Evaluation of different irrigation techniques on dentin erosion and smear layer removal: A scanning electron microscopy study.

Aim: The purpose of the present study is to evaluate the effectiveness of different irrigation techniques EndoVac, RinsEndo, Canal CleanMax (CCMax), SonicMax, Passive Ultrasonic Irrigation (PUI), and Manual Needle Irrigation (MNI) on dentin erosion and smear layer removal using Scanning electron microscopy (SEM). Materials and
Methods: Seventy extracted single-rooted teeth were instrumented with ProTaper rotary instruments. The roots were randomly divided into six experimental groups (n = 10): EndoVac, RinsEndo, CCMax, SonicMax, PUI, and MNI. Final irrigation was performed with NaOCl followed by ethylenediaminetetraacetic acid and NaOCl. Six roots served as control and were irrigated with only NaOCl. Next, the roots were sectioned in a buccolingual direction and the halves were examined by SEM. Smear layer and erosion scores were recorded in the cervical, middle and apical third of the roots. Data analysis was performed using the Kruskal-Wallis and Mann-Whitney U-tests with a level of significance α = 0.05.
Results: PUI had the greatest amount of smear layer compared to other groups (P < 0.001). However, SonicMax had the greatest degree of erosion compared to RinsEndo, MNI, PUI, and EndoVac groups (P < 0.001) and CCMax group (P < 0.05). Conclusions: RinsEndo and EndoVac techniques left the least amount of smear layer while causing erosion the least compared to CCMax, PUI, and MNI techniques. Copyright:

INTRODUCTION

A favorable prognosis after endodontic treatment depends on the elimination of microorganisms and making a leakage-proof filling during treatment. Microorganisms in the untouched areas remain a challenge during root canal treatment due to the complexity of the root canal system with existing isthmuses, anastomosis, and any irregularities that cannot be cleaned easily.[12] Root canal irrigation aims to dissolve pulp and organic tissue remnants and is required to remove not only biofilm, microorganisms, and their byproducts but also debris and smear layer formed after mechanical instrumentation in the root canal.[34] After removal of the smear layer, underlying dentin wall and tubules are exposed for disinfection and sealing by root canal filling materials, thus removing smear layer overall root canal disinfection and filling.[56]

Sodium hypochlorite (NaOCl) solutions are the most commonly used irrigants in root canal treatment based on their organic tissue dissolving effect and excellent antimicrobial properties.[1] Ethylenediaminetetraacetic acid (EDTA) is a chelator agent and removes the inorganic part of the smear layer.[7] Application of the irrigants to the root canal is as important as the properties of the irrigant used. EDTA use after irrigation with NaOCl solution is the most commonly used final irrigation regimen in endodontic treatment.[1]

The widely used irrigation technique is the conventional (or manual) needle irrigation (MNI) technique which uses a syringe and a needle to deliver the irrigant into the root canal system. The mechanical flushing action of irrigants created by MNI is considered insufficient to thoroughly clean the root canal walls. The penetration of irrigant and its capacity to disinfect dentinal tubules are limited, especially in narrow or curved canals.[89]

Several new techniques and devices have been introduced to improve the efficacy of irrigation.

EndoVac (Discus Dental, Culver City, CA, USA) and Canal CleanMax (CCMax) (Maximum Dental Inc., Secaucus, NJ, USA) both are designed as conjoined irrigation and suction systems. The irrigation solution is pushed into the canal to the working length (WL) and suctioned by negative pressure with EndoVac and CCMax. Nielsen and Baumgartner[10] observed that the EndoVac showed no extrusion of the solution following the deep intracanal administration and pulling of the irrigation solution from the pulp chamber to the full WL.

The RinsEndo (Dürr Dental GmbH and Co KG, Bietigheim-Bissingen, Germany) is a hydrodynamic root canal irrigation system that irrigates the canal by using the pressure-suction technology. RinsEndo was shown to have a higher penetration depth of the irrigant into the root canal dentin when compared to syringe irrigation.[11]

Ultrasonics amplify the flushing action of irrigation solution.[12] Passive Ultrasonic Irrigation (PUI) achieved significantly cleaner canals when compared to passive sonic agitation system.[13] SonicMax (Maximum Dental Inc., Secaucus, NJ, USA) is a sonic irrigation system and is powered by a dental unit compressor. It utilizes a small file for irrigation which should be placed in the center of the canal and activated sonically.

