|Year : 2013 | Volume
| Issue : 3 | Page : 114-119
Effect of irrigation needle depth in smear layer removal: Scanning electron microscope study
Department of Dental, King Faisal Hospital, Makkah, Saudi Arabia
|Date of Web Publication||20-Nov-2013|
Department of Dental, King Faisal Hospital, P.O. Box 30236 Makkah, Saudi Arabia 21955
Source of Support: None, Conflict of Interest: None
Aim: To evaluate the cleanliness of rotary prepared root canals when the irrigation needle was placed at full or half the working length. Materials and Methods: Forty-five root canals were collected from extracted human teeth and divided into three groups each group of fifteen roots. Group 1: Root canals were instrumented using Profile® system and irrigated with 3% EDTA and 0.5% NaOCl. Group 2: Root canals were instrumented in the same manner as group 1 and irrigated with 18% EDTA and 5.25% NaOCl and the tip of the irrigation needle was introduced to the full working length. Group 3: Root canals were instrumented in the same manner as group 2 except that the tip of the irrigation needle was introduced half the working length. The roots were sectioned longitudinally and evaluated for smear layer at coronal, middle and apical thirds of the canals under SEM. The results were analyzed using the Kruskal-Wallis test. Results: No statistically significant difference was found in the distribution of the scores between all groups. However, the scores in the apical part of group 1were significantly higher than the middle and the coronal areas. Conclusion: The placement depth of irrigation needle or concentration of irrigants solutions has no influence on the cleanliness of rotary prepared canals.
Keywords: Chelating agents, dentin debris, needle depth, scanning electron microscope, smear layer
|How to cite this article:|
Mandorah A. Effect of irrigation needle depth in smear layer removal: Scanning electron microscope study. Saudi Endod J 2013;3:114-9
| Introduction|| |
Successful root canal treatment requires effective mechanical and chemical debridement of all contents of the canal system that may serve as a substrate for bacterial growth and periapical inflammation. , Instrumentation alone is not enough to create a clean environment.  Consequently, for effective cleaning and shaping, it is important to use irrigation as an adjunct to mechanical preparation.  Irrigation with antibacterial solutions is considered an essential part of chemo-mechanical preparation.  The action of endodontic instruments during canal preparation will allow the dentin chips and the organic remnants of the pulp tissue to form a smear layer that adhere to the canal walls. , This smear layer consists of a superficial layer approximately 1-2 μm in thickness and deeper layer packed into dentinal tubules to a depth up to 40 μm.  This thick layer consists of organic and inorganic substances that include bacteria, pulpal tissue debris and toxins. The presence of smear layer and debris is contraindicating the primary goals of endodontic treatment, since it may prevent penetration of intracanal medications into dentinal tubules.  Therefore, removal of this layer will improve both the effect of the disinfectant solution and root canal filling materials sealing quality. ,
The most commonly used irrigation agent in Endodontics is sodium hypochlorite (NaOCl) in concentrations of 0.5% to 5.25%. However, NaOCl was ineffective to remove the entire smear layer when used alone.  A chelating solution has been introduced to demineralize and remove the smear layer.  The most common chelating irrigant used is ethylenediaminetetra-acetic acid (EDTA), which was initially used in root canal therapy by Nygaard-Østby in 1957.  EDTA can be applied in liquid, past-type, or gel forms.  Many studies suggested alternating the use of EDTA and NaOCl as an effective method for smear layer removal. ,, They found that NaOCl removes the organic part whereas EDTA removes the inorganic part.  In addition, smear layer removal provide better adaptation and adhesion of the root filling material to the dentin wall. ,,
It has been reported that the position of the irrigation needle in the root canal was important for the removal of intra-canal debris  and in the reduction of bacterial counts during canal irrigation.  In addition, the effect of irrigants into the instrumented root canal system is determined by relative diameter of the irrigating needle and the canal  and smaller needle will provide deeper penetration.  However, the needle should not bind to the canal wall during irrigation because this will increase the risk of irrigant extrusion into periapical tissue  Therefore, exact information about the external diameter of the needles tip is very important during root canal treatment. 
The aim of this study was to evaluate the cleanliness of rotary prepared root canals with different concentrations of irrigants by means of scanning electron microscope (SEM) to investigate if there is a difference between placement of the irrigation needle tip at full or half the working length in comparison to standard irrigation technique.
| Materials and Methods|| |
Forty-five intact straight single rooted canals were collected from extracted human teeth with completely formed apices and stored in chlorohexidine (0.5% chlorohexidine solution Apoteksbolaget, Sweden). The teeth were used in this study with the patient's verbal permission.
The sample size was chosen on the basis that the teeth will be divided randomly into three groups with fifteen teeth per group, and this should be adequate for statistical analysis. This is based on that a t-test with a 0.05 two-sided significance level will have 80% power to detect a clinical significant difference of the same magnitude as the standard deviation.
