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ORIGINAL ARTICLE
Year : 2020  |  Volume : 10  |  Issue : 3  |  Page : 240-246

Efficacy of a simple apical negative pressure kit on smear layer removal from the root canal surface. An in vitro study


1 School of Dentistry, Mae Fah Luang University, Chiang Rai, Thailand
2 Department of Dentistry, Bueng Kan Hospital, Bueng Kan, Thailand
3 Department of Restorative Dentistry and Periodontology, Division of Endodontics, Faculty of Dentistry, Chiang Mai University, Chiang Mai, Thailand

Date of Submission06-Oct-2019
Date of Decision09-Nov-2019
Date of Acceptance16-Nov-2019
Date of Web Publication27-Aug-2020

Correspondence Address:
Dr. Anat Dewi
Department of Restorative Dentistry and Periodontology, Division of Endodontics, Faculty of Dentistry, Chiang Mai University, Suthep Road, T. Suthep, A. Muang, Chiang Mai 50200
Thailand
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sej.sej_151_19

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  Abstract 


Introduction: The objective of this study was to assess the efficacy of a simple irrigation kit, employing the apical negative pressure principle, assembled from easily obtainable materials in the dental hospital setting, on smear layer removal from the apical third of the root canal surface.
Materials and Methods: The root canals of forty single-rooted mandibular premolars were mechanically prepared, and the teeth were then randomly divided into three groups to be irrigated with conventional needle irrigation (CNI) system, passive ultrasonic irrigation (PUI) system, and the simple apical negative pressure (ANP) kit. Four specimens were used as a negative control. After irrigation, the teeth were split longitudinally and examined under scanning electron microscopy at 1 mm, 3 mm, and 5 mm from the working length. The remaining smear layer was analyzed to assess the efficacy of each irrigation system.
Results: The least remaining smear layer was observed in the ANP group at all three distances from the working length (P < 0.001). Furthermore, significantly less remaining smear layer was observed in the PUI group 3 mm and 5 mm from the working length than the CNI group (P < 0.01), whereas there was no significant difference between the use of PUI and CNI 1 mm from the working length.
Conclusions: In this in vitro study, the assembled simple ANP kit had greater efficacy at delivering irrigants to remove the smear layer from the apical third of the root canal surface than the CNI and PUI systems.

Keywords: Apical negative pressure, dental pulp cavity, passive ultrasonic irrigation, root canal irrigants, smear layer


How to cite this article:
Upara C, Vechpanich C, Dewi A, Srisuwan T, Louwakul P. Efficacy of a simple apical negative pressure kit on smear layer removal from the root canal surface. An in vitro study. Saudi Endod J 2020;10:240-6

How to cite this URL:
Upara C, Vechpanich C, Dewi A, Srisuwan T, Louwakul P. Efficacy of a simple apical negative pressure kit on smear layer removal from the root canal surface. An in vitro study. Saudi Endod J [serial online] 2020 [cited 2020 Oct 31];10:240-6. Available from: https://www.saudiendodj.com/text.asp?2020/10/3/240/293570




  Introduction Top


The objective of root canal treatment is to eliminate infection caused by intracanal microorganisms.[1] During mechanical instrumentation, a smear layer is created on the root canal surface. It loosely adheres to the root canal surface and is comprised of organic materials, which may contain bacteria and their by-products, and inorganic materials such as dentin debris.[2],[3] Therefore, it is necessary to remove the smear layer to obtain a good seal between the root canal surface and the filling material[4] and to decrease the number of bacteria and leakage after the canals are filled[5],[6],[7] using ethylenediaminetetraacetic acid (EDTA) and then sodium hypochlorite (NaOCl) solution for the optimal result.[8]

Traditionally, conventional needle irrigation (CNI) has been used for root canal irrigation, but one of the limitations is a restricted flow of irrigant in the root canal, especially in the apical third. Most studies suggest either placement of the needle tip a minimum of 2 mm from the working length or the use of a side-vented needle to avoid the incidence of a NaOCl accident.[9] The use of the CNI system usually results in poor debridement, demonstrated by remaining debris, bacteria, and smear in the apical third of the canal.[8],[9],[10] Inadequate debridement can also be caused by an apical vapor lock, the entrapment of air bubbles formed in the closed system of the root canal, preventing the irrigant from contacting the apical third of the root canal.[11],[12]

