Etidronic acid and ethylenediaminetetraacetic acid associated with sodium hypochlorite have limited effect on the compressive fracture resistance of roots ex vivo

Abstract

Aims:

To assess the effect of etidronic acid (EA) mixed with sodium hypochlorite (NaOCl) and two ethylenediaminetetraacetic acid-containing preparations (EDTA and SmearClear) alternated with NaOCl, as a final rinse, on root fracture resistance to a compressive force.

Materials and Methods:

Seventy-two premolar roots were randomly allocated to the following groups according to the irrigant solutions. For the EA group, 9% EA + 2.5% NaOCl were used throughout the assays (n = 21). The remaining groups received 2.5% NaOCl during and immediately after chemo-mechanical instrumentation. Intermediately, the roots received 17% EDTA (n = 19), or SmearClear (n = 16), or no irrigation (control) (n = 16) plus a final rinse with 2.5% NaOCl. The specimens were subjected to a vertical compressive force loaded at a crosshead speed of 0.02 mm/s parallel to the long axis of the root until fracture occurred. The results were compared statistically using the one-way analysis of variance for intergroup comparisons.

Results:

The negative control presented with the highest values, whereas the SmearClear presented with the lowest values, though no significant differences were found when comparing the different groups (P = 0.82).

Conclusions:

The use of EA + NaOCl or two EDTA formulations in association with NaOCl does not affect the fracture resistance of previously chemo-mechanically prepared roots.

INTRODUCTION

Endodontic procedures may harm dental tissues, potentially predisposing root canal treated teeth to fracture. Among these, the use of chelating agents, ethylenediaminetetraacetic acid (EDTA) in particular, associated with sodium hypochlorite (NaOCl), aiming to remove and/or prevent the formation of a smear layer during root-canal instrumentation.[1,2,3,4] The use of EDTA leads to the exposure of intra-radicular organic matter, which is subsequently depleted by NaOCl thus exposing the inorganic component of the dentin, which is then removed if a chelating agent is used, and vice versa.[5] Alternated rinses with these irrigants are expected to weaken the dentin further,[5,6,7] by causing damage to the organic component and wall erosion.[5,6,7] Furthermore, there is a reduction in the free available chlorine in the NaOCl-EDTA mixtures, with a potential decline of the tissue dissolution and antimicrobial effects of NaOCl.[8] Among the various EDTA commercially-available formulations, SmearClear (SybronEndo, Orange, CA, USA) contains surface-active agents.

Etidronic acid (EA), an alternative chelating agent, has been proposed as a mixture with NaOCl, with the preparations not losing their original desired chemical characteristics.[9] A further advantage of the NaOCl + EA mixture is that the formation of a smear layer is prevented if used throughout instrumentation, as the mixture is effective against both its organic and inorganic parts.[6] Furthermore, the use of EA + NaOCl in combination has been shown to enhance bond strength when different sealers are used.[10,11] EA used per se is unable to remove the smear layer.[12]

There is limited evidence regarding the effect of EA + NaOCl combinations on root fracture resistance, the sole study included a relatively long contact with the irrigant solutions,[13] which may lead to excessive damage to the dentinal tissue, thus negatively affecting fracture resistance ex-vivo.

Therefore, considering that root fracture is considered a catastrophic complication of root canal treatment and the paucity of data regarding the use of EA + NaOCl mixtures with clinically-relevant contact times, the aim of the present study was to compare the effect of EA + NaOCl with EDTA-containing preparations alternated with NaOCl, and NaOCl per se, on root fracture resistance to a compressive force. The null hypothesis tested is that there are no differences in root fracture resistance to compressive force following root canal irrigation using EA + NaOCl and EDTA-containing preparations alternated with NaOCl when used as a final rinse.

MATERIALS AND METHODS

The procedures followed were in accordance with the ethical standards of the Ethics Committee of the European University of Madrid (CIPI/005/2017) and with the Helsinki Declaration of 1975, as revised in 2000 (available at https://www.wma.net/policies-post/wma-declaration-of-helsinki-ethical-principles-for-medical-research-involving-human-subjects/).

Tooth selection and preparation

Seventy-two recently extracted single-rooted premolars were assessed under ×20 magnification using a dental operating microscope (OPMI pico Dental Microscope, Carl Zeiss, Oberkochen, Germany), to exclude those with open apices, resorptive defects, and longitudinal fractures. The presence of a single canal and the absence of a previous root canal filling were assessed radiographically by exposing two angulated films. The teeth included were stored in a 0.1% thymol water solution at 6°C and used within 1 month of extraction.

