Printed in U.S.A. VOL. 26,No. 6,JUNE2000
JOURNAL OF ENCODONTICS Copyright 0 2000 by The American Association of Endodontists
Smear Layer Influence on the Apical Seal of Four Different Obturation Techniques Jose Antbnio Valle Froes, DDS, MSc, HQnnio Geraldo Parreira Horta, DDS, PhD, and AntBnio Barbosa da Silveira, DDS, MSc
The purpose of this study was the in vitro evaluation of four techniques for the obturation of the root canal system in the presence or absence of a smear layer. Ninety-six human upper central incisors were instrumented using the pressureless crown-down technique and irrigated with 5.25% NaOCI. The teeth that had the smear layer removed were irrigated with this solution in combination with 17% EDTA. The teeth were obturated with lateral condensation with an accessory or standardized cone as the main cone, with vertical condensation of warm gutta-percha or with thermoplasticized injectable gutta-percha. Apical leakage was assessed by measuring the linear penetration of methylene blue dye with a stereomicroscope. The results showed no significant differences in the degree of leakage with and without the smear layer when the samples were considered as a whole. However, when the groups were assessed separately, teeth in the lateral condensation with an accessory main cone group and teeth in the thermoplasticized group leaked less with a smear layer present. In contrast teeth with lateral condensation and a standardized main cone leaked more with a smear layer present. In the vertical condensation groups there was no difference attributable to the smear layer.
The proportions of the components of the smear layer have not yet been determined, but electron microscopic examination shows that they consist of an organic portion (coagulated proteins, necrotic and nonnecrotic pulpal tissue, odontoblast process, saliva, blood cells, and microorganisms) and an inorganic portion (minerals from the dentinal structure) (2). Because of these two portions, removal of the smear layer requires a combination of irrigants, since only one irrigation solution is not able to dissolve both the organic and the inorganic components. According to Yamada et al. (3), the use of 17% EDTA followed by 10 ml of 5.25% NaOCl has produced the best results for smear layer removal. Because the smear layer covers the canal walls, contains necrotic tissue and bacterial remnants, and blocks the penetration of intracanal medication into the dentinal tubules, its removal may have beneficial effects in terms of the result of endodontic treatment (3, 4).Elimination of the smear layer from the root canal system leaves cleaner and patent dentinal tubules, promoting a better apical sealing with the filling material by permitting easier penetration of the dentinal tubules (3, 5). Perhaps a filling technique may prove to be more advantageous for the apical sealing of root canals depending on whether or not the smear layer is removed. The purpose of the present study was to evaluate the apical sealing obtained with four obturation techniques in vitro in the presence or absence of a smear layer, using a solution of methylene blue dye to measure the linear penetration of the dye under stereomicroscopy.
MATERIALS AND METHODS Teeth The study was conducted on 96-well preserved extracted human central incisors with straight roots, measuring on average 22.5 mm in length. After slight superficial scaling with periodontal curettes to remove the debris, the teeth were stored for 2 days in 5.25% NaOC1, and then in saline solution until time for the experiment. The same trained operator performed all work steps.
The success of endodontic therapy depends on the method and quality of instrumentation, irrigation, and disinfection, and the tridimensional obturation of the root canal system. Chemomechanical preparation usually provides root canals free of debris that can be safely obturated. However even with the best technique a complete cleaning of the root canal system may not be achieved, especially in irregular and curved roots, due to the deposition on the dentinal walls of a layer of material known as smear layer, which is produced by the cutting action of the endodontic instruments during chemomechanical preparation (1).
Radiographic Technique After selection, the teeth were positioned with the buccal and mesial surfaces facing the operator on an acrylic support filled with kneadable elastomeric polysiloxane for preliminary impressions 351
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before final setting. Disposable Dixie cups (10 cm height) were attached to this support upon which the X-ray cone was fixed, thus allowing the standardization of all radiographic takes during the experiment (focal object distance = 3.5 cm).
needle was positioned at a distance of -3 mm from the apex in order to inject the gutta-percha, and filling was completed according to the manufacturer’s manual. To assess obturation, new radiographs of all samples were taken in the two positions fixed in the impression material previously described.
Instrumentation Technique All procedures were conducted with the teeth fixed in a vise and.# wrapped with wet gauze to avoid drying and to facilitate handling. Pressureless crown-down technique using K-type files was employed for the instrumentation of all samples. The working length was determined as 1 mm short of the total length of the tooth, which was determined by a radiograph. A ##40file was standardized as the last working instrument, and a #15 file was used for cleaning the foramen. The apical preparation was considered ideal when a #40 spreader reached the working length. The samples were copiously imgated with a syringe and a 23-gauge needle using 10 ml of 5.25% NaOCl during the instrumentation procedure. For smear layer removal this solution was used in combination with EDTA; a final flush of 10 ml of 17% EDTA was followed by 10 ml of 5.25% NaOCl. The teeth were dried with #35 absorbent paper points.
