File Length Research Articles

A resource guide for practice development through technology

A resource guide for practice development through technology

A new insight into the oscillation characteristics of endosonic files used in dentistry

The aim of this study was to assess the oscillation characteristics of unconstrained endosonic files using a scanning laser vibrometer (SLV). Factors investigated included file vibration frequency and node/antinode location as well as the variation in file displacement amplitude due to increasing generator power setting. A 30 kHz Mini Piezon generator (Electro-Medical Systems, Switzerland) was used in conjunction with a #15 and #35 K-file. Each file was fixed in position with the long axis of the file perpendicular to the SLV camera head. The laser from the SLV was scanned over the length of the oscillating file for generator power settings 1 to 5 (minimum to half power). Measurements were repeated ten times. The fundamental vibration frequency for both files was 27.50 kHz. Scans of each file showed the positions of nodes/anti-nodes along the file length. The #15 file demonstrated no significant variation in its mean maximum displacement amplitude with increasing generator power, except at power setting 5, where a decrease in displacement amplitude was observed. The #35 file showed a general increase in mean maximum displacement amplitude with increasing power setting, except at power setting 4 where a 65% decrease in displacement amplitude occurred. In conclusion, scanning laser vibrometry is an effective method for assessing endosonic file vibration characteristics. The SLV was able to demonstrate that (unloaded) file vibration displacement amplitude does not increase linearly with increasing generator power. Further work is being performed on a greater variety of files and generators. Vibration characteristics of files under various loads and varying degrees of constraint should also be investigated.

A comparison of the length between mesio-buccal and mesio-lingual canals of the mandibular molar

The aim of this study was to compare the initial apical file (IAF) length between the mesio-buccanl and mesio-lingual canals of the mandibular molar before and after early coronal flaring. Fifty mandibular molars with complete apical formation and patent foramens were selected. After establishing the initial working length of the buccal and lingual canal of the mesial root using the Root-ZX, radiographs were taken for the working length with a 0.5 ㎜ short of #15 K-file tip just visible at the foramen under a surgical microscope (OPMI 1-FC, Carl Zeiss Co. Germany) at 25X. After early coronal flaring using the K 3 file, additional radiographs were taken using the same procedure. The root canal morphology and the difference in working length between the buccal and lingual canals were evaluated. These results show that the difference in the length between the mesio-buccal and mesio-lingual canals of the mandibular molar was ≤ 0.5 ㎜. If one canal has a correct working length for the mesial root of the mandibular molar, it can be used effectively for measuring the working length of another canal when the files are superimposed or loosening. In addition, the measured the working length after early coronal flaring is much more reasonable because the difference in the length between the mesio-buccal and mesio-lingual canals can be reduced. [J Kor Acad Cons Dent 29(6):541-547, 2004]

Accuracy of a new apex locator: an in vitro study.

The purpose of this study was to test in an in vitro model the accuracy of a Bingo 1020 electronic apex locator, to compare the results to those of a well known apex locator, Root ZX, as well as to those of the radiographic method of tooth length determination. A total of 120 extracted teeth, preserved in Thymol solution and kept refrigerated, was used for the study. The experiment was performed on single-rooted teeth and on one-root canal, chosen randomly, in multirooted teeth. The teeth were randomly divided into 12 groups of 10 teeth each. After access preparation, the actual length (AL) was measured. The teeth were embedded in an alginate model specially developed for testing apex locators. Electronic tooth length measurements (EL) were carried out prior to root canal preparation using the two electronic apex locators (EAL) - Root ZX and Bingo 1020; three measurements were taken and an average computed. After the third measurement, the file was left in the root canal and a periapical radiograph was taken. The radiographic length (RL) was recorded by measuring the file length from the coronal reference point to the tip of the file. Each root canal was then prepared to a no. 40 K-file diameter using a standardized technique; saline was used for irrigation. Upon completion of the root canal preparation, EL measurements were taken by each EAL in dry conditions and with different irrigation solutions. Each measurement was repeated three times. The RL was recorded according to the last EL measurement. Results were subjected to statistical analysis. In all parameters tested, a significant statistical difference was found between Bingo 1020 and the Root ZX. Measurements obtained using the Bingo 1020 were consistently closer to the AL (0.08 mm) than those obtained using the Root ZX. Both EALs measured the tooth length with great accuracy and a positive correlation of 0.76 (P = 0.00) existed between the two devices. No significant difference was found between the two apex locators when measurements were taken with the different irrigants (P = 0.34) and the content of the root canal did not affect the accuracy of the measurements. Lengths obtained by calculations from the radiographs were longer than the AL as well as the length obtained by both EALs (P = 0.00). The Bingo 1020 proved to be as reliable as Root ZX and was user friendly. Under the experimental conditions, electronic measurements were more reliable than radiographs in the process of root length determination.

