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Year : 2022  |  Volume : 12  |  Issue : 1  |  Page : 38-42

Effect of sonic and ultrasonic irrigation on improving root canal cleanliness after post space preparation: A confocal laser scanning microscopic study

Department of Conservative Dentistry, Faculty of Dentistry, Universitas Indonesia, Jakarta, Indonesia

Date of Submission09-Jan-2021
Date of Acceptance23-Mar-2021
Date of Web Publication8-Jan-2022

Correspondence Address:
Ratna Meidyawati
Jl. Salemba Raya No. 4, Jakarta 13410
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sej.sej_6_21

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Introduction: Removing the secondary smear layer has been presumed to increase the micromechanical retention of fiber posts. The additional use of irrigation techniques is intended to improve the cleanliness of the root canal walls. The present study aimed to determine the effectiveness of sonic and ultrasonic irrigation techniques on root canal cleanliness after the post space preparation.
Materials and Methods: A total of 27 extracted single-rooted premolar samples underwent root canal treatment using gutta-percha and AH Plus that was labeled with rhodamine B. Gutta-percha was removed during the post preparation. The sample was then divided into three groups (n = 9): irrigation with sonic activation, ultrasonic activation, or without activation, respectively. The teeth were subsequently cut in the middle third area of the root, and the remnant of smear layers was observed using a confocal laser scanning microscope. Cleanliness was expressed as a percentage of the angle that contained part of the red area representing the smear layer. The results were statistically analyzed with a one-way ANOVA test and post hoc Bonferroni test set at 5% significance level.
Results: The sonic group had the greatest percentage of root canal wall cleanliness (89.00 ± 2.77), followed by the ultrasonic (78.33 ± 3.09) and nonactivated groups (67.77 ± 3.37). Conversely, there was no significant difference in root canal wall cleanliness between the sonic and ultrasonic groups (P = 0.067) or the ultrasonic and nonactivation groups (P = 0.071).
Conclusions: Irrigation with sonic activation improved cleanliness of the root canal dentinal wall after post space preparation.

Keywords: Confocal laser scanning microscopy, post space preparation, root canal cleanliness, sonic, ultrasonic

How to cite this article:
Yunus RM, Meidyawati R, Margono A, Prameswhari AD. Effect of sonic and ultrasonic irrigation on improving root canal cleanliness after post space preparation: A confocal laser scanning microscopic study. Saudi Endod J 2022;12:38-42

How to cite this URL:
Yunus RM, Meidyawati R, Margono A, Prameswhari AD. Effect of sonic and ultrasonic irrigation on improving root canal cleanliness after post space preparation: A confocal laser scanning microscopic study. Saudi Endod J [serial online] 2022 [cited 2022 Sep 24];12:38-42. Available from: https://www.saudiendodj.com/text.asp?2022/12/1/38/335246

  Introduction Top

Posts in the root canals are frequently required in the endodontically treated teeth to improve the support of the crown structure.[1] Fiber-reinforced composite posts can be bonded to inter-radicular dentin via adhesive cementation using resin cement.[2] The binding mechanism of the post dentinal wall to the luting systems is based on resin tag formation and the hybridization of the demineralized surface.[3],[4]

There are many factors that affect the bonding of luting cement to the dentinal walls, including micromechanical retention of luting cement. This micromechanical retention can be improved by modifying or removing the smear layer containing gutta-percha and sealer remnants.[5],[6] Clinical studies have shown fiber post debonding was mainly a result of cementation failure.[7]

Post space preparation produces a secondary smear layer containing dentinal debris, with gutta-percha and sealer residues plasticized by the friction heat of the drill. The secondary smear layer may reduce the orthophosphoric acid's penetration and chemical action.[8] Therefore, before fiber post cementation, the root canal's dentin surface needs to be adequately cleaned in order to facilitate the adhesive material infiltration to the dentinal wall.[9] However, at present, there are no clear protocols regarding the inter-radicular irrigation before post cementation. Still, chemical irrigating solutions and sonic or ultrasonic activation methods have been appraised for removing smear layer in endodontic treatment.[10]

Only a few studies have demonstrated the effectiveness of smear layer and debris removal after post space preparation with additional irrigant with activation.[9],[10] Serafino et al., Carrasco et al., and Chen et al. stated that the use of ultrasonic or sonic activation during irrigation after post preparation resulted in a smaller debris area than without activation.[9],[11],[12] Poletto et al. obtained different results, telling that there was no improvement in the cleanliness of the secondary smear layer upon the use of ultrasonic activation during irrigation.[13] However, these studies have assessed dentinal wall cleanliness after removing root-filling materials using scanning electron microscopy (SEM). These studies only examined a small portion of the root canal wall's circumference.[9],[11],[12],[13]

The use of confocal laser scanning microscopy (CLSM) to analyze fluorescein-tagged materials and quantitatively measure remain secondary smear layer after post preparation on root canal wall will provide better visualization of root canal wall's circumference.[14] This study was aimed to compare the effectiveness irrigation techniques with sonic and ultrasonic activation on the root canal cleanliness after post space preparation.

