Dry Heat Sterilization Research Articles

A COMPARATIVE EVALUATION OF EFFECTS OF DIFFERENT KINDS OF STERILIZATIONS ON LOAD DEFLECTION CHARACTERISTICS, TENSILE PROPERTIES OF COPPER NITI WIRES- AN INVITRO STUDY

Copper NiTi wires were introduced by Sachdeva R and Miyasaki S in 1994. This latest innovation in the evolutionary scale gives us the opportunity of choosing the force level by choosing the temperature at which the wires will deliver its optimum force level. With so many advantages and their ability to return to their original form coupled with the high cost of copper NiTi many clinicians started reusing the wire. This raises concern about disinfecting/sterilizing the wire before using in another patient for prevention of cross infection. Hence, various sterilization procedures like cold sterilization using 2% acidic glutaraldehyde, dry heat sterilization and autoclaving were used to prevent this cross infection.

Properties of endotracheal tubes reprocessed by two procedures

Background Reusing endotracheal tubes (EITs) has been performed in Indonesia with no evidence of its safety. Objective To evaluate sterility, as well as the mechanical, surface, and matrix properties of reused EITs following 2 different reprocessing procedures.Methods Reused EITs were cleaned and disinfected, then sterilized by ethylene oxide gas sterilization (group A) or dry heat sterilization (group B). New EITs were used as the standard for comparison. Microbes were identified and microbial counts were determined as colony forming units (CFUs). Evaluation of mechanical properties was perfonned by a Universal Testing machine. All samples underwent tensile and compression tests.Load defonnation curves were recorded from F max and strain at F max. Microstructure analysis was done using X􀁅ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX).Results Positive cultures of commensal bacteria were found in 2/12 samples in group A, and 5/17 samples in group B. T here was no statistically significant difference between them (P =0.07). Pseudomonas aeruginosa or other common pathogens were not found. Samples from both groups showed equal flaccidity, compared to the standard. Surface microstructure analysis of reused EITs 'With XPS and EDX showed degradation of the matrixcomponent. SEM analysis detected some large particles and fissures. EDX analysis on the large particles detected sodium and calcium signals. Altogether, signs of contamination and material damage were very strong.Conclusion Both reprocessing methods of reused EITs gave comparable results on sterility and mechanical behavior, but reprocessing may cause decreased surface and matrix quality.

Difference between post curing composite hardness with heating using dry sterilizer and radiation using light box

Introduction: Composite resin has been used as a restoration material for quite a long time. Two different methods were expected to show result of which method that would be the most promising. Aim of study is to analyzed differences the hardness of one composite resin subjected to two post curing treatments. Methods: This study was a true experimental research (in vitro). The subjects were 30 specimens of the hybrid light cured resin composites made in a mold (6 mm diameter and 4 mm high). The hardness of all specimens were tested using Rebound Hardness Tester. Data were compared using ANOVA and post hoc analysis (for pairwise independent groups) using t-tests. Results: This study showed that post curing treatment by heat (for 10 min at 110 oC ) showed higher hardness (p<0.005). Conclusion: There was difference of hardness between two methods of post curing. Moreover, post curing with dry heat sterilizer at 110oC for 10 min was found to be the most promising post curing method.

Influence of microwave sterilization on the cutting capacity of carbide burs

Objective:This study compared the cutting capacity of carbide burs sterilized with microwaves and traditional sterilization methods.Material and Methods:Sixty burs were divided into 5 groups according to the sterilization methods: dry heat (G1), autoclave (G2), microwave irradiation (G3), glutaraldehyde (G4) or control – no sterilization (G5). The burs were used to cut glass plates in a cutting machine set for twelve 2.5-min periods and, after each period, they were sterilized (except G5) following the protocol established for each group. The cutting capacity of the burs was determined by a weight-loss method. Data were analyzed statistically by Kruskal-Wallis and Dunn's test.Results:The means of the cutting amount performed by each group after the 12 periods were G1 = 0.2167 ± 0.0627 g; G2 = 0.2077 ± 0.0231 g; G3 = 0.1980 ± 0.0326 g; G4 = 0.1203 ± 0.0459 g; G5 = 0.2642 ± 0.0359 g. There were statistically significant differences among the groups (p<0.05); only dry heat sterilization was similar to the control.Conclusion:Sterilization by dry heat was the method that least affected the cutting capacity of the carbide burs and microwave sterilization was not better than traditional sterilization methods.

