Scanning electron microscopic evaluation of different concentrations of sodium gluconate and its time-dependent effects on radicular dentin

Abstract

Context:

Ethylenediaminetetraacetic acids (EDTA’s) limitations have spurred the quest for alternative irrigants with effective chelation and minimal dentinal erosion.

Aims:

The aim is to determine the ideal concentration and contact time of sodium gluconate by assessing its effectiveness in removing the smear layer and its impact on radicular dentin.

Materials and Methods:

Eighty single-rooted mandibular premolars with a single canal were decoronated to a standardized length. Following chemo mechanical preparation, the teeth were randomly allocated into four groups based on the final irrigant: Group I: 17% EDTA, Group II: 15% sodium gluconate, Group III: 17% sodium gluconate, and Group IV: 20% sodium gluconate. Each group was further divided into two subgroups based on contact time (30 s and 1 min). Samples were longitudinally split for scanning electron microscope analysis at ×5000, and images were examined across the coronal, middle, and apical third to assess smear layer removal and dentinal erosion.

Statistical Analysis Used:

Data were statistically analyzed using Student’s t-test and analysis of variance with post hoc test.

Results:

Seventeen percent sodium gluconate at both 30 s and 1 min demonstrated minimal dentinal erosion and showed comparable performance to 17% EDTA at 1 min, with no statistically significant difference.

Conclusions:

Seventeen percent sodium gluconate at 30 s may be considered a promising alternative to 17% EDTA.

INTRODUCTION

Endodontic therapy encompasses the three-dimensional cleaning, shaping, and sealing of intricate root canal network. The smear layer formed during chemo-mechanical preparation is effectively removed by the sequential use of sodium hypochlorite (NaOCl) followed by 17% ethylenediaminetetraacetic acid (EDTA).[1] However, it leads to tubular erosion and affects root dentin microhardness.[2]

Sodium gluconate, a chelator derived from corn, has emerged as a promising alternative with potentially less dentinal erosion.[3] Considering the scarcity of research regarding its ideal concentration and contact time, the present study aims to determine the optimum concentration and contact time of sodium gluconate as a final irrigant.

MATERIALS AND METHODS

Eighty single-rooted mandibular premolars, extracted for orthodontic reasons, were selected and stored in normal saline. The presence of a single canal was confirmed using bucco-lingual and mesio-distal radiographs. Teeth exhibiting caries, fractures, open apices, calcified canals, anatomical variations, or those previously restored or endodontically treated were excluded from the study.

Sample preparation

Teeth were decoronated to a standard length of 14 mm. The patency of the root canal was established using a #10 K-file (Mani, Japan). The working length was determined to be 1 mm short of the apex and confirmed radiographically. Two longitudinal grooves were created on the mesial and distal sides, ensuring no involvement of the root canal space. Canals were prepared using the ProTaper Gold rotary system (Dentsply Maillefer, Ballaigues, Switzerland) with a torque-controlled motor (X-Smart, Dentsply Maillefer, Ballaigues, Switzerland), in accordance with the manufacturer’s specifications, up to the F4 master apical file. During each instrument change, copious irrigation was performed with saline and 3% NaOCl, followed by recapitulation using the #10 K-file (Mani, Japan).

Preparation of sodium gluconate solution

15 mg, 17 mg, and 20 mg of sodium gluconate powder were mixed with 100 ml of distilled water and adjusted to a pH of 9 by the addition of sodium hydroxide, resulting in 15%, 17%, and 20% sodium gluconate solutions, respectively.

Final irrigation protocol and sample preparation for scanning electron microscope analysis

Following chemomechanical preparation, the samples were randomly divided into four groups based on the final irrigating solution, with 20 samples in each group. Each group was further subdivided into two subgroups containing 10 samples each, according to the contact time.

1. Group I

   • IA: 5 ml of 17% EDTA (Desmear, Anabond Stedman Pharma Research (P) Ltd., Chennai, India) (n = 10) for 30 s

   • IB: 5 ml of 17% EDTA (Desmear, Anabond Stedman Pharma Research (P) Ltd., Chennai, India) (n = 10) for 1 min.

2. Group II

   • IIA: 5 ml of 15% Sodium gluconate [Nice chemicals, Edappally, Cochin, Kerala, India] (n = 10) for 30 s.

   • IIB: 5 ml of 15% Sodium gluconate [Nice chemicals, Edappally, Cochin, Kerala, India] (n = 10) for 1 min.

3. Group III

   • IIIA: 5 ml of 17% Sodium gluconate [Nice chemicals, Edappally, Cochin, Kerala, India] (n = 10) for 30 s.

   • IIIB: 5 ml of 17% Sodium gluconate [Nice chemicals, Edappally, Cochin, Kerala, India] (n = 10) for 1 min

4. Group IV

   • IVA: 5 ml of 20% Sodium gluconate [Nice chemicals, Edappally, Cochin, Kerala, India] (n = 10) for 30 s

   • IVB: 5 ml of 20% Sodium gluconate [Nice chemicals, Edappally, Cochin, Kerala, India] (n = 10) for 1 min.