The teeth were radiographed to confirm canal patency and complete root formation.
The pulp chamber was opened by standard endodontic access cavity preparation using a diamond bur (Horico, cylindrical tip rounded diamond bur, FG 141/012, Nordenta, Enkoping, Sweden) with a high speed hand piece (Synea HS, TA 98-LW, Wand H, Bürmoos, Austria) and a low speed hand piece (Synea LS, WA-56LT, WandH, Bürmoos, Austria) to allow direct access to the root canals.
A K-type file size 15 (Dentsply, Maillefer, Ballaigues, Switzerland) was inserted into the canal until its tip was just visible at the apical foramen, the length of the file was measured and 1 mm was subtracted from this length to provide an optimal root canal preparation length. Apical foramen was blocked by small piece of wax to control the flow of the irrigation solutions. Teeth were randomly divided into 3 groups; each group with 15 roots.
Group 1 (control group)
Fifteen root canals were instrumented using a crown-down technique in combination with Profile® nickel-titanium system (Dentsply, Maillefer, Ballaigues, Switzerland) at 250-r.p.m with a hand piece (16:1, ATR-16M, Wand H, Bürmoos, Austria) using a high torque motor for constant speed (TCM3000, Nouvag, Goldach, Switzerland) according to the manufacturer's instructions.
The apical preparation was made by hand using an apical ISO size 30 K file. After each instrument, the canal was irrigated with 2 mL 0.5% NaOCl solution (Dakins® solution, Apoteksbolaget, Sweden) using a syringe (Becton Dickinson, and Co., Luer-Loc, TM, 3 mL, USA) with an irrigation 30 gauge Navi tip needle (Navi tip, Ultradent products, Utah, USA) [Figure 1].
The needle was advanced into the canal until it binds to the canal walls at the apical region and was retracted by 1 mm to allow easy back flow of the irrigating solution.
At the end of the instrumentation sequence, each canal was filled with Tubulicid Plus (Dental therapeutics AB, Nacka, Sweden) containing 3% EDTA for 20 s and dried with paper points (Nordenta, Enkoping, Sweden). These procedures were repeated once then followed by a final flush with 2 mL 0.5% NaOCl solution.
Fifteen root canals were instrumented in the same manner as group 1 (Control group). After the instrumentation sequence, each canal was filled with 18% EDTA (Ultradent, Products, Utah, USA) for 20 s and dried by paper points. These procedures were repeated once, then followed by a final flush with 2 mL 5.25% NaOCl solution, using an irrigation 30 gauge Navi tip needles that was placed 2 mm short of the full length of the root canal.
Fifteen root canals were instrumented in the same manner as group 2 in all the steps except that the tip of the irrigation 30 gauge Navi tip needle was introduced half the distance to the working length (WL) of the root canal. After preparation all canals were dried out with paper points.
A cotton pellet was placed in the access opening to block the canal orifice from debris entering the canal during sectioning. The long axis of the root was grooved on the buccal and lingual surfaces with a diamond disc (DT-126, PHP, Dentatus, Hägersten, Sweden), and then splitted with a plastic instrument.
Assessment of preparation
By means of light microscope, the investigator chose the intact root halves with the full length of the canal. These were submitted for scanning electron microscope evaluation (ULTRA 55, Carl Zeiss NTS Gmbh, Oberkochen, Germany).
The samples were coded to allow blind evaluation. Each sample was divided into 3 areas (apical, middle, coronal) by making small grooves with a sharp knife on the side of the root.
The samples were firmly mounted on aluminum stubs (Silverpaint® , Agar Scientific Ltd, Essex, UK), vacuum dried and covered with 20-nm platinum coating (Polaron®, Instruments Inc, Hatfield, UK) using a sputtering machine (SCD 500). These samples were evaluated by means of SEM using a magnification of ×800. Microphotographs were taken for each root canal at the coronal, middle and apical area.
Canal walls were quantitatively evaluated for the amount of smear layer for each microphotograph. Smear layer is defined as: A surface film of debris retained on dentin surface after instrumentation with either rotary instruments or endodontic files. Evaluation of the cleanliness with reference to smear layer was done using a five levels scale system  as follows:
- Score 1: No smear layer, dentinal tubules open
- Score 2: Small amount of smear layer, some dentinal tubules open
- Score 3: Homogeneous smear layer covering the root canal wall, only few dentinal tubules open
- Score 4: Complete root canal wall covered by a homogeneous smear layer, no open dentinal tubules
- Score 5: Heavy, inhomogeneous smear layer covering the complete root canal wall.