  Materials and Methods Top

Tooth selection and preparation

The study obtained ethical approval from the Dental Research Ethics Committee (ethical clearance no: 20/ethical approval/FKGUI/XII/2019). Twenty-seven extracted sound human first mandibular premolar single-rooted teeth were collected with the criteria of apically fully formed teeth, no crack or caries, and root canal length 20 mm ± 2 mm. A sample size of 9 teeth per group was estimated using Federer's formula.[15]

The crowns were removed at the cementoenamel junction using a diamond disc to obtain a similar root length of 15 mm on all tooth samples, and then, the root face was polished using abrasive discs. The canals were prepared with ProTaper Universal (Dentsply, Switzerland) rotary instrument until size F5. During instrumentation, the canals were irrigated using syringes with side-vented needles with 2.5% sodium hypochlorite (OneMed, Indonesia) and 17% ethylenediaminetetraacetic acid (EDTA, Meta-Biomed, Korea). The root canals were dried with paper points after the final irrigation.

The root canals were filled with gutta-percha cones and the sealer AH Plus (Dentsply, Switzerland) using the lateral condensation technique. The sealer was mixed at a 1:1 ratio, according to the manufacturer's instructions. During the mixing procedure, 10 parts of the sealer were mixed with one part of 0.1% rhodamine B dye (MERCK, Germany) to allow visualization under a confocal laser scanning microscope.

Filling removal and irrigation protocol

After 7 days stored at 37°C in room temperature for complete setting, the gutta-percha was removed by a Peeso reamer #5 (MANI, Japan), leaving 5 mm of apical gutta-percha. A #1 drill (Ivoclar, USA) was used creating a post space with a diameter of 1.5 mm in the coronal area. The post space was irrigated with 5 ml EDTA 17% (MD-Cleanser, Metabiomed, Korea) and 5 ml chlorhexidine 2% (Hexidine, OneMed, Indonesia) and rinsed with 5 mL distilled water. The samples were then divided into three groups (n = 9).

Group 1 had all irrigants sonically activated for 1 m via EndoActivator (Dentsply, Swiss). Group 2 activated all irrigants for 1 m tip IrriSafe tip (Satelec, France), which was driven by the ultrasonic device P5 (Satelec, France) at power setting 6. Finally, in Group 3, all irrigants were flushed into the post space and left in place for 1 m. Paper points were used to absorb the former irrigant during irrigant replacement. All irrigants were applied using a 5-mL syringe and a 27G side-vented needle. Paper points were then applied to dry the root canals.

Sample preparation and confocal laser scanning microscopy evaluation

Each sample was placed in a mold (8 mm × 8 mm × 25 mm) and embedded in self-curing resin and then sectioned perpendicular to its long axis using Accutom 2 cutting machine (Struers, United States) set at 500 rpm. The cutting machine was operated using a low-speed diamond wheel with continuous water cooling. The horizontal cutting level was set at 7 mm from the apex, and a 1.0 ± 0.1 mm-thick specimen section was collected which represented the middle portion of the root canal.

The root slice was mounted onto a slide glass with a Vectashield Antifade Mounting Medium (Vector Laboratories, United States) and then examined using confocal laser scanning microscope LSM 700 (Carl Zeiss Microscopy, Germany) with 488-nm wavelength. High-resolution composite images were made to encompass the specimen's entire cross-sectional area. The samples were analyzed with ×5 magnification.

A protractor was placed at the center of the post space [Figure 1]. The clean walls' angular distribution was assessed in degrees. Cleanliness was expressed as a percentage of the angle that could be accessed by the post drill and then the nonaccessible area was excluded. The images were evaluated by two observers who blindly evaluated the cleanliness of the root canal using assessment criteria. Cohen's weighted kappa coefficient was used to calculate agreement between observers.
Figure 1: The red areas are rhodamine B-tagged remnants of sealer and plasticized gutta-percha (red arrow). The green circle shows the outline of the post drill. The center of the circle is marked by the meeting point of the yellow line. The angles formed by the red lines between the red areas represent unclean areas. Clean areas are classified as inaccessible if they fall outside the green circle

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Statistical analysis

The data were statistically analyzed using SPSS software (version 22.0, IBM Corp., New York, USA). One-way ANOVA and Bonferroni post hoc tests were used. The statistically significant level was set at 5%.

  Results Top

A comparison of root canal cleanliness between the groups appears in [Table 1]. For the image analysis of the root canal cleanliness, the inter-observer agreement was strong (kappa coefficient = 0.80). In general, there was a significant difference in the cleanliness percentage after post preparation between the sonic, ultrasonic, and nonactivated groups (P < 0.001).
Table 1: Distribution percentage of root canal wall cleanliness between groups

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The sealer and gutta-percha remnants displayed red fluorescence because of the rhodamine B's fluorescein label, as shown in [Figure 2]. In Group 1 (sonic activation), significant sealer and gutta-percha removal on the dentinal walls occurred. Large red remnants still coated the walls in Group 2 (ultrasonic activation) and Group 3 (nonactivated).
Figure 2: Horizontal cross-section of roots viewed with confocal laser scanning microscopy. The image sets correspond to the (a) sonic, (b) ultrasonic, and (c) nonactivated groups. The presence of sealer and gutta-percha remnants can be identified as a congested red area along the root canal walls (red arrow)

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Regarding root canal cleanliness percentage, the groups ranked from highest to lowest as follows: sonic (89.00% ± 2.77%), ultrasonic (78.33% ± 3.09%), and nonactivated (67.77% ± 3.37%).

