Discussion - References.
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
- for placement and replacement of the irrigation solution (Wu & Wesselink 1995);
- for placement of intracanal dressing; and
- 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 (SpĂĄngberg 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.
Ando N, Hoshino E (1990) Predominant obligate anaerobes invading the deep layers of root canal dentine. International Endodontic Journal 23 , 20-7.
Armitage GC, Ryder MI, Wilcox SE (1983) Cemental changes in teeth with heavily infected root canals. Journal of Endodontics 9 , 127-30.
Briseno BM, Sonnabend E (1991) The influence of different root canal instruments on root canal preparation: an in vitro study. International Endodontic Journal 24 , 15-23.
Buchanan LS (2000) The standardized-taper root canal preparation - Part 1. Concepts for variably tapered shaping instruments. International Endodontic Journal 33 , 516-29.
Hand RE, Smith ML, Harrison JW (1978) Analysis of the effect of dilution on the necrotic tissue dissolution property of sodium hypochlorite. Journal of Endodontics 4 , 60-3.
Ka s t'?kov? A, Wu M-K, Wesselink PR (2001) An in vitro experiment on the effect of an attempt to create an 'apical matrix' during root canal preparation on coronal leakage and material extrusion. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 91 , 462 - 7.
Lumley PJ, Walmsley AD, Walton RE, Rippin JW (1993) Cleaning of oval canals using ultrasonic or sonic instrumentation. Journal of Endodontics 19 , 453-7.
Lussi A, Portmann P, Nussb?cher U, Imwinkelried S, Grosrey J (1999) Comparison of two devices for root canal cleansing by the noninstrumentation technology. Journal of Endodontics 25 , 9-13.
Nagy CD, Bartha K, Bernath M, Verdes E, Szabo J (1997) A comparative study of seven instruments in shaping the root canal in vitro. International Endodontic Journal 30 , 124- 32.
Peters LB, Wesselink PR, Buijs JF, van Winkelhoff AJ (2001) Viable bacteria in root dentinal tubules of teeth with apical periodontitis. Journal of Endodontics 27 , 76-81.
Reynolds MA, Madison S, Walton RE, Krell KV, Rittman BRJ (1987) An in vitro histological comparison of the step-back, sonic, and ultrasonic instrumentation techniques in small, curved root canals. Journal of Endodontics 13 , 307-14.
Schneider SW (1971) A. comparison of canal preparations in straight and curved root canals. Oral Surgery, Oral Medicine and Oral Pathology 32 , 271-5.
Siqueira Jr JF, Araujo MCP, Garcia PF, Fraga RC, Dantas CJS (1997) Histological evaluation of the effectiveness of five instrumentation techniques for cleaning the apical third of root canals. Journal of Endodontics 23 , 499-502.
Sp?ngberg LSW (1998) Instruments, materials, and devices. In: Cohen S, Burns RC. eds. Pathways of the Pulp , 7th edn. St. Louis, MO, USA: Mosby, 476-531.
Tang MPF, Stock CJR (1989) The effects of hand, sonic and ultrasonic instrumentation on the shape of curved root canals. International Endodontic Journal 22 , 55-63.
Walton RE, Torabinejad M (1996) Principles and Practice of Endodontics, 2nd edn. Philadelphia, PA, USA: W. B. Saunders Company.
Weine FS (1996) Endodontic Therapy, 5th edn. St. Louis, MO, USA: Mosby.
Wu M-K, Roris A, Barkis D, Wesselink PR (2000) Prevalence and extent of long canals in the apical third. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 89 , 739-43.
Wu M-K, Wesselink PR (1995) Efficacy of three techniques in cleaning the apical portion of curved root canals. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 79 , 492-6.
Zuolo ML, Walton RE, Imura N (1992) Histologic evaluation of three instrument/preparation techniques. Endodontics and Dental Traumatology 8 , 125-9.