| Abstract|| |
Introduction: Overzealous application of endodontic irrigants affects the root canal dentin mechanical properties. The effect of volume of endodontic irrigants on the microhardness of root canal dentin has not been studied. Aim: This study assessed the effect of volume of endodontic irrigants used in different final irrigation activation techniques on root canal dentin microhardness (RCDM). Methodology: Sixty human maxillary central incisors were embedded in acrylic resin in Kuttler's endodontic cube to the level of cementoenamel junction. The root samples were randomly divided into 4 experimental groups (n = 15): Group-NI-needle irrigation, Group-PUI–continuous passive ultrasonic irrigation, Group-EndoVac–apical negative pressure system, Group combination– EndoVac + PUI irrigation. Root canals were instrumented up to size 40 (F4). The resin mounted specimens were sectioned longitudinally into two halves and were reassembled in Kuttler's kube to carry out final irrigation activation. A predetermined standardized volume of irrigants was used in each group. The RCDM was measured after root canal instrumentation and after final irrigation using Vicker microhardness tester (coronal, middle, and apical third). The reduction in RCDM values (p < 0.0086) were analyzed using Kruskal Wallis and Mann Whitney-U tests. Results: Reduction in RCDM was observed with all the endodontic irrigating techniques tested. EndoVac and combination irrigation techniques showed maximum reduction in RCDM in all thirds of root canal. Conclusion: It is concluded that the volume of irrigants and agitation plays a role in reducing RCDM. The overall volume of irrigants to cause maximum reduction was 25 ml, beyond which neither volume nor agitation affects RCDM.
Keywords: EndoVac irrigation, passive ultrasonic irrigation, root canal irrigants, sodium hypochlorite
|How to cite this article:|
Arul B, Suresh N, Sivarajan R, Natanasabapathy V. Influence of volume of endodontic irrigants used in different irrigation techniques on root canal dentin microhardness. Indian J Dent Res 2021;32:230-5
|How to cite this URL:|
Arul B, Suresh N, Sivarajan R, Natanasabapathy V. Influence of volume of endodontic irrigants used in different irrigation techniques on root canal dentin microhardness. Indian J Dent Res [serial online] 2021 [cited 2022 Aug 13];32:230-5. Available from: https://www.ijdr.in/text.asp?2021/32/2/230/330863
| Introduction|| |
The mechanical instrumentation of root canal system effectively instruments only 65% of root canal surface. The uninstrumented root canal surfaces can harbor tissue debris, microbes, and their byproducts and this may lead to decrease in predictable treatment outcomes. Hence, endodontic irrigants are used in combination with mechanical instrumentation to ensure effective debridement of the root canal system. It has been proven that sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) produces better disinfection and cleaner root canals, thus making it the widely used endodontic irrigants.,, Nevertheless, the overzealous application of endodontic irrigants can weaken the root canal dentin.,
Factors like concentration,, contact time, and sequence of usage of endodontic irrigants affects the mechanical properties of root canal dentin. The extended application time of higher concentration of these irrigants negatively affects the mechanical properties of root canal dentin., Till date, the effect of volume of endodontic irrigants used with different irrigation techniques on the microhardness of root canal dentin has not been reported in endodontic literature.
Apical negative pressure system (ANP) debrides the root canal effectively when compared to other irrigation techniques. The volume of irrigant delivered with ANP is approximately 42 ml which is more than that of needle irrigation over the same duration of time. It has been reported that the combination of ANP and passive ultrasonic irrigation (PUI) allows effective three dimensional penetration of irrigants both up to working length (WL) as well as into the lateral canals. The volume of irrigant delivered by this method may be more and its effect on root canal dentin microhardness is not known.
Therefore, the aim of this study was to assess the effect of volume of endodontic irrigants used in needle irrigation (NI), passive ultrasonic irrigation (PUI), apical negative pressure system (EV), combination (CB) of ANP and PUI on root canal dentin microhardness.
| Materials and Methods|| |
Ethical clearance was obtained from the Institutional review board of the University (MAHER/COE-023/14). Sixty freshly extracted human maxillary central incisors with straight root, type I canal anatomy with intact and mature root apices were selected and stored in 0.1% thymol solution under refrigeration until use. Teeth with caries, cracks, and restorations were excluded. The teeth were decoronated 2 mm above the cementoenamel junction (CEJ) by using high speed diamond bur (Mani Inc.) and the sample length was standardized to an average of 18 mm. The dimensions of the pulp cavity were assessed by taking radiographs buccolingually and mesiodistally to standardize to a round canal anatomy. The specimens were embedded into a Kuttler's endodontic cube (K-Kube) to the level of CEJ using acrylic resin (DPI RR Cold Cure; DPI Mumbai, India) [Figure 1].
