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PubMed1994

An in vitro investigation into the cutting ability of ultrasonic K files.

Endosonic files vary in their oscillation when operated in air with the greatest displacement at the unconstrained tip. It was the aim of this study to investigate how files of different lengths and sizes varied in their ability to cut dentine. Single rooted teeth were sectioned to produce 1 mm dentine discs. These were positioned on a plastic block connected to a load transducer. Endosonic K-files (#15 to 25) were used to cut the disc for 10 s using operator assisted movement. The files contacted the disc at the following points along their length; apical (3 mm from tip), middle (8 mm from tip) and coronal (13 mm from tip) under applied loads of 30 and 50 g. The depth of cut produced by each file was measured using light microscopy. The #15 and #25 were similar in their pattern of dentine removal. The #20 file produced a large variation in its cutting ability and was also susceptible to fracture. The tip of the files was prone to constraint at higher loading with the thicker part of the file producing more cutting. It was concluded that the pattern of dentine removal of endosonic files was affected by the amount of load applied. The displacement amplitudes of endosonic files in air would not appear to be a good indicator of file cutting ability.

Analysis of Variance↗

PubMed2004

A SEM evaluation of debris removal from endodontic files after cleaning and steam sterilization procedures.

BACKGROUND: In recent times, it has been proposed to classify endodontic files as single-use items due to a perceived inability to adequately clean the instruments. The purpose of the present study was to quantify the surface debris on files removed from the manufacturer's packaging, and after cleaning using an ultrasonic bath or a thermal disinfector. METHODS: Stainless steel and rotary nickel-titanium files were examined after removal from the manufacturer's packaging, after instrumentation in broth-contaminated human teeth, and after various cleaning procedures. The cleaning procedures consisted of either a thermal disinfector cycle, ultrasonication with the files placed in a perforated container or ultrasonication with the files loosely placed in a beaker. The presence of manufacturing debris and biological debris was evaluated using scanning electron microscopy and quantified using image analysis software. RESULTS: The effectiveness of cleaning was not affected by variation in the size or taper of the files when an effective cleaning procedure was used. Cleaning the files in a thermal disinfector or by ultrasonication within a container did not consistently achieve complete removal of biological debris. Placing the files loosely in the ultrasonic bath achieved the most effective cleaning, an average of 98.33 per cent of the file surface area was freed of any biological debris. CONCLUSIONS: A conventional cleaning method is capable of effectively removing biological debris from endodontic files. The efficacy of ultrasonic cleaning was impaired when the files were placed within a perforated container.

Dental Alloys↗

PubMed2001

Electronic teaching files: seven-year experience using a commercial picture archiving and communication system.

With the advent of electronic imaging and the internet, the ability to create, search, access, and archive digital imaging teaching files has dramatically improved. Despite the fact that a picture archival and communication system (PACS) has the potential to greatly simplify the creation of, archival, and access to a department or multifacility teaching file, this potential has not yet been satisfactorily realized in our own and most other PACS installations. Several limitations of the teaching file tools within our PACS have become apparent over time. These have, at our facility, resulted in a substantially reduced role of the teaching file tools for conferences, daily teaching, and research purposes. With the PACS at our institution, academic folders can only be created by the systems engineer, which often serves as an impediment to the teaching process. Once these folders are created, multiple steps are required to identify the appropriate folders, and subsequently save images. Difficulties exist for those attempting to search for the teaching file images. Without pre-existing knowledge of the folder name and contents, it is difficult to query the system for specific images. This is due to the fact that there is currently no fully satisfactory mechanism for categorizing, indexing, and searching cases using the PACS. There is currently no easy mechanism to save teaching, research, or clinical files onto a CD or other removable media or to automatically strip demographic or other patient information from the images. PACS vendors should provide much more sophisticated tools to create and annotate teaching file images in an easy to use but standard format (possibly Radiological Society of North America's Medical Image Resource Center [MIRC] format) that could be exchanged with other sites and other vendors' PAC systems. The privilege to create teaching or conference files should be given to the individual radiologists, technologists, and other users, and an audit should be kept of who has created these files, as well as keep track of who has accessed the files. Vendors should maintain a local PACS library of image quality phantoms, normal variants, and interesting cases and should have the capability of accessing central image repositories such as the RSNA's MIRC images. Commercial PAC systems should utilize a standard lexicon to facilitate the creation and categorization of images, as well as to facilitate sharing of images and related text with other sites. This should be combined with a very easy to use mechanism to write images and related text when appropriate onto removable media (while maintaining a high level of security and confidentiality) to make it easier to share images for teaching, research, or clinical purposes.

