Efficacy of passive ultrasonic irrigation, continuous ultrasonic irrigation versus irrigation with reciprocating activation device in penetration into main and simulated lateral canals.

CONTEXT: The use of chemicals solutions and means of activation is of utmost importance in endodontic treatment. AIMS: This study compared three activation techniques used in the final irrigation of the endodontic treatment. SUBJECTS AND METHODS: Eighty uniradicular teeth were instrumented with the Protaper Universal system up to F4 file. After decalcification, the teeth had artificial lateral canals created at 2, 4.5 and 6 mm from working length (WL). The groups were randomly divided into four groups (n = 20): control group (C), passive ultrasonic irrigation (PUI) group, continuous ultrasonic irrigation (CUI) group, and easy clean (EC) group. The penetration of the irrigant into the samples was evaluated using image observation using the Image J program. STATISTICAL ANALYSIS USED: The level of agreement among the observers was determined by the Cronbach's alpha test. The likelihood ratio test was used to evaluate possible differences between the groups and the Kendall's W statistic test to verify possible differences between the irrigant penetration levels in the lateral canals. The Fisher's exact test was applied to verify differences by the studied group considering the WL variables and lateral canals.
RESULTS: The results showed no statistical difference in the penetration of the irrigator in the main canal when compared to the C, PUI, CUI, and EC groups (P > 0.05).
CONCLUSIONS: The method using a positive syringe and needle pressure was not able to effectively carry the irrigator to the artificially made lateral canals, whereas PUI, CUI, and EC were equally efficient in this regard (P < 0.01).

INTRODUCTION

Regardless of the canal preparation system, the anatomical complexity of the root canal system (RCS) makes it difficult to completely clean and disinfect it.[1] The regions of isthmus, constrictions, anastomoses and other morphological irregularities harbor tissues, microorganisms, and debris that may result in the development or maintenance of endodontic and periradicular pathologies.[2] Even with advances in metallurgy and kinematics, no system can completely mold the root canal, leaving some walls of the canals untouched.[3] According to Haapasalo et al.,[4] the main objective of the instrumentation is to facilitate effective irrigation, disinfection, and obturation. Furthermore, because the automated instruments provide a faster preparation of the canals compared to conventional systems,[5] there is a reduced time of action of the irrigating agents inside the canal, which makes essential the introduction of means to potentiate its action.

Among the means of agitation of the chemical substance, passive ultrasonic irrigation (PUI) is the most widespread and promotes the cavitation effect by producing bubbles that rupture close to the dentin walls, in addition to the formation of micro-acoustic current that promotes hydrodynamic agitation of the liquid potentiating cleaning.[6] To this purpose, small diameter metal inserts must be positioned within the canal near the apical region so as not to touch the dentin walls.

Continuous ultrasonic irrigation (CUI) also promotes the physical phenomena of micro-acoustic current and cavitation; however, it is based on the activation of a needle directly connected to the ultrasound unit, which allows a continuous flow of the irrigant into the canal. The irrigating solution passes through the needle into an activated state, avoiding the need to insert the needle into the working length (WL).[7]

The EasyClean (EC) system (EC, Easy Dental Equipment, Belo Horizonte, MG, Brazil) is an acrylonitrile-butadiene-steroid polymer device, 25.04, with a wing-shaped cross-section of an airplane. Its basic principle is the mechanical agitation of the chemical substance, promoting cleaning of walls, and recesses of the root canal due to the mechanical drag of debris adhered to the walls.[8]

Considering that action of the chemical solutions occurs primarily when in contact with the tissue or microorganism, it is essential to understand and verify the depth at which the irrigating agent acts on the RCS when using these different activation systems. The objective of this study was to evaluate the penetration of the irrigating liquid into the main root canal and simulated lateral canals in extracted and diaphanized unirradicular teeth, comparing the activation techniques of PUI, CUI, and EC irrigators during the final irrigation of the canals. The null hypothesis was that there would be no significant difference between the final irrigation techniques tested.

SUBJECTS AND METHODS

The research project was approved by the Ethics and Local Research Committee (# 1.006207). Eighty human maxillary unirradicular teeth with fully-formed roots, straight canals, absence of cracks, fractures, calcifications, or previous endodontic treatment were selected. The measurement of the vestibular-lingual and mesiodistal distances on the external surface was performed with a digital caliper (Mitutoyo Sul América, São Paulo, Brazil), to provide a greater standardization of the samples, allowing a maximum deviation of 10% of the determined average.[9] Root length was standardized in 16 mm with a double-sided diamond disk (KG Sorensen, Cotia, Brazil). The samples were stored in 0.1% thymol solution until the beginning of the research.

A K #10 file (Dentsply, Maillefer, Balaigues, Switzerland) was inserted into the canal until it was visualized in the apical foramen. The WL was determined by subtracting 1 mm from this measurement. Canal instrumentation was performed by a single experienced operator using the ProTaper Universal Rotary System (Dentsply, Maillefer, Balaigues, Switzerland) up to the F4 file (40.06), according to the speed and torque recommended by the manufacturer. Irrigation with 3 mL of 5.25% Sodium Hypochlorite (NaOCl) (Lenza Farma, Belo Horizonte, Brazil) was performed at each instrument change using 30 G needle (Ultradent, South Jordan, UT, USA) at 2 mm below the WL, totaling a volume of 20 mL of irrigating solution per experimental unit.