This study aims to evaluate the effect of EndoVac, RinsEndo, CCMax, SonicMax, PUI, and MNI on dentin erosion and smear layer removal using SEM analysis.

MATERIALS AND METHODS

Selection and preparation of teeth

This study was approved by Hacettepe University, the institution's Research Ethics Committee, with the Number: Lut08/67-21. Seventy single-rooted human mandibular premolars with mature apices recently extracted teeth were used. The presence of a single canal was verified with two digital radiographs from the buccal and proximal directions. Once the debris and soft-tissue fragments were cleaned, the teeth were stored in the physiological saline solution until required.

Each tooth was decoronated at the cement-enamel junction with a diamond disc. A size 10 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was inserted into the root canal until it can be seen in the apical foramen, and the WL was determined 1 mm short of this length. All canals were instrumented using ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) rotary instruments in a crown-down manner (Sequence-S1-Sx-S2-F1-F2-F3-F4) according to the manufacturer's recommendations. Each canal was prepared with a size F4 finishing file. A size 10 K-file was used to check the apical patency among each instrumentation. After each file was used, the canals were irrigated with 1 mL of 2.5% NaOCl with a syringe and a 27-gauge needle for 20 s. The needle was positioned into the canal until a small resistance was felt.

Final irrigation of the root canals

After the root canals were prepared, the specimens were randomly divided into six experimental (n = 10) CCMax, SonicMax, RinsEndo, MNI, PUI, and EndoVac and control groups (n = 6), which did not receive final irrigation. Final irrigation of the root canals in experimental groups was carried out with 5 mL of 2.5% NaOCl solution followed by 5 mL of 17% EDTA solution and then again with 5 mL of 2.5% NaOCl solution. Finally, the canals were irrigated with 5 mL of saline solution to remove residual solution remaining in the canal, and then, the root canals were dried with the paper points. All specimens were prepared by the same operator under standardized conditions.

The irrigation techniques and materials used in this study were as follows:

CCMax (Maximum Dental Inc., Secaucus, NJ, USA): Final irrigation solution was transferred using CCMax disposable cannula, and the used irrigation solution and debris were aspirated through the cannula again

SonicMax (Maximum Dental Inc., Secaucus, NJ, USA): A K-file number 15 was used with SonicMax to activate the irrigation solution. The file was introduced into the canal 1 mm shorter than the WL and kept centered without contacting the root canal wall

RinsEndo (Dürr Dental GmbH and Co KG, Bietigheim-Bissingen, Germany): The irrigation solution was delivered by the activation of RinsEndo handpiece by using its needle (size 45 with a lateral opening of 7 mm). The delivery rate was set at 6.2 mL/min based on the manufacturer's instructions. The RinsEndo was positioned in the coronal third of the canal and kept without binding during the irrigation procedure[11]

MNI: It was performed with a syringe and Endo-Eze Needle (Endo-Eze, Ultradent, South Jordan, UT, USA): The 27-G side-vented needle was placed into the canal 2 mm shorter than the WL without any binding. During the delivery of the irrigation solution, the needle was moved 1–2 mm up-and-down manner

Passive Ultrasonic Irrigation: Size 15 file (Irrisafe K 15 Satelec, Merignac, France) connected to an ultrasonic device (Suprasson Pmax Satelec, Acteon, Marignac, France) was used. An Irrisafe was placed 1 mm shorter than the WL and activated. The root canals were irrigated copiously with ultrasonic activation of a vibrating file at power setting 5.[12] The file was positioned into the center of the canal without contact

EndoVac (Discus Dental, Culver City, CA, USA): Master delivery tip (MDT) was placed into the coronal part, and during the transfer of irrigant to the coronal part, the macro-cannula was advanced into the canal while moving constantly up-and-down motion. Afterward, in the same manner, as MDT transferred the solution to the coronal part, the micro-cannula was applied into the canal 1 mm shorter than the WL, by using 1–2 mm up-and-down motion.[10]

