Comparative evaluation of push-out bond strength of bioceramic and epoxy sealers after using various final irrigants: An in vitro study.

Aim: The aim of the study is to compare the push-out bond strength of bioceramic and epoxy sealers after using various final irrigants. Materials and
Methods: Hundred single-rooted teeth were divided into two groups (n = 50) according to the sealer used: Group A: Bio C (bioceramic sealer), Group B: Dia-Proseal (epoxy sealer). Each group was subdivided into five subgroups (n = 10) according to the final irrigation protocol: Group A1 and B1 - 5% glycolic acid (GA), Group A2 and B2 - 17% GA, Group A3 and B3 - 0.2% chitosan, Group A4 and B4 - 17% ethylenediaminetetraacetic acid, and Group A5 and B5 - 0.9% saline. Samples were obturated in combination with one of the mentioned sealers and were allowed to set for 1 week. Two horizontal slices were obtained from each sample and subjected to push-out test. Statistical Analysis: The data were statistically analyzed using two-way ANOVA and independent Student's t-test.
Results: Both the sealers exhibited higher push-out bond strength after treatment with GA with no significant difference between 5% and 17% GA. Bio C sealer with GA as final irrigant showed higher bond strength than Dia-Proseal (P < 0.05).
Conclusion: The push-out bond strength of the sealer was significantly affected by the final irrigation solution used. The highest push-out bond strength was seen with Bio C sealer after treatment with GA with no significant difference between 5% and 17% GA. Copyright:

INTRODUCTION

The successful endodontic treatment relies on eradication of microorganisms and establishing bacterial tight seal of root canal by endodontic sealer to prevent the regrowth of microorganisms or newly gained infection due to leakage in the coronal or apical region.[1]

The relation between gutta-percha and the endodontic sealer is important for an ideal root canal filling. A root canal sealer should exhibit appropriate physicochemical and biological properties. An ideal root canal sealer should display excellent sealing ability, biocompatibility, dimensional stability, insolubility, and slow setting time.[2]

Of late, new root canal sealers have been launched as an alternative to conventional sealers that enhance clinical outcomes. One of them is Dia-Proseal sealer (Dia-Proseal, Diadent, Cheongju, Korea). It is an epoxy resin-based sealer with suitable physicochemical properties, cell viability, and root canal sealing ability.[3]

Recently introduced premixed, hydraulic tricalcium silicate-based sealer is Bio C sealer (Angelus, Londrina, PR, Brazil). It has a short setting time, alkaline pH, radiopacity, low volumetric shrinkage. According to the manufacturer, it has various characteristics such as fast setting time, good sealing of complex root canal system, volume stability, long-term storage ability, and dual syringe system allowing easy mixture.[4]

The presence of smear layer on radicular dentin compromises the penetration of sealers, irrigating solutions, and medicaments into the dentinal tubules.[5] This smear layer prevents intimate contact between the root canal sealer and dentin walls, which hinder the adhesion of sealers, as it decreases their dislodgment resistance to root dentin.[6]

Sequential administration of sodium hypochlorite (NaOCl) solution and ethylenediaminetetraacetic acid (EDTA) is the most common final irrigation method to ensure effective disinfection, smear layer removal, and organic tissue dissolution in root canals. However, the use of EDTA in root canal treatment has several potential drawbacks. First, the combined application of EDTA and NaOCl was shown to decrease the amount of free available chlorine in the mixture, which would reduce the antibacterial and tissue-dissolving capacity of the NaOCl.[7] The research for alternative final irrigants which are biocompatible, effective in smear layer removal without causing damage to the root dentin structure and properties is needed to ensure the success of the root canal treatment.[8] Some of the alternative final irrigants included in the present study are glycolic acid (GA) and chitosan.

GA or hydroxyethanoic acid is an alpha hydroxy acid which is a colorless, odorless, substance with high solubility in water.[9] The activity of this acid is based on the removal of free radicals and induces the formation of collagen fibers.[10] It is effective in smear layer removal, similar to EDTA and citric acid. GA was less cytotoxic than EDTA. It has also been suggested as an alternative final irrigation solution for root canal preparation.[11]

Chitosan is a natural polysaccharide that is biocompatible and biodegradable, exhibits a broad-spectrum antimicrobial property, and is associated with high chelating characteristics.[12]

Bond strength of endodontic sealers to dentin is an essential property because it reduces the risk of disengagement of filling material from dentin during restorative procedures or the masticatory function, making sure that sealing is maintained and thus the clinical success of endodontic treatment.[13]

However, there are some data regarding physiochemical properties of the Dia-Proseal, Bio C sealer, and GA. To our knowledge, there is no study evaluating the effect of GA or different irrigation solutions on the push-out bond strength of Dia-Proseal and Bio C sealer.