After the instrumentation, all the teeth were irrigated with 3 mL of ethylenediaminetetraacetic acid (Lenza Farma, Belo Horizonte, Brazil) for 3 min with syringe and needle positioned 2-mm short of WL, followed by irrigation with NaOCl 5.25%.

The teeth were separated into 10 mL glass bottles, numbered, and the decalcification process[10] started. The samples were submerged in 5 mL of 5% nitric acid (Itafarma, Itaobim, Brazil) and kept at rest for 36 h. Once decalcified, the samples were washed with running water for 3 min, and the lateral canals were created by inserting, perpendicularly to the outer surface, a C-Pilot file (VDW, Munich, Germany) from the buccal wall to the lingual wall at 2, 4.5, and 6 mm from the root apex. The samples were dehydrated in an ascending sequence of 80% ethyl alcohol (Lenza Farma, Belo Horizonte, Brazil) for 8 h, 90% for 2 h and 100% for 2 h. After dehydration, they were submerged in 99.9% methyl salicylate (Lenza Farma, Belo Horizonte, Brazil) to make them transparent and rigid. The roots were covered with white orthodontic wax (Maquira, Maringá, Brazil) creating a closed irrigation system.

After diafanization of the roots, a contrast solution containing 5.25% NaOCl (80%) and Nankin ink (20%) (Talens, Apeldoorn, Netherlands) was prepared and injected into the root canals, following the methodology described by Castelo-Baz,[10] and the specimens randomly distributed m (http://www.random.org) into three experimental groups according to the final canal irrigation system.

Experimental groups

Control group (n = 20): Control-irrigation with syringe and needle

A total volume of 6 mL of contrast solution was injected into the canals 1 mm below the WL with a syringe and 30G needle in a total time of 1 min for each tooth. The solution was not activated in this group.

Passive ultrasonic irrigation group (n = 20): Passive ultrasonic irrigation

A total volume of 2 mL contrast solution was injected into the canals with a syringe and 30 G needle. Ultrasonic activation was performed by the Jet Sonic ultrasound unit (Gnatus, Ribeirão Preto, Brazil) with the Irrisonic 20.01 stainless steel instrument (Helse Dental Technology, Santa Rosa do Viterbo, Brazil). The instrument was inserted passively at 2 mm below the WL and activated with a defined power of 20%. The procedure was repeated in three sequences of 20 s, renewing the solution every cycle, totalizing a total volume of 6 mL of contrast solution and a total activation time of 1 min for each tooth. The ultrasound tip was handled gently with short, up-down movements.

Group continuous ultrasonic irrigation (n = 20): Continuous ultrasonic irrigation

Ultrasonic activation was performed with a StreamClean™ (Ultrasonic Irrigation System, Vista Dental Products, Racine, USA) mounted on a Jet Sonic ultrasound unit. A volume of 10 mL syringe containing contrast solution was attached to the Luer-lock connection on the needle. The inactive needle was inserted into the canal 2 mm from the WL, and the solution was injected. Once the canal was filled, the ultrasound device was activated with the power set at 20%. A continuous irrigation flow of 6 mL/min was maintained, and the active ultrasound tip handled smoothly with short up and down movements.

Group EasyClean (n = 20): EasyClean

A total volume of 2 mL contrast solution was injected into the canals with a syringe and 30G needle. The EC insert was inserted passively into the WL and activated by the X-Smart Plus (Dentsply Maillefer, Balaigues, Switzerland) in the reciprocating movement as recommended by the manufacturer using the WaveOne program. The irrigation method was identical to the PUI group.

Criteria for evaluating the images

The penetration of the irrigant into the samples was evaluated by direct observation of images recorded under an operative microscope with a magnification of ×10, after which the samples were photographed with Canon Ti5 machine. The images were transferred to a computer and evaluated in the Image J program. The measurement was performed from the canal entrance to the most apical portion and, in the lateral canals, the measurement was performed from the canal entrance to the outermost portion.

The penetration of the contrast solution into the main canal was evaluated using the following scores: “0” = partial penetration of the irrigant in the main canal and “1” = total penetration of the irrigant in the main canal until reaching the WL.

In relation to the penetration of the contrast solution in the lateral canals, scores ranging from 0 to 2 were used, considering the penetration by at least 50% of the total length individually for each level (2, 4.5, and 6 mm):[10]“0” = no lateral canal penetrated by the irrigant, 1 = penetration of the irrigator in one lateral canal and 2 = penetration of the irrigant in the two lateral canals. Two trained, blind evaluators scanned all samples.

Statistical analysis

The level of agreement among the observers was determined by the Cronbach's test, which found a high level of agreement (<0.001). The likelihood ratio test was used to evaluate possible differences between the groups for both the WL variable and the lateral canal variable and the Kendall W Statistic test to verify possible differences between the irrigant penetration levels in the lateral canals. The Fisher's exact test was applied to verify significant differences by the studied group considering the WL variables and lateral canals. All statistical calculations were performed using the IBM Statistical Package for Social Sciences, version 23.0 (IBM, Armonk, NY, United States of America).

