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Corrosion rates of stainless-steel files in different irrigating solutions.

AIM: The present study was designed to evaluate and compare the corrosion rates of the stainless-steel endodontic files when immersed in 0.2% chlorhexidine gluconate, 5.25% NaOCl, chlorinated soda with KOH, and 17% EDTA irrigating solutions. METHODOLOGY: Corrosion rates of stainless-steel K-files in irrigating solutions were determined electrochemically by the Tafel extrapolation method. The cutting flutes of files were immersed in solutions and used as an electrode. A saturated calomel electrode (SCE) was used as a reference, and a platinum plate was used as a counter electrode. In order to determine corrosion rates, the linear part of anodic currents obtained from electrochemical current-potential curves, was extrapolated to corrosion potentials. RESULTS: The corrosion rates of stainless-steel files in the tested solutions from the highest to the lowest were: 0.2% chlorhexidine gluconate>5.25% NaOCl>chlorinated soda with KOH>17% EDTA. The differences between the corrosion rates of files were not found to be statistically different for chlorinated soda with KOH and EDTA (P >0.05), but statistically significant differences were found amongst other groups. CONCLUSIONS: The results of the present study indicated that 0.2% chlorhexidine gluconate, 5.25% NaOCl and chlorinated soda with KOH cause severe corrosion on the surface of selected stainless-steel files.

Analysis of Variance↗

Root-canal shaping with manual and rotary Ni-Ti files performed by students.

AIM: To investigate root-canal shaping with manual and rotary Ni-Ti files performed by students. METHODOLOGY: Thirty undergraduate dental students prepared 150 simulated curved root canals in resin blocks with manual Ni-Ti files with a stepback technique and 450 simulated curved canals with rotary Ni-Ti files with a crowndown technique. Incidence of fracture, preparation length, canal shape and preparation time were investigated. Questionnaires were then issued to the students for them to note their experience of the two preparation methods. RESULTS: Zips and elbows occurred significantly (P < 0.001) less frequently with rotary than with manual preparation. The correct preparation length was achieved significantly (P < 0.05) more often with rotary files than with manual files. Instrument fractures were recorded in only 1.3% of cases with both rotary and manual preparation. The mean time required for manual preparation was significantly (P < 0.001) longer than that required for rotary preparation. Prior experience with a hand preparation technique was not reflected in an improved quality of the subsequent rotary preparation. Approximately 83% of the students claimed to have a greater sense of security in rotary than in manual preparation. Overall 50% felt that manual and engine-driven preparation should be given equal status in undergraduate dental education. CONCLUSIONS: Inexperienced operators achieved better canal preparations with rotary instruments than with manual files. No difference in fracture rate was recorded between the two systems.

Attitude↗

Formats of image data files that can be used for routine digital light micrography. Part one.

Failing to open computer files that describe image data is not the most frustrating experience that the user of a computer can suffer, but it is high on list of possible aggravations. To ameliorate this, the structure of uncompressed image data files is described here. The various ways in which information that describes a picture can be recorded are related, and a primary distinction between raster or bitmap based and vector or object based image data files is drawn. Bitmap based image data files are the more useful of the two formats for recording complicated images such as digital light micrographs, whereas object based files are better for recording illustrations and cartoons. Computer software for opening a very large variety of different formats of digital image data is recommended, and if these fail, ways are described for opening bitmap based digital image data files whose format is unknown.

Computer Graphics↗

Formats of image data files that can be used in routine digital light micrography. Part two.

This is part two of an article that describes the properties of the image data files that are encountered routinely in digital light micrography. In the current part of the article, the differences between saving image data as large intact files and smaller files that have had some information removed, i.e., using lossy compression, are related first. Subsequently, appropriate ways of configuring computers to deal with the large intact image data files are suggested. The structures of the image data files used for recording dynamic sequences and kinematic animations of series of digital light micrographs, i.e., movie formats, are then described. Finally, some information is supplied about choosing file formats for compressing both static and dynamic image data sets.

Computer Graphics↗

Identifying deaths before 1979 using the Social Security Administration Death Master File.

For cohort studies, the Social Security Administration (SSA) traditionally has been the principal source of deaths that occurred before 1979. In 1988, the SSA abolished a system that provided a relatively complete accounting of deaths and replaced it with the Death Master File. We examined the completeness of the SSA Death Master File by comparing it with the U.S. Vital Statistics records and by searching the SSA Death Master File for known decedents from seven cohorts. Overall, only 53% of reported U.S. deaths and 75% of known deaths in our seven cohorts were included in the SSA Death Master File. Ascertainment was better after 1975 (89-95%). A re-analysis of two cohorts that excluded deaths before 1979 not found in the SSA Death Master File resulted in 20-35% decreases in both standardized mortality ratios and dose-response trends. Although the SSA system before 1988 provided relatively complete vital status information, the SSA Death Master File is inadequate for vital status determination. New cohorts with a substantial number of deaths before the inception of the National Death Index in 1979 will be most seriously affected.

