Results - Discussion - References.
The categories of smear layer remaining in each third are reported in Table 1.
There were no differences between groups 1 and 2 (positive control for smear layer and teeth instrumented with only sodium hypochlorite, respectively). Group 3, which was instrumented and irrigated with sodium hypochlorite and EDTAC, was statistically similar to the negative control for smear layer (group 4). Groups 1 and 2 were significantly different from groups 3 and 4 (P < 0.001). When groups were examined separately, there were no statistical differences between root canal thirds (Table 1, P > 0.05), i.e. the amount of smear layer found on cervical, middle and apical thirds was similar for each specific group.
Table 1. Scores of smear layer remaining in root canals after treatment.
Scores: 1, no smear layer; 2, few areas covered by smear layer; 3, most areas covered by smear layer; 4, all areas covered by smear layer.
One of the greatest challenges of root canal treatment is the complete cleaning of the root canal in order to eliminate pulp remnants, bacteria, smear layer, predentine and other organic material.
Sodium hypochlorite (NaOCl) is the most commonly used irrigant in root canal treatment, and has proven to be an excellent irrigating solution, due to its tissue dissolving capability and microbicidal activity. According to Moorer & Wesselink (1982), the active principle of NaOCl solutions is the amount of undissociated HOCl molecules, which are consumed in the interaction with organic matter. However, its action does not affect inorganic material.
Ethylenediamine tetra-acetic acid complements the action of sodium hypochlorite, by chelating calcium ions in dentine and making instrumentation of the root canal easier, especially in narrow canals. Because it is a chelating agent, EDTA is not dependent on a high hydrogen ion concentration to accomplish decalcification, and is effective at neutral pH (Patterson 1963).
These solutions, however, must be in direct contact with the surfaces for effective action. Due to the small diameter of root canals, it is often difficult for the irrigating solutions to reach the apex of the tooth. Ultrasonically activated files may be a means of reaching the entire length of the root canal with irrigating solutions. According to Walmsley et al. (1992), the cleaning ability of such files is assisted by acoustic microstreaming.
In this experiment it was presumed that the low surface tension caused by the cationic surfactant (CetavlonÂ®) and the agitation caused by the file activated by ultrasound efficiently cleaned the root canal walls in their entire length, enlarging the lumens of the dentinal tubules. Goldberg & Abramovich (1977) reported that EDTAC may facilitate the action of drugs by increasing dentinal permeability and provide greater adhesion for obturating materials.
In this study, sodium hypochlorite alone did not clean smear layer better than distilled water, proving that irrigation with NaOCl alone is not effective. Baumgartner & Cuenin (1992) also observed that ultrasonically energized NaOCl, even in higher concentrations such as 5.25%, did not remove smear layer from the root canal walls.
Cameron (1995a) reported that irrigation with EDTAC between files during instrumentation and extensive use of ultrasound with 15% EDTAC alternated with 4% NaOCl produced dentinal walls free of smear layer. The present study showed that 15% EDTAC alternated with 1% sodium hypochlorite produced the same results, but with less use of ultrasound and lower NaOCl concentration.
Although significant differences were found regarding treatments, no statistical differences were found between root thirds when groups were examined separately. Goldman et al. (1982) observed the same with EDTA during instrumentation with a final flush of 5.25% sodium hypochlorite. Other researchers have reported a greater amount of smear layer found at the apical level of root canals treated with NaOCl and EDTA (Yamada et al. 1983) or NaOCl alone (Baumgartner et al. 1984).
The lack of differences between root thirds in the same group can be explained by the low surface tension of the solutions provided by the cationic surfactant, as well as the use of ultrasound. Due to the combined action of these two factors, the irrigating solutions probably reached the entire extent of the root canal.
Abbott PV, Heijkoop PS, Cardaci SC, Hume WR, Heithersay GS (1991) An SEM study of the effects of different irrigation sequences and ultrasonics. International Endodontic Journal 24, 308-16.
Baumgartner JC, Brown CM, Mader CL, Peters DD, Shulman JD (1984) A scanning electron microscopic evaluation of root canal debridement using saline, sodium hypochlorite, and citric acid. Journal of Endodontics 10, 525-31.
Baumgartner JC, Cuenin PR (1992) Efficacy of several concentrations of sodium hypochlorite for root canal irrigation. Journal of Endodontics 18, 605-12.
Cameron JA (1995a) The choice of irrigant during hand instrumentation and ultrasonic irrigation of the root canal: a scanning electron microscope study. Australian Dental Journal 40, 85-90.
Cameron JA (1995b) Factors affecting the clinical efficiency of ultrasonic endodontics - a scanning electron microscopy study. International Endodontic Journal 28, 47-53.
Cheung GS, Stock CJ (1993) In vitro cleaning ability of root canal irrigants with and without endosonics. International Endodontic Journal 26, 334-43.
Ciucchi B, Khettabi M, Holz J (1989) The effectiveness of different endodontic irrigation procedures on the removal of the smear layer: a scanning electron microscopic study. International Endodontic Journal 22, 21-8.
Cohen S, Burns RC (1998) Pathways of the Pulp, 7th edn. St. Louis, MO, USA: Mosby.
Goldberg F, Abramovich A (1977) Analysis of the effect of EDTAC on the dentinal walls of the root canal. Journal of Endodontics 3, 101-5.
Goldman M, Goldman LB, Cavaleri R, Bogis J, Lin PS (1982) The efficacy of several irrigating solutions for endodontics: a scanning electron microscopic study, part II. Journal of Endodontics 8, 487-92.
Hill PK (1959) Endodontics. Journal of Prosthetic Dentistry 9, 142.
Huque J, Kota K, Yamaga M, Iwaku M, Hoshino E (1998) Bacterial eradication from root dentine by ultrasonic irrigation with sodium hypochlorite. International Endodontic Journal 31, 242-50.
Koskinen KP, Meurman JH, Stenval H (1980) Appearance of chemically treated root canal walls in the scanning electron microscope. Scandinavian Journal of Dental Research 88, 397-405.
Martin H, Cunningham MJ, Morris JP, Cotton WR (1980) Ultrasonic versus hand filing of dentine: a quantitative study. Oral Surgery, Oral Medicine and Oral Pathology 49, 79- 81.
Moorer W, Wesselink PR (1982) Factors promoting the tissue dissolving capability of sodium hypochlorite. International Endodontic Journal 15, 187-96.
Ostby NB (1957) Chelation in root canal therapy. Odontologisk Tidskrift 65, 3-11.
Patterson S (1963) In vivo and in vitro studies of the effect of the disodium salt of ethylenediamine tetra-acetate on human dentine and its endodontic implications. Oral Surgery, Oral Medicine and Oral Pathology 16, 83-103.
Saunders WP, Saunders EM (1992) Effect of noncutting tipped instruments on the quality of root canal preparation using a modified double-flared technique. Journal of Endodontics 1, 32-6.
Seidberg BH, Schilder H (1974) An evaluation of EDTA in endodontics. Oral Surgery, Oral Medicine, Oral Pathology 37, 609-20.
Sen BH, Wesselink PR, T?rk?n M (1995) The smear layer: a phenomenon in root canal therapy. International Endodontic Journal 28, 141-8.
Walmsley AD, Laird WR, Lumley PJ (1992) Ultrasound in dentistry - Part II: Periodontology and endodontics. Journal of Dentistry 20, 11-7.
Yamada RS, Armas A, Goldman M, Lin PS (1983) A scanning electron microscopic comparison of a high volume final flush with several irrigating solutions: part III. Journal of Endodontics 9, 137-42.