Dentinal defects after root canal preparation with rotary nickel-titanium files using different irrigants: An in vitro study.

Aim: This in vitro study aims to detect the dentinal defects associated with different irrigants during biomechanical preparation using rotary nickel-titanium (Ni-Ti) files (Hyflex CM). Materials and
Methods: For the study, 120 extracted mandibular incisors were taken. Depending on the irrigant used, teeth were divided into six groups (n = 20). In Group 1, teeth were not biomechanically prepared considered as, control group. In Group 2, Group 3, Group 4, Group 5, and Group 6, biomechanical preparation was with Hyflex CM rotary Ni-Ti files using saline, 3% sodium hypochlorite (NaOCl), 17% ethylenediaminetetraacetic acid (EDTA), SmearClear, and 2% chlorhexidine (CHX), respectively, as irrigant. IsoMet Saw was used to section samples at 3, 6, and 9 mm from the apex perpendicular to the long axis of tooth. Segments were seen at 30x magnification under a digital stereomicroscope. Statistical Analysis: Statistical analysis was done using two-tailed t-test.
Results: Maximum number of dentinal defects was seen with 17% EDTA, followed by 3% NaOCl, SmearClear, and 2% CHX. Conclusions: Irrigation with 17% EDTA causes more dentinal defects as compared to irrigation with 3% NaOCl, SmearClear, and 2% CHX. Copyright:

INTRODUCTION

The main objective of biomechanical preparation is to clean and remove smear layer from the root canal. Due to heterogeneity of root canal system, biomechanical preparation is aided with irrigants to achieve our goal.[1] Therefore, irrigants play a vital role in root canal treatment.

Instrumentation with rotary files provides upper hand to hand files as they reduced operator fatigue and time required to finish preparation as well as it leads to less procedural errors as compared to stainless steel files.[234]

Various substances that are being used as irrigants are citric and phosphoric acid (acid), ethylenediaminetertraacetic acid (chelating agent), proteolytic enzymes, hydrogen peroxide (oxidizing agent), local anesthetic solution, sodium hypochlorite (NaOCl), sodium hydroxide, and potassium hydroxide (alkaline solution), and saline.

NaOCl is an effective antibacterial agent and has the ability to dissolve tissues, making it the standard endodontic irrigant. Hypochlorite is used in concentrations between 0.5% and 6%.[5]

Nygaard – Ostby, in 1957, introduced ethylenediaminetetraacetic acid (EDTA),[6] it forms calcium chelates by reacting with the inorganic component of dentin. It has limited antimicrobial activity.

The penetrability of root canal irrigants into the dentinal tubules has been increased by adding surfactants. Surfactants reduce surface tension and increase the wettability of irrigants, which enables solutions to reach deep into the dentin.[7] SmearClear (SybronEndo, Orange, CA, USA), a chelator agent, is a combination of 17% EDTA, a cationic, and an anionic surfactant.

Chlorhexidine (CHX) has a wide range of activity against Gram-positive and Gram-negative bacteria, spores, viruses, yeast, and dermatophytes. In low concentration, it exerts a bacteriostatic effect, and in high concentration exerts bactericidal effect.[8] It is commonly used in concentration of 2% in endodontic procedures.

Irrigation solutions affect the chemical composition of dentin, which may have an impact on its physical properties.[9] The objective of this study was to compare the incidence of the damage observed in root dentin after biomechanical preparation using Hyflex CM rotary nickel-titanium (Ni-Ti) file system with different irrigants.

MATERIALS AND METHODS

This study was approved by the Ethical Committee of our institute numbered PUIEC/2015/12/R/17/09. One hundred and twenty single-rooted mandibular incisors extracted due to orthodontic and periodontic reasons were used in the study. Teeth with no carious lesion, restoration, and fracture were included, and teeth with the carious lesion, restoration, and fracture were discarded for further use. Teeth were examined under stereomicroscope to rule out crack and fracture. Single canal was confirmed by buccolingual and mesiodistal radiographs. To standardize root length of 12 ± 1 mm, teeth were decoronated with a diamond disc in a micromotor under copious water cooling. Samples were coated with silicone impression material to simulate periodontal ligament (PDL) space.

