Machining efficiency of endodontic K files and Hedstrom files.

Methods for the objective evaluation of the machining property of endodontic files were described earlier. These methods were used in this investigation to assess the characteristics of machining of 7 different brands of K files and 10 brands of Hedstrom files. The results show that there are large variations in amounts of material removed by the files. These variations are large between brands of instruments as well as between files of the same brand. Thus, among the 510 files evaluated, the file with the highest machining quality was more than 40 times as effective as the least effective instrument. The highest values among K files were obtained with files manufactured by Maillefer followed by Antaeos, Healthco, JS Dental, Brasseler, and Miltex. Among the Hedstrom files, the most efficient brands were Antaeos and Zipperer followed by Healthco, Hygenic, JS Dental, Miltex, Maillefer, Union Broach, and the least efficient Brasseler. The files did not wear noticeably during these testing procedures. These results clearly indicate that the provider needs more information from the manufacturer in regard to machining and cutting in order to intelligently select instruments. It is suggested that procedures be agreed upon to evaluate machining and cutting of root canal files in order to provide the endodontist with better information about instruments.

Machining efficiency of endodontic files: a new methodology.

The ability of endodontic files to effectively remove hard tissues is difficult to assess as results from published investigations often vary considerably. An analysis is presented of errors occurring during efficiency assessments. It was found that the machining property varies around the circumference of a single file as well as between various files of the same brand. A new method is proposed for the assessment of the quantity and quality of the machining properties of an endodontic file.

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.

Root canal instruments are poorly standardized.

In an earlier study we demonstrated that root canal instruments vary greatly in their effectiveness in removing substrates. To further analyze the reason for this variation of results, the dimensions of the instruments used were considered of interest as their matching effectiveness may be size dependent. Nine different brands of Hedstrom files, seven brands of K files, and four brands of special files were examined. The measurements were done in a computerized measuring microscope and the data were compared with earlier reported data on machining. Although the dimensions of the instruments varied greatly, no correlation could be found between the machining and dimensions. Only one brand of files was completely within allowable size range.

The endodontic file is a disposable instrument.

Most cutting and machining tools wear when properly operated on intended substrates. Little is known about endodontic files when machining on human dentin. It was shown earlier that the efficiency of files was very variable when evaluated on Plexiglas substrates. The present study of seven different brands and types of files was undertaken to understand their wear better when machining human dentin. It was shown that all files evaluated rapidly deteriorated when machining dentin. This decline in efficiency was significant but different within, as well as, among brands. It was suggested that endodontic files be disposable.

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.

A comparison of stainless steel and nickel-titanium H-type instruments of identical design: torsional and bending tests.

OBJECTIVE: For a true comparison of clinically relevant qualities of instruments manufactured from different alloys, the instrument must be identical in design. The purpose of this study was to perform mechanical tests on stainless steel and nickel-titanium instruments of identical design. STUDY DESIGN: Identical experimental endodontic files of H-type with double helix were fabricated from stainless steel and nickel-titanium alloys. Torsional and bending tests were carried out according to American National Standards Institute/American Dental Association specification No. 58 and International Standards Organization No. 3630/1. Changes in instruments during the testing were also analyzed with scanning electron microscope technique. RESULTS: The results indicated that the torsional moment of the stainless steel files was significantly higher than for the nickel-titanium files (P <.001), whereas the mean angular deflection for the nickel-titanium files was significantly higher. The mean bending moment for the nickel-titanium files was significantly lower (P <.001) than the mean value for the stainless steel files. The scanning electron microscope demonstrated that the fracture surfaces of the stainless steel files were brittle, whereas the nickel-titanium files had a ductile fracture. CONCLUSIONS: When the design of endodontic instruments of different alloys is identical, the nickel-titanium files are more flexible in bending. However, nickel-titanium files require less force to deform to fracture.

Cytokines and growth factors modify the upregulation of contractile endothelin ET(A) and ET(B) receptors in rat cerebral arteries after organ culture.

AIM: Experimental cerebral ischaemia and organ culture of cerebral arteries induce an increased endothelin ET(B) receptor-mediated contraction. The aim of this study was to examine whether cytokines and growth factors, known to be activated in ischaemia, can influence the expression and function of endothelin receptors after organ culture. METHODS: Rat middle cerebral arteries were cultured for 24 h at 37 °C in humidified 5% CO(2) and air in culture medium alone, or with tumour necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), platelet-derived growth factor (PDGF), epidermal growth factor (EGF) or basic fibroblast growth factor (bFGF). Concentration-response curves were obtained for sarafotoxin 6c (ET(B) receptor agonist) and endothelin-1 (here ET(A) receptor agonist, because of ET(B) receptor desensitization). The receptor mRNA expression was examined by real-time PCR and the protein expression by immunohistochemistry and Western blot. RESULTS: Tumour necrosis factor-α (100 ng mL(-1) ) and EGF (20 ng mL(-1) ) potentiated the ET(B) receptor-mediated contraction (increase in pEC(50) without change in E(max) ). bFGF (10 ng mL(-1) ) and IL-1ß (10 ng mL(-1) ) induced an enhanced ET(A) receptor-mediated contraction. bFGF (10 ng mL(-1) ) significantly increased the ET(B) mRNA level, and EGF (20 ng mL(-1) ) increased the ET(A) receptor protein. Increased ET(B) receptor mRNA and protein level also were observed after treatment with IL-1ß (10 ng mL(-1) ). CONCLUSION: This study shows that TNF-α, IL-1ß, EGF and bFGF can modify the expression and function of endothelin receptors during organ culture. Because there is similar receptor upregulation in experimental stroke, the effect of cytokines and growth factors on endothelin receptor upregulation is an interesting aspect to study in vivo.

