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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 3  »  Does the first file to bind correspond to the diameter of the canal in the apical region?
Does the first file to bind correspond to the diameter of the canal in the apical region?
Discussion - References.



Discussion.
 If the apical root canal has a round shape and the first file that binds indeed reflects the diameter of the apical canal, the inner layer of dentine of the root canal that may be heavily infected, can be removed by preparing the canal using three successively larger files. However, many apical root canals are oval (Wu et al. 2000) and indeed, the results of this study have shown that the first file to bind did not reflect the apical diameter and that the size of the file was noticeably smaller than the size of root canal at the WL (Figs 1, 2). Therefore, the aim of removing the infected layer of dentine may not be achieved.
The aim of canal preparation is to widen the apical canal enough

  1. for placement and replacement of the irrigation solution (Wu & Wesselink 1995);
  2. for placement of intracanal dressing; and
  3. to facilitate obturation procedures. On the other hand, it should not be so wide that it unnecessarily weakens the root and increases the risk of fracture.

The coronal portion, rather than the tip, of a K-file may bind the wall because it has a larger diameter coronally. Therefore, a K-file that binds may not bind at the WL. The modified Lightspeed instrument, however, has the largest diameter at its tip. In addition, the Lightspeed instrument may follow the curvature better than K-file because of its enhanced flexibility (Spångberg 1998). Therefore, it was hypothesized that the modified Lightspeed instruments could provide a solution. Unfortunately, the results showed that the Lightspeed instruments did not reflect the apical canal diameter (Table 1). At the WL in four canals, the Lightspeed instrument did not touch any region of the canal wall (Fig. 2), showing on one hand, its centring ability in curved canals, and on the other hand, that other factors, including existence of calcified tissues or dense collagen fibres, may lead to a sense of binding.
Another purpose of the approach to use successively larger files to the same working length is to create an apical stop. Considering the fact that the first file to bind frequently bound at one side of canal wall, the apical stop may be created only on one side. Although this small shelf may prevent the master file moving apically, it is questionable whether it has any function in reducing leakage and material extrusion.
The Gates Glidden drills straightened the coronal twothirds of the root canals in an attempt to reduce binding in the coronal region. Obviously, even this procedure could not guarantee that the instruments bound only at the working length. Clinically, it is not always possible to straighten the coronal two-thirds of root canal because sometimes the radius of root curvature is long.

References.

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