Measurement of Endodontic File Lengths: Calibrated Versus Uncalibrated Digital Images

This in vitro study compared the accuracy of file length measurements made on calibrated and uncalibrated direct digital images. Endodontic files of known lengths and ISO sizes were used in 10 single-rooted, relatively straight teeth within cadaver specimens. The crowns of the teeth were ground flat and an orthodontic wire of known length was secured to the coronal surface. This wire was placed mesiodistally and perpendicular to the root and served as the reference point for the file measurement and as a calibration reference length. A #20 file was hand-measured to a length that reached the apical third of each tooth. It was inserted and a radiographic image was secured. The instrument was remeasured three additional times at different lengths on the same tooth and reinserted before each image acquisition. Thus 40 digital images were acquired using a GE X-ray unit and a Schick Computed Dental Radiography (CDR) #2 sensor. These images were placed in random order, and an independent, blinded investigator determined the file lengths using on-screen calibrated and uncalibrated measurement of the CDR image with a straight-line and multiple-line measuring technique. The experimental measurements were compared with each other and with the known clinical measurements. A two-way analysis of variance indicated that there was a statistically significant difference showing that the calibrated measurements were more accurate than the uncalibrated measurements (p = 0.0001), and there was no significant difference between the straight-line and multiple-line measuring techniques (p = 0.14).

Equilibrium and nonequilibrium molecular dynamics studies of diffusion in model one-dimensional micropores

Molecular dynamics simulation results are reported for self-diffusion of a hard-sphere fluid in a one-dimensional interconnected spherical cavity-cylindrical pore model of zeolites. The mode of transport within the cylindrical sections of the structure is by single-file diffusion and a scaling relationship between the self-diffusivity and the length of the particle files proposed in recent work is verified using two different nonequilibrium simulation techniques. It is also shown that strong nonlocal spatial correlations can exist between the fluid particles in pore systems containing single-file channels and these results in conjunction with the local spatial dependence of the transport and equilibrium properties indicate that care needs to be exercised when interpreting experimental measurements of diffusivities within zeolitic structures.

An optimal service ordering for a world wide web server

We consider alternative service policies in a web server with impatient users. User-perceived performance is modeled as an exponentially decaying function of the user's waiting time, reflecting the probability that the user aborts the download before the page is completely received. The web server is modeled as a single server queue, with Poisson arrivals and exponentially distributed file lengths. The server objective is to maximize average revenue per unit time, where each user is assumed to pay a reward proportional to the perceived performance. When file lengths are i.i.d., we prove that the optimal service policy is greedy, namely that the server should choose the job with the highest potential reward. However, when file lengths are independently drawn from a set of exponential distributions, we show the optimal policy need not be greedy; in fact, processor sharing policies sometimes outperform the best greedy policy in this case.

