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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 5  »  A scanning electron microscopic study of debris and smear layer remaining following use of GT rotary instruments
A scanning electron microscopic study of debris and smear layer remaining following use of GT rotary instruments
Results - Discussion - References.



Results.
Mean canal preparation time was 7.20 min (SD 0.5).
Mean scores for debris removal in the coronal, middle and apical thirds were 1.06, 1.38 and 2.25, respectively. Although the best results were observed in the coronal sections, statistical analysis showed that there was no significant difference (P > 0.05) in debris between the three regions of the root canals.
Mean scores for smear layer removal in the coronal, middle and apical thirds were 1.50, 2.00 and 3.38, respectively. Comparison of the removal of smear layer between the three regions showed that there was a statistically significant difference (P < 0.001) between all parts, especially between the coronal and apical thirds (Table 1).
The uninstrumented canals showed walls completely covered with tissue, confirming that specimen preparation alone did not remove tissue.

Table 1. Comparison of the removal of the smear layer between the three regions of the canal.

Comparison of the removal of the smear layer between the three regions of the canal

Discussion.
The ability to clean effectively the endodontic space is dependent on both instrumentation and irrigation. Endodontic instruments may, in themselves, vary in their debris removal efficacy and in their smear layer production, due to their specific flute design (Bertrand et al. 1999). Irrigation plays a key role in successful debridement and disinfection. Sodium hypochlorite is an irrigant solution widely used in root canal treatment because of its bactericidal properties and ability to dissolve organic tissue, however, it is not effective in removing the inorganic smear layer. Therefore, a combination of NaOCl and EDTA has been reported to be suitable for removing both the organic tissues and inorganic smear layer (Baumgartner & Mader 1987). More recently, it has been shown (Gambarini 1999) that cleaning can be significantly improved once the shaping procedure has been completed (the ‘shaping and cleaning’ concept). At the end of instrumentation, root canal diameters have been adequately enlarged to a funnel-form shape that provides easier and superior penetration of the irrigants in the apical portions. At this stage, no further instrumentation is required and, consequently no more smear layer is produced. This allows the irrigating solutions, which are left undisturbed for an adequate period of time, to efficiently remove the remaining debris. The results of the present study showed that GT™ rotary instrumentation followed by a specific final irrigation sequence could produce good canal cleanliness. In most cases, canal surfaces were smooth and free of pulpal remnants.

Figure 2. Standardized score of the smear layer for specimen evaluation:
(a) score 1; (b) score 2; (c) score 3; (d) score 4; (e) score 5.
Original magnification x1000

Standardized score of the smear layer for specimen evaluationn

The new file design seemed to be effective in debris removal. However, it is important to note that the GT rotary instrumentation sequence used in our study is the one recommended by the manufacturer, which consisted of eight rotary instruments. No Accessory GT rotary instruments were used. It means that after initial use of the four standard GT rotary instruments, apical preparation was completed with .04 tapered GT rotary instruments sizes 20–35. Those instruments are essentially ProFile .04 instruments. Cleaning in the apical third is therefore related to the combined action of two different rotary instruments (GT and ProFile) and the large apical stop produced.
Use of the rotary instrumentation resulted in a substantial amount of smear layer. This smear layer consists of dentine particles and pulp tissue closely compacted against the root canal wall and extending into the dentinal tubules (McComb & Smith 1975, Mader et al. 1984, Bechelli et al. 1999). The smear layer produced by instrumentation should be removed, because it could contain bacteria and increase leakage of the canal filling (Yamada et al. 1983, Aktener et al. 1989). Following this hypothesis, additional irrigation with antibacterial solutions or chelating agents has been recommended by many authors to remove debris as well as the smear layer, however, this did not produce the expected smear-free surfaces in the apical third of the canal.

References.

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