Currently, many root canal irrigation systems are available, and they offer different results in cleaning the root canal system. The passive ultrasonic irrigation (PUI) system is one of the most widely used root canal irrigation systems. The PUI system can increase the efficacy of root canal debridement when compared with the CNI system.[13] However, a report by de Gregorio et al. shows that only 65% of the samples irrigated with the PUI system were able to deliver the irrigant to the working length.[14] Their study demonstrated that the apical negative pressure (ANP) system, which features the placement of a small aspirating needle at the working length, delivers the irrigant to the working length with greater efficacy than the PUI system.

One disadvantage of the ANP system is the need for special instruments, which must be imported at high cost. To overcome such high cost, a simple ANP kit was assembled for the purpose of investigating its efficacy in the removal of the smear layer from the apical third of the root canal surface. Therefore, this study aimed to compare the efficacy of an assembled simple ANP kit to that of the CNI and PUI systems being used routinely.


  Materials and Methods Top


Specimen preparation

This study was approved by the Human Experimentation Committee of the institution where the study was conducted, Faculty of Dentistry, Chiang Mai University, Chiang Mai, Thailand (Reference number 20/2017).

Forty single-rooted mandibular premolars, which had never undergone root canal treatment, had complete root formation and no root caries, and were extracted for orthodontic reasons (informed consent obtained), from patients aged between 18 and 25 years and stored in 0.1% thymol solution for no longer than 2 months, were used in the study. The tissues covering the external tooth surfaces were cleaned with a scalpel and ultrasonic scaler (Hu-Friedy, Chicago, IL, USA). Mesiodistal and buccolingual radiographs of the teeth were recorded to exclude teeth with more than one root canal. The radiographs were also used to determine the root canal curvature as described by Schneider,[15] and only those with <30° of curvature were included in this study. The occlusal tables of the teeth were then flattened to standardize the tooth length at 18 mm. After that, endodontic access was achieved and teeth with an initial apical file size larger than 25 were excluded from the study. Two longitudinal grooves, 0.5 mm in depth, were created on the buccal and lingual surfaces with a diamond disc (3M ESPE, St. Paul, MN, USA) to facilitate the splitting of teeth. The roots were then coated with two layers of nail polish and embedded in putty silicone (3M ESPE) to simulate a closed system and ease of handling. The root canals were then prepared using rotary instruments (MTwo, VDW GmbH, Munich, Germany) up to size 40/.04 at a working length of 17 mm. During instrumentation, 20 ml of 5.25% NaOCl solution (Sigma-Aldrich, St. Louis, MO, USA) was used to irrigate the canal with a side-vented 27-gauge needle placed 2 mm short of the working length, and a size 10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was used for recapitulation.

Experimental groups

The specimens were randomly divided into three groups for each irrigation system (CNI, PUI, and ANP) with a total of 12 specimens per group and four specimens for negative control. The experimental details of each group are as follows [Figure 1]:
Figure 1: Forty single-rooted mandibular premolars were mechanically prepared before being randomly divided into three irrigation groups and a control group. The experimental groups had an equal total irrigation time (depicted by the line in each box) and amount of irrigant

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Control (negative) group

The canals in the control group were irrigated with normal saline solution for 7 min before being aspirated and dried with paper points.

Group 1: Conventional needle irrigation group

The canals in the CNI group were irrigated with 4 ml of 5.25% NaOCl for 3 min using a side-vented 30-gauge needle (KerrHawe SA, Bioggio, Switzerland) placed 2 mm short of the working length. The NaOCl was left in the canal for another 1 min before being aspirated, and the canal was dried with paper points. After that, the canal was irrigated with 2 ml of 17% EDTA (Chematek SpA, Rome, Italy) for 1 min. The EDTA solution was then aspirated, and the canal was dried immediately. Finally, the canal was irrigated with 2 ml of 5.25% NaOCl for 1 min. The NaOCl was left in the canal for another 1 min before being aspirated and dried.

