Journal of Conservative Dentistry

: 2015  |  Volume : 18  |  Issue : 4  |  Page : 321--325

Effectiveness of different irrigation techniques on smear layer removal in apical thirds of mesial root canals of permanent mandibular first molar: A scanning electron microscopic study

Pranav Khaord1, Aesha Amin2, Manish B Shah2, Roshan Uthappa1, Nirmal Raj2, Tejal Kachalia2, Hiral Kharod3,  
1 Department of Conservative Dentistry and Endodontics, College of Dental Sciences, Amargadh, Bhavnagar, Gujarat, India
2 Department of Conservative Dentistry and Endodontics, Karnavati School of Dentistry, Gandhinagar, Gujarat, India
3 Department of Prosthodontics, College of Dental Sciences, Amargadh, Bhavnagar, Gujarat, India

Correspondence Address:
Dr. Pranav Khaord
B/601 Himalaya Skyz, Waghawadi Road, Bhavnagar - 364 002, Gujarat


Aim: The aim of this study was to compare smear layer removal after final irrigant activation with sonic irrigation (SI), manual dynamic agitation (MDA), passive ultrasonic irrigation (PUI), and conventional syringe irrigation (CI). Materials and Methods: Forty mesial canals of mandibular first molars (mesial roots) were cleaned and shaped by using ProTaper system to size F1 and sodium hypochlorite 3% and 17% ethylenediaminetetraacetic acid. The specimens were divided into 4 equal groups (n = 10) according to the final irrigation activation technique: Group 1, PUI; group 2, manual dynamic activation (MDA); group 3, SI; and group 4, control group (simple irrigation). Samples were split longitudinally and examined under scanning electron microscope for smear layer presence. Results: Control groups had the highest smear scores, which showed the statistically significant highest mean score at P < 0.05. This was followed by ultrasonic, MDA, and finally sonic, with no significant differences between them. Conclusions: Final irrigant activation with sonic and MDA resulted in the better removal of the smear layer than with CI.

How to cite this article:
Khaord P, Amin A, Shah MB, Uthappa R, Raj N, Kachalia T, Kharod H. Effectiveness of different irrigation techniques on smear layer removal in apical thirds of mesial root canals of permanent mandibular first molar: A scanning electron microscopic study.J Conserv Dent 2015;18:321-325

How to cite this URL:
Khaord P, Amin A, Shah MB, Uthappa R, Raj N, Kachalia T, Kharod H. Effectiveness of different irrigation techniques on smear layer removal in apical thirds of mesial root canals of permanent mandibular first molar: A scanning electron microscopic study. J Conserv Dent [serial online] 2015 [cited 2022 May 26 ];18:321-325
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Irrigation is an essential part of root canal debridement. It allows for cleaning beyond what might be achieved by root canal instrumentation alone. [1] It helps by killing microorganisms, flushing debris, and removing the smear layer from the root canal system. Smear layer prevents the penetration of intracanal medicaments into dentinal tubules and influences the adaptation of filling materials to canal walls. It consists of organic and inorganic substances, including fragments of odontoblastic processes, microorganisms, their by-products, and necrotic materials. [2] The alternate use of sodium hypochlorite (NaOCl), a deproteinizing agent, and ethylenediaminetetraacetic acid (EDTA), a calcium-chelating agent, has been recommended for its efficient removal.

These irrigants must be brought into direct contact with the entire canal wall for effective action. During conventional needle irrigation, replenishment, and fluid exchange do not extend much beyond the tip of the irrigating needle. [3] Vapor lock that results in trapped air in the apical third of root canals might also hinder the exchange of irrigants and affect the debridement efficacy of irrigants. That is why different techniques and irrigant delivery devices have been proposed to increase the flow and distribution of irrigating solutions within the root canal system. [4]

The Endoactivator system (Advanced Endodontics, Santa Barbara, CA) has been purported to improve disinfection. This device uses a cordless sonic handpiece to activate strong, highly flexible polymer tips. Noncutting tips have tapers and terminal diameters that closely match the dimensions of the final root canal preparation. [5] Mechanical oscillations are produced mainly at the tip of the activator with a frequency ranging from 1 to 10 kHz.