A post hoc Bonferroni test comparison between all groups showed a significant difference between the sonic and nonactivated groups (P = 0.001). Conversely, there was no significant difference in root canal wall cleanliness between the sonic and ultrasonic groups (P = 0.067) or the ultrasonic and nonactivation groups (P = 0.071).

  Discussion Top

A secondary smear layer was produced after post space preparation using a post drill. This layer contained residual gutta-percha and sealer, which plasticized from the friction heat generated by the drill.[5] Serrafino revealed that not all sealer and gutta-percha remnants can be wholly removed from the root canal wall, especially in areas with anatomical irregularities.[11] The present study also had residual gutta-percha and sealer as part of the secondary smear layer in the root canal wall, as observed via CLSM. The CLSM analysis of the fluorescein-tagged materials is seemingly economical and suitable for evaluating root canal wall cleanliness. Notably, CLSM yields reliable labeled material identification, more straightforward sample preparation, and minimizes the presence of artifacts compared to SEM.[16]

As demonstrated in this study, the sonic activation group had the highest percentages of root canal wall cleanliness. There are some explanations that support these results. Sonic energy produces movements in the irrigation area that increase shear stress.[17] A robust, flexible, and noncutting tip vibrates to activate the irrigant by creating bubbles that extend and then collapse. In total, 25,000–30,000 implosions occur per second of vibration or shock wave. This bubble implosion then increases the temperature and produces intracanal pressure that cleans the root canal surface.[18],[19]

Mancini et al. stated that the sonic EndoActivator system is significantly more effective than ultrasonic activation at 8 mm from the apex.[20] This statement was also confirmed by Carrasco et al., who compared the efficacy of sonic and ultrasonic irrigation after post space preparation through SEM.[12]

Ultrasonic activation can improve the cleaning efficacy of root canal irrigants to detach the secondary smear layer via acoustic streaming from a passive tip.[21] The literature indicates that ultrasonic devices can transmit energy from files to irrigants with ultrasonic waves that induce two physical phenomena: acoustic streaming and cavitation. Moreover, the ultrasonic files' oscillation moves the irrigation fluid forward and backward. Then, the irrigant pressurizes and causes shear stress on the root canal wall. This mechanism explains why shear stress and pressure lead to fatigue in the debris, thereby detaching it from the dentinal wall.[18]

This study demonstrated that the cleaning efficacy of ultrasonic irrigation does not significantly differ from a regular rinse. This result is in line with Gu et al. and Poletto et al., who confirmed that additional ultrasonic irrigation did not produce higher efficacy to irrigation without activation.[13],[22] However, this study's results contradict Serafino et al. and Chen et al., who claimed that ultrasonic activation during post space irrigation is more beneficial in smear layer removal.[9],[11] These discrepancies might be due to the difference in irrigation materials used and the duration of activation.

Ultrasonic irrigation's reduced efficacy in this study was probably due to the increased distance between the ultrasonic file and the root canal wall, as the root canal wall diameter was wider after post preparation. The speed of the oscillatory component also decreases dramatically when further away from the ultrasonic file; the highest oscillating effect is obtained when the file is close to the root canal wall, whereas the speed of the nonoscillatory component only slightly decreases when the distance is elongated.[13] A large-diameter root canal might thus generate ineffective ultrasonic activation irrigation after post preparation.[22]

EDTA was chosen as the irrigant used in this study because of its effectiveness in dissolving inorganic materials, including hydroxyapatite. The use of EDTA will open up the dentinal tubules with very little superficial smear debris on the canal surface.[23]

The middle third of the root canal in this study was chosen to figure out the differences between the groups because of some reasons. The apical third of the root canal contains a smaller number and irregular structures of dentinal tubules which may affect the cleaning process[24] while the cervical third of the root canal is wider than middle and apical third so that more accessible in receiving the treatment.[25]

As for the limitations of this in vitro study, it only evaluated cleanliness, as it intended to add new insights concerning the use of irrigation systems after post space preparation. Accordingly, further studies are needed to investigate the effect of post space cleanliness on fiber post adhesion bonding strength. However, this study presents evidence that additional irrigant activation improved the removal of the secondary smear layer after post space preparation.

  Conclusions Top

Sonic activation proved the most effective method to clean the root canal wall after post preparation, compared to irrigation without activation.


The authors would like to thank Universitas Indonesia for funding this research through PUTI Q3 Grant with contract number NKB-1911/UN2.RST/HKP. 05.00/2020.

Financial support and sponsorship

This study was financially supported by the Grant from the Directorate of Research and Community Engagement at Universitas Indonesia.

Conflicts of interest

There are no conflicts of interest.

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  [Figure 1], [Figure 2]

  [Table 1]


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