Introduction - Materials and methods.
W. Niu, T.Yoshioka, C. Kobayashi & H. Suda Pulp Biology and Endodontics, Department of Restorative Sciences, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.Introduction.
The smear layer is produced by instrumentation of the root canal; it is not observed on uninstrumented surfaces. This thin amorphous structure is composed of both organic and inorganic components, and it occludes the orifices of dentinal tubules (McComb & Smith 1975, Goldman et al. 1982, Mader et al. 1984, Sen et al. 1995). Because the smear layer prevents the penetration of irrigants, medications and filling materials into dentinal tubules, and may even impede their contact with the canal wall, many researchers believe it to be detrimental (Kennedy et al. 1986, Cergneux et al. 1987, Karagozkucukay & Bayirli 1994). The use of a combination of EDTA and NaOCl solutions has been recommended for efficient removal of the smear layer from the surface of the root canal wall (Yamada et al. 1983, Cengiz et al. 1990, Garberoglio & Becce 1994, Liolios et al. 1997). However, reports have also indicated that the use of EDTAand NaOCl may lead to dentinal erosion in the root canal wall (Baumgartner & Mader 1987, Calt & Serper 2000). Numerous reports indicate that the removal of the smear layer, as well as soft tissue and debris, is expedited by the alternate use of EDTA and NaOCl (Yamada et al.1983, Cengiz et al. 1990, Garberoglio & Becce 1994, Liolios et al.1997). However, less information is available about how final irrigation with EDTA and NaOCl results in the dentinal erosion.
The purpose of the present study was to morphologically evaluate dentinal erosion caused by final irrigation with EDTA and NaOCl. Materials and methods.Preparation of specimens.
Twenty-five intact single-rooted human mandibular anterior teeth stored in distilled water were used. Crowns were removed at the cemento-enamel junction level. After determining the working length (0.5 mm shorter than root canal length) by inserting a fine file (size 1 hand Profile, Dentsply Tulsa Dental, Tulsa, OK, USA), the root canal was prepared with rotary nickel- titanium Series 29 Profile instruments (0.04 taper, Dentsply Tulsa Dental, Tulsa, OK, USA) driven by a Tri Auto ZX (Morita Mfg Corp, Kyoto, Japan).The preparation sequence of instruments is showed in Table 1.After each step of instrumentation, 6% NaOCl solution (3 mL) (Purelox Oyalox, Tokyo, Japan) was applied to the root canal, with a size 27-gauge blunt-tip needle (Nissho, Osaka, Japan) using an up-down motion.
Table 1. The preparation sequence of instruments.
Grouping of specimens and scanning electron microscopic observation
Composition of the 15% EDTA solution was as follows: EDTA disodium salt (17 g), 5 N sodium hydroxide solution (9.25 mL) and distilled water (100 mL). Teeth were randomly divided into five groups according to the irrigation regimens (see Table 2).
Roots were split longitudinally, and one-half was dried and sputter-coated with platinum-palladium (Eiko Ion Coater IB-5, Ibaragi, Japan). Specimens were observed at 3000x magnification using a scanning electron microscope (Hitachi S-4500, Tokyo, Japan), and photomicrographs were taken at1, 3 and 6 mm from the apex.
Table 2. Grouping of the specimens and final irrigating solutions.Qualitative SEM evaluation.
The amount of remaining debris on the root canal wall (representative areas: 37 mm _ 30 mm) was evaluated in each specimen at 1, 3 and 6 mm from the apex, and graded using the qualitative scale advocated by Gorman et al. (1995) (0 = none, 1 = minimal, 2 = moderate and 3 = heavy). Quantitative evaluation of SEM microphotographs.
Dentinal tubule orifice diameters were measured in each of the photomicrographs. One-way anova and Fisherâ€™s PLSD tests were used to evaluate differences amongst the groups in the amount of remaining debris, and amongst the groups in the open orifice diameters. Values were expressed as mean _ SD, and P-values less than 0.05 were considered significant.