RESULTS

The penetration of the contrast solution into the WL and along the lateral canals was analyzed in all samples from each group [Figure 1].

Figure 1

Representative sample of each group. 1 - Control Group; 2 - Passive ultrassonic irrigation; 3 - Continous ultrassonic irrigation; 4 - EasyClean

In Group C, the irrigant solution reached WL in 60% of the samples, in the PUI 80%, CUI 85%, and EC 90% groups, respectively. The values obtained did not show a significant difference, P > 0.005, in the ability of the final irrigation protocols to reach the WL [Table 1].

Table 1

Irrigated samples for working length and number of lateral canals penetrated by irrigating liquid according to four irrigation systems

Variable/group	C (%)	PUI (%)	CUI (%)	EC (%)
WL, n (%)	12 (60.00)a	16 (80.00)a	17 (85.00)a	18 (90.00)a
Lateral canals, n (%)
6 mm	13 (32.50)a	34 (85.00)b	32 (80.00)b	36 (90.00)b
4.5 mm	4 (10.00)a	29 (72.50)b	29 (67.50)b	27 (72.50)b
2 mm	2 (5.00)a	26 (65.00)b	31 (80.00)b	32 (77.50)b
Penetration of lateral canals n (%) - total	19 (15.83)a	89 (74.17)b	91 (75.83)b	96 (80.00)b

The mean penetration of the irrigating solution to the lateral canals was 15.83% in Group C, 74.17% in PUI group, 75.83% in CUI group and 80.00% in EC group. The value of Group C differed significantly from the other groups (P < 0.001), but the difference between the PUI, EC, and CUI groups was not statistically significant, P > 0.005.

DISCUSSION

The null hypothesis tested was partially accepted considering that regarding the penetration of the irrigating fluid in the WL, there was a similarity between the groups, with no statistically significant differences (P > 0.05) and also there was no significant difference in the penetration of the irrigating liquid in the lateral canals, between the PUI, CUI, and EC activation techniques (P > 0.05). However, the control group was inferior to the other groups in relation to the penetration of the irrigant in the lateral canals (P < 0.01).

The root canal should be modeled under constant irrigation to remove inflamed or necrotic pulp tissue, microorganisms, biofilms, and other debris. The volume of liquid and contact time influences the effectiveness of irrigation solutions, and hence, it is essential to establish a protocol capable of promoting proper cleaning of the RCS.[8] Clinically, this means that the irrigant should ideally reach the full length of the RCS, dentinal tubules, lateral canals, deltas, and isthmus.[11]

The literature presents methods to optimize penetration and potentiate the action of irrigating substances in the RCS, such as manual agitation with gutta-percha or files, mechanical agitation with plastic instruments, and sonic and ultrasonic agitation.[121314]

Different methodologies were proposed to evaluate the activation of irrigants: histological sections;[17] methods of bacteriological culture;[15] scanning electron microscope analysis;[16] Micro-CT,[17] and diafanization.[18] The simulation of lateral canals in diafanized teeth allows the evaluation of the irrigation solution penetration in the canals.[10] Several studies have evaluated different irrigation protocols regarding the penetration of the irrigating solution into lateral canals.[1011]

PUI and CUI use ultrasonic vibration with the purpose of increasing the contact of the irrigating solution with the walls of the canal mainly in its apical portion, potentializing the properties of the chemical agents. One of the characteristics of the ultrasonic activated instruments is the cleaning promoted by acoustic flow and cavitation,[19] which requires an enlargement of the root canal for an adequate performance,[46] and for this reason as well as for the anatomic possibility of the teeth used in this study the root canals were instrumented until protaper F4. They also promote greater penetration of the irrigation solution in the isthmus and lateral canals.[20]

The EC system promotes cleaning using mechanical agitation of the irrigation solution and mechanical drag of the debris adhered to the canal walls.[21] This system has already been evaluated in previous studies regarding the potential to cause dentin erosion,[21] ability to clean canals and isthmus, and ability to penetrate the irrigating solution in lateral canals.[22] The efficacy of the EC system in bringing the irrigant to the problematic access sites of the RCS, represented in this study by the simulated lateral canals, was proven when compared to the ultrasonic irrigations (CUI and PUI). This has already been demonstrated in the literature as efficient and more effective compared to conventional irrigation with syringe and needle.[17] The use of instruments for the activation of the liquid allowed a more significant portion of the RCS to be reached by the irrigating liquid, in agreement with previous studies.[2324] There were no significant differences between the three techniques of irrigant activation, regarding the penetration in the simulated lateral canals, confirming results obtained in previous studies, in which irrigation activation techniques were significantly superior to the traditional irrigation technique using positive syringe pressure and needle.[2425]

CONCLUSIONS

That the conventional endodontic irrigation method using a positive syringe and needle pressure was not able to effectively carry the irrigator to the more confined areas of the RCS, represented in this study by artificially made lateral canals, whereas PUI, CUI, and EC were equally efficient in this regard.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.