Root canal instrumentation
Access opening was made in all teeth with no 2 endodontic access bur (Dentsply Maillefer, Ballaigues, Switzerland). The working length was established by inserting a no. 10 K file (Mani Inc, Tochigi Ken, Japan) into each root canal until it was just visible at the apical foramen (observed under magnifying loupes) and by subtracting 1 mm from this point. The root canals were instrumented using Protaper rotary system (Dentsply Maillefer, Ballaigues, Switzerland) in the sequence of SX to F4 (40/06). The samples were randomly divided into 4 experimental groups (n = 15).
Volume of irrigants used during cleaning and shaping and final irrigation
The volume of irrigants used during instrumentation and after final irrigation was predetermined (by a pilot study) and standardized for all the respective groups. A pilot study was performed with the sample size of 8 in each experimental group to determine the volume of irrigants used during instrumentation and after final irrigation. The amount of irrigant used in each experimental group according to the recommended protocol was measured. The average of volume of irrigants of all samples was used in the main study. The pilot study was performed by a single trained operator to avoid discrepancy in flow rates. The volume of irrigants used during instrumentation was standardized to an overall of 10 ml of 5% NaOCl for needle irrigation (NI) and passive ultrasonic (PUI), respectively. For apical negative pressure system (EV) and combination (CB) groups, 13 ml of 5% NaOCl was used. Whereas, for final irrigation, 6 ml of irrigants (2 ml 5%NaOCl + 2 ml 17%EDTA + 2 ml 5%NaOCl) was used for NI and PUI group. A total of 12 ml of irrigants for EVgroup (4 ml 5%NaOCl + 4 ml 17%EDTA + 4 ml 5% NaOCl) and 18 ml of irrigants for CB group (12 ml of EV + 6 ml of PUI) was used during final irrigation.
Irrigation protocol during cleaning and shaping
GROUP-NI and PUI: During instrumentation, 5% NaOCl (Prime dental products, Thane, India) was replenished at each file change with Max-I-Probe (Dentsply Tulsa Dental, York, PA) which was placed 2 mm short of apex leaving the canal filled with irrigant between instrumentation for a period of 30 seconds.
GROUP-EV and CB (EV + PUI): After reaching the WL with master apical file, macroirrigation was accomplished with 5%NaOCl for a period of 30 seconds. This was done using the EndoVac delivery/evacuation tip (Discus Dental, Culver City, CA, USA) while the macrocannula was constantly moved up and down in the canal from a point where it started to bind to a point just below the orifice. The canal space was then left undisturbed, full of irrigant for 60 seconds. This was followed by saline rinse using a side vented 25 mm, 30-gauge Max- I- Probe which was placed 2 mm short of WL.
Determination of microhardness at coronal, middle, and apical third of root canal post instrumentation (CM1, MM1, AM1)
The microhardness of root canal dentin at coronal, middle, and apical third were determined at two stages during the experiment (Post instrumentation and after final irrigation) using Vickers microhardness tester in the same sample. Post instrumentation, the resin mounted specimens were sectioned longitudinally (buccolingually) with hard tissue microtome (Leica Biosystems, Wetzler, Germany) which provided even and smooth sections. The root samples were divided into three sections and the midpoint of each section (coronal, middle, apical) was considered as points of indentation which were marked in the acrylic block [Figure 2]a. Root canal dentin microhardness of all samples was measured with a Vickers diamond microhardness testing machine (Metsuzawa Co Ltd, Japan). Three separate indentations were made at the pulp dentin interface, [Figure 2]b each using 100 g load at 10 seconds dwell time were made at a magnification of X400. The length of two diagonals was used to calculate microhardness value (Vickers hardness number, VHN). The representative hardness values were obtained as the average of the results for the three indentations.
|Figure 2: (a) Schematic illustration of three separate indentation at pulp dentin interface made in the midpoints in coronal, middle, and apical third of root canal dentin (Post instrumentation and after final irrigation). (b) Schematic illustration of measurement points for indentation at pulp dentin interface|
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Irrigation protocol during final irrigation regimen
All the specimens were reapproximated and reassembled in K-kube. The reapproximated root canal dentin surfaces were sealed with modelling wax.
Final irrigation was performed using a side vented 25 mm, 30-gauge Max-I-Probe and the needle was placed 1 mm short of WL. Three cycles of irrigation for 30 seconds each were performed. The first and third cycle was performed with 5%NaOCl. The second cycle was performed with 17% EDTA (Dent Wash, Prime Dental products, Thane, India).
