Relationship between file size and stiffness of nickel titanium instruments

Abstract – The purpose of this study was to evaluate the relationship existing between file size and stiffness for 3 endodontic files made of nickel titanium. Three groups of instruments with different cross-sections were tested: a triangular cross-section, a square cross-section and a modified triangular cross-section. The instruments were tested from size 15 to size 40 or 60 according to ANSI/ADA specification n°28 for binding moment evaluation. There was a statistically significant difference between the 3 groups: the square cross-section K files presented a larger bending moment than the triangular cross-section K files, which presented a larger bending moment than the modified cross-section K files. Like the stainless steel instrumens, there was an exponential relationship between file size and bending moment for triangular and square cross-section K files, but a linear relationship between file size and bending moment for the files with a modified triangular cross-section.     

A comparison of bending and torsional properties of K-files manufactured with different metallic alloys

The purpose of this study was to compare bending (bending moment) and resistance to fracture by twisting (torsional moment and angular deflection) of triangular cross-section K-files made of either nickel titanium (Nitiflex, Naviflex), titanium (Microtitane) or stainless steel (Flexofile, Flex-R). A total of 200 files were tested, 10 instruments for each type from size 25 to 40, according to ANSI/ADA specification no. 28 and ISO reference no. 3630. Files made of nickel titanium, especially Nitiflex, were the most flexible. Stainless steel instruments presented a higher bending moment than files made of nickel titanium and titanium, particularly Flex-R sizes 35 and 40. With regard to resistance to fracture, measured by angular deflection at the failure point, Flexofile followed by Flex-R were the most resistant to fracture and Nitiflex were the least resistant. Differences in angular deflection among file groups were greater than those for torsional moment. Thus, it seems that angular deflection is a more specific measurement for assessing resistance to fracture by twisting.     

Cutting efficiency of K-files manufactured with different metallic alloys

Abstract The aim of this study was In compare, in vitro, the machining efficiency of different triangular cross-section K-files made of nickel titanium (Nitiflex, Naviflex), titanium (Microtitane), and stainless sleel (Flexofile, Flex-R). Ten instruments of each K-file From size 25 to 40 were tested. The cutting efficiency was assessed in a linear motion using an indentation caliper lo measure the depth of grooves. The load applied (in grams) was equal to the ISO file size. Each file was allowed lo do 100 back-and-forward movements. Files made of stainless steel were the most effective, in particular Flexofile. There were statistically significant differences between Flexofilc and Flex-R in all sizes. In the group of nickel titanium instruments, Niliflex was significantly more efficient than Naviflex in all sizes. The machining ability of titanium files was higher than thai of Naviflex but lower than that of Nitiflcx and stainless sleel files.     

Machining efficiency of nickel-titanium K-type files in a linear motion

The purpose of this study was to compare, in vitro, the machining efficiency of four brands of nickel-titanium files and two brands of stainless steel K-type files. Instruments sizes 15 to 40 were tested in a linear motion simulating the clinical motion used to remove a file from the canal. The tips of the loaded files were in contact with a resin block. The load applied increased with file size. An indentation varnish caliper was used to measure the depth of the groove after 100 back-and-forward motions. The stainless steel instruments with a triangular cross-section were more efficient than the stainless steel instruments with a square cross-section. There was a significant discrepancy between the machining ability of the nickel-titanium K files. The Maillefer instruments were the most efficient.     