Computer-Assisted Instruction↗

PubMed2000

The influence of interfacial forces and duration of filing on root canal shaping.

The aim of this study was to investigate the possible relationship between interfacial forces, duration of instrumentation and effectiveness of root canal shaping by filing. All factors were standardised except the manner of manipulation of the files and the dependent variables (interfacial force and duration of filing). The outcome measured was the final prepared canal shape. The study tested the hypothesis that if interfacial forces and duration of filing had predictive value for effective canal shaping, a relationship between them should be apparent. If it was not, it could be inferred that the remaining uncontrollable variable, "manner of file manipulation" had a dominating influence. 18 operators used a standard filing technique to instrument a root canal each in single rooted teeth matched for anatomy. The teeth were mounted in a custom-made transducer designed to measure laterally applied interfacial forces between file and dentine. The length of time taken with each instrument in the series was measured giving a total duration of instrumentation. The final canal shape measured by standardised "before" and "after" radiographic images of the roots was judged against an "ideal" canal shape calculated from the size of instruments used and based on the preliminary canal shape. Although some trends were revealed, no obvious relationship was demonstrated between interfacial force, duration of filing and final canal shape. Operators clearly used a range of interfacial forces characteristic for each individual and for the different file sizes. Both light and heavy forces could produce a satisfactory canal shape. Use of light or heavy forces did not obviously affect speed of preparation. Tactile discrimination was not dependent on use of light or heavy forces. It was inferred that the "manner of file manipulation" remained undefined and was probably the dominant factor influencing outcome of canal shaping.

Analysis of Variance↗

PubMed2000

Effect of rotational speed on the breakage of nickel-titanium rotary files.

Nickel-titanium 0.04-tapered rotary files were evaluated for breakage at different rotational speeds in semicircular bovine bone simulated root canals of identical size and radius for each file size group tested. The bovine bone canals had a radius of curvature of 5 mm and a canal width equivalent to the D1 diameter of the file plus 0.04 mm. Profile instrument #3, #4, and #5 were tested at 150, 250, and 350 rpm. A contra-angle electric handpiece was mounted on an Instron machine that was set to deliver a constant downward speed of 5 mm/min. The electric handpiece and Instron machine were activated until the files broke. The amount of file tip penetration into the semicircular bovine bone canal was measured in degrees with a protractor from a radiographic image taken of the file inside the bone model. Greater degrees of tip penetration indicated greater resistance to breakage. Statistical analysis was done and the results indicated that there was a significant difference for all file sizes in the extent of file tip penetration before breakage. In the rotation range between 150 and 350 rpm the greatest extent of penetration occurred at 150 rpm. This study concluded that 0.04 taper nickel-titanium rotary file breakage is less likely to occur if the files are rotated at lower speeds.

Animals↗

PubMed2002

Failure mechanism of Hedstroem endodontic files in vivo.