Sample Processing After obturation, the samples were attached in the cervical region to a 0.025 mm orthodontic wire and covered with three layers of nail polish, except for approximately the final 3 mm of the root, with a period of 2 hr between applications. Afterward they were immersed in 2% methylene blue dye (pH 7.2) and kept in a bacteriological oven at 37°C for 7 days. After this period, they were washed in running water for 5 min and dried at room temperature for 24 hr. Nail polish was removed with a scalpel, and a guide groove was prepared with a diamond disc mounted on a mandril in the crown-apex direction on the vestibular and buccal surfaces. The teeth were longitudinally split with end-cutting pliers.
Leakage Analysis Obturation Technique After instrumentation of each tooth, a randomized selection was performed for the order of application of the procedures (obturation technique and irrigating solution) to avoid bias. A control group of 12 teeth was used: 6 instrumented, unfilled teeth coated with nail polish up to the apical limit and immersed in a dye solution (positive control); and 6 instrumented, obturated, fully coated teeth immersed in a dye solution (negative control). The sealer used in all techniques was Pulp Canal Sealer (EWT) handled according to the manufacturer’s instructions and applied to the canal walls with a #30 file. The samples were divided into two groups of 48 teeth each according to the irrigant solution used: group 1 (irrigation with 5.25% NaOCl) and group 2 (irrigation with 5.25% NaOCl and 17% EDTA). Within each group the root canals were obturated with four techniques: (i) lateral condensation with an accessory cone as the main cone; (ii) lateral condensation with a standardized cone as the main cone; (iii) vertical condensation of warm gutta-percha; and (iv) thermoplasticized gutta-percha injected by the Obtura I1 System. Twelve teeth were obturated with each technique. One sample in the vertical condensation group with warm gutta-percha in the presence of smear layer was eliminated from consideration because it exhibited gross leakage (i.e. >10 mm). In lateral condensation with the use of an accessory cone as the main cone group, a medium cone was selected with its tip calibrated with a calibration ruler for gutta-percha points, making sure that it corresponded to a #40 file. The rest of the canal was filled with fine medium (FM)cones with the help of a #25 spreader. When the #40 standardized cones were used, their tips were checked with the same ruler, and the final filling was performed with F%l cones and #25 spreaders. The vertical condensation technique for obturation was performed with a medium cone with the tip measured with the same calibrating instrument, using the heat carrier heated on a flame and the remaining condensation with pluggers compacting small fragments of gutta-percha. In the Obtura I1 System, the 25-gauge
Linear dye penetration was measured by two different examiners under a stereomicroscope with a magnification of X 10. Taking into consideration the region of greatest penetration, the following classification was adopted: mild, up to 2 mm; moderate, from 2 to 4 mm; and intense, above 4 mm of dye penetration.
Statistical Analysis Student’s t test was used to compare average leakage of the samples in the presence and absence of a smear layer. The influence of the obturation techniques and the presence or absence of a smear layer on dye penetration was evaluated by analysis of variance. When the effect was found to be significant, the multiple comparison test based on the least significant difference method was used to analyze the data.
RESULTS The results obtained with the obturation techniques studied are shown in Table 1. There was no significant difference (p > 0.05) in the presence or absence of the smear layer when all samples were considered together (i.e. independent of the obturation technique used). However there was a significant difference (p = 0.0010) in the degree of leakage when the lateral condensation technique with an accessory cone as the main cone was used. The penetration depth for the group of teeth obturated in the presence of a smear layer (average of 3.6 mm) was less than that for the group of samples obturated in the absence of a smear layer (average of 5.5 mm). The opposite result was obtained with the vertical condensation technique, with a significantly greater dye leakage occumng in the group where the smear layer was present. Concerning the lateral condensation technique with a standardized cone, the smear layer had no effect on methylene blue penetration, whereas in the group of teeth obturated with the use of the Obtura II System, teeth filled
Smear Layer and Apical Seal
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TABLE 1. Characteristics of the degree of sample leakage Descriptive Measurements Smear Layer
Independent of the techniques used (total no. of teeth) Lateral condensation with an accessory cone
Vertical condensation of warm gutta-percha
Lateral condensation with a standardized cone
Obtura II System
No. of Teeth
Minimum Linear Leakage -
Maximum Linear Leakaae
Notes: The p value refersto Student'sttest for independentsamples. All groups were made up of 12 samples,with the exceptionof the vertical condensation group with warm gutta-percha in the presence of the smear layer.
in the presence of a smear layer leaked less than when a smear layer was absent. Comparing the four techniques, in the presence and absence of a smear layer, the lateral condensation technique with a standardized main cone had the best result, followed by vertical condensation of warm gutta-percha, lateral condensation with an accessory main cone, and finally thermoplasticized gutta-percha injected by the Obtura II System.
