Introduction - Materials and methods.
R. C. Martins, M. G. A. Bahia & V.T. L. BuonoDepartment of Restoration Dentistry, Faculty of Dentistry, Department of Metallurgical and Materials Engineering, Engineering School, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil.Introduction.
The machining of nickel-titanium (NiTi) endodontic files is a complex procedure, generally resulting in surfaces with a high concentration of defects such as debris and metal strips, in addition to pits and blunt cutting edges (Serene et al.1995, Marsicovetere et al.1996, Marending et al. 1998, Eggert et al. 1999). Morphometric variations have also been observed amongst instruments of the same size (Marsicovetere et al. 1996). The detection of a variable amount of material adhering to the tips and cutting edges of new NiTi instruments (Marsicovetere et al. 1996, Marending et al. 1998), and the observation that the amount of these deposits increases after root-canal instrumentation (Marending et al. 1998, Eggert et al. 1999) may be important. Eggert et al. (1999), when reporting an increase of debris on instruments after usage, indicate that a review of instrument cleaning procedure was justified. The exchange of debris via instruments from one patient to another is undesirable as theycanact as antigens, infecting agents or nonspecific irritants (Murgel et al.1990). Because microorganisms are the major cause of endodontic disease, asepsis and microbiological control are essential for endodontic success (Hurtt & Rossman 1996). As pointed out by Reams et al. (1995), if the bioburden (blood, saliva, debris) is not removed from endodontic instruments, any method of sterilization may be ineffective.
The purpose of this preliminary study was to analyze surface irregularities on ProFile NiTi rotary instruments before use, after sterilization by two different methods and after root-canal instrumentation. The main objective was to investigate the nature of these irregularities and how they might influence the use of the instruments during root-canal treatment. Materials and methods.
A total of 15 ProFile NiTi rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland), five with 0.04 taper, size 20, five with 0.04 taper, size 25 and five with 0.06 taper, size 20were analyzed. They were with drawn from sealed boxes and sequentially numbered on the handle, using a high-speed diamond bur. The instruments were washed with a brush and liquid detergent in running water and ultrasonically cleaned at a frequency of 40 kHz (Thornton-INPEC, Vinhedos, SP, Brazil) for 5 min in commercially hydrated ethyl alcohol.
The files were then inspected in a stereomicroscope (Wild M8, Heerbrugg, Switzerland), at magnifications between 6x and 50x, using a support where they could be rotated 3608 for observation. Morphometric changes, surface imperfections and the presence of particles were then observed, using an endodontic ruler, to establish the position of the surface irregularities in relation to the instrument tip. Each instrument was provided with an identification record, used to guide the analysis by scanning electron microscopy (SEM) (Jeol JSM 5410, Tokyo, Japan). Secondary electron images, showing the topographic characteristics of the irregularities, were recorded. X-ray energy-dispersive spectroscopy (EDS) (Noran TN-M3055, Middleton, WI, USA) was used to identify and characterize semi-quantitatively, chemical elements present in deposits found on instrument surfaces.
Following this initial analysis, the instruments were washed again as previously described, but not ultrasonically cleaned, and randomly divided into two groups: nine instruments (three of eachtaperand size) were sterilized at 170 8C for 1 h in a dry heat sterilizer (Fanen 311CG, Saâ¹ o Paulo, SP, Brazil) and the remaining six instruments (two of each taper and size) were sterilized for 20 min in an autoclave (Cristofoli, Campo Mourao, PR, Brazil), at 128 8C, a pressure of 1.6 kgf cm_2. After sterilization, the instruments were ultrasonically cleaned and inspected as described before.
Finally, each instrument was used top repare six molar root canals with average curvature between 258 and 408. Canal instrumentation was performed using a crown-down technique, following the clinical protocol described in Table 1. The files were operated at 300 rpm, using a slow-speed high-torque endodontic electric motor (TC Motor 3000, Nouvag, Goldach, Switzerland), with a16 :1gear reduction handpiece. Rc-Prep (Premier Dental Products, Norristown, PA, USA) was used for lubrication and a 2.5% sodium hypochlorite solution was employed as irrigant. Dry heat sterilization, which is the most common procedure used in Brazil for sterilizing endodontic instruments, was applied between canal preparations. After use, the files were washed again, ultrasonically cleaned as described before, and then observed using the same techniques.
Table 1. Preparation technique.