Hypersensitivity reactions to dental materials in a referred group of patients.

151 patients referred to the Department of Oral Diagnosis, University of Umeå, for investigation regarding potential side-effects of dental materials were subjected to epicutaneous testing at a dermatology clinic. Twelve persons in this group had oral mucosal changes. Among the 151 patients 39 women and 7 men had positive skin reactions to one or more of the test substances used. The majority of the positive reactions were related to metals, particularly nickel, but a number of positive reactions to organic test substances were also noted. In many cases the substance which caused the positive skin reaction was also a known constituent of the restorative or prosthetic materials present in the oral cavity of the patient concerned. The clinical relevance of such findings should, however, be evaluated with great caution and this and connected problems are discussed.

Description of persons with symptoms presumed to be caused by electricity or visual display units--oral aspects.

A questionnaire containing 20 questions was sent to 127 members of the Association for Those Injured by Electricity and Visual Display Units in northern Sweden, of whom 103 (81%) answered. The questionnaire consisted of questions about age, sex, and place of work. Furthermore, the members were asked to state: 1) their general and oral symptoms; 2) whether they thought that dental amalgam and other types of dental filling materials had affected their symptoms; 3) whether they were replacing or had replaced their amalgam fillings and, if so, what effect it had had on their symptoms; 4) whether they had been medically examined; and 5) whether they were or had been sick-listed for their complaints. Of those who answered the questionnaire, 79% were women (mean age 45 yr) and 21% men (mean age 42 yr). Sixty percent worked in offices. In 82%, the symptoms had started at work. The mean duration of the symptoms was 5.2 yr. The symptoms were aggravated mostly in "electric environment in general" and in "office with computers". Skin complaints, fatigue, and eye symptoms were the most common general symptoms. Sixty-five percent mentioned that they had oral symptoms. Gustatory disturbances, burning mouth, and temporomandibular joint (TMJ) dysfunction were the most common oral symptoms. Fifty-six percent considered that dental amalgam and 24% that other dental materials affected the symptoms. Twenty-one percent were in the process of replacing the amalgam fillings; 40% had already done so. After replacement, 37% had noticed a decrease of symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Odontologic survey of referred patients with symptoms allegedly caused by electricity or visual display units.

Twenty-eight consecutive patients with symptoms allegedly caused by electricity or visual display units were odontologically investigated according to a specially designed registration form including an anamnestic interview and a clinical protocol. The most common oral and general symptoms reported were burning mouth, craniomandibular dysfunction symptoms, skin complaints, and fatigue. Oral symptoms such as craniomandibular dysfunction and general symptoms such as eye complaints and dizziness scored highest on a visual analog scale regarding mean symptom intensity. The patients reported various numbers of medical diagnoses, such as allergic rhinitis or asthma and hypothyroidism. Various dental diseases were found; the most common were temporomandibular joint and masticatory muscle dysfunctions, lesions in the oral mucosa, and periodontal diseases. Urinary-Hg (U-Hg) analysis showed a mean U-Hg concentration of 8.5 nmol Hg/L urine, and none of the patients exceeded the limit of 50 nmol Hg/L urine. The U-Hg concentration was positively correlated with the number of amalgam fillings (P< 0.01) and craniomandibular disorders (P < 0.05). No or low secretion of the minor mucous glands was found in 43% of the patients. One patient showed hypersensitivity to gold and cobalt. The present study showed that various odontologic factors might be involved in some of these patients' suffering. Thus, it is important that professionals from other disciplines collaborate with dentistry if these patients are to be properly investigated.

Clinical study of patients referred for investigation regarding so-called oral galvanism.

Fifty-four patients referred to the Faculty of Odontology, University of Umeå, for investigation regarding "oral galvanism" were subjected to a general oral investigation. In addition the following parameters were studied: the highest calculated current between two metallic restorations in contact and the electrogustometrically determined threshold value for each person. No differences were found regarding these two parameters between the patients and a control group consisting of 15 persons. However, the general oral investigation had revealed that a relatively large number of patients had periodontal conditions which, together with mucous membrane affections and hypersensitivity reactions could explain some of the unpleasant sensations which bothered them. Furthermore, the results of a stomatognathic investigation which will be presented separately revealed that about three fourths of the patients needed treatment for their stomatognathic and/or temporomandibular joint conditions.

Clinical registration of charge transfer between dental metallic materials in patients with disorders and/or discomfort allegedly caused by corrosion.

Thirty referred patients and 15 control subjects were investigated with reference to the occurrence of bimetallic corrosion in the oral cavity. No differences between patients and controls could be found regarding the registered charge transfer between dissimilar short-circuited dental metallic restorations and/or appliances. However, a relatively large number of periodontal and mucous membrane affections, carious lesions and stomatognathic and/or temporomandibular joint disturbances were found within the patient group.

Plasma-selenium, glutathione peroxidase in erythrocytes and mercury in plasma in patients allegedly subject to oral galvanism.

Twelve patients with subjective symptoms, ascribed by the patients themselves to mercury released from dental restorations, were investigated. In addition to a general dental examination the following parameters were registered: the total number of amalgam surfaces in the mouth; potential and polarization of existing and accessible dental metallic restorations for calculation of intraoral currents. As regards the highest calculated intraoral current for each individual there was a statistically significant difference between the patient group and a control group consisting of 12 persons. An analysis of the amount of selenium, glutathione-peroxidase and mercury in the blood showed no differences between the patient and the control group. However, a statistically significant positive correlation could be seen between the total number of amalgam surfaces and the plasma-mercury level for patients and controls pooled together. The numerous other blood parameters analyzed did not reveal any differences between the groups.