Intracanal fracture of endodontic Hedstroem files (H-files) jeopardizes the outcome of endodontic therapy. The aim of this study was to evaluate the fracture mechanism of H-files after multiple in vivo uses. Five each of size #20 and #25 ISO H-files fractured during clinical use were collected from different dental clinics. Four fractured files of each size and three unused files of each corresponding size were embedded in a resin along their longitudinal axis and after metallographic grinding and polishing studied under an incident light microscope. One specimen in the fractured group was investigated under a scanning electron microscope. Light microscopy results showed that unused files were free of structural defects (cracks, pores, etc.), whereas fractured files demonstrated the presence of many cracks mostly located at the flute depth region. Secondary cracks were identified beyond the fracture plane of fractured files both with a light microscope and a scanning electron microscope. Experimental results demonstrated that fatigue is closely associated with the fracture mechanism of H-files (#20, #25) under clinical conditions.

Dental Instruments↗

PubMed2005

Atomic force microscopy study of stainless-steel and nickel-titanium files.

Atomic force microscopy (AFM) is a well established and documented tool for materials investigation. The aim of this study was to evaluate the topography of conventional stainless-steel files and both hand and rotary nickel-titanium (NiTi) files by using AFM. One endodontic file of each of the following was selected: stainless-steel K-file Dentsply, stainless-steel K-file Moyco, hand NiTi K-file Nitiflex, hand NiTi Greater Taper, rotary NiTi Greater Taper, and rotary NiTi Quantec. The analyses were performed on twenty different points located along a 3-mm section starting at the tip of each file. Root mean square (RMS) parameters for contact mode imaging microscopy variations were measured. The differences between RMS values were tested by ANOVA with Fisher's protected LSD test for multiple comparisons (p < 0.05). RMS of depth profile data was used to determine any statistically significant difference in vertical amplitude. According to results, all instruments showed topographic irregularities distributed on surface. Endodontic files manufactured by the same method and alloy demonstrated significant differences, whereas no significant differences were found for instruments produced by different alloys and methods (p < 0.05). The hand NiTi Greater Taper, rotary NiTi Greater Taper, and rotary NiTi Quantec showed greater values of vertical amplitude topography compared to K-Dentsply and Nitiflex files (p < 0.05). The AFM technique proved to be a valuable research tool in the investigation of endodontic files topography.

Dental Alloys↗

PubMed1991

Streaming patterns produced around endosonic files.

Acoustic microstreaming is known to be an important phenomenon associated with the use of clinically available endosonic systems. However, it has proved difficult to calibrate its pattern and effectiveness around the oscillating file. An in-vitro model system consisting of slow setting plaster was developed to demonstrate the activity of streaming around both ultrasonically and sonically activated files. For ultrasonic files, streaming occurred mainly in front of and behind the file, in contrast to the sonic file, where the plaster was disturbed evenly around it. With both types of file most activity occurred around the file tip, and became reduced towards the driver. Streaming patterns associated with the ultrasonic device were found to be dependent on the power setting of the instrument and whether the side of the file was constrained or lightly touched. The sonic device produced a large disturbance around the freely oscillating tip. Under load this streaming occurred along the whole length of the file, and was unaffected by constraint. This investigation demonstrated that streaming does occur with the instruments currently available, although it is dependent on their operating conditions. Clinical users of such equipment should be aware of the characteristic three-dimensional patterns of streaming that occur around these endosonic files, in order to maximize their efficiency.

Acoustics↗

PubMed1996

Factors affecting the wear of sonic files.

The aim of this study was to investigate factors affecting the wear and cutting ability of sonic files. A model system was used and the following variables evaluated, file type; Heliosonic, Rispisonic or Shaper, load; 25, 50 or 100 grams and length of time in use; new, 30 or 60 seconds. A 3(3) full factorial analysis with two replications into the effect of the above variables on the cutting ability of the Heliosonic, Rispisonic and Shaper files powered by the MM1500 sonic instrument was performed. A new file size 25 (Heliosonic and Shaper) or No 3 (Rispisonic) was used for each cut together with water irrigation and the substrate used was 1 mm thick sections of bovine bone. All variables had a significant effect on cutting (ANOVA. p < 0.001). However examination of the F values showed that the most significant variable was load, followed by file type, and time. The most significant interaction was between file type and load followed by time and file type. The interaction between time and load was not significant (p > 0.05). The Rispisonic file was most susceptible to wear during use especially at higher loads and the Heliosonic file cut least. It is suggested that the Shaper file is the better design of the three with respect to cutting ability and wear with use.