Measurement of Endodontic File Lengths: A Density Profile Plot Analysis

The purpose of this study was to evaluate measurements of endodontic files of known length and diameter using a density profile plot analysis of digital images. Ten single-rooted teeth with relatively straight roots in cadaver specimens were used. The crowns of the teeth were removed and a rectangular orthodontic wire, 5.13 mm in length, was placed horizontally on the occlusal surface to serve as a calibration reference point. The #8, #10, #15, and #20 FlexOFiles were measured to the nearest 0.5 mm and then placed to four working lengths that terminated within the apical third of each root. A GE X-ray unit and a Schick CDR #2 sensor were used to digitally acquire 160 images. The digital images were placed in random order and an independent, blinded investigator determined the file length using a density profile plot analysis. The measurements generated by the histogram analysis (experimental) were compared with the original clinical measurements. The paired t test, intraclass correlation coefficient, and the Bradley-Blackwood test were used to assess reliability. The results revealed that the means of the experimental measurements of all file sizes were within 0.5 mm of the known lengths and were always shorter than the known lengths. Also, the larger the file size the less deviation from the known lengths: #20, -0.16 mm (p = 0.0001); #15, -0.21 mm (p = 0.0001); #10, -0.34 mm (p = 0.0001); and #8, -0.45 mm (p = 0.0001). This study demonstrated that the density profile plot analysis might be a useful adjunct for the measurement of endodontic file lengths on a digital image.

Parasitic Computer Viruses

A computer virus is a piece of self-replicating code, that is code which can make copies of itself is such a way as to infect parts of operating system or environment.
 In this study a new virus has been created "947" virus, which is a memory-resident parasitic. It is capable of infecting COM and EXE files an adds 947 bytes to the length of infected files. The scanning & cleaning programs has been created also.

Theory and simulation of jump dynamics, diffusion and phase equilibrium in nanopores

We review theory and simulation of rare event dynamics, diffusion and phase equilibrium in nanopores, focusing on benzene in Na-X and Na-Y zeolites because of persistent experimental discrepancies. We discuss transition state theory and its application to zeolite-guest systems, suggesting that calculations on flexible lattices and at finite guest loadings are important areas for future research. We consider many-body adsorption and diffusion in zeolites, focusing on the coupling between rare event dynamics and strong guest-guest interactions. We explore the possibility that benzene can undergo phase transitions from low to high sorbate density in Na-X, and find that this type of phase transition might explain intriguing loading dependencies of water and ammonia diffusion in terms of a subcritical droplet picture of adsorption in zeolites. We discuss various formulations of non-equilibrium diffusion through finite lattices, and describe a tracer counter-permeation simulation technique. We find that transport in finite single-file systems is characterized by a diffusivity that decreases monotonically with file length, but that this transport is otherwise completely described by Fick's laws. We conclude by speculating on the prospect for cross-fertilization between zeolite science and other fields.

Comparison of Digital Dental X-ray Systems with Self-Developing Film and Manual Processing for Endodontic File Length Determination

Human skulls were sectioned into 15 sextants. Teeth were then removed and 45 canals were instrumented to their apical foramina. Endodontic files were glued in place at random distances from the apical foramina. Image geometry was maintained by a custom mounting jig. Images were captured with self-developing film, manually processed D-speed film, and a digital radiographic system (Dexis). Digital images were read on a conventional color monitor (cathode ray tube) and a laptop screen (active-matrix liquid crystal display). Fifteen dentists measured the distance from the file tip to the apical foramen of the tooth. Results showed that the measurement error was significantly less for the digital images than for the film-based images. It is likely that these statistical differences may not be of great clinical significance because the digital images could be measured in increments < 0.25 mm.

The effects of developer age on diagnostic accuracy: a study using assessment of endodontic file length

The effects of developer age on diagnostic accuracy: a study using assessment of endodontic file length

Self-diffusion in single-file zeolite membranes is Fickian at long times

We have developed a theory for self-diffusion in single-file Langmuirian zeolites of finite extent, which has been validated by open system kinetic Monte Carlo simulations. Our theory is based on a two-stage, Fickian diffusion mechanism, wherein a vacancy must traverse the entire file length to produce particle displacements of one lattice spacing. For times shorter than the vacancy diffusion time, tc, particle transport proceeds via the nonFickian, single-file diffusion mode, with mean-square displacements increasing with the square-root of time. For times longer than tc, however, we find that self-diffusion in single-file systems is completely described by Fick’s laws. We find that the fraction of time in the single-file diffusion mode scales inversely with file length for long files, suggesting that Fickian self-diffusion dominates transport in longer single-file zeolites. Through correlations among the particle movements, the single-file self-diffusivity is sensitive to sorption limitations for short files, and scales inversely with file length for long files. Experimental verification of the theory by pulsed field gradient NMR and tracer zero-length column experiments is discussed.