Cohort Studies↗

Integrating a digital dictation system with a network data base for creating and managing radiologic teaching files.

RATIONALE AND OBJECTIVES: A method for facilitating the creation and management of radiologic teaching files is described. METHODS: A digital dictation system was integrated with a personal computer data base. The data base is maintained with user-friendly, graphically oriented software. Radiologists can dictate any examination for the teaching file from any dictation station in the department with minimal interruption of their clinical activities. The data base resides on a file server, thus providing department-wide access for radiologists and students. RESULTS: Attending radiologists and residents have responded favorably to the system. Maintenance and retrieval of teaching files are facilitated by using a computer for otherwise tedious aspects of information management. Data are stored in a well-organized manner, thus increasing the value of the teaching file while reducing redundant data entry. CONCLUSION: Computer technology can facilitate the maintenance of radiologic teaching files. Radiology departments that have a convenient, department-wide method for entering cases--such as a digital dictation system and existing computer network--are ideal for the technique that we describe.

Humans↗

Torsional properties of stainless-steel and nickel-titanium files after multiple autoclave sterilizations.

This study tested the hypothesis that multiple sterilizations of endodontic stainless-steel and nickel-titanium files will lead to a continuous decrease in the resistance of files to separation by torsion. One hundred stainless-steel and 100 nickel-titanium #30 K-type files were divided into 20 groups of 10 and sterilized in increments of 10 cycles, using a full cycle and a fast cycle autoclave. These files were tested by twisting each of them in a clockwise direction until fracture (torque g-cm). Samples of the fractured files were embedded in an epoxy resin and polished for Knoop hardness tests. In addition, the samples were chemically etched to reveal changes in microstructure. The findings of this study indicate that neither the number of sterilization cycles nor the type of autoclave sterilization used affects the torsional properties, hardness, and microstructure of stainless-steel and nickel-titanium files.

Acid Etching, Dental↗

Wear resistance of cryogenically treated stainless steel files.

Cryogenic treatment, which involves ultra-sub-zero treatment of metal alloys, has been shown to improve the wear resistance of several types of stainless steel. The purpose of this study was to examine the effect of cryogenic treatment on wear resistance of Flex-R and Hedstrom (Union Broach) files. These instruments were attached to an Instron testing machine and underwent 300 push-pull strokes (6-mm movement range, 600-mm/min speed, 1-N loading) against 1.5-mm thick dentin wafers. Their wear was determined by comparing the depth of grooves (without changing file position) cut in acrylic specimens (1.5-mm thick) before and after machining dentin. The mean and standard deviation (n = 20) of the relative change in cutting efficiency was determined for the files. An analysis of variance showed that the cutting efficiency of all files decreased significantly after wearing on dentin (p < 0.0001). However, when comparing the post-/pre-cutting efficiency ratios of the files, it was seen that cryogenic treatment did not affect the wear resistance of the files.

Acrylic Resins↗

The deterioration of rotary nickel-titanium files under controlled conditions.

It has been shown that rotary nickel-titanium files cannot be used indefinitely. Researchers and clinicians have not been able to agree on how many times a file can be used before being discarded, except if a file has fractured or become visibly distorted. This study used ISO size 20 files of 0.04 taper in the curved canals of extracted mandibular molars. The canals had been previously instrumented to an ISO size 15 with stainless steel hand files. The irrigant used during rotary and hand instrumentation was Glyde. The rotary files were closely examined with scanning electron microscopy before use to detect any defects. They were then reexamined after each of five uses to document deterioration. An electric handpiece was configured to rotate at 150 rpm and secured to the testing device, which also held the extracted tooth. The testing device controlled the load at 8 N, the depth of penetration for each canal and the rate of penetration (12 mm/min). Used instruments demonstrated surface fatigue wear and cracking. Torsional moment at failure was determined on a torsiometer for used and new instruments. Data (n = 10) were analyzed by analysis of variance. The torsional moment for used and new instruments was not affected by use (p = 0.25).

Dental Instruments↗

The quality of apical canal preparation using hand and rotary instruments with specific criteria for enlargement based on initial apical file size.