Inactivation of Escherichia coli endotoxin by soft hydrothermal processing.

Bacterial endotoxins, also known as lipopolysaccharides, are a fever-producing by-product of gram-negative bacteria commonly known as pyrogens. It is essential to remove endotoxins from parenteral preparations since they have multiple injurious biological activities. Because of their strong heat resistance (e.g., requiring dry-heat sterilization at 250 degrees C for 30 min) and the formation of various supramolecular aggregates, depyrogenation is more difficult than sterilization. We report here that soft hydrothermal processing, which has many advantages in safety and cost efficiency, is sufficient to assure complete depyrogenation by the inactivation of endotoxins. The endotoxin concentration in a sample was measured by using a chromogenic limulus method with an endotoxin-specific limulus reagent. The endotoxin concentration was calculated from a standard curve obtained using a serial dilution of a standard solution. We show that endotoxins were completely inactivated by soft hydrothermal processing at 130 degrees C for 60 min or at 140 degrees C for 30 min in the presence of a high steam saturation ratio or with a flow system. Moreover, it is easy to remove endotoxins from water by soft hydrothermal processing similarly at 130 degrees C for 60 min or at 140 degrees C for 30 min, without any requirement for ultrafiltration, nonselective adsorption with a hydrophobic adsorbent, or an anion exchanger. These findings indicate that soft hydrothermal processing, applied in the presence of a high steam saturation ratio or with a flow system, can inactivate endotoxins and may be useful for the depyrogenation of parenterals, including end products and medical devices that cannot be exposed to the high temperatures of dry heat treatments.

Bioindicator production with Bacillus atrophaeus’ thermal-resistant spores cultivated by solid-state fermentation

Bacillus atrophaeus' spores are used in the preparation of bioindicators to monitor the dry heat, ethylene oxide, and plasma sterilization processes and in tests to assess sterilizing products. Earlier production methods involved culture in chemically defined medium to support sporulation with the disadvantage of requiring an extended period of time (14 days) besides high cost of substrates. The effect of cultivation conditions by solid-state fermentation (SSF) was investigated aiming at improving the cost-productivity relation. Initial SSF parameters such as the type of substrate were tested. Process optimization was carried out using factorial experimental designs and response surface methodology in which the influence of different variables--particle size, moisture content, incubation time, pH, inoculum size, calcium sources, and medium composition--was studied. The results have suggested that soybean molasses and sugarcane bagasse are potential substrate and support, respectively, contributing to a 5-day reduction in incubation time. Variables which presented significant effects and optimum values were mean particle size (1.0 mm), moisture content (93%), initial substrate pH (8.0), and water as a solution base. The high-yield spore production was about 3 logs higher than the control and no significant difference in dry heat resistance was observed.

Effects of steam and dry-heat sterilization on bending properties of NiTi wires

Purpose Nickel–titanium arch wires have a prominent role in orthodontic appliances due to their desirable mechanical properties. The purpose of the present study is to determine the effects of autoclave and dry-heat sterilization on the bending properties of three types of NiTi superelastic wires. Methods In this experimental study, three commercial types (Force I, Rematitan LITE, and G & H) of superelastic NiTi wires, 0.016 in. in diameter, were selected. From each type of wire, 20 specimens were prepared. The specimens were initially subjected to the three-point bending test at a rate of 1 mm/min on the Dartec testing machine in order to determine their load-deflection properties before sterilization. Then, 10 specimens of each type of wire were subjected to dry-heat sterilization (160 °C, 120 min) and 10 to autoclave sterilization (121 °C, 15 psi, 24 min). After sterilization, the specimens were subjected to the three-point bending test again and their load-deflection curves were plotted. The values for bending properties obtained before and after sterilization were subjected to the Duncan and ANOVA tests at the 0.05 significance level. Results Our findings revealed considerable changes in the load-deflection properties of the test wires as a result of dry-heat sterilization. These changes included decreasing in applied force in both loading and unloading phases and reducing of wire superelasticity. Conclusion Steam and dry-heat sterilization cause changes in the mechanical properties of superelastic NiTi arch wires.