Comparison of six files to prepare simulated root canals. Part 1

A total of 300 simulated root canals of various angles and positions of curvature in clear resin blocks were prepared by hand using either K-files, K-Flex files, Flexofiles, Flex-R files, Hedstrom files or Unifiles. Each file type was used to prepare 50 canals employing a linear filing motion and an anticurvature stepback technique. Part 1 of this two-part report describes the efficacy of the files in terms of preparation time, instrument failure, loss of canal length and weight loss from the blocks. Two-way analysis of variance confirmed that there was significant variation for each parameter between instruments, between canal types, and with interaction between instruments and canal types. Overall, preparation with Hedstrom files was significantly quicker than with any other file, whilst preparation with K-files and K-Flex files took significantly longer. Fracture and deformation of instruments occurred substantially less often with Flex-R and Hedstrom files, but significantly more often with Unifiles. Loss of working distance occurred with all file types, but was significantly greater in canals prepared with K-files. Unifiles and Hedstrom files were responsible for significantly more weight loss than the other files, whilst K-files produced significantly less weight loss. Canals with rough undulating walls were created most often by Hedstrom files and Unifiles. Overall, under the conditions of this study, Flexofiles, Flex-R files and Hedstrom files appeared to be substantially more effective than K-files, K-Flex files and Unifiles.     

Cutting pattern of nickel-titanium files using two preparation techniques

Abstract— The aim of this study was to examine the cutting patterns of recently introduced nickel-titanium endodontic files and compare them with similarly shaped stainless steel files using both balanced-force and stepback techniques. Simulated canals were constructed in resin blocks with 40° curvature. Fifty blocks were prepared by a balanced-force technique: 25 with Nitiflex (Maillefer) and 25 with Flexofiles (Maillefer) to a master apical file size 40. Fifty blocks were prepared by a stepback technique: 25 with Nitiflex and 25 with Flexofiles to a master apical file size 30. Composite prints were made of pre- and post-instrumentation canals using a computerized imaging system. The amount of material removed from the inner and outer canal curvatures was measured at eight levels in the apical 11 mm of the canal. The results were analysed by Krus-kal-Wallis ANOVA. Using the balanced-force technique, Nitiflex files removed less material on the outer curve apically and less on the inner curve mid-canal (P<0.05), while Flexofiles caused more apical transportation. In the stepback technique, the Nitiflex files removed more material from the outer curve apically (P<0.05); the Flexofiles removed more material along the entire inner curve (P<0.05), and maintained canal curvature better than Nitiflex files. It appeared preferable to use Nitiflex files in a balanced-force technique, and Flexofiles in a filing technique as stainless steel files can be precurved.     

Shape of the root canal after ultrasonic instrumentation with K-Flex files

Abstract This study investigated the feasibility of using K-Flex files with the Cavi-Endo ultrasonic unit. The effectiveness of the K-Flex files in shaping canals was compared with the ultrasonic Cavi-Endo K-files. Simulated curved canals in clear resin blocks were instrumented ultrasonically using the 2 file types. Pre- and postinstrumentation photographs were taken and the following were evaluated: apical and coronal areas, the incidence of the narrowing of the canals coronal to the apical transport (elbows). Displacement amplitude measurements were carried out in order to see any relationship between the incidence of elbows and displacement amplitudes of the files. The results indicated that the K-Flex files were more efficient than the ultrasonic K-files and resulted in less elbow formation. No direct relationship was observed between displacement amplitudes and the incidence of elbow formation. It is suggested that the manufacturers of ultrasonic units consider different file designs.     

Effectiveness of different endodontic files for preparing curved root canals: a scanning electron microscopic study

Abstract In this study, the effect of using four endodontic files from different manufacturers on the final shape of 80 prepared curved root canals of extracted single-rooted teeth were comparatively analyzed with scanning electron microscopy. The instruments tested were Tri-files, Flex-R files, Flexofiles and conventional K-type files. All files were used with in and out linear movements with a circumferential motion starting with a size 15 file. Final preparation of the apical thirds was performed with a size 30 file. Shaping effectiveness of the tested files was qualitatively evaluated in terms of respect for conservation of the apical constriction and the presence or absence of ledging, specially in the apical third of the root canals. A well-centered and tapered preparation without apical transportation or ledging was detected when Tri-file or Flex-R files were used. Conversely, the use of Flexofile or conventional K-type files resulted in frequent alteration of the initial pattern of the root canals, showing an hourglass preparation with alteration of the apical constriction and ledge formations.     