Manual dynamic activation (MDA) has been described as a cost-effective technique for cleaning the walls of the entire root canal. It involves repeated insertion of a well-fitting Gutta-percha cone to working length of a previously shaped canal. The Gutta-percha cone is applied in short; gentle strokes to hydrodynamically displace and activate an irrigant. [6] It is hypothesized that this technique might be useful in breaking the air bubble located at the apical 0-2 mm of the canal. [7]

Passive ultrasonic irrigation (PUI) refers to an irrigation protocol in the presence of an ultrasonically activated file, which is non-contacting the canal wall. It has been shown to be more effective than syringe needle irrigation in removing pulpal tissue remnants and dentin debris, bacterial reduction, and smear layer removal. [8]

The aim of this study was to compare smear layer removal after final irrigant activation with sonic irrigation (SI), manual dynamic activation, and PUI. The null hypothesis tested was that there is no difference in smear layer removal by using different final irrigant activation protocols.

 Materials and Methods

A total of 20 extracted human mandibular permanent first molars, with angle (>20°) were selected. And only mesial canals were included in the study. Conventional access opening was done. The canals were located and working length was obtained by viewing the number 10 K file from the apex in ×25 magnification. The initial glide path was prepared with hand files number 15 and number 20 K files. ProTaper rotary system was used for canal preparation and each canal was prepared up to an apical preparation of F1 size because the use of the rotary files creates a significant amount of smear layer. The apical portion of each canal was enlarged to F1 size to allow adequate cleaning and penetration of the solution to the apical third of each root canal. 3% NaOCl was used as an intracanal irrigant in between each file size for the experimental samples. After instrumentation was complete the final irrigation of the samples was done with 17% EDTA (1 ml) and 3% NaOCl (3 ml), followed by normal saline (3 ml).

Irrigation was done with 3 ml NaOCl (3%), after each file. Then the teeth were randomly divided into two groups (20 canals).

Group A: PUI group.Group B: MDA group.Group C: SI group.Group D: Conventional irrigation (CI) group.

In Group A 1 ml of 17% EDTA solution for 1 min was applied, followed by 3 ml of 3% NaOCl solution for 30 s, with PUI, followed by 3 ml of normal saline with a 26 gauge needle. The same procedure was followed for the sonic group at 10,000 rpm. And for manual dynamic activation group, 1 ml of 17% EDTA was agitated for 100 strokes (small vertical strokes over a period of 1 min) and 3% NaOCl was agitated for 30 s. Followed by 3 ml of normal saline without activation. The conventional group was irrigated with a normal 26 gauge needle 1 ml of 17% EDTA solution for 1 min was applied, followed by 3 ml of 3% NaOCl solution followed by 3 ml of normal saline. Teeth were then sectioned longitudinally and viewed under scanning electron microscope (SEM). Sectioning was done with Diamond discs and Chisel-mallet. Diamond discs were used to prepare a groove on buccal and lingual surface of the roots. At this time, a master cone of F1 was constantly placed within the canal to prevent accidental contamination of dentin debris. Followed by using chisel and mallet for sectioning the roots in two halves. Scanning electron microscopy allows an examination of morphologic details of the surfaces of prepared root canal. The SEM images were then analyzed for the amount of smear layer present by two independent observers without knowing which group they were analyzing. The amount of smear layer remained on the surface of the root canal or in the dentinal tubules was scored according to the following criteria: 0 = no smear layer: No smear layer was detected on the surface of the root canals and all tubules were clean and open; 1 = moderate smear layer: No smear layer was observed on the surface of the root canal, but tubules contained debris; and 2 = heavy smear layer. The smear layer covered the root canal surface and the tubules.