Final irrigation was performed using continuous passive ultrasonic activation 1 mm short of the WL using an ultrasonic IrriSafe size 25 file (Satelec, Acteon group, Merignac, France) mounted on a Suprasson P5 booster ultrasonic unit (Satelec) at a power setting of 5. PUI was performed in three cycles (2 ml 5%NaOCl + 2 ml 17%EDTA + 2 ml 5%NaOCl) of 30 seconds each.
All samples were irrigated using EndoVac irrigation activation system (Discus Dental, Culver City, CA, USA) according to the protocol described by Nielson and Baumgartner. Three cycles (4 ml 5%NaOCl + 4 ml 17%EDTA + 4 ml 5% NaOCl) of microirrigation for 30 seconds each were performed.
GROUP- CB (EV + PUI)
In combination group, each cycle was accomplished using EV irrigation technique (4 ml 5%NaOCl + 4 ml17%EDTA + 4 ml5%NaOCl) for 30 seconds followed by PUI irrigation (2 ml 5%NaOCl + 2 ml 17%EDTA + 2 ml 5%NaOCl) for 30 seconds. The activation was performed in three cycles. The final irrigation in all groups were followed by saline rinse.
Determination of microhardness at coronal, middle and apical third of root canal after final irrigation activation (CM2, MM2, AM2)
The samples were disassembled from K-Kube and evaluated for root canal dentin microhardness. The indentations were made on each specimen adjacent to previous measured point under magnification taking care to avoid overlapping between them. The microhardness values were recorded after final irrigation in coronal, middle and apical third of root canal dentin (CM2, MM2, AM2). The mean difference in microhardness values between post instrumentation and final irrigation was calculated (CM1-CM2). The decrease in microhardness was calculated as percentage for each specimen.
CM1 = post instrumentation coronal third VHN
CM2 = final irrigation coronal third VHN
The same formula was used to calculate the percentage of decrease in microhardness for middle and apical third of root canal dentin.
The microhardness value data were analyzed using IBM SPSS 16.1. The overall microhardness values were statistically analyzed using Kruskal –Wallis and the intergroup comparison was done using Mann-Whitney U multiple comparison tests with Bonferroni correction set at a 95% confidence level P < 0.008.
| Results|| |
The mean difference of the root canal dentin microhardness values and the statistical difference between experimental groups are presented in [Table 1]. The EV and CB groups showed significant reduction of microhardness when compared to NI and PUI groups in all thirds. The percentage reduction of microhardness between post instrumentation and final irrigation within the coronal, middle and apical third of NI group was 3.4%, 3.9%, 5.3% and 5.8%, 5.6%, 5.4% in PUI group. The reduction was 10.2%, 11.1%, 11% in EV group and 10.5%, 10.7%, 10.8%, respectively in CB group in coronal, middle, and apical third of root canal.
|Table 1: The mean difference of the root canal dentin microhardness values for experimental groups|
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| Discussion|| |
Alteration in chemical composition of root canal dentin can be caused by a change in the calcium phosphorus ratio (Ca/P) which ultimately affects the mechanical properties of root canal dentin. This alteration can be caused by use of endodontic irrigants. NaOCl causes oxidation of organic matrix and denaturation of collagen, changing the chemical structure of dentin and EDTA demineralizes the inorganic components of dentin by chelating calcium ions which reduces the microhardness. In this study, final irrigation activation was performed with 5% NaOCl and 17% EDTA. This combination is accepted irrigating regimen for debriding and disinfecting root canal as proposed by Zehnder et al.
The assessment of root canal surface hardness can be performed using Atomic force microscopy assisted nanoindentation. However, endodontic literature has proven that the determination of root canal microhardness provides valuable evidence on mineral loss (or gain) in dental hard tissues., Microindentation methods are a proven and practical way to evaluate surface changes of dental hard tissues treated with chemical agents.,, Recently, Keine et al. assessed the effect of 1% periacetic acid as endodontic irrigant on root canal dentin microhardness. Also, in a study by Naseri et al., the effect of calcium hydroxide on root canal dentin was evaluated using microhardness test.