The aim of this study was to compare the quality of apical enlargement of mesiobuccal canals of mandibular molars using conventional stainless steel hand files (K files) and nickel-titanium (Ni-Ti) rotary instruments (LightSpeed). Thirty freshly extracted mandibular molars were randomly assigned to three equal groups (n = 10 each group). The mesiobuccal canals were instrumented with K file using step-back technique without coronal flaring (control; group 1), K file using step-back technique after coronal flaring (group 2), and LightSpeed instrumentation (group 3). Specific criteria for apical enlargement based on initial apical size were used. For step-back techniques, the master apical file sizes were based on the Grossman criterion of three sizes larger than the first file that bound at working length, without coronal flaring (group 1) and with flaring (group 2). For the LightSpeed (LS) group, the master apical rotary sizes were based on the manufacturer's recommendation. Canal cleanliness, canal transportation, and final canal shapes were determined histologically at 1-mm and 3-mm levels short of the working length. Canals were prepared to significantly larger sizes using LS instrumentation than with either hand instrumentation techniques (15-17 ISO units, p < 0.001). LS instrumentation allowed greater apical enlargement with significantly cleaner canals, less apical transportation, and better canal shape than both hand instrumentation groups at both levels (p < 0.05). None of the three techniques was totally effective in cleaning the apical canal space. It was concluded that greater apical enlargement using LS rotary instruments is beneficial as an attempt to further debride the apical third region in mesiobuccal canals of mandibular molars. Instrument designs, alloy properties, and canal curvature are important factors that determine the feasibility of greater apical enlargement in narrow canals.

Analysis of Variance↗

Effectiveness of sodium hypochlorite in preventing inoculation of periapical tissues with contaminated patency files.

The aim of this study was to analyze the effectiveness of 5.25% sodium hypochlorite (NaOCI) in preventing inoculation of periapical tissues with contaminated patency files. Twenty-eight extracted human permanent teeth with single canals were used in the study. Group I teeth were filled with NaOCl, and #15 stainless steel files contaminated with Streptococcus sanguis (ATCC #10556) were allowed to pass through the NaOCI into the culture medium. The teeth in group II were also filled with NaOCl, but the contaminated files used in group II canals were immersed in NaOCl for 10 s prior to being placed into the canals and cultured. The negative control group used sterile files (0% growth), the first positive control group used contaminated patency files in teeth with empty canals (100% growth), and the second positive control group placed contaminated files into broth next to teeth filled with NaOCl (to evaluate potential chlorine leakage; 100% growth). The experimental results showed no positive growth of S. sanguis for groups I and II, indicating that the NaOCl present in the canal after irrigation was sufficient to kill the test organism.

Dental Alloys↗

Why most workers with occupational repetitive trauma do not file for workers' compensation.

Despite the availability of no fault insurance for wage replacement and medical care costs, the majority of workers diagnosed with an occupational disease do not apply for workers' compensation. The objective of the study was to determine the reasons why workers diagnosed with work-related musculoskeletal disease did not apply for workers' compensation benefits. A cross-sectional study of 1598 individuals diagnosed with neck, upper extremity, and low back work-related musculoskeletal disease from April to June 1996 was performed. All individuals were interviewed over the telephone using a standardized questionnaire. The questionnaire included questions about the precipitating event; demographics; health limitations; mood; pain level; and attitudes toward their health care provider, fellow workers, management, work environment, and filing for workers' compensation. Whenever possible, standardized questions from previous surveys were used. The interviewed individuals with work-related musculoskeletal disease were reported by health care practitioners as required by the state of Michigan's occupational disease reporting law. Workers reported during 12 weeks in the spring of 1996 by a Michigan health care professional as having a neck, back, or upper extremity musculoskeletal disorder were eligible to participate. Among the 2703 reports received, 490 individuals could not be reached, 22 did not speak English, 12 had died or were too incapacitated by other medical conditions, and 581 refused. We interviewed 59% of all eligible workers and 73% of all workers who were reachable and capable of responding in English. Only 25% of workers diagnosed with musculoskeletal disease filed a workers' compensation claim. The factors significantly associated with filing a claim were (1) increased length of employment (> 21 years: odds ratio [OR], 3.01, 95% confidence interval [CI], 1.31 to 6.90); 11 to 20 years: OR, 2.34, 95% CI, 1.01 to 5.47; 6 to 10 years: OR, 1.76, 95% CI, 0.73 to 4.25; 1 to 5 years: OR, 2.36, 95% CI, 1.03 to 5.42; < 1 year: OR, 1.00; (2) lower annual income (< $40,000: OR, 1.75, 95% CI, 1.06 to 2.88 vs > or = $80,000: OR, 1.00); (3) workers' dissatisfaction with coworkers (OR, 1.76, 95% CI, 1.01 to 3.06); (4) physician restrictions on activity (OR, 2.16, 95% CI, 1.55 to 3.00); (5) type of physician providing treatment (specialist, including surgeon or orthopedist: OR, 3.63, 95% CI, 2.37 to 5.55); physical and occupational therapist: OR, 2.15, 95% CI, 1.35 to 3.43); family practitioner: OR, 1.33, 95% CI = 0.89 to 2.01; company physician: OR = 1.00); (6) off work > or = 7 days (OR, 14.85, 95% CI, 10.57 to 20.85); (7) decreased current health status (OR, 0.82, 95% CI, 0.70 to 0.96); and (8) increased severity of illness (OR, 1.24, 95% CI, 1.06 to 20.88). This study showed that only 25% of workers with a work-related musculoskeletal condition filed for workers' compensation and refutes the common perception that an individual with a work-related problem is likely to file a workers' compensation claim. The strongest predictors of who would file were those factors associated with the severity of the condition. Other factors were increasing length of employment, lower annual income, and worker dissatisfaction with coworkers. Our study population consisted mainly of unionized autoworkers, and our findings may not be generalizable to the total workforce.