The aim of the present study is to evaluate the influence of different final irrigation solutions on the push-out bond strength of Bio C sealer and Dia-Proseal sealer. The null hypotheses were as follows:

There is no difference in the efficacy of different irrigants used on the push-out bond strength of sealers

There is no difference in the push-out bond strength of both the sealers.

MATERIALS AND METHODS

After approval from the Ethics Committee for Research, one hundred single-rooted human teeth extracted for orthodontic or periodontal reasons were obtained. Teeth with surface defects and cracks, calcified roots, open apices, accentuated curvatures, multirooted teeth, restored and fractured tooth, and previous endodontic treatments were excluded from the study.

The extracted teeth were decoronated to provide 16 mm ± 1 of root length using a diamond disk underwater coolant system. The root canal was negotiated with stainless steel endodontic K file size 10 (Mani, Japan) until visualized at the apical foramen. Working length was determined by taking radiographs 1 mm short of apical foramen with K file. The canal diameter is standardized with apical file #25.

Standardized biomechanical preparation of the canals was completed using PROTAPER GOLD rotary files (DENTSPLY) in a crown-down manner till F3. Canals are irrigated with 2 ml 5.25% NaOCl solution intermittently except for the group irrigated with saline.

The samples obtained are randomly divided into two groups (n = 50) as per the endodontic sealer used: Group A: Bio C sealer (Angelus, Londrina, PR, Brazil) and Group B: Dia-Proseal sealer (Dia-Proseal, Diadent, Cheongju, Korea) [Table 1].

Table 1

Materials used in the study, their manufacturer, and their chemical compositions

Tested materials	Manufacturer	Chemical composition
Bio C sealer	Angelus, Londrina, PR, Brazil	Tricalcium silicate, dicalcium silicate Tricalcium aluminate, calcium oxide Zirconium oxide, silicon oxide Polyethylene glycol, iron oxide
Dia-Proseal sealer	DiaDent Group, Cheongju-si, Korea	Base: Bisphenol-F epoxy resin, bisphenol A-co epichlorohydrin, zirconium oxide, siloxanes and silicones, calcium hydroxide, iron oxide Catalyst: Zirconium oxide, hexamethylenetetramine, siloxanes, silicones, calcium tungstate, calcium hydroxide

PR: Parana

Each group is further subdivided into five subgroups (n = 10) as per the final irrigant used [Table 2 and Figure 1].

Table 2

Experimental groups

Groups	Final irrigation protocol
Group A1 and B1	5% glycolic acid
Group A2 and B2	17% glycolic acid
Group A3 and B3	0.2% chitosan
Group A4 and B4	17% EDTA
Group A5 and B5	0.9% saline

EDTA: Ethylenediaminetetraacetic acid

Figure 1

Experimental groups

Then, each sample was irrigated with 5 ml of each irrigant for 1 min using a side vented endodontic irrigating needle (RC Twents, Prime Dental Products). The final flush is performed with 5 ml saline solution and dried with #30 paper points.

Group A: Premixed Bioceramic sealer is placed into the canal with the provided syringe tip to fill the canal and the Gutta-percha cone is inserted into the canal coated with the Bio C sealer until it reaches the working length. Lateral compaction was achieved with a hand spreader size 20, and 2% accessory GP was placed to fill up the remaining space by lateral condensation technique.

Group B: According to the manufacturer's instructions, an appropriate amount of base and catalyst (1:1 wt ratio) is dispensed onto a mixing pad. They were mixed with the spatula for 10–20 s until the ivory color is obtained. After thorough drying of canals, the sealer was applied with Lentulo spiral on the walls of the canal and tips of dry disinfected gutta-percha points dipped into the Dia-Proseal sealer and placed up to the working length.