Analysis of Variance↗

PubMed1998

Cutting pattern of nickel-titanium files using two preparation techniques.

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 degrees curvature. Fifty blocks were prepared by a balanced-force technique: 25 with Nitiflex (Maillefer) and 25 with Flexofiles (Maillefer) to 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 Kruskal-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.

Analysis of Variance↗

PubMed2004

Microbiological evaluation of endodontic files after cleaning and steam sterilization procedures.

BACKGROUND: Infection control procedures are essential for modern dental practice and they are continually evolving to meet the dental profession's high standards. The present study evaluated the efficacy of two cleaning procedures to reduce bacterial numbers on endodontic files, and evaluated the effect of biological debris on the subsequent sterilization of files. METHODS: Stainless steel and nickel-titanium (NiTi) files were examined upon removal from the manufacturer's packaging, after instrumentation in root canals of human teeth inoculated with a broth containing two anaerobic species and one facultative anaerobic species of bacteria, and after instrumentation and cleaning with either an ultrasonic bath or a thermal disinfector. For each file, the bacterial numbers were quantified using routine microbiological techniques in an anaerobic chamber. RESULTS: No bacteria were detected from files direct from their packets. The size, taper and type of file did not affect the ability of either of the cleaning procedures to reduce bacterial numbers. However, an absence of bacteria was more likely when files were cleaned in the thermal disinfector. No bacteria were detected from files that were-subjected to steam sterilization irrespective of the type of prior cleaning procedure. CONCLUSIONS: Steam sterilization eliminated all bacteria from the endodontic files irrespective of the presence of biological debris. The majority of bacteria were eliminated from endodontic files after either ultrasonic cleaning or using a thermal disinfector.

Colony Count, Microbial↗

PubMed1983

The effect of autoclave sterilization on endodontic files.

This study evaluates the effect of cyclic autoclave sterilization and simulated clinical usage on a mechanical property of one brand of stainless steel endodontic files. The angular deflection moments were measured by a torque apparatus approved by the American Dental Association for such purposes. Comparisons of values for sterilized and nonsterilized files were made. 1. A significant decrease in angular deflection values exists for stainless steel endodontic files having undergone ten cycles of autoclave sterilization versus files having undergone only two or five similar cyclings. 2. All file sizes (15, 20, 25, 30, 35, 40) tested in torsion were detrimentally affected by the autoclave sterilization. 3. Of the files investigated, sizes 35 and 40 were the most adversely affected by the steam-under-pressure sterilization. 4. The angular deflection values of those files subjected to repeated autoclavings were not decreased below the minimum value accepted by the American Dental Association for resistance to torquing forces. It can therefore be concluded that repeated sterilization of a stainless steel endodontic file does result in a significant reduction in the torque resistance of that file. This reduction of the metal property is not significant clinically, however.

Endodontics↗

PubMed1983

Rate theory models for ion transport through rigid pores. III. Continuum vs discrete models in single file diffusion.