Sterilizers, Part I: Heat Sterilization

Sterilizers, Part I: Heat Sterilization

Sterilization of glycerin

The sterilization of glycerin is described. Glycerin is used in a wide variety of pharmaceutical formulations, including oral, otic, ophthalmic, topical, and parenteral preparations. Of the myriad uses for glycerin, some require a sterile solution. Due to the nature of dry heat sterilization with resulting equipment and validation needs, sterile filtration is the preferred sterilization method for glycerin at the Mayo Clinic Pharmacy Services Production Laboratory in Rochester, Minnesota. A practical procedure was attained with the use of a chemically compatible 0.22-microm capsule filter, peristaltic pump, and sterile tubing. The sterile tubing is attached firmly, with a twisting motion, to the hose barb ends of the filter. The peristaltic pump is set at minimum speed, and a sterile syringe is used to capture the sterile glycerin filtrate. After filtration, filter integrity testing using the bubble point test is performed on the filter used to sterilize the solution. Packaging was then completed by placing glycerin aliquots into unit-of-use sterile syringes, placing a sterile tip cap on each syringe, and labeling the syringe. End testing is needed for preparations, such as sterile glycerin, that are made from nonsterile components, regardless of sterilization technique. This quality-control testing includes but is not limited to visual checks, pH checks, and tests for bacterial endotoxins, particulate matter, and sterility. Beyond-use dating is then assigned based on chemical, physical, microbiological, and packaging considerations. A practical method for sterilization of glycerin by compounding pharmacists is attainable through the use of membrane filtration. Sterility assurance is achieved through appropriate validation, and quality-control checks must be completed before release of the injectable preparation.

Vapor hydrogen peroxide as alternative to dry heat microbial reduction

The Jet Propulsion Laboratory (JPL), in conjunction with the NASA Planetary Protection Officer, has selected vapor phase hydrogen peroxide (VHP) sterilization process for continued development as a NASA approved sterilization technique for spacecraft subsystems and systems. The goal was to include this technique, with an appropriate specification, in NASA Procedural Requirements 8020.12 as a low-temperature complementary technique to the dry heat sterilization process. The VHP process is widely used by the medical industry to sterilize surgical instruments and biomedical devices, but high doses of VHP may degrade the performance of flight hardware, or compromise material compatibility. The goal for this study was to determine the minimum VHP process conditions for planetary protection acceptable microbial reduction levels. Experiments were conducted by the STERIS Corporation, under contract to JPL, to evaluate the effectiveness of vapor hydrogen peroxide for the inactivation of the standard spore challenge, Geobacillus stearothermophilus. VHP process parameters were determined that provide significant reductions in spore viability while allowing survival of sufficient spores for statistically significant enumeration. In addition to the obvious process parameters of interest: hydrogen peroxide concentration, number of injection cycles, and exposure duration, the investigation also considered the possible effect on lethality of environmental parameters: temperature, absolute humidity, and material substrate. This study delineated a range of test sterilizer process conditions: VHP concentration, process duration, a process temperature range for which the worst case D-value may be imposed, a process humidity range for which the worst case D-value may be imposed, and the dependence on selected spacecraft material substrates. The derivation of D-values from the lethality data permitted conservative planetary protection recommendations.

Effect of different methods of sterilization on the inactivation of bacterial endotoxin (LPS) in endodontic files

This study evaluated the presence of lipopolysaccharide (LPS) in endodontic files after in vitro contamination with E. coli LPS and sterilization in dry heat or wet heat, with or without previous immersion in a Ca(OH)2 suspension. LPS was quantified using the Kinetic QCLTM test and data were analyzed statistically by the t-test. LPS was quantified only in the contaminated group, not submitted to any immersion or sterilization procedure (0.262±0.1296 endotoxin units/mL) (p=0.0003). In conclusion, both wet heat and dry heat sterilization were effective in inactivating LPS without the need of previous immersion of the files in a Ca(OH)2 suspension.