The samples were coronally restored with cavit G and stored in an incubator at 37°C and 95% relative humidity for 1 week before pushing out the assessment.

Root specimens in each of the groups were completely embedded in clear acrylic. Then, each root was sectioned horizontally using a diamond disk into 2-mm thick slices [Figure 2a] approximately at 3 and 7 mm from the root apex. (The apical most 3-mm portion of each root was discarded to avoid apical ramifications.) The thickness of each slice was calculated with a digital caliper to ensure uniformity in specimen dimension.

Figure 2

Sample preparation for push-out test: (a) 2-mm thick slices were made using a diamond disk. (b) Specimen positioned on a metallic platform of a universal testing machine

Push out bond strength test

The root slices were placed on custom made acrylic mold with a cavity in the centre to enable the push out of filling material. Each specimen was subjected to a push-out test by means of a Universal Testing Machine (Kelvn Labs, Hyderabad) using a cylindrical stainless steel plunger of 0.5 mm applying a dislodging force in an apical-coronal direction at a crosshead speed of 2 mm/min until debonding occurred [Figure 2b]. The maximum force was converted to megapascals (Mpa) after the dislodging force was measured in Newton by the formula:

Bond strength = F/A

F = maximum force (N)

A = Area

A = πh (r)

π = Constant 3.14

r1= apical radius

r2= coronal radius

h = thickness of the sample in millimeters

Statistical analysis

The analysis was performed using SPSS software version 16 (Statistical Package for Social Sciences (SPSS) version 16.0, IBM Corporation, Armonk, New York, USA). P < 0.05 was considered statistically significant. Two-way ANOVA, independent Student's t-test has been used to assess the significance among various groups.

RESULTS

The mean and standard deviation of push-out bond strength of sealers after using different irrigants are presented in Table 3.

Table 3

Comparison of mean push-out bond strength values based on sealers and different root canal irrigants using two-way ANOVA test

Sealer	Irrigants	Mean±SD	n
Angelus bio c-sealer	5% GA	1.32±0.41	10
	17% GA	1.26±0.3	10
	0.2% chitosan	0.99±0.32	10
	17% EDTA	0.76±0.3	10
	0.9% saline	0.44±0.21	10
Dia-Proseal	5% GA	0.77±0.23	10
	17% GA	0.73±0.19	10
	0.2% chitosan	0.52±0.18	10
	17% EDTA	0.58±0.09	10
	0.9% saline	0.36±0.16	10

GA: Glycolic acid, EDTA: Ethylenediaminetetraacetic acid, SD: Standard deviation

Comparing between the sealers, Bio C sealer showed significantly higher bond strength than Dia-Proseal sealer. The interaction between irrigants and root canal dentin showed significantly higher push-out bond strength for GA with no significant difference between 5% and 17% concentrations.

The interaction between sealer and irrigant was evaluated using Student's t-test. The mean push-out bond strength calculated is shown in Table 4 and Graph 1. The push-out bond strength values of Bio C sealer with 5% and 17% GA irrigant showed significantly higher bond strength among all the irrigants and sealers used, whereas 0.9% saline showed the least bond strength values.

Table 4

Independent Student’s t-test for comparison of mean push-out bond strength between sealer materials based on the application of different final irrigants

Irrigants	Group	n	Mean±SD	SEM	Mean difference	P	t
5% GA	Bio-C	10	1.3165±0.40752	0.09113	0.549	0.000*	5.258
	Dia-Proseal	10	0.7675±0.22787	0.05095
17% GA	Bio-C	10	1.2610±0.29503	0.06597	0.535	0.000*	6.840
	Dia-Proseal	10	0.7260±0.18796	0.04203
0.2% Chitosan	Bio-C	10	0.9895±0.31804	0.07112	0.47	0.000*	5.788
	Dia-Proseal	10	0.5195±0.17530	0.03920
17% EDTA	Bio-C	10	0.7585±0.30146	0.06741	0.1775	0.016*	2.521
	Dia-Proseal	10	0.5810±0.09095	0.02034
0.9% saline	Bio-C	10	0.4325±0.20807	0.04653	0.0695	0.243	1.187
	Dia-Proseal	10	0.3630±0.15908	0.03557

*Statistically significant. GA: Glycolic acid, EDTA: Ethylenediaminetetraacetic acid, SD: Standard deviation, SEM: Standard error of mean

