< First part

Results

Table 1: Canal debridement between groups
(mean values and SD)

Results are shown in Table 1. Overall,there were significant differences in the mean score between the two groups. Physiological saline solution (Group B) showed minimal effects on the removal of the smear layer (Fig.6). Most experimental group A canals showed clean or minimal debris in the observed areas, especially in the coronal and middle thirds (Figg.3-4)..Mean values for group A were0.35, 0.40 and 0.80 at the coronal,middle and apical third, respectively. Mean values for group B were 1.10, 1.20 and 1.65 at the coronal,middle and apical third,respectively.Figures 3 to 6 show representative micrographs of the specimens.

For apical versus middle and coronal thirds the Kruskal-Wallis test showed significant differences (p < 0.05) in both groups. Cleanliness of apical portion was less satisfactory.Fig.5). Mean canal preparation time was 6.55 min.(SD 2.5)

Fig.3 (Coronal - Group A)	Fig.4 (Middle third- Group A)
Fig.5 (Apical - Group A)	Fig.6 (Coronal - Group B)

Discussion
A heavy smear layer was observed at all levels in specimens irrigated with the saline group ( B). These findings are consistent with the results of other studies. ProFile NiTi rotary instrumentation produced moderate to heavy smear layer which needed to be removed with the combinate use of EDTA and NaOCl solutions. The excellent debridement capabilities of these two irrigants can be easily shown by the comparision of results of Groups A and B specimens.

No irrigant is able to efficiently remove smear layer and organic debris. Therefore, a correct choice of two or more irrigants is essential to enhance the debridement effect. During root canal preparation the action of endodontic instruments on the canal walls produces a smear layer, that is compacted directly on the walls. According to several studies ( 13,14) the elimination of the smear layer seems to be of great importance,since it could allow NaOCl to penetrate more easily into the dentinal tubules,thus enhancing its bactericidal action. Moreover,endodontic smear layer may affect the sealing efficiency of root canal obturation, acting as a physical barrier interferring with adhesion and penetration of sealers into dentinal tubules. 17% EDTA was alternated to 5% NaOCl throughout instrumentation, to effectively remove soft tissue remnants as well as the inorganic/organic smear layer. Figures 3-4 showed that in most cases canal surfaces are smooth, free of pulpal remnants and hard tissue debris.

The average good cleanliness of the canal walls produced by the EDTA+NaOCl irrigation technique may be also due to the coronal-apical preparation technique, in which the coronal and middle thirds are instrumented first,followed by the apical third.Coronal flaring enhances irrigant efficacy as it provides radicular access necessary to position the needle tip effectively. Abou-Rass and Piccinino (1) stated that in order to be effective,irrigating needles needed to come in close proximity to the material to be removed.

Moreover the portion of the canal that has already been shaped acts as a reservoir for the irrigant,to better cleanse the root canal space ( 4). The greater coronal space for the irrigating solution and the prolonged contact with the canal walls could explain the statistically significant differences between debridement of the apical and coronal portions.

Wall surfaces of apical thirds showed a greater amount of superficial debris and smear-layer, confirming previous studies (4,11), which have cited insurmountable challanges to the chemical cleaning of tha apical portions of root canals. Anatomic complexities and minimal tissue contact,such as within narrow apical space, limit debridement capability of irrigants (17).It have been speculated (2) that prolonged contact of intracanal chemicals might overcome this limited action. However, NiTi rotary instrumentation was found significantly faster than hand-filing,as previously demonstrated by other research works(8,9); consequently, tissue-chemical contact is shorter and solvent effect could be reduced.

It would be important to overcome this tissue-irrigant contact problems.The success of endodontic treatment depends on the canal system being thoroughly cleansed and disinfected,before three-dimensional obturation of this space.Innovative approaches or materials should be used to achieve more effective debridement. Ni-Ti rotary instrumentation give practitioners a predetermined root canal funnel shape,eliminating all the tedious step-back previously required to create a tapered root canal shape, and saving much time over conventional methods,as well. According to Gambarini & Berutti (7) the saved time should be spent to increase debridement during and after instrumentation ( shaping and cleaning the root canal system).

Bibliografy

1. ABOU-RASS M,PICCININO MV .The effectiveness of four clinical methods on the removal of root canal debris. Oral Surgery;Oral Medicine and Oral Pathology 198;54,323-8
2. ANDERSEN M,ANDREASEN JO,ANDREASEN FM . In vitro solubility of human pulp tissue in calcium hydroxide and sodium hypochlorite. Endodontics and Dental Traumatology 1992,8,104-8
3. BAUMGARTNER JC,MADER CL . A scanning electron microscopic evaluation of four root canal irrigation regimens. Journal of Endodontics 1987;13,147-57
4. BERUTTI E,MARINI R. A scanning electron microscopic evaluation of the debridement capability of sodium hypochlorite at different temperatures. Journal of Endodontics 1996;22,463-6
5. CALHOUN G,MONTGOMERY S.The effects of four instrumentation techniques on root canal space. Journal of Endodontics 1988,14,273-7
6. ESPOSITO PT,CUNNINGHAM CJ .A comparison of canal preparation with nickel-titanium and stainless steel instruments. Journal of Endodontics 1995;21,173-9
7. GAMBARINI G,BERUTTI E Can nickel-titanium rotary instruments efficiently and safely prepare the apical portions of curved canals? Presentation at the 8th Biennial Congress European Society of Endodontology,Goteborg,Sweden 12-14 June 1997
8. GAMBILL JM,ALDER M,DEL RIO CE Comparison of nickel-titanium and stainless steel hand-file instrumentation using computed tomography. Journal of Endodontics 1996;22,369-75
9. GLOSSON CR,HALLER RH,DOVE BS,DEL RIO CE A comparison of of root canal preparation using Ni-Ti hand,Ni-Ti engine driven, and K-flex endodontic instruments. Journal of Endodontics 1995;21,146-51
10. GOLDMAN M,WHITE RR,MOSER CR,TENCA JI. A comparison of three methods of cleaning and shaping the root canal in vitro. Journal of Endodontics 1988;14,7-12
11. PANIGHI MM,JACQUOT B.Scanning electron mocroscopic evaluation of ultrasonic debridement comparing sodium hypochlorite and Bardac-22. Journal of Endodontics 1995;21,272-6
12. ROME WJ,DORAN jE;WALKER WA III . The effectveness of gly-oxide and sodium hypochlorite in preventig smear layer formation. Journal of Endoodntics 198511,281-8
13. 13.SAUNDERS WP,SAUNDERS EM.The effect of smear layer upon the coronal leakage of gutta-percha root fillings and a glass ionomer sealer. International Endodontic Journal 1992;25,245-9
14. SEN BH,WESSELINK PR,TURKUN M. The smear layer: a phenomenon in root canal therapy.International Endodontic Journal 195;28,141-8
15. WALIA H,BRENTLEY W,GERSTEIN H . An initial investigation of the bending and torsional properties of Nitinol root canal files. Journal of Endodontics 1988;14,346-50
16. WEINE FS,KELLY RF,LIO PJ. The effect of preparation procedures on original canal shape and on apical foramen shape. Journal of Endodontics 1975;1,255-62
17. YANG SF,RIVERA EM,WALTON RE,BAUMGARDNER KR. Canal debridement: effectiveness of sodium hypochlorite and calcium hydroxide as medicaments. Journal of Endodontics 196;22,521-5