Effects of Various Chelating Agents in Combination with Sodium Hypochlorite on Root Fracture Toughness of Endodontically Treated Teeth after Ultrasonic Activation: An In-Vitro Study

Abstract

Background and Objective:

Various chelating compounds in combination with sodium hypochlorite were tested for their effects on root fracture toughness of ultrasonically activated endodontically treated teeth.

Materials and Methods:

Based on irrigant combination, 50 extracted lower premolar teeth were randomly assigned to five groups of 10. Group 1 (negative control), Group 2 (positive control), Group 3 (3% sodium hypochlorite [NaOCl] +17% ethylenediaminetetraacetic acid), Group 4 (3% NaOCl + 18% etidronic acid), and Group 5 (3% NaOCl + 10% citric acid). Ultrasound is used to activate irrigants. The obturated samples were tested using a universal testing machine for root fracture toughness.

Results:

It was found that endodontic treatment decreased root fracture toughness. Additionally, chelating agents reduce fracture resistance. This study found that 10% citric acid has the least effect on root dentin fracture resistance.

Conclusion:

Irrigation with various chelating agents and sodium hypochlorite reduces endodontic tooth fracture resistance. Citric acid was the most effective against fractures.

INTRODUCTION

Endodontic treatment often weakens the root due to mechanical instrumentation and chemical irrigation. The choice and combination of irrigating fluids affect dentin’s physical qualities, particularly fracture resistance. Sodium hypochlorite (NaOCl), a common endodontic irrigant, has significant antibacterial and organic tissue dissolution but can negatively impact dentin when administered alone or combined with specific chelating agents.[1] Chelating chemicals such as 17% ethylenediaminetetraacetic acid (EDTA), 18% etidronic acid (HEBP), and 10% citric acid are used to dissolve the smear layer and improve disinfectant penetration into dentinal tubules. Their effects on root dentin mechanical qualities, particularly when combined with NaOCl and triggered by ultrasonic methods, are still debated. Ultrasonic activation promotes irrigant penetration and efficacy and could increase dentin structure chemical effects, changing root fracture resistance.[2] As long-term results and post-treatment fracture prevention become more important, these irrigation regimens must be examined to determine the factors that affect root fracture toughness. The study examined the effects of ultrasonic activation of 17% EDTA, 18% HEBP, 10% citric acid, and 3% NaOCl on root canal (RC)-treated root fracture resistance.

MATERIALS AND METHODS

The study was conducted in vitro at the Department of Conservative Dentistry and Endodontics, Mar Baselios Dental College, Kothamangalam, Kerala. Fracture toughness was evaluated at the J. J. Murphy Research Centre in Rubber Park, Nellad. The study included 50 single-rooted human mandibular premolar teeth removed for periodontal or orthodontic causes. Sclerotic dentin-free, calcified, resorbed, tortuous canals, and multirooted teeth were excluded.

Teeth were kept in 0.5% chloramine-T at 4°C until needed. Each specimen was checked for tooth cracks with magnification loupes and illumination. The mean mesiodistal and buccolingual dimensions were measured with vernier callipers for specimen standardization. All teeth below the cementoenamel junction (CEJ) had their roots lengthened to 14 mm using a diamond disc and straight handpiece. Ten teeth were randomly chosen as negative controls. We measured all other teeth’s working length (WL). The RCs were expanded to F3 protaper size. Changing files required intracanal saline irrigation of instruments. Then, 40 specimens were randomly assigned to four groups of 10 and irrigated as per the protocols. A 30-gauge side-vented needle was 2 mm short of the apex, and irrigation solutions were given.

Groups were Group 1: Negative control (uninstrumented). In Group 2 (positive control), RCs were irrigated with 3-mL saline and NaOCl. The RCs were filled with 1 mL of 3% NaOCl using a 30-gauge side-vented needle 2 mm short of the WL. A size 21, 2% taper ultrasonic file was then put into the RC, halting 1 mm short of the WL. The piezoelectric ultrasonic device activated in 30 s (three cycles with 1 mL irrigant). Each RC was irrigated with 3 mL of saline after ultrasonic activation like NaOCl. Each irrigant remained 90 s in the canal. Total irrigation volume was 3 mL per irrigant.

In Group 3, RCs were irrigated with 3 mL of 17% EDTA and 3% NaOCl, and sterile saline. Passive ultrasonic irrigation (PUI) for 30 s (three cycles) was performed after the canal space was saturated with 17% EDTA, as in Group 2. Each RC was then irrigated with 3 mL of 3% NaOCl for 90 s (three cycles) and 17% EDTA for 90 s (three cycles) at 1-mL volume.

