than the nickel-titanium ProFile files. However, no statistical differences were found (p>0.05) between the two groups at the inner aspect of the curvature.
Figures 2 and 3 are graphs plotted from the mean width of resin removed by each file type, at the outer and inner aspects of the curve, respectively.
Mean time for canal preparation was 3'50" for Group 1 and 4'01" for Group 2. No cases of fractured instruments were recorded. However, one ProFile instrument (.04/20) became permanently distorted. The working length was always maintained in both groups.
Instrumentation of curved root canals is difficult and a challenge to endodontists. In order to improve results, many techniques, equipment and materials have been suggested in the literature. The instruments have a great influence on the final shaping of the root canal in these cases.
The objective of this research was to compare, under controlled laboratory conditions, the action of ENDOflash and ProFile systems in epoxy resin simulated root canals (5,6). If natural teeth were used, canals could not be standardized.
Stainless steel instruments have been used for a long time, and it has been proven that they cause alterations in the original path of curved canals (7,8). Alteration of the tip of these instruments has been suggested in order to decrease such deformations (9,10).
This new generation of nickel titanium instruments has been researched extensively, confirming the efficiency of these tools in maintaining the original path of the root canal when compared to stainless steel files (11,12).
Aiming at faster and better endodontic therapy, the nickel-titanium rotary root canal files should be used with low speed, high torque motors that promote 360º spins in the root canal, causing less deformation of the canal walls, as observed in this study. The wear of the simulated root canal walls instrumented with these files was lower than with the stainless steel files. The outer aspect of the curve suffered more wearing than the inner aspect, a fact that was also observed by Bryant et al. (13).
The ENDOflash system was developed for the use of flexible stainless steel files, with a higher cutting efficacy, durability and lower risk of fractures. The wearing of the outer aspect of the curve was higher than that observed with nickel-titanium files. The inner aspect of the curvature, however, was similar.
Torque control proved to be efficient in Group 1, stopping the file before clogging inside the canal.
When the file stuck inside the canal, reverse rotation was applied until it was released. This occurred in 6 specimens from Group 2 with file .06/25. Caution must be exercised when using a motor without torque control, since the risk of fracture is high if the file becomes stuck in the canal and the pedal is not released immediately.
Schäfer et al. (14), using simulated root canals to compare the action of nickel-titanium and stainless steel instruments, reported that alterations in canal shape occurred in all cases and that better results were obtained with flexible, non-cutting tip instruments.
Greater transportation of the original path of the canal with ENDOflash files may be due to the technique recommended by the manufacturers. When ENDOflash was used, canals were enlarged up to a #40 file, whereas canals prepared with ProFile instruments received a #20, taper .06 file as the last instrument.
Additional research is necessary to test the performance of nickel-titanium files with the ENDOflash handpiece, as well as other studies using natural teeth, where clinical conditions can be reproduced in spite of other undesirable variables.
Fariniuk LF, Baratto-Filho F, Guerisoli DMZ, Barbizam JVB, Pécora JD, Sousa-Neto MD. Capacidade de modelagem das limas ENDOflash em canais simulados. Braz Dent J 2001;12(1):39-42.
Com o desenvolvimento das limas rotatórias NiTi e suas aplicações
em Endodontia, o conceito de preparo biomecânico do canal radicular
tem mudado. O objetivo desta pesquisa foi avaliar o transporte de canais
simulados causado pelas limas de aço inoxidável ENDOflash
em comparação com as limas de níquel
titânio ProFile .04/.06 & Orifice Shapers. Vinte e quatro canais simulados em resina com curvatura de 30o foram divididos em dois grupos, preparados com limas ENDOflash ou com o sistema ProFile. Em ambos os grupos foram seguidas as técnicas recomendadas pelos fabricantes. A respeito do transporte do canal, diferenças significantes (p<0,001) foram observadas entre os grupos instrumentados com o sistema ENDOflash e ProFile, com maior deformação dos canais instrumentados com as limas ENDOflash. Houve um caso de deformação do instrumento ProFile (#20/.04) e nenhum caso de fratura. Não foi observada perda do comprimento de trabalho.
Unitermos: preparo químico-mecânico, limas de níquel-titânio, ENDOflash, ProFile.
1. Schilder H. Filling the root canal in three dimensions. Dent Clin North Am 1967;11:723-744.
2. Marshall FJ, Pappin J. A crown-down pressureless preparation root canal enlargement technique. Manual. Portland, OR: Oregon Health Sciences University. 1980.
3. Goerig LA, Michelich RJ, Schultz H. Instrumentation of root canals using the step-down technique. J Endodon 1982;8:550-554.
4. Dummer PMH, Alodeh MHA, Al-Omari MAO. A method for the construction of simulated root canals in clear resin blocks. Int Endod J 1991;24:63-64.
5. El Deeb ME, Boraas JC. The effect of different files on the preparation shape of severely curved canals. Int Endod J 1985;18:1-7.
6. Thompson SA, Dummer PMH. Shaping ability of ProFile .04 Taper Series 29 rotary nickel-titanium instruments in simulated root canals. Int Endod J 1997;30:8-15.
7. Weine FS, Kelly RF, Lio PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. J Endodon 1975;1:255-262.
8. Alodeh MHA, Dummer PMH. A comparison of the ability of K-files and Hedstrom files to shape simulated root canals in resin blocks. Int Endod J 1989;22:226-235.
9. Al-Omari MAO, Dummer PMH, Newcomb RG. Comparison of six files to prepare simulated root canals. Part 1. Int Endod J 1992;25:57-66.
10. Al-Omari MAO, Dummer PMH, Newcomb RG. Comparison of six files to prepare simulated root canals. Part 2. Int Endod J 1992;25:67-81.
11. Zmener O, Balbachan L. Effectiveness of nickel-titanium files for preparing curved root canals. Endod D Traumat 1995;11:121-123.
12. Gambill JM, Alder M, Del Rio CE. Comparison of Ni-Ti and stainless steel hand files using computed tomography. J Endodon 1996;22:369-375.
13. Bryant ST, Thompson AS, Al-Omari MAO, Dummer PMH. The shaping ability of ProFile rotary nickel-titanium instruments with ISO sized tips in simulated root canals: Part 2. Int Endod J 1998;31:275-281.
14. Schäfer E, Tepel J, Hoppe W. Properties of endodontic hand instrument used in rotary motion. Part 2. Instrumentation of curved canals. J Endodon 1995;21:493-497.
Accepted June 2, 2000
Braz Dent J 12(1) 2001