The evaluation of the microphotographs was performed blindly by two examiners after inter and intra examiner calibration. The statistical analysis was done using the Kurskal-Wallis rank test for comparison between the study groups at each level. The differences within each group were analyzed using Friedman ANOVA by ranks. A P < 0.05 was considered statistically significant.
| Results|| |
Evaluation of coronal, middle area of root canals shows the majority of scores approximately ranging from score 1 [Figure 2]a to 3] [Figure 2]b in all groups, while group 3 have relatively more scores of 4 [Figure 2]c. Evaluation of the apical areas shows the majority of scores approximately ranging from 2 to 3 in all groups, while group 1 has relatively more scores of 1 and 4. However, the statistical analysis did not demonstrate any significant difference between all areas in all groups, coronal P = 0.88, middle P = 0.47 and apical P = 0.99.
|Figure 2: Microphotograph showing smear layer (a) score 1, (b) score 3 and (c) score 4. Magnification ×800|
Click here to view
Within group analysis
Friedman's ANOVA did reveal a significant difference in cleanliness between the areas within the study group [G1 (P = 0.015)]. Pairwise comparisons found that the scores in the apical part were significantly higher than the middle and the coronal areas. However, Friedman's ANOVA did not reveal any significant difference in cleanliness between the coronal, middle and apical part within the study groups [G2 (P = 0.48) and G3 (P = 0.13)].
| Discussion|| |
It was expected that the area around the tip of the needle would be cleaner than the other areas. Crown-down preparation with Profile nickel-titanium rotary system was employed in this study to provide sufficient adequate shape for irrigation and obturation.  Scanning electron microscope has been used in this study to evaluate the cleanliness of root canals by using five levels scale reference photographs and considered a useful and reliable tool and offers a high-resolution images to observe opened dentinal tubules and areas covered by smear layer. 
It was found that the majority of scores of smear layer in the coronal and middle areas in all groups were judged to fall between score 1 and 3 and appeared overall cleaner in comparison with those scores of the apical areas. The type and size of needle used for endodontic irrigation and apical enlargement of the root canal affects the degree of cleanliness in the apical third of the canal. ,
In this study, the 30-gauge irrigation needle was employed to coincide with apical preparation size #30 file, which has been claimed to be the minimum instrumentation size needed for penetration of irrigants into the apical part of the root canal.  However, larger-sized apical preparation has been associated with a greater reduction in numbers of bacteria following chemo-mechanical preparation, possibly due to the ability to place the needle tip more apically.  It has been reported that gauge irrigation needle thinner than the diameter of the prepared canal was more effective than larger gauge for deeper penetration and consequently removing more smear layer from the apical part.  However, a thinner gauge needle may provide more resistance to flow of irrigants, a factor that will reduce the amount of delivered volume.  In the other hand, the risk of extrusion of irrigant beyond the apex is minimized by controlling the depth of irrigating needle in the canal  and increasing size of apical preparation beyond size 35 will allow more irrigant volume to flow in the coronal direction. 
Another factor may influence on cleanliness of root canals in this study is the volume of irrigation solution use during instrumentation. The total amount of volume of EDTA solution used in this study was 1 mL. However, using larger volumes of EDTA have been reported to provide cleaner canal walls than smaller volumes. ,,,,, Yamada et al.  found that 10 mL of 17% EDTA followed by 10 mL of 5.25% NaOCl was the most effective methods in removing smear layer. In contrast, another study showed that EDTA irrigation volume greater than 1 mL did not improve smear layer removal. 
It can be argued that lacking significant difference in cleanliness between any of the study groups in this study may be also influenced by the short application time and different concentration of EDTA rather than depth of the irrigation needle. The total time of 18% EDTA application in this study was 40s. However, in group 1 (control group) the concentration was 3% EDTA but the application time was the same.
Many studies have demonstrated the effect of application time and EDTA concentration on removal of smear layer; the duration of application of EDTA was ranging from 30 s to 10 min and the concentration was ranging from 3% to 24%. ,,,,, However, there was no accepted consensus duration or concentration of irrigation agents. Goldberg and Spielberg  reported that application of 17% EDTA for 30 s did not remove all smear layer plugs in some specimens. Gettleman et al.  showed that a contact time of 3 min of 17% EDTA was effective for smear layer removal. Meryon et al.  reported that smear layer was completely removed with 10% EDTA for 1 min and resulting in increased tubular orifice size. Cergneux et al.  also reported the same finding when 15% EDTA was applied in root canal for 4 min. However, when 17% EDTA has been applied up to 10 min, excessive erosion will occur and lead to dissolution of peritubular and intertubular dentin, therefore 17% EDTA must not be applied for longer than 1 min.  In another study, it was shown that irrigation with 15% EDTA and 1% NaOCl for 1, 3 and 5 min were equally ineffective in removing smear layer from the canal walls.  It has been reported that optimal cleaning of dentin walls with 17% EDTA was only achieved after 15 min. 
| Conclusion|| |
It can be concluded that within the limits of this study, no difference was found in the cleanliness of rotary prepared canals between placements of the irrigation needle tip at full or half working length.
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[Figure 1], [Figure 2]
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