Group 2: Passive ultrasonic irrigation group

The canals in the PUI group were irrigated with 4 ml of 5.25% NaOCl for 3 min using a side-vented 30-gauge needle placed 2 mm short of the working length. The irrigant was left in the canal for another 1 min before being aspirated, and the canal was dried with paper points. Next, the canal was irrigated for 1 min with 2 ml of 17% EDTA, activated with an ultrasonic generator (Newtron P5, Acteon Satelec, Merignac, France) together with an IrriSafe tip size #25IRR (Acteon Satelec) with the power setting at level 6 and the tip placed 1 mm from the working length. After that, the irrigant was aspirated and the canal was dried immediately. Finally, the canal was irrigated with 2 ml of 5.25% NaOCl for 1 min, ultrasonically activated as well, and the irrigant was left in the canal for another 1 min before being aspirated, and the canal was dried with paper points.

Group 3: Apical negative pressure group

The simple ANP system was assembled using two intravenous infusion sets connected to a Y-shaped three-way connector. One end of the kit was connected to a dental unit high-powered suction and the other two ends functioned as an irrigant delivery and aspirator. The irrigant delivering end connects to a syringe and a 26-gauge needle using a three-way connector and only delivers irrigants to the pulp chamber and suctions any overflowed irrigant. The aspirating end connects to either a calcium hydroxide applicator tip (ApexCal, Ivoclar Vivadent, Schaan, Liechtenstein) to aspirate irrigants from the coronal and middle third of the root canal or a side-vented 30-gauge needle (KerrHawe SA) to aspirate irrigants from the working length [Figure 2].
Figure 2: The two IV sets were connected using a Y-shaped three-way connector. One end will be used to deliver irrigant while the other aspirates. The last end connects to a high-powered suction to operate

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The canals in the ANP group were first irrigated with 2 ml of 5.25% NaOCl for 1 min. During this first cycle of irrigation, a calcium hydroxide applicator tip was used to aspirate the irrigant from the middle portion of the root canal. The calcium hydroxide applicator tip was inserted as deep as the canal permitted without binding to the canal walls. After that, the irrigant was left in the canal for another 1 min before being aspirated. After the first cycle, three more irrigation cycles were performed using a side-vented 30-gauge irrigating needle. The needle was placed directly at the working length, and vertical movement, with an amplitude of 2 mm, was performed during irrigation. The first of these three irrigation cycles was performed using 2 ml of 5.25% NaOCl for 1 min. The irrigant was left in the canal for another 1 min before being aspirated, and the canal was dried with paper points. The second cycle was performed using 2 ml of 17% EDTA for 1 min before immediately aspirating the irrigant, and the canal was dried with paper points. The last cycle was performed using 2 ml of 5.25% NaOCl for 1 min, and the irrigant was left in the canal for another 1 min before being aspirated, and the canal was dried with paper points.

Smear layer evaluation

After the irrigation procedures were completed, all specimens were split in half along the longitudinal grooves created previously, using a mallet and chisel, and the specimens were sealed individually and dehydrated in a dry-heat oven at 50°C for 48 h. Then, the specimens were kept in 1% osmium tetroxide in 0.1% phosphate-buffered saline (PBS), pH 7.1 at 4°C for 2 h. Each specimen was then rinsed with PBS, for 5 min, three times, sequentially dehydrated using 30%, 50%, 70%, 90%, and 100% ethyl alcohol, critical point dried with liquid carbon dioxide, and sputter coated with gold. All specimens were examined under a scanning electron microscope (SEM) (JSM 6610 LV, JEOL, Akishima, Japan) at a magnification of 2000 to assess the effectiveness of smear layer removal in each experimental group. Four images were randomly recorded at each of three locations on each specimen: 1 mm, 3 mm, and 5 mm from the working length.

The remaining smear layer was assessed according to the method of Gutmann et al.,[16] as follows:

  • Score 1: a little or no smear layer covering up to 25% of the specimen; tubules visible and patent
  • Score 2: little to moderate or patchy amounts of smear layer covering between 25% and 50% of the specimen; many tubules visible and patent
  • Score 3: moderate amounts of scattered or aggregated smear layer covering between 50% and 75% of the specimen; minimal to no tubule visibility or patency
  • Score 4: heavy smear layer covering over 75% of the specimen; no tubule orifices visible or patent.