In the present study, in order to avoid bias and to assess the exact reduction between post instrumentation and final irrigation the microhardness evaluation was done at two stages (Post instrumentation and post final irrigation activation) in the same sample. To achieve this, a K-Kube was used so that precise placement and tight approximation of samples were possible. To enable this two-staged microhardness assessment, samples were sectioned using a microtome to obtain a smooth root canal dentin surface. Various irrigation dynamics are used in endodontics for removal of smear layer. But the volume of irrigants utilized by these techniques and its role in altering the root canal dentin microhardness is not known. Nielson and Baumgartner measured the volume of irrigant delivered by ANP and NI irrigation techniques by standardizing the time of irrigation in each group. Based on this method, a pilot study was conducted and the volume of irrigants was calculated for all the 4 experimental groups used in this study.
In this study, the maximum reduction in microhardness was observed with combination and EV group in comparison to that of PUI and NI. EV and CB groups used approximately 1.6 and 1.9 times in comparison to the volume of irrigants used by NI group and 1.3 and 1.7 times the volume of irrigant used by PUI group. This increase in volume used in EV and CB groups could have attributed to more mineral loss. The other reason could be that these groups had macroirrigation followed by 60 seconds of standing time with irrigant as a part of the irrigation regime. This might have increased the contact time of irrigant to the canal wall which could have increased the mineral loss of dentin. This study results are in contrast to that of Capar et al., who reported that final irrigation activation protocols with NI, Self-Adjusting file, endoactivator, EV, PUI, manual dynamic agitation did not alter the mineral levels of root dentin surface. This probably could be due to the use of similar volume of irrigant in all experimental groups. It is proven that fluid dynamics of EV lacks any measurable turbulence, thus, the mineral loss observed in EV group in this study is purely attributed to volume of irrigants used.
In this study, PUI group showed significant reduction of root canal dentin microhardness compared to NI group in the coronal and middle third of root dentin between post instrumentation and final irrigation. This could probably be due to the acoustic streaming of PUI which could have enhanced the agitation of irrigants. However, in the apical third it was not statistically significant, this may possibly be due to the dampening effect of the canal walls on to the PUI agitation.
The overall volume of irrigants used in NI, PUI, and EV groups concurs with the previous studies., The volume of irrigants used by CB and EV groups was more than NI and PUI groups. This may be due to the additional steps in CB and EV groups. Also, the needle diameter of master delivery tip of EV is larger than the Max-I-Probe which has a finer diameter. As a result, the intrabarrel pressure will vary for these modes of irrigation. This would have influenced the increased volume of irrigants delivered in these groups. The reduction in root canal dentin microhardness can affect the sealing ability of resin based materials and adhesion of root canal sealers. Thus, an irrigation regimen that will ensure adequate disinfection without causing much alteration in root canal dentin structure has to be developed.
The interesting finding in this study is that this inverse relationship is observed only till a maximum overall volume of 25 ml of irrigants (5%NaOCl + 17%EDTA). The reduction of microhardness after final irrigation when compared to post instrumentation between the EV and CB groups was not statistically different. Not only the volume of irrigant delivered by CB was 1.2 times higher than EV, the acoustic streaming activation and increased contact time of irrigant failed to reduce the microhardness beyond a threshold. This proves that the cut-off volume of irrigants (5%NaOCl + 17%EDTA) is approximately 25 ml to produce maximum reduction of microhardness. This volume probably induces the maximum loss of minerals and alteration of collagen on the surface of root canal dentin. It is observed that the maximum threshold limit of irrigants that cause reduction of microhardness is 25 ml. PUI used as an adjunct with EV does not result in reduction of microhardness of root canal dentin in comparison to EV.
The clinical importance of this study is that clinical situations which warrants the use of EV can be safely substituted safely by CB activation technique. CB technique ensures thorough debridement as it allows irrigant penetration up to full WL and also into lateral canals without alteration in microhardness.
The limitation of this study is that the delivery of irrigants was manual to mimic clinical scenario, but this could have led to variability in rate of delivery of irrigants. This could be overcome by use of mechanized devices for irrigant delivery for experimental purpose (but may not mimic clinical scenario). The volume of endodontic irrigants could not be standardized in all the experimental groups because clinically, the irrigation regimen for these techniques are variable with regards to duration and volume. As irrigants can alter the mechanical behavior of root canal dentin, further studies are required to evaluate the crack propagation in root canal dentin conditioned with different endodontic irrigants.
| Conclusion|| |
Within the limitations of this study, it is concluded that volume of endodontic irrigants and the method of final irrigation activation reduces the root canal dentin microhardness. The EV and CB groups caused higher reduction in root canal dentin microhardness when compared to NI and PUI.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Nandini Suresh
Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Meenakshi Academy of Higher Education and Research (MAHER), Alapakkam Main Road, Maduravoyal, Chennai - 600 095, Tamil Nadu
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]