Samples in each group were irrigated with the respective final irrigating solution and specified contact time using a 30-gauge double-side vented endodontic irrigation needle (NeoEndo, Orikam Healthcare India Pvt Ltd.), positioned 1 mm short of the working length, and manual dynamic agitation was employed. All teeth were subsequently dried using sterile paper points (Dentsply, Maillefer, Switzerland) and were longitudinally split into two halves by placing a chisel and mallet along the longitudinal grooves on the mesial and distal sides. One-half of each sample, containing a sufficient portion of the canal, was selected for scanning electron microscope (SEM) analysis. Selected samples were dehydrated, mounted on metallic stubs, and sputter-coated with gold. SEM images were captured at ×5000 at the cervical, middle, and apical third levels [Figure 1 and 2]. Six images were obtained for each sample and were analyzed by a blinded investigator based on the criteria established by Hülsmann et al.[4] and Akçay et al.[5] for evaluating smear layer removal and dentinal erosion, respectively.

Figure 1.

Scanning electron microscopic images of Group I, II, III, IV at 30 s contact time across coronal, middle, and apical third

Figure 2.

Scanning electron microscopic images of Group I, II, III, IV at 1 min contact time across coronal, middle, and apical third

Hülsmann et al. criteria[4] for evaluating smear layer removal:

• Score 1: No smear layer and dentinal tubules are open

• Score 2: Small amounts of scattered smear layer and open dentinal tubules

• Score 3: Thin smear layer and partially open dentinal tubules

• Score 4: Partial covering of dentinal tubules with a thick smear layer

• Score 5: Total covering of dentinal tubules with a thick smear layer.

The scores assigned are inversely proportional to the efficacy of smear layer removal.

Akçay et al. criteria[5] for evaluating dentinal erosion:

• Score 1: No erosion, normal tubular appearance and diameter

• Score 2: Slight erosion involving peritubular dentin

• Score 3: Moderate erosion, minimal erosion in intertubular dentin, and some dentin tubules were connected

• Score 4: Severe erosion, severe erosion in intertubular dentin, most dentin tubules were connected

• Score 5: Destructive erosion, severe erosion in intertubular and peritubular erosion, causing layer-by-layer peeling from the dentinal wall.

The scores were tabulated and statistically analyzed using SPSS Statistics version 24.0 (IBM Corp, Armonk, New York, USA). P value was set at 0.05.

RESULTS

In the present study, the mean and standard deviation for all samples were calculated. To compare the effectiveness of smear layer removal and dentinal erosion among the different groups in the coronal, middle, and apical third, analysis of variance (ANOVA) was conducted as a parametric test. To elucidate multiple comparisons between groups, post hoc test was employed in conjunction with ANOVA. To compare the effectiveness of smear removal at different contact time, student’s t-test was performed.

Upon comparing the efficacy of 17% EDTA at different contact time, it was observed that in the apical third, 17% EDTA at 1 min outperformed 17% EDTA at 30 s with a statistically significant difference [Table 1].

Table 1.

Student’s t-test comparing 17% EDTA at 30 s and 1 min

17% EDTA	n	Mean	SD	SEM	Significant (two-tailed), P
30 s	10	4.0000	0.81650	0.25820	0.002*
1 min	10	2.7000	0.82327	0.26034

*The mean difference is significant at the 0.05 level. SD: Standard deviation, SEM: Standard error of mean, EDTA: Ethylenediaminetetraacetic acid

On comparing different concentrations of sodium gluconate with 17% EDTA at 1 min, it was observed that the latter outperformed both 15% and 20% sodium gluconate in the apical third with a statistically significant difference. Moreover, 17% sodium gluconate at 30 s exhibited performance akin to 17% EDTA at 1 min, with no significant difference at all three cross-sectional levels. Similar result was observed with 17% sodium gluconate at 1 min, with the exception of the middle third. At this level, 17% sodium gluconate at 1 min notably surpassed Group IB with a statistically significant difference [Table 2].

Table 2.

Multiple comparisons between groups at different cross-sectional levels

Multiple comparisons
LSD		Mean difference (I−J)	SE	Significant	95% CI
I	J				Lower bound	Upper bound
17% EDTA 1 min	Apical third
	15% SG 30 s	−1.90000*	0.28415	0.000	−2.4830	−1.3170
	15% SG 1 min	−1.70000*	0.28415	0.000	−2.2830	−1.1170
17% EDTA 1 min	Apical third
	17% SG 30 s	−0.50000	0.30062	0.108	−1.1168	0.1168
	17% SG 1 min	0.20000	0.30062	0.512	−0.4168	0.8168
	Middle Third
	17% SG 30 s	0.10000	0.28964	0.732	−0.4874	0.6874
	17% SG 1 min	0.50000*	0.21344	0.025	0.0671	0.9329
	Coronal third
	17% SG 30 s	0.10000	0.27183	0.715	−0.4513	0.6513
	17% SG 1 min	0.20000	0.19720	0.317	−0.1999	0.5999
17% EDTA 1 min	Apical third
	20% SG 30 s	−1.50000*	0.25240	0.000	−2.0179	−0.9821
	20% SG 1 min	−1.40000*	0.25240	0.000	−1.9179	−0.8821

*The mean difference is significant at the 0.05 level. SE: Standard error, CI: Confidence interval, LSD: Least significant difference, EDTA: Ethylenediaminetetraacetic acid, SG: Sodium gluconate

None of the experimental groups and subgroups exhibited erosion of dentinal tubules across three cross-sectional levels.

DISCUSSION

Microorganisms lurking in the uninstrumented regions of the intricate root canal system present a significant challenge during endodontic treatment. Adequate irrigation is crucial for dissolving tissue remnants and eliminating biofilm, microorganisms, debris, and smear layer. NaOCl, a widely employed irrigant, effectively dissolves the organic components of the smear layer and has notable antimicrobial properties.[5] Chelating agents, facilitate the negotiation of narrow and calcified canals and play a pivotal role in the effective removal of the inorganic part of smear layer.[2] Among the various chelating agents, 17% EDTA, the gold standard chelating agent, is synthesized from 1,2-diaminoethane (ethylene diamine), formaldehyde, water, and sodium cyanide, resulting in tetrasodium salt. This is subsequently converted into its acid form via acidification. EDTA binds to metals through four carboxylate and two amine groups, forming robust complexes with Mn(II), Cu(II), Fe(III), and Co(III).[6] It reacts with calcium ions in dentin to form soluble calcium chelates, thereby diminishing the microhardness of root dentin.[7] Furthermore, an increased contact time and the combined use of NaOCl and EDTA lead to peritubular and intertubular erosion.[8]

These limitations of EDTA have necessitated an arduous search for alternative irrigating agents exhibiting optimal chelating properties. Sodium gluconate, the sodium salt of gluconic acid derived from Zea mays (corn), is utilized across various sectors, including cosmetics, pharmaceuticals, and medicine, owing to its well-established chelating properties. It forms stable complexes by chelating calcium from an organized calcium hydroxyapatite crystal framework, rendering it less aggressive than 17% EDTA.[3]

In the present study, single rooted mandibular premolars with root length of approximately 20-22 mm and curvature less than 5 degrees were selected to minimize anatomical variation and to maintain standardization.[9] The presence of a single canal was confirmed through bucco-lingual and mesio-distal radiographs, as suggested by Wu et al.[10]

In this study, apical preparation was performed up to size 40/0.06 taper to facilitate the flow of irrigants to the apical third of the root canal. Irrigation was conducted using the syringe and needle technique, which allows for precise control over volume, depth of needle penetration, and the consequent flow of the irrigating solution to the apical region of the root canal system.[11] A 30-gauge side-vented needle was employed, as it is deemed more effective for accessing the apical area compared to larger gauge needles.[12] The needle was positioned 1 mm short of the working length to enhance debridement and facilitate irrigant replacement.[13]

SEM analysis was conducted at ×5000 to investigate the morphological characteristics of the radicular dentin.[14]

According to the results of the present study, 17% EDTA at 1 min demonstrated superior smear removal efficacy than its counterpart at 30 s. The duration of contact may have significantly influenced the effectiveness of EDTA.

Regarding different concentrations of sodium gluconate, in the apical third, the performance of 17% sodium gluconate at 30 s and 1 min was comparable to that of 17% EDTA, likely attributable to the lower molecular weight of the former in comparison to EDTA, which may have enhanced its penetration into the dentinal tubules thereby improving its efficacy even with a shorter contact time.

Notably, despite increasing the contact time, 15% sodium gluconate consistently underperformed relative to other experimental groups across all three cross-sectional levels. This diminished efficacy may be a consequence of its reduced concentration.

At both 30 s and 1 min, 20% sodium gluconate exhibited performance akin to that of 17% sodium gluconate in the coronal third; however, its efficacy declined progressively in the middle and apical thirds. This might be because increasing the concentration might have increased the viscosity of the irrigant thereby compromising its effectiveness. Its superior performance in the coronal third can be attributed to the larger canal diameter, which facilitated improved flow of the irrigant and enhanced smear removal in this region.[15]

Concerning dentinal erosion, the scoring scale was originally established by Torabinejad et al.[16] was expanded from three levels (scores 1–3) to five levels (scores 1–5), in accordance with the previous study by Akçay et al. to precisely define the morphological change in dentin.[5]

Based on the results of the current investigation, sodium gluconate exhibited no dentinal erosion, even with increased concentration and contact time. Consistent with previous studies,[8] no erosion was observed with 17% EDTA as it has been utilized only for a maximum contact time of 1 min.

Despite these valuable insights, certain limitations persist. The results of the study may differ under in vivo conditions. Moreover, outcomes may vary in posterior teeth with narrow and curved canals.

CONCLUSIONS

Within the confines of the study, sodium gluconate emerges as an effective irrigant for the removal of the smear layer. Its efficacy is influenced by time, concentration, and viscosity, exhibiting no detrimental effects on the structure of radicular dentin, even with extended exposure. Given these findings, 17% sodium gluconate at 30 s can be considered a promising alternative to the traditional 17% EDTA, offering a viable option as a final irrigant while exhibiting no erosion of dentinal tubules.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.