Effect of sterilization on the properties of CDHA-OCP-beta-TCP biomaterial

The effect of the method of sterilization on the physical, chemical and mechanical properties of a new bone repairing material was studied. The material was obtained by thermal hydrolysis of beta-tricalcium phosphate/orthophosphoric acid cement and was composed of calcium deficient hydroxyapatite, octacalcium phosphate (OCP), and beta-tricalcium phosphate. Partial decomposition of the OCP was observed after sterilization for the three methods. Decomposition increased to the following sequence of sterilization methods: ethylene oxide; autoclaving; dry oven. On the other hand, mechanical strength decreased with regard to non sterilized material in the sterilization sequence: ethylene oxide; dry oven; autoclaving. The compressive strength was 8.5 ± 1.0; 9.0 ± 1.2; 8.2 ± 0.8 and 6.5 ± 1.0 MPa, whereas diametral tensile strength was 2.1 ± 0.3; 2.5 ± 0.1; 1.9 ± 0.9 and 1.6 ± 0.3 for the material sterilized by ethylene oxide, dry oven, and autoclaving, respectively. Several compositional and microstuctural changes were detected after dry heat and autoclave sterilization. Ethylene oxide sterilization had lesser effect on the chemical composition and strength than dry heat and autoclaving.

Influence of sterilization on mechanical properties and fatigue resistance of nickel–titanium rotary endodontic instruments

To evaluate the effect of repeated sterilization cycles in dry oven or autoclave, on the mechanical behaviour and fatigue resistance of rotary endodontic Ni-Ti instruments. New Ni-Ti instruments were subjected to five consecutive sterilization cycles in a dry oven or steam autoclave. Microhardness was measured in the nonmachined parts of the shanks of instruments using a Vickers indenter. Specimens of Ni-Ti wires were submitted to the same sterilization protocol and tensile tested until rupture. A group of instruments were fatigued to one half of their average fatigue life and then sterilized. New and sterilized instruments were fatigue tested until rupture. anova tests at alpha = 0.05 were used for statistical analysis. Sterilization procedures resulted in no significant changes in Vickers microhardness, nor in the parameters describing the mechanical behaviour of the wires. However, the number of cycles to failure was statistically higher for all instruments after dry heat or autoclave sterilization cycles. In the instruments previously fatigued to one half of their fatigue life, autoclave sterilization gave rise to an increase of 39% in the remaining number of cycles to failure. Changes in the mechanical properties of Ni-Ti endodontic instruments after five cycles of commonly used sterilization procedures were insignificant. The sterilization procedures are safe as they produced a significant increase in the fatigue resistance of the instruments.

Effect of heat sterilization on surface characteristics and microstructure of Mani NRT rotary nickel–titanium instruments

To evaluate the effect of repeated dry heat sterilization on surface characteristics and microstructure of Mani nickel-titanium rotary instruments. Thirty-three new Mani NRT instruments, size 30, taper 0.04 and 25 mm in length were examined. Twenty-seven instruments were divided into three groups for surface characterization by scanning electron microscopy (SEM). In the first group (n = 3), instruments were examined in the 'as-received' condition and after they had been subjected to 11 sterilization cycles. In the second and third subgroups (n = 12), 12 instruments were prepared for cross-section and a further 12 for longitudinal sectional analysis and evaluated in subgroups of three, after 0, 1, 6 and 11 sterilization cycles. The remaining six instruments were analysed with differential scanning calorimetry (DSC), three in the 'as-received' condition and three after being subjected to 11 cycles of sterilization. Scanning electron microscopy observations indicated the presence of debris, pitting and deep milling marks in both new and sterilized files. After 11 sterilization cycles, debris remained and surface roughness was increased significantly (P = 0.05). DSC analyses showed that the specimens in the 'as-received' condition and after 11 sterilization cycles were in the austenite phase or a mixture of austenite and R-phase at 37 degrees C. The machining defects and structural imperfections of new Mani instruments are indicative of the difficulty in manufacturing nickel-titanium endodontic instruments. DSC measurements suggest that Mani instruments are capable of superelastic behaviour under clinical conditions.