Preparation of samples

Smear layer and erosion analysis by SEM

Following final irrigation, specimens were split into two halves longitudinally using a diamond disc and chisel for SEM evaluation. Four teeth were discarded from the control group due to improper separation. Samples were sectioned into apical, middle, and coronal thirds by marking grooves at the root margins. Each specimen was dehydrated in gradually concentrated ethanol solutions, gold coated, and examined at ×1500 magnification under an electron scanning microscope (SEM) (JEOL JSM-6400, Japan), as described previously by Paqué et al.[14] The central light of the SEM is directed at the center of the root region to be imaged at ×10 magnification, and the magnification ratio is gradually increased up to ×1500. Then, smear layer and erosion levels in the apical, middle, and coronal thirds of the root canals were evaluated at ×1500.

The SEM images were evaluated blindly by two endodontists after a calibration exercise. The kappa test was performed separately for smear and erosion evaluations to verify the inter-observer agreement.

The smear layer scoring was assigned using the following 5-scale scoring systems developed by Hülsmann et al.:[15] score 1, no smear layer, dentin tubules open; score 2, small amount of smear layer, most tubules open; score 3, homogeneous smear layer covering the root canal wall, only a few tubules open; score 4, complete root canal wall covered by homogeneous smear layer, no open dentinal tubules; and score 5, heavy nonhomogenous smear layer covering the complete root canal wall.

A previously developed erosion score by Torabinejad et al.[16] was modified and was scored the degree of erosion of dentinal tubules by the same observers: score 1, no erosion, tubules in normal condition in appearance and diameter; score 2, slight erosion, peritubular dentin erosion; score 3, moderate erosion, small amount of erosion in intertubular dentin, some dentin tubules were connected; score 4, severe erosion, severe erosion in intertubular dentin, most dentin tubules were connected; and score 5, destructive erosion, severe erosion in intertubular and peritubular erosion, causing layer by layer peeling from the dentinal wall.

Statistical analysis

Kolmogorov–Smirnov test was used to test the normality of the data distributions. Kruskal–Wallis and Mann–Whitney U-tests were used in pairwise multiple comparisons. Results of groups for smear and erosion evaluations were compared at the apical, middle, and coronal third levels. All statistical calculations were performed using the PASW Statistics for Windows (Version 18.0. Chicago: SPSS Inc., IL, USA), with a level of significance of 5% (α = 0.05).

RESULTS

Inter-observer agreement

Kappa values in the present study were equal to 0.70 for smear and >0.75 for erosion evaluations.

Normality of data

Kolmogorov–Smirnov test resulted that the data are not distributed normally in the groups (P < 0.05). Kruskal–Wallis and Mann–Whitney U-tests were used in pairwise multiple comparisons.

Smear layer

When groups are compared at the apical third level, PUI had the greatest amount of smear layer compared to other groups (P < 0.001) [Figure 1a] except control (P > 0.05), while MNI group showed a greater amount of smear layer compared to SonicMax and EndoVac groups (P < 0.05) [Figure 1a-h and Table 1].

Figure 1

SEM (×1500): (a) Passive Ultrasonic Irrigation apical, (b) Manual Needle Irrigation apical, (c) SonicMax apical, (d) EndoVac apical, (e and f) CCMax apical, (g) RinsEndo apical, (h) control apical, (i) Passive Ultrasonic Irrigation middle (j), CCMax middle, (k) control middle, (l) Manual Needle Irrigation coronal, (m) Passive Ultrasonic Irrigation coronal, (n) EndoVac coronal

Table 1

Means of smear layer score aspect to root thirds. No difference between the control group and Passive Ultrasonic Irrigation at apical third

Smear layer Mean of scores±SD
Groups	Apical third	Middle third	Coronal third
CCMax (n=10)	1.90±1.66b	1.70±0.82c,*	1.40±0.52b
SonicMax (n=10)	1.00±0.00b,†	1.00±0.00c	1.00±0.00b
RinsEndo (n=10)	1.30±0.48b	1.40±0.52c	1.30±0.67b
MNI (n=10)	2.4±1.26b†	1.00±0.00c	1.00±0.00b
PUI (n=10)	3.83±0.39a	2.58±1.08b,*	1.25±0.45b
EndoVac (n=10)	1.17±0.39b,†	1.16±0.39c	1.17±0.39b
Control (n=6)	5.00±0.00a	5.00±0.00a	5.00±0.00a