In studying the single file model in its discrete as well as in its continuum form the relationship between the phenomenological continuum theory of diffusion and the rate theory approach is analyzed. The single file model in its original form is discrete and represents the most general rate theory model for ion transport through rigid pores in biological membranes. In neglecting the interionic interactions which the single file model takes into account, the Nernst-Planck equation of macroscopic free diffusion can be derived from single file by means of the procedure n leads to infinity (where n is the number of binding sites within a pore) and the classical diffusion theory can thereby be integrated into the more general concept of single filing transport. Moreover, the single file model has been transformed in the limit n leads to infinity into the corresponding continuum form involving interionic interactions. The essential differences between the two derived continuum forms are: In the macroscopic diffusion model, the interionic interactions are regarded in the form of a "mean field". Thus we only get one equation of motion (Nernst-Planck equation) for the ionic concentration c(x, t) within the membrane. In the continuum version of the single file model, however, we obtain a hierarchy of Fokker-Planck equations for the probability density functions Pm(x1, . . . , xm, t) (where m is the number of ions within a pore). The interactions of the single file system are incorporated in detail into the Fokker-Planck equation as well as into the corresponding boundary conditions. As a consequence, the boundary conditions are highly complex in comparison with periodic conditions or Dirichlet conditions often used for the Nernst-Planck equation in electrophysiology. Two types of boundary conditions have been found which are principally different: The first one is to regulate the entry and exit of the ions at the pore mouth by a negative feedback mechanism, the second one describes the collisions of the ions within multiply occupied pores. In this context the question is discussed of whether the continuum version of single file has advantages over the discrete one.

Binding Sites↗

PubMed1997

Effect of tip design of nickel-titanium and stainless steel files on root canal preparation.

The purpose of this study was to evaluate the effect of modified and non-modified tip designs of both stainless steel and nickel-titanium endodontic hand files on root canal preparation. Root canals of mesial roots of extracted mandibular molars were prepared using a quarter-turn-pull technique. The experimental design permitted comparison of the effects of nickel-titanium alloy construction or file tip modification alone, with effects when these two factors were incorporated into a single file design. Transportation, centering ratio, and dentin removal were evaluated using a modified Bramante technique. Nickel-titanium files, regardless of tip design, remained significantly more centered and demonstrated less apical transportation than stainless steel files at size 25. When instrumentation was continued to size 40 apically with step-back, there were no significant differences in transportation in the apical or coronal sections. However, during instrumentation to size 40 with step-back, the combination of modified tip and nickel-titanium alloy produced significantly more transportation and dentin removal, as well as greater deviation from the center at the mid-root level than did other file designs. Thus, of the file design parameters evaluated in this study, construction from nickel-titanium was most important in defining canal configuration at small file sizes in the apical region. Although the combination of nickel-titanium and modified tip design resulted in more transportation at larger file sizes in the midroot region, such alterations in canal configuration may be of little importance clinically. Nonetheless, it is suggested that other factors, such as tactile sensation and instrumentation technique, should be considered as important as the type of alloy or tip design.

Analysis of Variance↗

PubMed1996

Machining efficiency and wear resistance of nickel-titanium endodontic files.

OBJECTIVE: Nickel-titanium endodontic files are more flexible than stainless steel. Little information is reported concerning machining efficiency and wear resistance of nickel titanium. This study assessed the dentin-machining ability and wear resistance of nickel titanium endodontic files in vitro. STUDY DESIGN: The method described earlier to assess machining efficiency and wear resistance of stainless steel files was used. Eight different types and brands of nickel titanium files were studied: Ultra-Flex Hedström, Ultra-Flex K, Mity Hedstrom, Mity K, Mity Turbo, Hedstrom Naviflex NT, NiTiFlex, and Hyflex X-file. Thirty files of each brand were evaluated. One-way ANOVA and t tests were performed to analyze the data. RESULTS: Considerable variation was found in matching efficiency and wear. The best initial machining ability of all nickel titanium instruments was recorded for the Hyflex-X file (0.60 +/- 0.16 mm2); the poorest performance was for the Mity Turbo file, which machined less than one third of the best performing instrument (0.19 +/- 0.12 mm2). CONCLUSIONS: We compared our results with results of a previous study of stainless steel endodontic files and concluded that nickel titanium instruments are as aggressive as or better than stainless steel instruments in removing dentin. They are also more durable than their stainless steel counterparts.

Analysis of Variance↗

PubMed2003

The effect of cleaning procedures on fracture properties and corrosion of NiTi files.