Relationship between design features of endodontic instruments and their properties. Part 3. Resistance to bending and fracture

Stainless-steel prototypes characterized by five different cross-sectional shapes (square, triangular, rhomboidal, "S"-shaped, and the cross-sectional design of H-type files) and three different number of flutes (16, 24, and 32) were used for investigation of the relationship between design features and the resistance to bending and fracture of root canal instruments. Both resistance to bending (bending moment) and resistance to fracture (angular deflection and torque) were determined in accordance to ISO 3630-1. Numbers 15, 25, and 35 prototypes were tested with a sample size of 10 instruments each. Whereas prototypes with the rhombus-shaped cross-sectional design displayed the lowest resistance to bending, those of the square cross-section showed the greatest. In general, S-shaped prototypes and those with the H-type cross-section achieved lower angular deflection than all other prototypes, whereas those with the triangular cross-sectional shape and 32 flutes reached the greatest angular deflection. Overall, rhombus-shaped prototypes showed lower torque values than all other prototypes. Results indicate that bending and torsional properties of endodontic instruments are mainly influenced by their cross-sectional design. Moreover, these properties are also affected by the number of flutes and the manufacturing process (twisted or milled) of endodontic instruments.     

Torsional and bending properties of stainless steel and nickel titanium Canal Master U and Flexogate instruments

Abstract The purpose of this Study was to assess and to compare the torsional and bending properties of the Canal Master U (CMU) and Flexogate instruments made of stainless steel and nickel titanium. The bending moment, the torsional moment and angular deflection were measured according to ANSI/ADA specification number 28 and ISO reference number 3630. Ten instruments of each size, sizes 25 to 40 were used for each test. Nickel titanium instruments were significantly more flexible than stainless steel files. With regard to the torsional moment, values obtained were below the standards in all sizes except stainless steel CMU sizes 25, 35 and 10, and nickel titanium CMU size 25. Nickel titanium instrument also showed the highest angular deflection values. There were statistically significant differences between nickel titanium files and stainless steel Flexogates and between stainless steel Flexogates and stainless steel CMU. Based on these findings, the use of nickel titanium CMU and Flexogates is encouraged. Given the perceived advantages of both CMU and Flexogate instruments over conventional files for canal preparation, it would appear desirable to have the torque resistance of these instruments improved.     

Dynamic fracture of hybrid endodontic hand instruments compared with traditional files

The purpose of this study was to analyze in vitro the dynamic fracture of some endodontic hand instruments. The K file and H file were tested as reference traditional files; the K-Flex, Flexofile, Unifile, and Helifile were tested as newly developed hybrid instruments. The files were mounted in a lathe and rotated with cyclical axial motion in the lumen of a curved tempered steel groove until failure occurred. The results showed that the life span of instruments, the distance between the instrument tip and the rupture point, and the resistance to fracture were dependent on the size and design of the instruments. Moreover, scanning electron microscopic photographs revealed two types of breakage patterns. The K file, H file, Unifile, and Helifile showed a distinct fracture starting point with crack striations and ductile fractures. The K-Flex and Flexofile showed only plastic deformations and axial fissures.     

Machining efficiency of Flex-R, K-Flex, Trio-Cut, and S Files

Many root canal instruments with several different designs have been introduced during recent years. This article evaluates the machining properties of four such instruments: the Flex-R, K-Flex, Trio-Cut, and S file. There are large variations in the machining properties of these instruments. The results are comparable to findings when evaluating conventional root canal files which show that the Hedstrom file is much more efficient when considering removal of material than the K file. The Flex-R file, K-Flex file, and Trio-Cut file are similar in design. The two former brands perform in a similar fashion, while the Trio-Cut file is less efficient than any of the evaluated K files. The S file performs as a Hedstrom file which can be expected from its similarity in design to that instrument.     