Means followed by the different superscript letters in the same columns are significantly different (P<0.001), † MNI left greater amount of smear layer compared to SonicMax and EndoVac groups (P<0.05), *Significance between PUI and CCMax P<0.05. SD: Standard deviation, PUI: Passive Ultrasonic Irrigation, MNI: Manual Needle Irrigation, CCMax: Canal CleanMax

When groups are compared at the middle third level, PUI had the greatest amount of smear layer [Figure 1i] compared to SonicMax, RinsEndo, MNI, and EndoVac groups (P < 0.001) and CCMax group (P < 0.05) [Figure 1j], except control (more smear layer was observed with control, P < 0.001) [Figure 1k].

There was no difference between the groups when the amount of smear layer is compared at the coronal third level, except control (P < 0.001) [Table 1 and Figure 1l n].

Erosion scores

When groups are compared at the apical third level, CCMax [Figure 2a and Figure 1f] showed a greater degree of erosion compared to RinsEndo, MNI, PUI, and EndoVac groups (P < 0.05) [Table 2]. However, SonicMax had the greatest degree of erosion [Figure 2b] compared to RinsEndo, MNI, PUI, and EndoVac groups (P < 0.001) and CCMax group (P < 0.05). Since the control group showed a continuous smear layer and lots of debris, erosion was not evaluated on control. MNI may serve as the control group for other groups since manual irrigation is the traditional method that has been used so far.

Figure 2

Representative images of samples (SEM, ×1500) with severe erosion (score 5): (a) CCMax apical third, (b) SonicMax apical third, (c) RinsEndo middle third, (d) EndoVac middle third

Table 2

Means of erosion score aspect to root thirds

Erosion Mean of scores±SD
Groups	Apical third	Middle third	Coronal third
CCMax (n=10)	4.63±0.37b*,†	2.80±1.48a, b	1.20±0.42b
SonicMax (n=10)	4.00±1.00a,*	4.10±0.57a,*	5.00±0.00a
RinsEndo (n=10)	1.90±0.57b,†	2.24±0.84b*	2.26±1.07b
MNI (n=10)	2.50±1.60b,†	3.40±1.35a, b	3.80±0.92b
PUI (n=10)	1.25±0.46b,†	2.60±1.26a, b	2.50±1.44b
EndoVac (n=10)	2.00±1.2b,†	3.42±1.50a, b	2.90±1.27b
Control (n=6)	N/A	N/A	N/A

Means followed by the different superscript letters in the same columns are significantly different (P<0.001). † CCMax also showed a greater degree of erosion compared to RinsEndo, MNI, PUI, and EndoVac groups (P<0.05), *P<0.05. MNI group may serve as a control since no control can be provided for erosion. SD: Standard deviation, PUI: Passive Ultrasonic Irrigation, MNI: Manual Needle Irrigation, CCMax: Canal CleanMax, N/A: Not available

When groups are compared at the middle third level, SonicMax had a greater degree of erosion compared to RinsEndo [Figure 2c] (P < 0.05). CCMax, MNI, PUI, and EndoVac [Figure 2d] groups were not significantly different from one another in terms of erosion in the middle third of the canals (P > 0.05).

At the coronal third level, SonicMax had the greatest degree of erosion compared to other experimental groups (RinsEndo, CCMax, MNI, PUI, and EndoVac) (P < 0.001). Furthermore, MNI showed a greater degree of erosion compared to PUI (P < 0.05) [Table 2].

DISCUSSION

The efficiency of any irrigation solution is related to its chemical effectiveness as well as its volume, contact time, transportation, and also type, diameter, and insertion depth of irrigation needle.[2] Owing to the recent increasing popularity of irrigation systems, the purpose of the present study was determined to compare the different irrigation techniques (CCMax, SonicMax, RinsEndo, MNI, PUI, and EndoVac systems) in terms of their cleaning effectiveness in final irrigation.