AIM: To evaluate the effect of repeated cleaning procedures on fracture properties and corrosion of nickel-titanium (NiTi) files. METHODOLOGY: New NiTi instruments were subjected to 2, 5 and 10 cleaning cycles with the use of either diluted bleach (1% NaOCl) or Milton's solution (1% NaOCl plus 19% NaCl) as disinfectant. Each cleaning cycle consisted of scrubbing, rinsing and immersing in NaOCl for 10 min followed by 5 min of ultrasonication. Files were then tested for torsional failure and flexural fatigue, and observed for evidence of corrosion using scanning electron microscope (SEM). Four brands of NiTi files were immersed in either Milton's solution or diluted bleach overnight and evaluated for corrosion. RESULTS: Up to 10 cleaning cycles did not significantly reduce the torque at fracture or number of revolutions to flexural fatigue (P > 0.05, two-way anova), although decreasing values were noted with increasing number of cleaning cycles using Milton's solution. No corrosion was detected on the surface of these files. Files immersed in 1% NaOCl overnight displayed a variety of corrosion patterns. The extent of corrosion was variable amongst different brands of files and amongst files in each brand. Overall, Milton's solution was much more corrosive than diluted bleach. Corrosion of file handles was often extreme. CONCLUSIONS: Files can be cleaned up to 10 times without affecting fracture susceptibility or corrosion, but should not be immersed in NaOCl overnight. Milton's solution is much more corrosive than bleach with the same NaOCl concentration.

Analysis of Variance↗

PubMed2001

Comparison of nickel-titanium file distortion using electric and air-driven handpieces.

The use of rotary instrumentation has increased dramatically in endodontics. Air-driven and electric handpieces are both currently available for use with the nickel-titanium files. To date no studies have compared the frequency of instrument separation and/or distortion while using the two types of handpieces with rotary files. The purpose of this study was to determine whether there is a difference in the frequency of file separation/distortion when an electric handpiece is compared with an air-driven handpiece. Extracted human molar teeth were instrumented with nickel-titanium Profile ISO .04 taper rotary files (Dentsply Tulsa Dental Products, Tulsa, OK) under controlled conditions and the results examined for statistical significance. The teeth chosen for the study fit the following criteria: minimal caries, curvature of any root no greater than 60 degrees and at least one root with a minimum of 30-degree curvature. The air-driven handpiece was used at 167.67 rpm and the electric handpiece at 150 rpm per manufacturer's recommendations. Files were examined both before and after use to evaluate whether breakage or deformation had occurred. There was no significant difference in file breakage or distortion when the handpieces were compared. There were, however, a significantly greater number of file separations/ distortions noted in the #8 Profiles (ISO size 20) than with the other files. It may be prudent to view this file as a disposable instrument.

Air↗

PubMed2001

Comparison of distortion and separation utilizing profile and Pow-R nickel-titanium rotary files.

The purpose of this study was to determine whether there was a difference in the frequency of file distortion and separation between nickel-titanium (Ni-Ti) ProFile 0.04 ISO taper rotary files and Ni-Ti Pow-R 0.04 ISO taper rotary files. For this study, 60 mesial root canals in 30 human mandibular first molars were chosen with the curvature angle of the mesiobuccal and mesiolingual canals of the same tooth within five degrees. ProFile and Pow-R files were randomly assigned to either the mesiobuccal or mesiolingual canal of the same tooth. Instrumentation proceeded per the manufacturer's recommendations, in a crown-down technique, using Gates Glidden burs and rotary files in sizes #50 to #20. Positive and negative controls were used. The instruments were evaluated for signs of distortion or separation by three independent evaluators using magnification under microscope. A total of 420 files were evaluated, 210 files for Pow-R and 210 files for ProFile. There was no statistically significant difference in the incidence of instrument distortion or separation between the two file systems that were studied.

Analysis of Variance↗