A survey of interfacial forces used during filing of root canals

Abstract – The pattern of dentine removal during endodontic instrumentation is influenced by many factors including the interfacial forces applied by the operator. The aim of this study was to investigate the influence of operators and different sizes and types of instruments on the magnitude of these interfacial forces. Single‐rooted teeth were mounted on a cantilevered aluminium beam to which two pairs of single element strain gauges were joined in a half‐bridge configuration and mounted at right angles to each other. The strain gauges were connected to an analogue‐to‐digital converter fitted in a micro‐computer via conditioning amplifiers. This enabled strains to be recorded over a period of time. Twenty operators instrumented root canals using a series of hand instruments for 1 min each. The mean interfacial forces used by operators demonstrated a wide variation ranging from 9.06 g to 149.42 g (range of forces from 0–331 g) but there was a consistency in the relative magnitude for each operator. The 20 operators could be divided into 13 groups which were significantly different (α=0.05) from each other. There were significant differences (α=0.05) between the forces used for each of the K‐Flex files (15, 25, 35, 45, and 70), the force increasing with the file size. There was also a significant difference (α=0.05) in the forces used between the Flexofile (#25) and the #25 K‐Flex and Hedström files. However, there was no significant difference between the K‐Flex and Hedström files.     

Comparison of six files to prepare simulated root canals. Part 2

A total of 300 simulated root canals of various angles and positions of curvature in clear resin blocks were prepared by hand using either K-files, K-Flex files, Flexofiles, Flex-R files, Hedstrom files or Unifiles. Each file type was used to prepare 50 canals employing a linear filing motion and an anticurvature stepback technique. Part 2 of this two-part report describes the efficacy of the files in terms of the prevalence of canal aberrations, the amount and direction of canal transportation and the overall postoperative canal shape. Hourglass shaped canals were found in 4.5% of curved canals, the majority of these being created by K-files and K-Flex files. Perforations were seen in 6.3% of curved canals, the majority being produced by Flex-R files and K-files. Excessive removal of material from along the inner aspect of the canal curve occurred in 10.4% of canals, by far the majority being created by Hedstrom files. Transportation of canals was a consistent finding with all instruments. Two-way analysis of variance revealed how significant differences in the absolute magnitude of transportation occurred between instruments, between canal types and by an interaction between instrument and canal type. In general, transportation was towards the outer aspect of the canal curve at the end-point of preparation and the zip and elbow, but towards the inner aspect at the beginning of the curve. Further towards the orifice, transportation reverted to the outer aspect of the canal curve.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of stainless steel Flexofiles and nickel-titanium NiTiFlex files during the shaping of simulated canals

The aim of this study was to compare the shaping ability of stainless steel Flexofiles and nickel-titanium NiTiFlex files during the preparation of simulated canals in resin blocks. A total of 80 canals with various angles and position of curvature were prepared by one operator using either Flexofiles or NiTiFlex files in a modified double-flared technique with balanced force method of instrument manipulation. Canal shape was assessed at two stages during the procedure, after apical enlargement to size 30 and subsequently at size 45. Pre- and post-operative images of the canals, were taken with a video camera and stored and manipulated in a computer with image analysis software. The presence of canal aberrations and the amount of material removed as a result of preparation were determined from composite images of superimposed pre- and post-operative views. Canal preparation using NiTiFlex files was significantly quicker (P<0.0001) up to size 30. More instrument failures occurred with Flexofiles (12) compared to NiTiFlex files (7) but there were no statistically significant differences between file type, instrument size or canal shape. Flexofiles created significantly more zips, perforations and ledges; there were no differences in terms of danger zones. Overall, canals prepared with Flexofiles were significantly wider because more material was removed from the outer aspect of the curve at the end-point of preparation and from the inner aspect of the curve at the apex. Under the conditions of this study, preparation with NiTiFlex files was more effective and produced more appropriate canal shapes than Flexofiles.     

Accuracy of the KontrolFlex AccuFile when used with the Root ZX electronic apex locator in vitro

The aims of this study were to determine the efficacy of the KontrolFlex™ Accufile™ compared to the READY•STEEL™ Flexofile® using an electronic apex locator and to evaluate the instrument's design via scanning electron microscopy. Actual canal lengths of 30 extracted teeth were determined under magnification. An alginate model was used to determine experimental canal lengths with the Root ZX II apex locator (EAL) and size #10 Accufiles and Flexofiles. Differences between actual lengths and experimental lengths were compared with Student's t test. The average experimental lengths were short of the actual length by −0.10 mm (±0.34) and −0.12 mm (±0.16) for the Accufile and Flexofile, respectively with no statistical difference (p > 0.05). SEM images revealed similar non-cutting Batt tips and a square cross-section for the Accufile and triangular for the Flexofile. Both files provided similarly high levels of reliability when used with the Root ZX II EAL.     