Following the removal of calculus and periodontal tissue using curettes, the lengths of the samples were standardized to 14 mm by removing the crown with a double-sided diamond disc (Kerr Dental, Madrid, Spain) mounted on a straight hand piece. Their mesio-distal width and length were verified using a 150 mm digital caliper (Vernier, Software and Technology, Beaverton, OR, USA). Roots were included if their buccal-lingual and mesio-distal dimensions of the most coronal part were within the mean values ± 10%. A ReadySteel size 10 K-File (Dentsply Maillefer, Ballaigues, Switzerland) was inserted in the root canals until it was visible through the apical foramen under magnification. The working length (WL) was established by reducing this length by one mm. Subsequently, the apical 10 mm of the specimens were inserted in hard pink wax (Dentaltix, Madrid, Spain), to prepare a customized receptacle for each sample.

Chemo-mechanical instrumentation

The samples were randomly allocated using a computer algorithm program (http://www.random.org) into three test groups, according to the chelating agent used in association with NaOCl (Dentaflux, Madrid, Spain); 17% EDTA (Dentaflux) (n = 19), SmearClear (n = 16), or EA (Zschimmer and Schwarz Chemie GmbH, Lahnstein, Germany) (n = 21), and a control group (no chelating agent used) (n = 16).

For chemo-mechanical preparation, for EDTA and SmearClear groups, 2.5% NaOCl was used, whereas for EA group a mixture of 5% NaOCl and 18% EA 1:1 v/v was used. During the instrumentation, 0.5 mL of irrigant was delivered during 10 s between each engine-driven file usage up to size 40 0.4 taper M-two file (VDW GmbH, Munich, Germany) mounted on a VDW. Gold Reciproc motor (VDW GmbH), following the instructions from the manufacturer. Thus, a total volume of irrigation of three mL for 60 s was used between files during root canal instrumentation. The irrigant solutions were delivered using a syringe and a side-vented 27 G needle (Monoject, Tyco Healthcare, Mettawa, IL, USA) positioned at WL-2 mm.

Irrigation assays

All were first irrigated during 60 s using 1 mL NaOCl alone or the ED + NaOCl mixture, as described above, using the microcannula (0.32 mm) part of the EndoVac System (Kerr Dental) at WL to draw up the irrigant solutions. Subsequently, 0.5 mL of NaOCl or the mixture with EA were delivered using syringe and needle as before and then agitated for 10 s using the Endoactivator (Advanced Endodontics, Santa Barbara, CA, USA), with a size 25, 22 mm length. 04 taper tip, set at 10000 cycles per minute, placed at WL-2 mm. Then, the root canals of the experimental groups were irrigated using 3 mL of EDTA, SmearClear, or the EA + NaOCl mixture according to the group, which were first drawn up to WL using the microcannula from the EndoVac during 3 min and agitated for 30 s using the Endoactivator as described above. The control group received no irrigant solution (i.e., chelating agent) at this stage. A final rinse with 3 mL NaOCl or the mixture EA + NaOCl during 60 s followed by distilled water, using syringe and needle, was carried out. Finally, the canals were dried using paper points (Kerr Dental) and removed from the wax receptacle, before storage in a humidity-controlled container at 36°C ± 2°C for 4 days.

Compression tests

The most apical 10 mm of the roots were embedded individually in cylindrical molds (20 mm in diameter and length) made of epoxy resin (Araldite^®M, Sigma Aldrich, Merck KGaA, Darmstadt, Germany), with the coronal 4 mm remaining exposed. This, to create a platten fitting into the platform in a universal testing machine (Servosis, Madrid, Spain) calibrated according to UNE-EN ISO 7500-1. A long stainless-steel rod with a rounded tip (4 mm in diameter ×10 mm in length) was positioned on the center of the coronal aspect of the samples. Data were evaluated using the computer software (TD2K, Servosis). The samples were subjected to a vertical compressive force loaded at a crosshead speed of 0.02 mm/s parallel to the long axis of the root until fracture occurred. The maximum load to fracture was recorded in tons. Data were evaluated using the computer software (TD2K, Servosis).

Statistical analysis

Quantitative variables were summarized with means and standard deviations (SDs). Histograms were used to assess normality. The one-way analysis of variance was used for the intergroup comparisons. Statistical analyses were performed using the STATA version 14 statistical package (StataCorp LLC, College Station, TX, USA). The level of P < 0.05 was adopted for statistical significance.

