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 »  Home  »  Endodontic Articles 5  »  Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation
Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation
Introduction - Materials and methods.

D. M. Z. Guerisoli, M. A. Marchesan, A. D. Walmsley, P. J. Lumley & J. D. Pecora
Ribeirao Preto Dental School, University of Sao Paulo, Ribeirao Preto, Brazil.
School of Dentistry, University of Birmingham, Birmingham, UK.

Root canal treatment can be summarized as a series of procedures for cleaning, shaping and filling the root canal system. One of the most important procedures during treatment is the chemo-mechanical preparation of the root canal, based on the correct use of instruments and irrigating solutions.
Currently, sodium hypochlorite is used as an irrigant because it combines important properties such as tissue dissolving capability and microbicidal activity (Moorer & Wesselink 1982, Cohen & Burns 1998). Østby (1957) proposed the use of ethylenediamine tetraacetic acid (EDTA) at a neutral pH to promote chelation of calcium in dentine. Seidberg & Schilder (1974) showed the self-limiting action of EDTA, by submitting a known amount of calcium in dentine powder to the solution for different periods of time, and found an equilibrium after 7 h Hill (1959) added the cationic surfactant Cetavlon® (cetyltrimethylammonium bromide) to an EDTA solution, lowering its surface tension and obtaining a bacteriostatic action; this solution is called EDTAC.
The smear layer is composed of organic and inorganic components, which can be removed by association of chelating solutions and sodium hypochlorite (Koskinen et al. 1980, Goldman et al. 1982, Yamada et al. 1983, Sen et al. 1995). The use of ultrasound associated with various irrigating solutions contributes to the removal of smear layer (Martin et al. 1980, Cheung & Stock 1993, Cameron 1995a, 1995b). Huque et al. (1998) reported that ultrasound increased the bactericidal action of 12% sodium hypochlorite, eliminating bacteria even in deep layers of root dentine.
On the other hand, Ciucchi et al. (1989) reported that ultrasound in association with 3% sodium hypochlorite did not remove all the smear layer and did not enhance the chelating capability of EDTA. They also observed a decline in the efficiency of the irrigation procedures toward the apical part of canals. Abbott et al. (1991) reported that NaOCl associated with EDTAC produced clean canal walls, but ultrasound did not enhance the cleansing action of these solutions.
The purpose of this investigation was to evaluate smear layer removal using sodium hypochlorite associated with EDTAC irrigation and ultrasonic agitation.

Materials and methods.
Twenty recently extracted mandibular incisors with a single root canal, and kept in 0.1% thymol solution under refrigeration, were randomly divided into four groups. Standard access to the pulp chambers was performed with diamond burs.
In group 1 (positive control for smear layer), the teeth were instrumented using the modified double-flared technique (Saunders & Saunders 1992) with K-Flex files (Kerr®, Romulus, MI, USA), using 1 mL of distilled water as irrigant between each instrument, to give a total of 10 mL. The irrigating solution was introduced with a plastic syringe and a 30-gauge needle (Accuject, Astra Pharm Products Inc, Westborough, MA, USA). After root canal preparation, a size 15 file energized by ultrasound (Piezon Master 400, EMS Electro Medical Systems, Le Sentier, Switzerland) was introduced 1 mm from the anatomical apex for 1 min, with small amplitude filing movements against the dentinal walls. Distilled water was used as irrigant, with a flow rate of 5 mL min–1.
In group 2, the same instrumentation technique as group 1 was followed, with 1.0% sodium hypochlorite as the irrigating solution, again total volume 10 mL. Ultrasound was used inside the root canal for 1 min, as described previously, but with 1.0% sodium hypochlorite as the irrigating solution at a flow rate of 5 mL min–1.
Following the same instrumentation technique, 5 mL of 1.0% sodium hypochlorite alternated with 5 mL 15% EDTAC (EDTA with 0.1% Cetavlon®, Sigma Chemical Co., St. Louis, MO, USA) was used for irrigation in group 3. Ultrasound was also used as previously described, 30 s with sodium hypochlorite and 30 s with EDTAC.
Group 4 (negative control for smear layer) was not manually instrumented, but was irrigated with 5 mL of 1.0% sodium hypochlorite and 5 mL of EDTAC. Ultrasound was used, for 30 s with sodium hypochlorite and 30 s with EDTAC.
After instrumentation, all teeth were dried with paper points and split along the long axis in the linguo-buccal direction to expose the entire extent of the root canal. One of the halves was then randomly chosen and submitted to scanning electron microscopy (JEOL 5300 LV, Peabody, MA, USA). Specimens eventually lost during the process were properly replaced by teeth that had undergone an identical treatment regimen.
The length of the root canal was measured and divided equally into cervical, middle and apical thirds, in order to be evaluated separately. After scanning and observing each region with the microscope, an image of the most representative area of that third was taken with 350magnification. Three pictures were obtained from each tooth, one for each third, to give a total of 60 pictures. The images were then analysed for the amount of smear layer by three previously instructed and calibrated post graduate students. Smear layer was scored as: 1 = no smear layer; 2 = few areas covered by smear layer, with many dentinal tubule openings visible; 3 = most areas covered by smear layer, with few dentinal tubule openings visible; 4 = all areas covered by smear layer, no dentinal tubule openings visible. The assessors were unaware of which group they were analysing.
Due to the non-parametric nature of the sample, statistical analysis was performed using Friedman’s test.

Article Series
This article is part 3 of a 3 part series. Other articles in this series are shown below:
  1. Accuracy of a new apex locator: an in vitro study
  2. The capability of two hand instrumentation techniques to remove the inner layer of dentine in oval canals
  3. Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation