The comparison between two irrigation regimens on the dentine wettability for an epoxy resin based sealer by measuring its contact angle formed to the irrigated dentine.

AIM: The aim was to assess the influence of two irrigation regimens having ethylenediaminetetraacetic acid (EDTA) and ethylenediaminetetraacetic acid with cetrimide (EDTAC) as final irrigants, respectively, on the dentine wettability for AH Plus sealer by comparing its contact angle formed to the irrigated dentine.
MATERIALS AND METHODS: Study samples were divided into two groups (n = 10). The groups were irrigated with 3% sodium hypochlorite (NaOCl) solution followed by either 17% EDTA or 17% EDTAC solution. AH Plus was mixed, and controlled volume droplet (0.1 mL) of the sealer was placed on the dried samples. The contact angle was measured using a Dynamic Contact Angle Analyzer and results were analyzed using SPSS 21.0 and 2 sample t-test.
RESULTS: There was a significant difference in the contact angle of AH Plus formed to the dentine irrigated with the above two regimens. AH Plus showed significantly lower contact angle with the regimen having EDTAC as a final irrigant than the one with EDTA (P < 0.05).
CONCLUSION: An irrigation regimen consisting of NaOCl with either EDTA or EDTAC solution as a final irrigant influences the dentine wettability and contact angle of a sealer. EDTAC as a final irrigant facilitates better dentin wettability than EDTA for AH Plus to promote its better flow and adhesion.

INTRODUCTION

Root canal sealers help to achieve a fluid-tight seal during endodontic obturation by filling minor discrepancies between the canal walls and the core obturating material.[1] However, this depends on flow and adhesion, which are two of the most important physicochemical properties of a sealer. Furthermore, these two properties are influenced by the wettability of the root canal dentine surface for a sealer.[123]

The wettability of a solid surface for a liquid is reflected by the relative surface free energy of a solid. It is measured and expressed in terms of a contact angle formed by the liquid to the solid surface. The contact angle has an inverse relationship with surface free energy. In endodontics, a contact angle formed by a sealer (liquid) to a dentine surface (solid) is crucial. A lower contact angle of sealer represents a greater surface free energy and wettability of dentine and suggests a tendency for better flow and adhesion of the sealer to the dentine surface.[345]

Irrigants are generally used for canal cleaning during an endodontic procedure. Sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) are two of the most commonly used irrigants. The former has good tissue dissolving and antimicrobial properties, and the latter has a chelating property.[5] However, in the backdrop of a highlighted need to yet find a single irrigant having all the aforementioned properties and a recent survey showing a higher percentage of response to a routine aim to remove smear layer, combined use of two or more irrigants is inevitable.[67] In this regard, for the effective removal of both organic and inorganic matter and complete removal of smear layer from the root canal, a combined but sequential or alternate use of NaOCl and EDTA solutions is suggested.[89]

Sodium hypochlorite and EDTA, either alone or combined as an irrigation regimen, are shown to alter the physicochemical characteristics and wettability of the dentine surfaces and contact angle of a sealer and thus have the potential to influence the flow and adhesion of a sealer.[235101112] However, the effect of NaOCl and EDTA irrigation regimen on the dentine wettability and contact angle of a sealer appears to depend on the final irrigant used in the regimen. In addition, the hydrophobic characteristics of any sealer, such as epoxy resin based AH Plus, may also affect its spreading on the irrigated dentine surface.[313] A previous study showed that the above regimen affected dentine wettability and reduced spreading of AH Plus when EDTA was the final irrigant and this was attributed to the weak demineralizing ability and surfactant action of EDTA.[5]

Ethylenediaminetetraacetic acid with cetrimide (EDTAC) irrigant is obtained by combining EDTA and cetrimide. Cetrimide, a quaternary ammonium bromide, is a cationic surfactant added to EDTA solution to reduce its surface tension and viscosity and enable its flow and penetration to the full depth of the canal.[891415] EDTAC largely removed the smear layer by chelating action and EDTAC/NaOCl/EDTAC irrigation regimen was found to be most effective for removing the smear layer.[616] It would be clinically relevant to know whether an irrigation regimen having EDTAC as final irrigant would have any effect on dentine wettability and contact angle of a sealer, particularly of hydrophobic AH Plus, when compared to EDTA. However, to the best of our knowledge, no such studies have been carried out.