RESULTS

The mean values of maximum load to fracture (SD) in t were as follows: Control 0.074 (0.016); EDTA 0.073 (0.23); EA + NaOCl 0.072 (0.023); SmearClear 0.067 (0.014). The results of the compressive force test are depicted in Figure 1. The negative control presented with the highest values, whereas the SmearClear presented with the lowest values. No significant differences were found when comparing the different groups (P = 0.82).

Figure 1.

Box plots with forces required to cause fracture for the different groups recorded in tons. Control: No chelating agent used; EDTA: Ethylenediaminetetraacetic acid, EA: Etidronic acid + NaOCl; SmearClear

DISCUSSION

The present study established that, when testing with a compressive force using a single-rooted premolar root model, the use of EA+NaOCl or EDTA-containing preparations alternated with NaOCl as a final rinse does not affect radicular fracture ex-vivo, though lower values were obtained with SmearClear. Therefore, the null hypothesis was not rejected.

The present study incorporated a large volume of irrigants, which were delivered and agitated using negative pressure as well as subsonic agitation. These agitation techniques are relatively common in general and specialist practice,[1,2,3] aiming to facilitate the dispersion of the irrigants solutions, thus likely having a more extensive effect on the root canal dentin. EndoVac system was used during irrigation with chelating agents to ensure penetration of the solutions to the desired length.[14]

An important difference between the present study and a previous one assessing root fracture resistance following irrigation with 18% EA+5% NaOCl[13] is the difference in contact time. In the previous study, the irrigation with the mixtures lasted 28 min, whereas in the present study, the total final irrigation total time was 5 min 40 s. Longer contact times are associated with lower fracture resistance values.[15,16]

One notable finding is that the use of NaOCl followed by EDTA or with SmearClear did not affect the fracture resistance in the present study when compared to the negative control. This is in agreement with similar previous studies where different concentrations of NaOCl/EDTA were tested with a 1 min contact time.[16,17] The absence of significant differences following the final rinse protocols tested, as mentioned above, may be related to the limited contact time between tooth tissue and the irrigant solution before shaping is complete, also considering the “radicular access” purported role of root canal instrumentation.[18] Finally, the reduced surface tension of SmearClear, which is 17% EDTA-based, did not influence our findings when compared with the plain 17% EDTA solution, however, there was a trend suggesting that this solution weakens the roots further. This preparation may have had a more profound effect by being able to penetrate further into dentin, though, the effect of adding surfactants to irrigant solutions in regards to penetration into less accessible areas requires further understanding, considering the paucity of evidence in the field.[19]

The present ex-vivo study presents some limitations. First, the forces applied (e.g., amount, direction, and speed) may not be representative of the clinical reality.[20] Overall, thermocycling and/or cyclic loading and simulation that normally is carried out in laboratory-based studies may not be representative of what occurs clinically. Similar limitations are present in recently published comparable studies.[13,15,17,21,22,23,24] Furthermore, root canals were not filled before compression testing. This, to avoid a likely confounding factor, as several materials influence fracture resistance.[10,11] Finally, for the compressive load testing, the periodontal ligament was not simulated based on a pilot study that demonstrated that the roots occasionally moved during testing and the difficulties to obtain a consistent thickness of material around the samples. This is in agreement with a previous study.[23] Finally, in the absence of an a priori power calculation, the results should be interpreted with caution, because inadequate power cannot be ruled out. However, the sample size per group of the present study was larger than those of several recently published studies testing fracture resistance following endodontic procedures.[13,16,21,22,23,24]

The role of root chelating agents in promoting tooth fracture following root canal treatment needs further understanding. It should be noted that there are several potential promoting factors for tooth fracture clinically. Among these, coronal tissue and structure loss-removal due to previous damage (e.g., caries, traumatic dental injuries, tooth wear, and previous operative procedures), intra-operative procedures (e.g., access cavity preparation, root canal instrumentation, irrigants, medicaments and obturation-related forces plus intracanal post preparation, and subsequent remaining pericervical dentine, as well as postoperative factors [coronal restoration, occlusion, and parafunction]).[10,11,20,21,22,23,24,25] Therefore, irrigants solutions per se may be considered only as one of the factors associated with accumulative damage during root canal treatment.

CONCLUSIONS

Within the limitations of this laboratory study, the use of EA + NaOCl, or two different formulations of EDTA as an intermediate irrigant solution in association with NaOCl, as a final rinse, does not affect the fracture resistance of chemo-mechanically prepared roots ex-vivo, when compared with the sole use of NaOCl.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.