The amount of smear layer was assessed by a blinded examiner who did not take part in the SEM imaging. A second assessment of the smear layer was performed with an interval of at least 24 h for intra-examiner calibration.

Statistical analysis

Intra-examiner calibration was performed using an intraclass correlation coefficient (ICC). The scores of the remaining smear layer were statistically analyzed using the Kruskal–Wallis and Mann–Whitney U-tests. The significance level was set at P < 0.05. Statistical analysis was carried out using SPSS Statistics 17.0 (IBM Corporation, Armonk, NY, USA).


  Results Top


SEM images recorded from the root canal surface 1 mm, 3 mm, and 5 mm from the working length are shown in [Figure 3]. The smear layer in the control group completely covered the dentinal tubules [Figure 3]a, [Figure 3]b, [Figure 3]c. In the CNI group, the smear layer covered most of the dentinal tubules at all tested locations [Figure 3]d, [Figure 3]e, [Figure 3]f. In the PUI group, the smear layer heavily covered the dentinal tubules 1 mm from the working length [Figure 3]g, but tubules were more patent 3 mm and 5 mm from the working length [Figure 3]h and [Figure 3]i. The dentinal tubules in the ANP group were mostly uncovered at all tested locations [Figure 3]j, [Figure 3]k, [Figure 3]l.
Figure 3: Scanning electron microscope images (×2000) representing the remaining smear layer. The dentinal tubules are completely covered with smear layer in the control group (a-c), heavily covered in the conventional needle irrigation group (d-f), partially covered in the passive ultrasonic irrigation group (g-i), and mostly patent in the apical negative pressure group (j-l)

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For the reliability test, the ICC was 0.966, confirming excellent intra-examiner reliability. There was no significant difference in smear layer removal between the CNI and PUI groups (P = 0.159). All smear scores (1–4) were present in both the CNI and PUI groups. However, the ANP group showed significantly less smear layer remaining in the canal than the CNI and PUI groups (P < 0.001). Only the scores 1 and 2 were present in the ANP group [Figure 4].
Figure 4: Stacked bar chart showing the percentage scores for the remaining smear layer at the apical third of the root canal of each irrigation system.*Significant difference between CNI and ANP groups with P < 0.001.**Significant difference between PUI and ANP groups with P < 0.001

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Furthermore, when examined individually at each tested location – 1 mm, 3 mm, and 5 mm from the working length – significantly less remaining smear layer was observed in the ANP group at all locations (P < 0.001). Furthermore, significantly less remaining smear layer was observed in the PUI group 3 mm and 5 mm from the working length than in the CNI group (P < 0.01), whereas there was no significant difference between the PUI and CNI groups 1 mm from the working length [Figure 5]. The median and interquartile range of the remaining smear layer score at every distance from the working length are depicted in [Table 1].
Figure 5: Stacked bar chart showing the percentage scores for the remaining smear layer 1, 3, and 5 mm from the working length of each irrigation system. *Significant difference with P < 0.01.**Significant difference with P < 0.001

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Table 1: Median and interquartile range of the remaining smear layer score

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  Discussion Top


This study aimed to assess the efficacy of the assembled simple ANP kit by comparing its smear layer removal capability from the apical third of the root canal with that of the CNI and PUI systems, both of which are used routinely. The results showed that after irrigating with the simple ANP kit, there was significantly less smear layer remaining in the apical third of the root canal than in the CNI and PUI systems, whereas there was no significant difference between those two systems.

Important factors contributing to the greater irrigation efficacy of the root canals are the volume and the flow of the irrigants.[17],[18] Essentially, the root canal systems are closed systems covered by the periodontium.[19] Such closed systems may cause the entrapment of air bubbles in the apical third of the root canal, especially the apical 0.5 mm–1.0 mm; this entrapment is defined as the vapor lock effect.[11],[12] The bubbles result in debris and smear layer remaining after irrigation.[20],[21] These bubbles cannot be dislodged with the use of the CNI and PUI systems.[19],[20],[21],[22]