OR 14 Measurement of endodontic file lengths: a density profile plot analysis of digital images

OR 14 Measurement of endodontic file lengths: a density profile plot analysis of digital images

Endodontic working length assessment: Comparison of storage phosphor digital imaging and radiographic film

Objective. This study compared the difference in interpretation of the position of endodontic file tips between two imaging systems: photostimulable storage phosphor luminescence imaging versus radiographic film. Study design. Thirteen patients were selected at random. Preoperative and trial file length radiographs were made with a dual image receptor composed of a Digora Digital Imaging Plate and a piece of Ektaspeed Plus film. Exposure techniques for E-speed film were used. Root length and file length measurements were made from digital images with the Digora system's measuring tools. Measurements were also made on radiographic film with a 7× measuring magnifier. Root length, file length, and their difference were compared for both film and digital images. Results. Differences were found to be less in digital than in film images. Photostimulable storage phosphor luminescence imaging performed similarly to Ektaspeed Plus film for measuring root lengths, but file tip positions (especially of small file sizes) were difficult to visualize with E-speed film. Conclusions. The smaller difference between file tip and root apex found with digital imaging suggests that this technique is more accurate to assess trial file length. This imaging modality for assessing file positions during root canal treatment may be beneficial to the practitioner.

Comparison of two endodontic handpieces during the preparation of root canals in extracted human teeth

This in vitro study compared and assessed two endodontic handpieces during the preparation of root canals in extracted human teeth. Eighty extracted human teeth, with single root canals, were divided into eight matched groups. They were prepared using Shaper files activated by the MM1500 Sonic Air handpiece (Micro-Mega, Besançon, France) or Excalibur files activated by the W & H Excalibur 969 handpiece (W & H, Bürmoos, Austria). The files were 21 mm or 25 mm in length. When preparing the canals, the files were used either in line with or perpendicular to any canal curvature. Preparation of the canals was carried out using the techniques described in the manufacturers' literature. A variety of parameters were used to compare the handpieces, including canal preparation time, deformation or fracture of instruments, loss of canal length, weight loss from the prepared teeth and the overall postpreparation canal shape. A microradiographic technique was used to produce a tracing record of the pre- and postpreparation canal shape. Both handpieces provided an efficient and easy method of preparing and shaping the root canal with little operator fatigue. The MM1500 Sonic air handpiece took significantly more time (P < 0.001) to prepare the canals than the Excalibur. Few aberrations in the shapes of prepared canals were created by either handpiece. No endodontic file fractured but a few of them were permanently deformed. The effects of two variables--file length and the plane of use of the file--on performance of the handpieces, were also assessed.

Fitting mixtures of exponentials to long-tail distributions to analyze network performance models

Traffic measurements from communication networks have shown that many quantities charecterizing network performance have long-tail probability distributions, i.e., with tails that decay more slowly than exponentially. File lengths, call holding times, scene lengths in MPEG video streams, and intervals between connection requests in Internet traffic all have been found to have long-tail distributions, being well described by distributions such as the Pareto and Weibull. It is known that long-tail distributions can have a dramatic effect upon performance, e.g., long-tail service-time distributions cause long-tail waiting-time distributions in queues, but it is often difficult to describe this effect in detail, because performance models with component long-tail distributions tend to be difficult to analyze. We address this problem by developing an algorithm for approximating a long-tail distribution by a hyperexponential distribution (a finite mixture of exponentials). We first prove that, in prinicple, it is possible to approximate distributions from a large class, including the Pareto and Weibull distributions, arbitrarily closely by hyperexponential distributions. Then we develop a specific fitting alogrithm. Our fitting algorithm is recursive over time scales, starting with the largest time scale. At each stage, an exponential component is fit in the largest remaining time scale and then the fitted exponential component is subtracted from the distribution. Even though a mixture of exponentials has an exponential tail, it can match a long-tail distribution in the regions of primary interest when there are enough exponential components. When a good fit is achieved, the approximating hyperexponential distribution inherits many of the difficulties of the original long-tail distribution; e.g., it is still difficult to obtain reliable estimates from simulation experiments. However, some difficulties are avoided; e.g., it is possible to solve some queueing models that could not be solved before. We give examples showing that the fitting procedure is effective, both for directly matching a long-tail distribution and for predicting the performance in a queueing model with a long-tail service-time distribution.