Therefore, the purpose of the present study was to evaluate and compare the effect of two irrigation regimens having EDTA and EDTAC as final irrigants, respectively, on the dentine wettability by analyzing the contact angle of AH Plus sealer formed to the dentine irrigated with these regimens.

MATERIALS AND METHODS

Ten intact extracted single rooted human teeth were decoronated at the cemento-enamel junction and sectioned longitudinally into 20 halves with a diamond disk. The sectioned surface of the root halves was smoothened and polished. The root halves were randomly divided into two groups (n = 10) depending on the dentine irrigation regimen. One group of samples was irrigated with 10 mL of 3% NaOCl (Vishal Dentocare Pvt. Ltd., India) solution for 5 min followed by final flush with 10 mL of 17% EDTA (B.N. Laboratories, India) solution for another 5 min. Similarly, the other group of samples was irrigated with 10 mL of 3% NaOCl for 5 min followed by final flush with 10 mL of 17% EDTAC (Vishal Dentocare Pvt. Ltd., India) solution for another 5 min. Following irrigation, all the samples were rinsed with 10 mL of saline solution and dried with paper points.

Contact angle measurement

The contact angle was measured using a Dynamic Contact Angle Analyzer (FTÅ 200, First Ten Angstroms, Inc., Portsmouth, VA, USA) under standard conditions of temperature and relative humidity. This equipment is used for measuring both the static and dynamic contact angles. The samples were dried in an incubator for 5 min, and care was taken to avoid over drying. AH Plus (Dentsply DeTrey, Konstanz, Germany), an epoxy resin-based sealer, was mixed according to the manufacturer's instructions. Each sample was positioned on a flat glass surface of the Dynamic Contact Angle Analyzer, and a controlled volume droplet (0.1 mL) of the sealer was placed on the dentinal surface of the sample. The volume of the sealer was controlled by means of a micropipette (Eppendorf AG, Hamburg, Germany). This micropipette could be manually handled through a tiny hole on the top of the measuring device to facilitate controlled placement of the sealer. The spreading of the sealer droplet was recorded, and images of the droplet were then captured using the FTÅ software to determine the static contact angles of the sealer on dentine surface of the samples. The results were statistically analyzed using the software SPSS 21.0 (Statistical Package for the Social Sciences 21.0) (IBM Corporation, New York, USA) and 2 sample t-test.

RESULTS

The mean contact angle of AH Plus to root dentine treated with two irrigation regimens having EDTA and EDTAC components, respectively, is shown in Table 1. There was a significant difference in the contact angle of AH Plus formed to the dentine irrigated with these two regimens. AH Plus showed significantly lower contact angle with the regimen having EDTAC as a final irrigant than the one with EDTA [P < 0.05, Table 1]. This suggested that the root dentine treated with an irrigation regimen having EDTAC as a final irrigant showed better dentine wettability to favor lower contact angle and better spreading of AH Plus.

Table 1

Mean values and SDs of contact angles (°) of AH Plus formed to the dentine irrigated with the two regimens having EDTA and EDTAC, respectively, as final irrigants

DISCUSSION

The present study was carried out using a standard methodology as contact angle (θ), used as a measure of the wetting of dentin by the sealer, can be affected by surface tension of the sealer, and by the surface free energy, homogeneity, contamination, and roughness of the dentine surface.[4517] The methodology was employed under standard environmental conditions as the surface tension and measurement of the contact angle of a sealer is also influenced by temperature change and humidity.[1718] AH Plus, an epoxy resin–based root canal sealer, was selected because it is said to be one of the commonly used sealers in endodontics and in clinical and experimental studies.[14] Although, AH Plus is used as two paste system, and contact angle of each paste may differ, its clinical application requires mixing of both the pastes. Therefore, the contact angle of the mixed sealer was measured. The samples were polished and carefully dried before sealer application as surface roughness and both excessive hydration and dehydration of dentine can influence its surface energy and wetting by the sealer.[11121719] A controlled volume (0.1 mL) of sealer was placed on the samples as any volumetric variations could influence the contact angle.[51720]