The ANP system was developed to debride the apical root canal and prevent the extrusion of irrigants into the periapical tissue. Siu and Baumgartner[23] found that canals irrigated with the ANP system were effectively debrided 1 mm from the working length. In addition, Mancini et al.,[24] in a comparison between the ANP, sonic, and PUI systems, reported that root canals irrigated with the ANP system had the cleanest root canal walls 1 mm from the apex. The findings of those two studies are consistent with those of this study and suggest that the penetration of the irrigant into the apical third of the root canal is one of the important factors in effectively removing the smear layer from the apical third. This is confirmed by de Gregorio et al.[14] who compared the effectiveness of different irrigation systems in facilitating the flow of irrigants to the working length. Their results show that the ANP system was significantly more effective, with all specimens (100%) irrigated at the working length. The PUI, sonic, and CNI systems were able to facilitate the flow of irrigants only to 65%, 40%, and 0%, respectively, of the working length of the root canals.

In contrast, there is much evidence to show that the PUI system is effective in removing debris[25] and smear layer from straight root canals[26] and also improves the efficiency of the irrigant.[13],[27],[28] The PUI system functions by creating acoustic microstreaming and cavitation. These two phenomena cause shear stress and force on the root canal walls, resulting in the removal of bacteria and debris.[29] Acoustic microstreaming and cavitation can occur only when the instrument is activated in a liquid phase. In the past, it was believed that air bubbles entrapped in the root canal could be dislodged using any instrument. A new study has proven that files or other instruments pass through the bubbles into the apical third of the canal without dislodging the bubbles.[12] Therefore, the use of the PUI system without the tip of the instrument being in the liquid phase does not create any acoustic microstreaming or cavitation, resulting in an inefficient cleaning of the apical third of the root canal system. The result is different with the ANP system, where there is a constant and continuous flow of new irrigant at the working length.

The positioning of the needle tip in an ANP system highly contributes to the cleanliness of the root canal surface because the root canal is a closed system and an air bubble is entrapped in the apical third. Therefore, if a needle can be placed at the working length, it ensures that the irrigant can penetrate to the apical third of the root canal and ensures a constant refreshment of irrigant throughout the main canal.[30],[31] A constant refreshment of irrigant increases the cleanliness of the root canal surface.[32] Neelakantan et al.[33] provided experimental evidence demonstrating that the PUI system, when the tip of the instrument is positioned 1 mm from the working length, and the ANP system can significantly increase dentinal tubule patency at the apical third of the root canal than the CNI system. The ANP system has a superior smear layer removal efficacy when compared to other irrigation systems even though the ANP system does not activate irrigant as did the PUI system. The placement of the needle tip at the working length in the ANP system is crucial in the removal of the apical smear layer, resulting in a cleaner root canal surface than when irrigated with other systems. However, the concurrent use of sonic or ultrasonic activation systems with the ANP system could provide a better debridement of the root canal system, especially where complex root canal anatomies, such as lateral canal, isthmus, or apical ramification, are present.[31],[34]

Limitations faced by this study include the variety of complex root canal anatomy that could disrupt the debridement and removal of smear layer which could be present in the apical third of the roots, especially in the lower premolar teeth. As such, the experimented teeth were examined radiographically both mesiodistally and buccolingually to exclude any tooth with more than one root canal and >30° curvature. The SEM image analysis could also present a selection bias; therefore, four images were randomly recorded at each of the three locations to be analyzed. Furthermore, the examiner of the SEM images was blinded and undergone intra-examiner calibration to reduce information bias.

One benefit of this simple ANP kit is its cost-effectiveness because the kit was assembled from inexpensive materials that are easily obtainable in the dental hospital setting. This simple ANP kit cost hundreds of time lower than commercially available ANP systems, can be easily assembled in <15 min, and the assembled kit does not require any further tuning or adjustment, reducing any technique sensitivity. Despite the low cost, it still performed satisfactory in this study, and the authors recommend a single-use approach to the kit as were intended of each component. However, the device required two hands to operate and could prove troublesome in some situations. Future studies could address this issue and could also investigate the efficacy of the kit to facilitate the disinfection of the apical third of the root canal system.


  Conclusions Top


The simple ANP kit assembled for this study had greater efficacy at delivering irrigants to remove the smear layer from the apical third of the root canal surface than the CNI and PUI systems.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
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