Limas Tipo K

International Endodontic Journal (1998) 31, 48–52

The effect of sterilization on bending and torsional properties of K-files manufactured with different metallic alloys
´ C . C A N A L DA - S A H L I a , E . B R AU - A G UA D É a & J. S E N T I S - V I L A LTA b
aDepartment of Dental Pathology and Therapeutics, Faculty of Dentistry, and bDepartment of Biostatistics, Faculty of

Medicine,University of Barcelona, Barcelona, Spain.

Summary
The purpose of this study was to assess the effect of dryheat or autoclave sterilization on the resistance to fracture in torque and angular deflection and the resistance to bending of K-type files made of nickel–titanium (Nitiflex, Naviflex), titanium (Microtitane) or stainless steel (Flexofile, Flex-R). Ten K-type files of each sort, from size 25to 40, were tested, according to ANSI/ADA specification 28 (1988) and ISO specification 3630 (1992). Sterilization with dry heat and autoclave slightly decreased the flexibility of files made of stainless steel and nickel–titanium for most of the sizes, although the values obtained satisfied ISO specifications. The files made of titanium showed an increased flexibility after sterilization with autoclave(sizes 30 and 35) and dry heat (sizes 30, 35 and 40). Resistance to fracture varied amongst the five groups of files tested as follows: it decreased in some sizes of stainless-steel instruments, decreased in all sizes of titanium files assessed by the torsional moment, and either increased or decreased in some sizes of nickel–titanium files. All files tested, however, satisfied relevant standards forangular deflection after being subjected to sterilization with an autoclave or dry heat. Keywords: mechanical properties, nickel–titanium files, stainless-steel files, sterilization, titanium files

Introduction
Whilst success in endodontics is related to thorough cleaning, adquate shaping and complete filling of the root canal system, there is a need to practise controlled asepsis and to preventcross-infection. Sterilized files are therefore used in the preparation of the root canal. Many endodontists in clinical practice re-use instruments,
Correspondence: Dr Carlos Canalda-Sahli, Mallorea 173, E-08036 Barcelona, Spain.

especially when instrument sizes above 20 or 25 are used. Re-use involves repeated exposure to sterilization between uses. The physical properties of these instruments(flexibility, resistance to fracture by twisting, and cutting efficiency) should not be significantly altered by sterilization procedures, so that previously used files can be expected to be useful to clean and shape canals. In most studies (Roulet 1983, Iverson et al. 1985), tensile strength and resistance to breaking of stainlesssteel files were not significantly altered by dry-heat or autoclavesterilization. Haïkel et al. (1997) have recently compared the values of torsional moment, torsional angular deflection, bending moment and permanent angular deflection of three designs of stainless-steel files (Unifile, Flexofile, H-File) before and after ultrasonic cleaning and sterilization in chemiclave, dry heat, and glass beads according to the American National Standards Institute American DentalAssociation (ANSI/ADA) specification 28 (American National Standards Institute 1988). An increase in value for all mechanical properties tested was observed after the treatment procedures with the exception of Flexofile, wherein a decrease in permanent angular deflection was evident. Generally, these changes were insignificant and still well within ANSI/ ADA specification 28 (American National StandardsInstitute 1988). In K-files of sizes 15–40, Mitchell et al. (1983) found a decrease in resistance to fracture by twisting after ten sterilization cycles in an autoclave, although all files satisfied the minimum standards according to ANSI/ADA specification 28 (American National Standards Institute 1988). Endodontic instruments manufactured with different metal alloys, such as nickel–titanium or titanium...