Dialyzer Reuse—Part I: Historical Perspective

The first apparatus for hemodialysis in animals, made painstakingly by Abel et al. in their laboratory at the beginning of 20th century, was cleaned with acid-pepsin to digest blood, disinfected with thymol, and reused for up to 30 experiments for as long as 8 months. The obvious incentive was saving time. In the early years of hemodialysis in patients, dialyzers and lines were assembled and sterilized immediately before dialysis. Various methods of dry and moist heat sterilization and miscellaneous chemical agents were employed for disinfection. Significant time was required to assemble the dialyzers, so there was an incentive to reuse previously assembled dialyzers to save time, especially for home hemodialysis. Bleach to clean and formaldehyde to disinfect the membranes and lines was used for this purpose. Preassembled dialyzers, commercially introduced in the 1950s, were the most expensive components of hemodialysis systems, therefore reprocessing of these dialyzers was the most effective way to save money. Refrigeration of coil dialyzers with blood, introduced in the mid-1960s, was associated with frequent febrile reactions and was soon abandoned. Preassembled coil and plate dialyzers permitted almost complete return of blood after dialysis and led to the introduction of chemical disinfection for dialyzer reprocessing. A variety of disinfectants have been used. Formaldehyde was the most common disinfectant until the end of the 1970s. Sodium hypochlorite was used to clean the majority of dialyzers and to sterilize dialyzers with polyacrylonitrile membranes. In the early 1980s, peracetic acid and glutaraldehyde started to compete with formaldehyde. By the 1990s, formaldehyde had become less popular than peracetic acid. In the mid-1990s, disinfection and membrane cleaning with acetic acid and heat was introduced. Manual reprocessing was replaced by early reuse machines in the mid-1970s and a more sophisticated second generation of automated hemodialyzer reprocessing machines followed in the late 1970s. Recently disinfection of dialyzers with moist heat has resumed. Saving both time for the patient and money for the provider were the main motivations for designing a new machine for daily home hemodialysis. The machine, developed in the 1990s, cleans and moist-heat disinfects the dialyzer and lines in situ so they do not need to be changed for a month. In contrast, the reuse of dialyzers in home hemodialysis patients treated with other hemodialysis machines has become less popular and is almost extinct.

Dry and moist heat sterilisation cannot inactivate pyrogenicity of Gram positive microorganisms

In the monocytic cell line Mono Mac 6 pyrogens induce interleukin-6 secretion dose dependently. The aim of this study is to examine the interleukin-6 inducing capacity of Gram positive Staphylococcus aureus and Bacillus subtilis endospores after moist and dry heat sterilisation. Moist heat sterilisation of B. subtilis endospores for 15 min at 121 °C and 134 °C can only reduce the interleukin-6 inducing capacity to 57% and 63%, respectively, compared to untreated. Moist heat sterilisation of S. aureus for 60 min at 121 °C and 134 °C does not reduce the interleukin-6 inducing capacity of S. aureus. On the contrary moist heat sterilisation at 134 °C for 10, 20 and 40 min significantly increases the interleukin-6 inducing capacity compared to untreated S. aureus. This is confirmed in the rabbit pyrogen test. Dry heat sterilisation of B. subtilis endospores at 220 °C for 45 min reduces the interleukin-6 inducing capacity to 2% compared to untreated endospores. Dry heat treatment of S. aureus at 220 °C for 30 min only reduces the activity to 55%. However, after 250 °C for 30 min or 220 °C for 6 h there is no detectable activity of S. aureus. In conclusion, neither the interleukin-6 inducing activity nor the pyrogenicity of S. aureus and endospores of B. subtilis can be inactivated by the heat sterilisation procedures described by the European Pharmacopoeia.

Flow-through ultrasonic emulsification combined with static micromixing for aseptic production of microspheres by solvent extraction

Final sterilisation of drug-loaded polymeric microspheres is problematic as dry heat or steam sterilisation are not applicable, and γ-irradiation may result in radiolytic scission of the polymer chains, and potentially damage the bioactive compound. Therefore, aseptic production is the method of choice to obtain a sterile product. A novel process for the production of microspheres is introduced based on the principle of double emulsion–solvent extraction. The process uses a flow-through ultrasonic cell for the preparation of the primary emulsion, in combination with a static micromixer for the production of the double emulsion. Because of its small scale, the equipment is readily accommodated in a laminar air-flow cabinet or an isolator. Thanks to the low technical complexity and easy handling of the process, only minimal manual interventions is required. Finally, the possibility for in-place cleaning and sterilisation makes the equipment and process well suited for aseptic microsphere preparation. Microspheres were prepared from poly(lactic-co-glycolic acid) (PLGA), and bovine serum albumin (BSA) served as model protein for microencapsulation. The BSA-in-PLGA (w/o) emulsions produced by the ultrasonic flow-through cell exhibited mean droplet sizes of <700 nm. Further processing into microspheres of 15–40 μm mean diameter resulted in approx. 70% BSA encapsulation efficiency. Batch-to-batch reproducibility was excellent. Microsphere batches produced under aseptic conditions to assure product sterility exhibited no microbial contamination when examined by a simplified sterility test. The presented technology offers great potential for aseptic microsphere production for batch-sizes suitable, e.g. for clinical investigations. Complete validation of product sterility would, however, demand more extended tests.