In Group 4, RCs were rinsed with sterile saline, then with 3 mL of 18% HEBP and 3% NaOCl. PUI was done for 30 s (three cycles) after filling the canal space with 18% HEBP, as in Group 2. Each RC was then irrigated with 3% NaOCl (3 mL) for 90 s (three cycles) and 18% HEBP (3 mL) for 90 s (three cycles), each cycle 1 mL. In Group 5, RCs with sterile saline, 3 mL of 10% citric acid, and 3% NaOCl were employed. PUI was done for 30 s (three cycles) after filling the canal space with 10% citric acid, as in Group 2. Each RC was then irrigated with 3 mL of 3% NaOCl for 90 s (three cycles) and 3 mL of 10% citric acid for 90 s (three cycles), each cycle 1 mL.

For 60 s, distilled water irrigated RCs after dentin conditioning. To remove solution residues, all specimens were washed with sterile saline. Canals were dried with a suction cannula and absorbent paper. Protaper F3 gutta-percha single cone obturation with AH Plus sealing was performed. The sealer was set by humidifying samples for seven days. The apex of each sample was wrapped in 0.2–0.3 mm plastic foil to 12 mm. To simulate clinical situations, samples were placed in self-cure acrylic resin blocks 2 mm below the cemento-enamel junction. The samples were removed from the block and loaded with polyvinyl siloxane 24 h later. An excess impression material was removed with a Bard–Parker blade. Periodontal ligament simulation using 0.2–0.3 mm polyvinylsiloxane impression material was employed. The universal testing machine (INTRON) measured fracture toughness. Customized 4 mm tips covered the canal opening at 0.5 mm/min vertical crosshead speed. The tooth fracture compressive load was measured in Newtons.

Statistical analysis

One-way analysis of variance (ANOVA) and Tukey’s post-hoc tests were used to compare fracture resistance between groups and for intergroup comparisons at 5% significance using SPSS 26.0 software.

RESULTS

This study found that 10% citric acid, 18% HEBP, and 17% EDTA had the highest mean fracture resistance on root specimens [Table 1]. The negative control group had the highest fracture resistance (731.735 ± 46.685). The positive control group had the lowest fracture resistance (341.844 ± 29.073). Citric acid outperformed EDTA (413.048 ± 32.401) and HEBP (515.537 ± 30.762). The group differences were statistically significant following ANOVA and Tukey’s post-hoc analysis (P = 0.000).

Table 1.

Comparisons of mean fracture resistance values

Groups		n		Mean±SD		Post-hoc analysis
						1Vs2		1Vs3		1Vs4		1Vs5		2Vs3		2Vs4		2Vs5		3Vs4		3Vs5		4Vs5
1		10		731.735±46.685		HS		HS		HS		HS		HS		HS		HS		HS		HS		HS
2		10		341.844±29.073
3		10		413.048±32.401
4		10		515.537±30.762
5		10		599.313±23.179
Total		50		520.2954±142.372
F-test		212.12
P		HS

HS: Highly significant (P=0.000)

DISCUSSION

NaOCl reduced root fracture strength in this investigation. Since NaOCl affects root dentin mechanical behavior, the lowest levels are allowed. This indicated that NaOCl lowers root dentin fracture stresses, influencing mechanical properties.[3,4] Gu et al.[5] observed that NaOCl increased EDTA permeability in mineralized dentin. EDTA dissolves the apatite layer, exposing collagen fibers and promoting NaOCl and proteolysis.[5] Mineralized dentin degrades in a concentration and time-dependent manner via diffusion. OCl⁻ anion acidification generates a friable mineral matrix and reduces flexural strength when it meets dentin walls. This may imply root fractureability.[3]

After citric acid and EDTA treatments, Eldeniz et al.[6] assessed root dentin roughness. Citric acid roughened surfaces. This may help endodontic sealers adhere micromechanically to RC surface defects. Changes in microhardness may alter fracture resistance. De-Deus et al.[7] showed that citric acid influenced microhardness less than EDTA and EDTA-C. Citric acid had the highest root dentin fracture loading resistance of all irrigants, supporting the current investigation. The literature recommends intermittent PUI with traditional syringe irrigation in the final stage of RC preparation, after system preparation, for clinical usage. Combining conventional and ultrasonic irrigation speeds up the procedure and eliminates the smear layer and bacteria in the canal system, enhancing endodontic outcomes.[8] The present experiment was standardized with single-rooted premolar teeth with straight canals. Thus, the findings may apply only to similar clinical situations. Future research ought to address how HEBP and citric acid impact multirooted curved RCs.

CONCLUSION

The study indicated that chelating agents decreased tooth fracture resistance. Citric acid at 10% concentration has the least impact on root dentin fracture resistance compared to other groups. As an intracanal irrigant, NaOCl alone proved to be the most damaging.

Conflict of interest

Nil.

Funding Statement

Nil.