DISCUSSION Because instrumentation was performed up to the root apex and obturation 1 mm short of the patent length of the canal, methylene blue dye penetration was observed in all samples. According to Kennedy et al. (6),this dye is visible under direct light, penetrates dental structures well, and does not react with tissues, thus allowing the measurement with a millimeter ruler directly on the teeth, as recommended by Madison and Krell (7). In the present study no significant difference in the degree of dye leakage was observed in the absence or presence of a smear layer when the samples were considered as a whole. Biesterfeld and Taintor (8) have also reported finding no difference in the apical sealing of the obturation. However, Kennedy et al. (6)stated that the lowest degree of infiltration in the apical region is obtained when the smear layer is removed from dentinal walls by increasing the contact surface between dentin and filling material. The highest degree of dye infiltration for the lateral condensation technique with an accessory cone as the main cone occurred in the absence of a smear layer. Probably the smear layer may have acted as a barrier-obstructing the filling materidcanal walls interface and making the penetration of methylene blue dye difficult. This explains the lower leakage found in the presence of the smear layer: perhaps the removal of this layer has created a void within the root canal, making the dye penetration between the obturation and the dentinal walls easier.
When the standard cone with lateral condensation technique was used no statistically significant difference was found when the root canal was irrigated with NaOCl alone or in combination with EDTA. Madison and Krell(7), using the same obturation technique and the same sequence of irrigation, also found no statistically significant difference in dye penetration when a chelating solution was used or not. Presenting opposite results, GenGoglu et al. (9) concluded that the smear layer interferes with the quality of the apical sealing, because they found a better obturation adaptation and bonding when the lateral condensation technique was used in the absence of a smear layer. When the techniques of lateral condensation with an accessory or standardized cone used as main cone were compared, the best result was found with the use of standardized cones. The differences found among cones (i.e. composition, shape and width) may have influenced the result. According to Tagger and Gold (lo), there are differences in the quality of apical seal with gutta-percha from different manufacturers. Perhaps better calibration of the standardizes cone tips has been a factor in their improved sealing ability in recent use. The narrower coronal region of the standardized cones facilitated the insertion of a greater number of additional cones in the remaining portion of the root canal, providing less leakage. Metzger et al. (11) in their results report that the standardized cones provide a better apical seal when used in round canals, and that accessory cones usually do not reach the apical portion of the root canal. They conclude that a good adaptation of the main cone is a crucial step of root canal obturation with the lateral condensation technique. De Deus (12) states that, in straight and wide canals, standardized cones are easily adapted to canal walls because they allow the insertion of additional accessory cones up to the root apex, thus improving the obturation quality in the apical third. In the technique of vertical condensation of warm gutta-percha a lower leakage of methylene blue dye was shown when the smear layer was removed from the samples. This result supports the
Frdes et al.
statement made by the author o f the technique (13) w h o reported that the vertical pressure in the apical direction allows the guttapercha, when plasticized, t o penetrate the intricacies o f the root canal, thus yielding a better apical sealing. According t o Goldberg et al. (14), the action o f EDTA, due to its demineralizing effect, leads t o a higher permeability o f dentinal tubules, promoting the penetration o f filling materials, thus permitting a better sealing.
When the Obtura I1 System was used, a higher degree o f die penetration was observed in the canals without a smear layer. Bradshaw et al. (15) report that gutta-percha when plasticized at high temperatures undergoes shrinkage as i t cools, creating a v o i d between dentinal walls and the obturation, thus allowing die penetration. In the present study, the v o i d created by the cooling o f gutta-percha may have been f i l l e d by a smear layer making the dye penetration difficult. Torabinejad et al. (16) reported different results: they showed that gutta-percha when plasticized at high temperatures presents a good adaptation t o the canal walls, which prevents die penetration. Evans and Simon (17) also reported different data f r o m those found in the present study. They reported that the smear layer does not influence the quality o f the apical seal when the technique o f injected thermoplasticized gutta-percha i s used. These variations may be attributable to differences in the methods o f canal preparation and obturation and in the way leakage was evaluated. We gratefully acknowledge the Pontificia Universidade Catolica de Minas Gerais and Odous Instruments for their extraordinary support. Dr. F r b s is associate professor of Endodontics, Dental School, Pontificia Universidade Catblica de Minas Gerais, Belo Horizonte, Brazil. Dr. Horta is full professor of Clinical Pathology and Surgery, Dental School, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil. Dr. Barbosa da Silveira is associate professor of Endodontics. Dental School, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil. Address requests for reprints to Dr. Jose Ant6nio Valle Frbs, Departamento de Odontologia, Pontificia Universidade Cat6lica de Minas Gerais, Avenida Francisco Deslandes 62, 30310-530Anchleta, Belo Horizonte. M.G., Brazil.
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1967;11:723-44. 14. Goldberg F, Bernart MI, Spielberg C, et al. Analysis of the effect of ethylenediaminetetraacetic acid on the apical seal of root canal fillings. J Endd o n 1985;11:544-7. 15. Bradshaw GB, Hall A. Edmunds DH. The sealing ability of injectionmoulded thermoplasticized gutta-percha. Int Endod J 1989;22:17-20. 16. Torabinejad M, Skobe 2,Krakow PA, et al. Scanning electron microscopic study of root canal obturation using thermoplasticized gutta-percha. J Endodon 1978;4:245-8. 17. Evans JT, Simon JHS. Evaluation of the apical seal produced by infected thermoplasticized gutta-percha in the absence of smear layer in root canal sealer. J Endodon 1986;12:101-7.