Several Aspects of Biological Indicators for Sterility Assurance

A biological indicator (Bl) for use in thermal or chemical sterilization processes consists of standardized bacterial spore preparations which are usually in the form either of suspensions or of spores dried on carriers. Bl is usually placed in dummy packs located at strategic sites in the sterilizer. After the sterilization process, the aqueous suspensions or spores on carriers are aseptically transferred to an appropriate culture medium, which is then incubated and periodically examined for signs of growth. Spores of Geobacillus stearothermophilus ATCC 7953 or 12980 are used for steam, formaldehyde, hydrogenperoxide, ozone sterilization monitoring, and these are incubated at 55°C. Spore of Bacillus atrophaeus ATCC 9372 is used for ethylene oxide and dry heat sterilization monitoring, and incubated at 30-35°C. When the paper strip type Bl is used, aseptic transfer is indispensable. Aseptic transfers can be avoided by the use of self-contained Bl where the spore strip and nutrient medium are present in the same device ready for mixing after use. This Bl is, however, not recommended for use in a validation study. Resistance of Bl is adjudged from the spore destruction curve obtained upon exposure to the sterilization process, as well as the recommended Bl spores and their decimal reduction times. Great care must be taken in the preparation and storage to ensure a reproducible response to sterilization processes to assure that Bl is a reliable monitor for steriliza tion validation. One of the drawbacks of Bl is that a long period of incubation is required to confirm a satisfactory sterilization process, which imposes an undesirable delay on the release of the product. To shorten the incubation period is now being discussed at ISO TC 198, but as sterilized Bls are injured spores, a short cultivation time may result in an inaccurate result.

Tissue reactions of in situ formed dextran hydrogels crosslinked by stereocomplex formation after subcutaneous implantation in rats

In this study, the in vivo biocompatibility of physically crosslinked dextran hydrogels was investigated. These hydrogels were obtained by mixing aqueous solutions of dextran grafted with l-lactic acid oligomers and dextran grafted with d-lactic acid oligomers. Gelation occurs due to stereocomplex formation of the lactic acid oligomers of opposite chirality. Since gelation takes some time, in situ gel formation is possible with this system. A number of sterilization methods was evaluated for their effect on the chemical and physical properties of the hydrogel. It was shown that of the investigated options (filtration, gamma irradiation, dry-heat and autoclaving) dry-heat sterilization was the preferred method to prepare sterile gels suitable for in vivo evaluations. Two types of stereocomplex gels were prepared and implanted subcutaneously in rats. The tissue reaction was evaluated over a period of 30 days. A mild ongoing foreign body reaction was observed characterized by infiltration of macrophages. Giant cells were only scarcely formed and the low numbers of lymphocytes showed that priming of the immune system is hardly involved. Importantly, the gels fully degraded in vivo within 15 days, which is in good agreement with the in vitro degradation behaviour of these gels. In conclusion, stereocomplexed dextran-oligolactic gels showed good biocompatibility which makes them suitable candidates for the design of controlled release devices for pharmaceutically active proteins.

Surface analysis of ProFile instruments by scanning electron microscopy and X-ray energy-dispersive spectroscopy: a preliminary study.

The purpose of this preliminary study was to analyze surface irregularities on ProFile nickel-titanium (NiTi) rotary instruments before use, after sterilization by two different methods and after instrumentation of molar root canals. Five new ProFile NiTi rotary instruments with 0.04 taper, size 20, five instruments with 0.04 taper, size 25 and five with 0.06 taper, size 20 were analyzed by scanning electron microscopy (SEM) and X-ray energy-dispersive spectroscopy (EDS). The instruments were then divided into two groups: three of each taper and size were sterilized in a dry heat sterilizer, whilst two of each taper and size were sterilized in an autoclave. After inspection by the same techniques, the files were used to instrument six molar root canals, and again analyzed by SEM/EDS. Together with the usual machining defects, a variable amount of material containing mainly carbon and sulphur was found on the surface of new instruments. This material was not removed by standard cleaning and sterilization procedures. The use of the files for instrumentation of root canals eliminated a considerable amount of the adhered substance, but deposits rich in calcium and phosphorus accumulated on the remaining impurities. The adherence of dentine on surface deposits found on new ProFile instruments requires special cleaning, prior to sterilization.