Graph 1

Comparison of mean push-out bond strength between sealer materials based on the application of different root canal irrigants

DISCUSSION

Capability of adhesion to dentin is a cardinal factor for root canal sealers. An ideal root canal sealer should bond to both root dentin and gutta-percha and must seal the root canal space.[14] Higher bond strength minimizes the leakage and improves the stability of root canal obturation material.[15]

The push-out test is frequently used to determine the bond strength between root canal sealer and root dentin, as this method allows better evaluation of bond strength because here, the fracture occurs parallel to the resin interface.[16]

In this study, the null hypothesis was rejected as there was a difference in the push-out bond strength between Dia-Proseal and Bio C root canal sealers and when used with 5% GA, 17% glycolic acid, 0.2% chitosan, and 17% EDTA irrigating solutions.

According to the results of the present study, higher bond strength is exhibited by Bio C sealer to root dentin compared to Dia-Proseal sealer due to the setting reaction of the sealer, which utilizes the moisture in the medium and results in the formation of calcium silicate hydrate gel.[17] It also exhibits an excellent flow rate[4] which allows the better penetration of the sealer into the minor irregularities of the root canal.[18] It shows chemical adhesion to dentin by promoting the formation of mineral infiltration zone.[19] Its bioactivity is due to hydroxyapatite formation after contact with phosphate on calcium silicate sealers’ surface.[20]

Benetti et al. demonstrated greater cytocompatibility, tenascin expression, and biocompatibility of Bio C sealer similar to white MTA Angelus.[21]

In the present study, the highest push-out bond strength was observed when samples are irrigated with GA. This could be due to its ability in smear layer removal similar to EDTA and citric acid even at 5% and 10% concentration of GA. Furthermore, it also causes demineralization of dentin by its acidic pH (2.36 and 2.18), which may lead to an increase of the surface roughness which enables a clinical benefit in micromechanical bonding of the adhesive materials.[11]

Bello et al. reported no changes in dentin flexural strength.[22] They also reported a reduction in microhardness and apatite/collagen ratio with increasing concentrations of GA.[1122]

As we have observed more bond strength for 5% GA compared to 17% GA (though not significant), the probable reason might be 17% GA might have caused more damage to the collagen of dentin, thereby compromising the bond strength of dentin.

Subsequent to GA, a better result was obtained when 0.2% chitosan is used with Bio C sealer. Chitosan is a hydrophilic polymer that is adsorbed onto the root dentin and enables it to penetrate deeper into dentinal tubules and consists of a higher number of free hydroxyl and amino groups which makes it cationic in nature, permitting the ionic interaction with the calcium ions of the dentin.[23] Antunes et al. reported that 0.2% of chitosan on the dentin surface removes the smear layer and unblocks the dentinal tubules with a small amount of erosion of peritubular dentin.[24] Mathew et al. reported that chitosan is an effective chelating agent with less alteration in root dentin and can be considered as a less invasive replacement to 17% EDTA.[25]

In the present study, the push-out bond strength of Bio C sealer is reduced by 17% EDTA when used as a final irrigant. This could be due to the chelation of calcium by EDTA that can disrupt the hydration of calcium silicate. The depletion of calcium at the sealer–dentin interface or degradation of the calcium silicate fraction in the sealer might inhibit the formation of the mineral infiltration zone, which may result in a weaker interaction between the root canal wall and the sealer.[19]

The lowest push-out bond strength is observed in the control group as the smear layer was left intact which indicates the negative impact of undisturbed smear layer on the push-out bond strength values.[26]

Limitations of the study

While the efficiency of individual irrigants was evaluated, their use in combination and their interactions are not tested in this study. Therefore, further in vivo studies need to be conducted to determine the correct action and sequence of different irrigants used to improve the push-out bond strength.

CONCLUSION

Bio C sealer exhibited the highest push-out bond strength compared to Dia-Proseal sealer when different final irrigants were used

Bio C sealer and Dia-Proseal sealer exhibited greater push-out bond strength after treatment with GA

When final irrigants were assessed, 5% and 17% GA has resulted in improved push-out bond strength compared to 0.2% chitosan and 17% EDTA for both the sealers

Hence, 5% GA can be suggested as a final rinse to improve the push-out bond strength.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.