PUI was previously shown to be a successful irrigation technique with less smear layer and debris when compared to passive sonic irrigation and manual irrigation methods.[13]

K type 15 file was used for PUI to prevent contact with the canal wall while creating more frequent acoustic waves (measured in Hz) by using a wider amplitude of oscillation. PUI was applied by continuous irrigation rather than intermittent, since the smear layer was reported to be removed more successfully by increasing the power of the device during PUI. Jiang et al.[12] obtained the best results in the removal of the smear layer by using the setting of maximum power in their study. In the present study, the maximum power option of the ultrasonic device was used to compare the irrigation performance of PUI to the other recent irrigation systems. The significantly greater amount of smear layer was removed on the apical and middle thirds of the root canals by using EndoVac, RinsEndo, SonicMax, and MNI method when compared to the smear removal performance of PUI and CCMax techniques. However, RinseEndo represents a higher risk of the apical extrusion of the irrigation solution.[11]

When the performances of PUI and CCMax were compared, smear layer removal was significantly poorer with the PUI method. The file used during PUI accidentally contacts the dentin walls, and as a result, the smear layer and debris are reproduced. This result of the present study was consistent with findings obtained by Gu et al.,[17] who observed more smear layers in the post cavities when irrigation was done with PUI versus without PUI. Contrary to the results of the current study, compared to PUI, the lack of efficacy of MNI was reported previously.[10] Smear layer was completely removed in the middle and coronal thirds of the canal when using MNI technique in this study; however, its effectiveness remains limited in the apical third of the canals.

In sonic devices, the frequency is <6.5 kHz, and in ultrasonic devices, the frequency range is 20–30 kHz. An ultrasonic oscillating file exerts three to five times more energy than an oscillating file sonically. Therefore, files with sonic vibration are expected to remove dentin less aggressively compared to a file with ultrasonic vibration.[18] In the SonicMax irrigation group, although the vibrating file has contact with the dentin wall, debris and smear layer formed can be easily removed from the canal by irrigation solutions. Following the previous studies, greater removal of smear layer and debris was observed with sonic irrigation.[1819] Besides the greater performance of SonicMax, by EndoVac and MNI techniques, a greater amount of smear layer was removed compared to PUI. Kumar et al.[20] obtained that EndoVac and EndoActivator performed much better than MNI in removing the smear layer from the apical third. EndoActivator uses sonic energy and with 0.2% chitosan showed better in the removal of the smear layer when compared to PUI.[21]

CCMax was developed based on the working principle of EndoVac; however, likewise findings in the present study, EndoVac showed less smear compared to CCMax. In the current study, SonicMax removed the smear layer greater than PUI and CCMax; however, SonicMax also caused the greatest degree of erosion in the apical, middle, and coronal thirds of the root canals.

Erosion changes the mechanical features of root dentin and does not create a favorable surface for sealing with contemporary root canal filling materials.[22] Sequential use of EDTA and NaOCl irrigation, long exposure time, acidic chemical structure, and low pH of irrigants cause erosion.[23] In the current study, 5 mL EDTA and 10 mL NaOCl solutions were used accordingly to be following clinical conditions for irrigation which requires us to compare the effects of the irrigation devices on dentin in terms of erosion as well. The scoring scale for erosion with three levels (score 1–3) used by Torabinejad et al.[16] was extended to five levels (score 1–5) in the present study since the various degrees of peritubular and intertubular dentin erosion were observed in the groups. MNI showed moderate erosion on dentin. Particularly, SonicMax resulted in severe erosion in the apical, middle, and coronal thirds of the root canals, not only on the surface of the root canal walls but also inside the dentin tubules, causing degradation of the dentin.

CONCLUSIONS

Within the limitation of this study, RinsEndo and EndoVac techniques left the least amount of smear layer while causing erosion the least compared to CCMax, SonicMax, PUI, and MNI techniques. SonicMax technique left the less amount of smear layer compared to CCMax, and PUI. However, SonicMax resulted in the greatest degree of erosion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.