Effectiveness of nickel-titanium files for preparing curved root canals

Abstract In this study, the effect of 2 different endodontic files on the final shape of curved root canals of extracted single rooted teeth were examined in the scanning electron microscope. The instruments tested were a newly designed nickel-titanium endodontic file and a conventional K-type file. The files were used with in and out linear movements with a circumferential motion starting with a size 15 file. Final preparation of the apical thirds of the canals was performed with a size 35 file. Shaping effectiveness of the tested instruments was evaluated in terms of respect for conservation of the apical constriction and the presence or absence of ledging. Our observations revealed that more centered and tapered preparations were obtained with the use of the nickel-titanium files than with the conventional K-type files.     

Torsional and stiffness properties of nickel–titanium K files

The purpose of this study was to compare stiffness and resistance to fracture of four brands of nickel titanium K files. Instruments of sizes 15 to 40 were tested according to ANSI/ADA Specification No. 28. Resistance to fracture was determined by twisting and measuring the maximum torque and angular deflection at failure. Stiffness was determined by measuring the moment required to bend the instrument 45°. The permanent deformation angle remaining between the tip and the flutes of the instruments after bending ceased was also recorded. Nickel titanium K files satisfied and far exceeded specification standards for stiffness. They also satisfied and exceeded the standards for angular deflection at failure. They met or exceeded the maximum torque at failure standards in all sizes except for the size 40 of the Maillefer Niti, and the size 30 of the Mac Spadden Niti. Nickel titanium K files presented a null permanent deformation angle. Clinical studies are required to evaluate the influence of low bending moment on other properties such as breakage and canal transportation.     

A survey of interfacial forces used during filing of root canals

The pattern of dentine removal during endodontic instrumentation is influenced by many factors including the interfacial forces applied by the operator. The aim of this study was to investigate the influence of operators and different sizes and types of instruments on the magnitude of these interfacial forces. Single-rooted teeth were mounted on a cantilevered aluminium beam to which two pairs of single element strain gauges were joined in a half-bridge configuration and mounted at right angles to each other. The strain gauges were connected to an analogue-to-digital converter fitted in a micro-computer via conditioning amplifiers. This enabled strains to be recorded over a period of time. Twenty operators instrumented root canals using a series of hand instruments for 1 min each. The mean interfacial forces used by operators demonstrated a wide variation ranging from 9.06 g to 149.42 g (range of forces from 0-331 g) but there was a consistency in the relative magnitude for each operator. The 20 operators could be divided into 13 groups which were significantly different (alpha = 0.05) from each other. There were significant differences (alpha = 0.05) between the forces used for each of the K-Flex files (15, 25, 35, 45, and 70), the force increasing with the file size. There was also a significant difference (alpha = 0.05) in the forces used between the Flexofile (#25) and the #25 K-Flex and Hedstr?m files. However, there was no significant difference between the K-Flex and Hedstr?m files.     

The influence of different root canal instruments on root canal preparation: an in vitro study

Nine endodontic instruments from different manufacturers (Reamers, K-files, Hedstrom files, K-Flex files, Flexofiles, S-files, Burns Unifiles, Flexicut files and Flex-R files) were used to prepare 180 simulated root canals in resin blocks. The instrument's ability to reproduce a theoretical pre-established ideal canal shape was assessed by comparing the original canal path with the resulting enlarged canal shape by a double exposure photographic method. The individual ability of each instrument to transport debris was also observed during instrumentation under a stereomicroscope. Regardless of the instrument type, none was able to reproduce ideal results; however, clinically acceptable results could be obtained with all of them. The coronal and apical debris transportation characteristics proved to be similar with all instruments.