Results obtained were tabulated and were statistically analyzed using SPSS software (SPSS Inc, Chicago). The mean values were compared by one-way ANOVA and Tukey's honest significant difference. Multiple comparison tests by the post-hoc procedure were employed for comparison among the groups. The level of significance was set at P = 0.05.

The null hypothesis was taken that; there would be no difference in the removal of smear layer by the four methods from the apical thirds of the mandibular first molar.


On the basis of the observations made in this study following results were obtained:

There was statistically significant difference between Group A and Group C, (P = 0.038, < 0.05) [Figure 1] and [Figure 2]. There was no statistically significant difference between the Group B [Figure 3] and Group C (P = 0.677, > 0.05), however, the mean value for the Group C was the lowest among all the four groups [Table 1]. The score shows that SI removes the highest amount of smear layer than other irrigation systems.{Figure 1}{Figure 2}{Figure 3}{Table 1}

Removal of smear layer was significantly more in Group C than Group A (P = 0.038, <0.05). There was statistically significant difference between Group A and Group D (P < 0.0001) [Table 2], showing that ultrasonic irrigation was better than the simple irrigation system. However, there was no statistically significant difference between the Groups B (MDA) and Group A (P = 0.346, > 0.05), although the mean value for Group B was lower than the Group A. These results show that MDA can remove equal or more smear layer from the apical thirds of a root canal than the ultrasonic group.{Table 2}

The Group B (MDA) was having mean values in-between the Groups A and C, showing without any significant difference, but the mean value lower than the Group A and higher than Groups B and C [Table 3]. Signifying that manual dynamic activation can remove comparable smear layer to the SI with Endo Activator and can remove more smear layer than the ultrasonic irrigation, without application of any specialized instrument for its operation, being one of the most cost-effective final irrigation system.{Table 3}

The examination of the surface of root canal walls in Group D) (control group) and showed the presence of a heavy smear layer in the apical thirds of the root canals. There was statistically significant difference between the smear layer scores when compared to all three groups with Group D (P < 0.0001).[Figure 4]{Figure 4}

Hence, the null hypothesis was rejected, as there was statistically significant difference between the groups.


The first researchers to describe the smear layer on the surface of instrumented root canals were McComb and Smith. [1] They suggested that the smear layer consisted not only of dentin as in the coronal smear layer, but also the remnants of odontoblastic processes, pulp tissue, and bacteria. Mader et al. [8] reported that the smear layer thickness was generally 1-2 μm. They discussed the smear material in two parts: First, superficial smear layer and second, the material packed into the dentinal tubules. Packing of smear debris was present in the tubules to a depth of 40 μm.

It was demonstrated that bacteria were able to survive and multiply in the smear layer. [4] It may also limit the effective disinfection of dentinal tubules by preventing NaOCl, calcium hydroxide, and other intracanal medicaments from penetrating the dentinal tubules. [7] Despite controversy over maintaining the smear layer, most of the investigations have focused on its removal. The reasons in support of the removal of smear layer are:

It has an unpredictable thickness and volume because a great portion of it consists of water.It contains bacteria, their by-products and necrotic tissue. Bacteria may survive and multiply and can proliferate into the dentinal tubules. [4] It may act as a substrate for bacteria, allowing their deeper penetration in the dentinal tubules.It may limit the optimum penetration of disinfecting agents. Bacteria may be found deep within dentinal tubules and smear layer may block the effects of disinfectants on them. [9] It can act as a barrier between filling materials and the canal wall and, therefore, compromise the formation of a satisfactory seal. [10],[11] It is a loosely adherent structure and a potential avenue for leakage and bacterial contaminant passage between the root canal filling and the dentinal walls. Its removal would facilitate canal filling. [12],[13]

The purpose of this study was to the evaluate effectiveness of different irrigation systems in removing dentin smear layer in roots of mandibular first molar teeth. First molars were used because they have maximum evidence of curvature of the mesial roots. Scanning electron microscopy was chosen because it has been used to determine the effectiveness of various irrigants to remove the smear layer. In a recent survey by Gopikrishna et al. [14] regarding irrigation protocol among postgraduates and faculties revealed that 68% respondents attempt to remove the smear layer. Plenty of studies have been presented the removal of the smear layer in the single rooted teeth. However, limited evidence is present to show the effectiveness of removal of the smear layer in posterior teeth.

