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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 7  »  Effects of rotary instruments and ultrasonic irrigation on debris and smear layer scores: a scanning electron microscopic study
Effects of rotary instruments and ultrasonic irrigation on debris and smear layer scores: a scanning electron microscopic study
Discussion - References.

The aim of this study was to test for differences between two rotary canal preparation techniques and the role of ultrasonic activated irrigation on the cleanliness of root canal walls. Two tips of different design and material, a cutting stainless steel K-file and a blunt Ni–Ti-wire, were compared as transmitters of ultrasonic energy to activate irrigants. Because of their cutting surfaces, fluted stainless-steel files were expected to produce more debris and smear layer than the smooth-surfaced Ni–Ti flexible wire.
Varying methods have been described in previous studies evaluating the effects of ultrasonics on canal wall cleanliness. Therefore, methodology should be initially considered before comparing results.

Canal size and instrument diameter.
The diameter of the canal determines the amplitude of the oscillating instrument tip. With this in mind, Cunningham & Martin (1982) used ultrasonic files for preparation but no definitive canal size was achieved. In contrast, Jensen et al. (1999) prepared canals up to size 55. These two studies, plus that by Goodman et al. (1985) showed improved root canal debridement, particularly in the middle and coronal thirds of canals. The oscillation of the tips of ultrasonic instruments is decreased by constraining it in the root canal. Because the amplitude of the oscillation is largest at the instrument’s tip, any attenuation affects the apical part most significantly (Walmsley & Williams 1989), where the diameter of the canal is smallest. The current results confirm that the apical part of the canals was least influenced by the activated irrigation.
The size 15 K-File used in groups 2 and 5 had a .02 taper with a diameter corresponding to a size 47 file at the point where the cutting flutes terminated. In contrast, the Ni–Ti-wire used was cylindrical and 0.26 in diameter. In narrow canals larger instruments have limited space to oscillate freely and may consequently be less efficient than similar instruments with a smaller diameter. The larger diameter of the Ni–Ti-wire in the apical part may have produced significantly higher mean smear layer scores at the 3 mm level compared to the 9 mm and the 6 mm levels.
Cavitation and acoustic streaming are considered important physical phenomena influencing canal debridement when using ultrasonic devices (Ahmad et al. 1987). Ultrasonically activated files produced streaming patterns close to the file, continuously moving irrigants around, thereby producing shear stresses, which could damage biological cells and remove debris (Ahmad 1989). Of the two procedures, acoustic streaming is considered more relevant than cavitation (Ahmad et al. 1987). These facts may explain the finding, that there was significantly more debris found at the 3 mm levels of both the K-File and Ni–Ti-wire groups compared to the 9 mm levels.

Volume of irrigant.
Another important factor is the volume of the irrigation. Previous studies have shown that the volume of irrigant influenced the cleanliness of the root canal. Larger volumes of NaOCl and EDTA yielded significantly cleaner canal walls than smaller volumes (Yamada 1983). For the current study, a continuos irrigation supply was not chosen so that the volume of irrigant was the same for both the two control and four test groups. Some ultrasonic units, such as the Piezon Master, can supply a continuous flow of irrigant. This produces a high volume irrigation of up to 20 mL min−1 and its effect can not be compared to the volume (2 mL of NaOCl or 2 mL of EDTA) delivered by a 27-gauge needle.
Cameron (1995) reported that the most effective regime with ultrasonic energy was to activate each and every dose of irrigant placed in the canal. In that study, the time required for irrigation was roughly 18 min per canal. In the current study, irrigating times of 1 min each for EDTA and NaOCl was selected after canal preparation, as this seems clinically practical. Consequently, the active irrigation time in the control and test groups was similar in the current study. Under these conditions, the use of ultrasonic energy for irrigant activation did not improve debridement compared to the control groups.
However, this finding is in contrast to previous studies (Cunningham & Martin 1982, Cameron 1995, Jensen et al. 1999). To highlight just how ultrasonic methods vary, a light microscopic study by Jensen et al. (1999) activated the irrigant after preparation, 2 mm short of working length, for 3 min; this enabled the ultrasonic instrument tip to oscillate more freely in the canal.

Scoring methods.
A variety of procedures have been described to score the amounts of debris and smear layer left on canal walls after instrumentation. Some studies used only one score at each level examined (Hülsmann et al. 1997, Peters & Barbakow 2000). However, in the current study, a 200- m square grid was superimposed over the photomicrographs and the amounts of debris and smear layer were evaluated in each assessment unit. However, a grid scoring method may be more accurate to score debris and smear layer because they are often non-uniformly distributed. Consequently, one could speculate that the grid method would yield more accurate findings than a single score per level examined (Wu & Wesselink 1995).
Of the two alloys tested in the current study, the stainless steel K-files used to transmit the ultrasonic energy yielded a more scratched surface than the flexible blunt Ni–Ti-wire. Two specimens ultrasonicated with the flexible blunt Ni–Ti-wire had defects compared to 12 specimens ultrasonicated using the stainless steel K-files. Despite the greater incidence of defects in the stainless steel groups, their canal walls were not significantly cleaner than the walls in the blunt Ni–Ti groups. Any possible antibacterial effects dependent upon the ultrasonic energy transmitted by the two alloys were not investigated. However, previous studies have shown improved antibacterial activity of NaOCl (Briseno et al. 1992), when used with ultrasonics. The antibacterial potential of ultrasonically activated irrigation may play an important role and should be investigated in future.
The clinical relevance of the current study indicated that activated irrigation did not significantly reduce smear layer and debris scores when using stainless steel K-files and Ni–Ti-wire as ultrasonic transmitters. However, antibacterial effects of the ultrasonically activated irrigants, transmitted with either Ni–Ti-wire or stainless steel K-files, may be more efficient when used with an ultrasonic unit compared to a disposable syringe and needle.


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