Wetting of the dentine by the sealer is dependent on dentine related factors such as chemical composition, surface roughness, hydration state and tubule density of dentine, sealer related factors such as hydrophobic or hydrophilic nature and surface tension of the sealer, and presence or absence of smear layer which is hydrophobic in nature.[3410121319]

Apart from influencing the properties of dentine such as its microhardness, irrigation regimens are also shown to influence the wettability of dentine for a sealer, though demonstrated in only few studies, depending on the final and type of irrigant used with them.[235101121]

An irrigant may improve dentine wettability by, either one or combination of, its surfactant, deproteinization, collagen denaturation, and demineralization or chelating action and through any one or more mechanism involving increase in free energy, roughness, and hydrophilicity of the dentine surface. An irrigant increases the dentine surface free energy by its surfactant property or by removal of hydrophobic smear layer. It increases the dentine surface roughness by removal of smear layer and exposure of dentinal tubules through demineralization or chelation to remove an inorganic portion or by collagen denaturation and removal of an organic portion of dentine. An irrigant also increases the dentine hydrophilicity by widening fluid-filled dentinal tubules and increasing surface hydration or by removing collagen fibrils through deproteinization.[23101112]

The final irrigants used in the regimens of the present study were EDTA and EDTAC, respectively. The results of the present study demonstrated that the irrigation regimen with EDTAC as a final irrigant led to significantly better dentine wettability for AH Plus when compared to one with EDTA. The lesser dentine wettability for AH Plus seen with EDTA as a final irrigant is in agreement with the previous study.[5] This can be attributed to either of two possible, but contradictory, explanations mentioned in the endodontic literature. According to one explanation, weak demineralization by EDTA leads to a relatively smooth dentine surface with reduced surface area, which could lead to reduced dentine wettability for adhesion.[2]

On the contrary, EDTA is said to effectively remove smear layer, demineralize underlying dentine, expose dentinal tubules, and thus increase surface roughness which, according to the Wenzel equation, increases wettability of dentin. However, the demineralization by EDTA is also shown to lead to a microporous, demineralized collagen network on the surface of intertubular dentine. Since collagen component of dentine has lower surface energy when compared to its apatite crystals and EDTA lacks surfactant and deproteinizing action, this demineralized collagen network could affect the dentine wettability.[351022232425] For these probable reasons and due to its hydrophobic nature, AH Plus tended to spread less on the dentine irrigated with EDTA as final irrigant and showed a higher contact angle.

On the other hand, significantly lower contact angle of AH Plus with EDTAC, when compared to EDTA, as final irrigant could be attributed to the presence of surfactant cetrimide in EDTAC and its effect on surface tension and efficiency of EDTAC in removing smear layer.[891415] The surface tension of a sealer (liquid) itself has an effect on its contact angle.[411] Surface tension occurs due to intermolecular attraction at the surface of a liquid in contact with a solid surface. It should be as low as possible for optimal wettability and may be reduced by using a surfactant or heat. Furthermore, the spreading of a liquid is dependent on relationship between its surface tension and the critical surface tension of wetting of a solid surface.[451226] Cetrimide, which reduces surface tension of EDTAC solution, could also influence the critical surface tension of wetting of dentine for AH Plus or surface tension of AH Plus itself resulting in its significantly lower contact angle to EDTAC irrigated dentine. In addition, cetrimide reduces the fluid viscosity of the EDTAC solution. A reduced surface tension and viscosity of an irrigant enables it to wet effectively and maintain an intimate contact with dentin and debris and penetrate into main and lateral canals and dentinal tubules. Therefore, EDTAC solution is more efficient than EDTA in completely removing the hydrophobic smear layer and widely exposing the dentinal tubules, which are the factors responsible for increasing the surface free energy, roughness, permeability and hydrophilicity of a dentine surface, and thus significantly improve the dentine wettability.[2348101112262728]

CONCLUSION

An irrigation regimen consisting of NaOCl with either EDTA or EDTAC solution as a final irrigant influences the dentine wettability and contact angle of a sealer. EDTAC as a final irrigant facilitates better dentin wettability than EDTA for a sealer, particularly a hydrophobic sealer such as AH Plus, to promote its better flow and adhesion.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.