Morphometric variations such as sharpened, attened or rounded tips, deeper or shallower U-plane concavities and wider or thinner radial lands, were observed by stereomicroscopy and SEM in new instruments. The presence of debris, metal ash and deep milling marks (Fig.1) was detected in all files. The irregularities were randomly distributed along the length of the instruments and the majority of them could only be observed by SEM with a relatively high magnification (between 200x and 1000x). These two aspects, size and distribution, rendered quantitative analysis of the irregularities impracticable.
Avariable amount of adherent material on the tip and along the 16-mm of the concavities and radial lands was observed in the majority of the new instruments (Figs 2 and 3). The exact location, distribution, size, thickness and chemical composition of the material varied from one instrument to another, irrespective of size and taper. The EDS analysis (Fig. 4) of this material on unused instruments showed that it contained mainly carbon (C) and sulphur (S), together with smaller amounts of other elements such as oxygen (O), sodium (Na), calcium (Ca) and aluminium (Al). The presence of Ni and Ti peaks in the EDS spectrum of Fig. 4 is owing to the fact that the electron probe also detects the substances underneath the deposits. It is also important to observe that the correlation between peak amplitudes and the concentration of chemical elements in the analyzed areas is only semi-quantitative.
After the files were subjected to the cleaning procedures and to one sterilization cycle in a dry heat sterilizer or in a steam autoclave, no appreciable changes were observed on the topographic aspect of the adhered material (Fig. 5), noron its chemical composition; EDS spectra displayed the same peaks shown in Fig. 4. These results indicate that the cleaning and sterilization procedures employed were not sufficient to remove the adhered substance.
Surface analysis of the instruments after shaping six root canals, followed by cleaning and sterilization showed wear marks and a decrease in the amount of the deposited material. Moreover, it has been verified that in the remaining adherent material, there was a tendency for the accumulation of new deposits (Fig. 6). Atypical EDS spectrum of these deposits, recorded with the same characteristics, is shown in Fig.7. The high concentrations of calcium (Ca) and phosphorus (P) in these new deposits show that they were of dentinal origin.
Figure 1. Deep milling marks on the radial land, affecting the cutting edge of a new size 25 ProFile instrument with 0.04 taper. Original magnification: 200x.
Figure 2. Material adhered along the surface of a new size 20 ProFile instrument with 0.04 taper. Original magnification: 35x.
Figure 3. Material adhered on the radial land of the same file shown in Fig. 2. Original magnification: 750x.
Figure 4. EDS spectrum of the adhered substance, showing the presence of carbon (C) and sulphur (S) and smaller amounts of oxygen (O), sodium (Na), calcium (Ca) and aluminum (Al).
Figure 5. Material adhered on the surface of a size 20 ProFile instrument with 0.04 taper, sterilized in autoclave. Original magnification: 750x.
Figure 6. Deposits accumulated on the adhered material on the surface of a size 20 ProFile instrument with 0.06 taper, after cleaning and shaping six root canals. Original magnification: 1000x.
Figure 7. EDS spectrum of the deposit shown in Fig. 6, with high concentrations of calcium (Ca) and phosphorus (P).