Measurement algorithm accuracy of the RVG-PCi in vertical and diagonal assessments at various beam energies

The Trophy RadioVisioGraphy model PCi was compared to Kodak Ektaspeed Plus film for accurate recording and estimation of the length of size 15 files placed vertically and diagonally across the receptor surface. Variations in kilovoltage (50, 70, and 75) and exposure were also factored. Eight observers estimated file lengths using the proprietary software measurement algorithm for the RVG-PCi and a millimeter rule for the film-based radiographs. Both modalities resulted in slight magnification for vertically oriented files; however, the RVG-PCi caused overestimation in the order of 6 to 8% with diagonally oriented instruments. Measurement interobserver variability was least when using the RVG-PCi. It was concluded that the proprietary software supplied with RVG-PCi is not sufficiently accurate for endodontic assessment. Furthermore, exposures above 0.15 s at 75 kVp resulted in pixel saturation resulting in apparent shortening of the instrument; hence, length calculations are particularly sensitive to overexposure when using the RVG-PCi.

Factors affecting the cutting ability of sonic files.

The aim of this study was to investigate the cutting ability of sonic files. A model system was developed and the following variables evaluated: file type. Heliosonic or Shaper; file length, 21 or 29 mm; power, air inlet ring opening of half or fully open; stroke length, 2 or 4 mm; stroke rate, one or two cycles per second; and load 50 or 100 g. A 2(6) full-factorial analysis with two replications into the effect of the above variables on the cutting ability of the MM1500 sonic instrument was performed. A new size 25 file was used for each cut, together with water irrigation, and the substrate used was 1-mm thick sections of bovine bone. The differences between the variables were significant (ANOVA, P < 0.001). However, examination of the F-values showed that the most significant variable to affect cutting was load, followed by power, file type, stroke length and stroke rate, with the least significant variable being file length. The most significant interaction was between rate and length of stroke. An increase in stroke rate from one to two cycles per second at a stroke length of 2 mm produced an increase in cutting for both the Heliosonic and Shaper files. However, at the longer stroke length of 4 mm, the same increase in rate resulted in a decrease in cutting for the Shaper files. Therefore, it is suggested that operators should press the file against the canal wall and move it slowly to maximise cutting.

Dose reduction of two digital sensor systems measuring file lengths

Objectives The aim of this study was to determine the effect of dose reduction on the image quality of two sensor systems with automatic greyscale adjustment. Study designs Two digital sensor systems, Sidexis (Siemens, Bensheim, Germany) and Digora (Soredex, Helsinki, Finland), were tested. The image quality of the systems was determined by comparing lengths of endodontic files (025, 020, 015, and 010 files) and a premolar root in the digital images with lengths on conventional radiographic films. For the experiments the exposure was changed to 100%, 50%, 25%, 12.5%, 6.25%, and 3.125% of that for Ektaspeed films. Results The lengths of 025 and 020 files and the premolar root in the digital images were comparable with the lengths on films even if the exposure was reduced to 6% of that used for Ektaspeed films. The lengths of 015 files reduced as the exposure was reduced. The lengths of 010 files were significantly shorter than the lengths on films. Conclusions With the systems tested, a dose reduction of approximately 95% compared with Ektaspeed films is possible to determine the lengths of a premolar root and 025 and 020 files. For thinner objects a dose reduction is questionable.