Adolescent↗

A comparison of the machining efficiency of two brands of stainless steel endodontic hand files.

The purpose of this study was to compare the machining efficiency of a flexible stainless steel K-type hand file recently introduced by Brasseler USA ("F-Style files"), with that of a well-studied Endodontic instrument ("Flex-o-files," Maillefer Dentsply), that has been on the market for more than 20 years. The comparison of machining efficiencies of these two brands of files was conducted on both dentin and plexiglas substrates, using an apparatus that allowed a constant force to be applied from each file being tested. The results indicated that the Brasseler instruments had poorer machining efficiency than those of the Maillefer files.

Dental Alloys↗

Use of attorneys and appeal filing in the Washington State workers' compensation program: does patient satisfaction matter?

LEARNING OBJECTIVES: Specify the frequency with which injured workers in Washington State's compensation system retained an attorney or filed an appeal, and the personal and job-related correlates of these actions. Analyze the relationship between workers' legal actions and their satisfaction in two domains: how well the claim was managed administratively, and how well the worker and claim manager communicated with one another. Characterize the relationship between retaining an attorney and long-term disability. ABSTRACT: Little is known about how often injured workers retain attorneys or file appeals in the workers' compensation system. We conducted a population-based study to examine the frequency of attorney retention and appeal filing in the Washington State workers' compensation program and the factors related to this event. Data for the study were provided by a survey conducted on 804 injured workers who were interviewed an average of 159 days after claim receipt. Attorney retention and appeal filing were examined up to 28 months later. Seven percent of the workers either retained an attorney or filed an appeal. Workers who were less satisfied with claims administration procedures were more likely to retain an attorney or file an appeal (P<0.05). The average length of time from claim receipt to attorney retention (368 days) suggests that retaining an attorney is a correlate rather than a predictor of long-term disability.

Adolescent↗

Dentine-removing characteristics of K-files energized by the Piezon-Endo.

This in-vitro study evaluated the pattern of dentine removal when a size 25 K-file energized by the Piezon-Endo was applied to flat surfaces of dentine under standardized conditions. The effects of power setting, interfacial force between file and dentine, direction of file oscillation and operator-assisted movement were examined. Vinyl polysiloxane impressions of the instrumented surfaces revealed characteristic patterns consisting of a series of oblique crests, similar to those observed in a previous study using the Cavi-Endo. Each crest was parallel to the next and separated by a relatively constant distance. These crests were disposed along the line of contact with the file. The Reflex microscope was used to determine the height, width and separation of these crests. There were differences in the amount and pattern of dentine removal compared with the study on the Cavi-Endo. When the file was held against the dentine surface using the minimum power setting and an interfacial force of 30 g, the pattern of dentine removal was very similar to that produced by the Cavi-Endo. Increasing the power setting to the maximum recommended for endodontics produced a slight but statistically non-significant increase in dentine removal. Further increase of the power setting to the absolute maximum produced significantly deeper and wider areas of dentine removal by the apical part of the file.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Cavity Preparation↗

The vibratory pattern of ultrasonic files driven piezoelectrically.

The pattern of oscillation of a Piezon-Master 400 ultrasonic file driven by a piezoelectric transducer was studied in air and on water. In addition, the displacement amplitudes of the files were measured. The findings were compared with those observed with the Cavi-Endo unit reported in another study (Ahmad 1969). It was observed that the file vibrated such that a standing wave was formed on the file and it exhibited points of maximum deflection (antinode) and points of minimum deflection (node) with the largest deflection occurring at the apical end. This pattern of oscillation was similar to that exhibited by the Cavi-Endo file which employed a magnetostrictive transducer. However, the displacement amplitudes were very much higher than those exhibited by the Cavi-Endo. It is considered that the 120 degrees angle of the file holder inherent in the Piezon-Master 400 unit and the more effective power transmission with the piezoelectric transducer may have contributed to the large amplitudes.

Dental Cavity Preparation↗

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.

Alloys↗

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.

Analysis of Variance↗