After shaping the root canal, cleaning can be completed with passive sonic/ultrasonic or a final flush of syringe irrigation. [15] PUI was first described by Weller et al. [9] The term "passive" does not adequately describe the process, as it is, in fact, active; however, when it was first introduced the term "passive" related to the "noncutting" action of the ultrasonically activated file. PUI relies on the transmission of acoustic energy from an oscillating file or smooth wire to an irrigant in the root canal. The energy is transmitted by means of ultrasonic waves and can induce acoustic streaming and cavitation of the irrigant. [16]

Sonic irrigation is somewhat different from ultrasonic irrigation because it operates at a lower frequency. For sonic application, the frequencies range from 1 to 10 KHz, which is lower as compared to ultrasonics (25-30 KHz). Consequently, the streaming velocity of the irrigant will be lower. Moreover, the oscillating patterns of the sonic instruments are different. They have one node near the attachment of the file and one antinode at the tip of the file as compared to the ultrasonically vibrating file, which has several nodes and antinodes along the length of the file. However, it is not known clearly about the exact difference in performance in clinical as well as laboratory situations between the two systems. SI is somewhat different from ultrasonic irrigation because it operates at a lower frequency (Singh, Chandra et al.). [17] In one study, PUI removed more dentin smear layer from the root canal than SI, [18] while in another study, [5] no significant difference was found among the two. In another study, [19] passive activation of endodontic files for irrigation with sonic or ultrasonic energy in canals, for as little as 30 s after hand instrumentation, produced canals with significantly less smear layer than canals instrumented by hand filing alone with syringe irrigation. In our study, SI has shown statistically significant better results than PUI.

MDA is relatively newer than the different debridement systems that have been used in the past. The MDA is done with either a master cone or a syringe at 100 vibrations per minute, in order to agitate the irrigant solution inside the root canal to remove remaining dentin smear layer. These are sterile and disposable. The use of MDA for irrigation seems beneficial and cost-effective because no separate equipment is required for irrigation as it can be done by the same size master cones as the master apical file used for shaping and cleaning of the root canal.

There is a paucity of studies in the literature comparing different irrigation methods with the MDA. There is a lack of information about the effectiveness of MDA to remove the smear layer from irregular canal extensions in comparison with other irrigation methods. However, Saber et al. (2011) [20] found little difference between the MDA and the ultrasonically activated number 20 K-file in removal of the smear layer with or without EDTA and concluded that the MDA was not any more beneficial in removing smear layer. Ribeiro et al. [21] used various agitation devices for smear layer removal (NaviTip FX needle, manual dynamic irrigation, continuous PUI, and apical negative pressure irrigation), found no statistical difference among them. Our study is in agreement with these studies. [22],[23],[24] However, it also signifies that even a simple method like MDA is able to clear smear layer in comparison to costly devices like ultrasonic and SI devices. Apart from the techniques mentioned above self-adjusting files do have a comprehensive irrigation protocol and removes smear layer simultaneously with canal preparation. [25]


Results of the present study show that endoactivator was most efficient in removal of the smear layer, followed by PUI, followed by manual dynamic activation, followed by CI (simple irrigation). However, there was no statistically significant difference between the two study Groups A and B also no difference was there between B and C. Showing that although SI is the most effective method, the newly introduced manual dynamic activation shows similar removal of smear layer, followed by ultrasonic irrigation. Manual dynamic activation does not require any kind of specialized equipment for functioning. Just utilization of the master cone can remove the smear layer comparable to the costly equipment's of sonic and ultrasonic irrigation devices. The most commonly used simple irrigation technique does not remove the smear layer.


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