Samples were divided into one control and five experimental groups (n = 20) depending on the irrigant used during biomechanical preparation:

Group 1: Control group, samples were not biomechanically prepared

Group 2: Samples were irrigated with saline

Group 3: Samples were irrigated with 3% NaOCl (PanReac Applichem, Darmstadt, Germany)

Group 4: Samples were irrigated with 17% EDTA (Prime Dental Products, India)

Group 5: Samples were irrigated with SmearClear (SybronEndo, Orange, CA, USA)

Group 6: Samples were irrigated with 2% CHX (Coltene Whaledent, Altstatten, Switzerland).

Biomechanical preparation was done using standardized technique with Hyflex CM (Coltene Whaledent, Altstatten, Switzerland) rotary Ni-Ti files to master apical size 25/04. Each time instrument was changed, samples were irrigated with the respective irrigant. 20 ml of irrigant was used in each sample.

Using IsoMet 1000 Precision Saw (Buehler, an ITW Company, IL, USA) [Figure 1], samples were sectioned at 3, 6, and 9 mm from the apex perpendicular to the long axis of root. Segments were seen under a digital stereomicroscope (Carl Zeiss, Oberkochen, Germany) at ×30. The image was blindly checked for defects by two operators.

Figure 1

IsoMet 1000 Precision Saw

Wilcox et al.[10] classification was used to define dentinal defects. “No defect” is defined as root dentin devoid of any defect. “Defect” defines as fracture lines and craze lines or partial cracks.

Results were demonstrated as number and percentage of roots showing dentinal defects in above groups. Statistical analysis of differences between experimental groups was executed using two-tailed t-test.

RESULTS

In the control group, no dentinal defects were found. Dentinal defects were observed in all experimental groups. Table 1 and Graph 1 show the number of root sections with dentinal defects. Maximum number of dentinal defects was seen in samples irrigated with 17% EDTA, followed by 3% NaOCl, SmearClear, and 2% CHX. Statistically significant difference was found between experimental and control groups [Table 2].

Table 1

Number and percentage of root sections presenting different types of dentinal defects in experimental groups

Groups	Root section at 9 mm		Root section at 6 mm		Root section at 3 mm
	Type I	Type II	Type I	Type II	Type I	Type II
Control	0	0	0	0	0	0
Saline	0	1 (5)	0	1 (5)	0	1 (5)
3% NaOCl	0	2 (10)	1 (10)	3 (15)	1 (5)	2 (15)
17% EDTA	0	2 (10)	3 (15)	3 (15)	1 (5)	3 (15)
SmearClear	0	2 (10)	0	3 (15)	1 (5)	2 (10)
2% CHX	0	1 (5)	1 (5)	2 (10)	0	1 (5)

EDTA: Ethylenediaminetetraacetic acid, CHX: Chlorhexidine, NaOCl: Sodium hypochlorite

Graph 1

Number of root sections having dentinal defects in all groups

Table 2

Statistical analysis between groups using two-tailed t-test

Groups	Defects	t-statics	P
Control	0	0	0
Saline	3	1.78	0.07493
3% NaOCl	9	3.84	0.00033
17% EDTA	12	5.20	0.00000
SmearClear	8	3.47	0.00102
2% CHX	5	2.45	0.01619

EDTA: Ethylenediaminetetraacetic acid, CHX: Chlorhexidine, NaOCl: Sodium hypochlorite

DISCUSSION

During irrigation, the crown and root dentin are affected by the irrigation solution, which can cause changes in the physical and chemical properties of the root canal dentin. Therefore, this study evaluated the effect of root canal irrigants 3% NaOCl, 17% EDTA, SmearClear, and 2% CHX on the incidence of dentinal defects.

The root size of selected mandibular incisors was the same. This was done to minimize variations in anatomy. The teeth with cracks or fractures were excluded from the study after viewing them in the stereomicroscope and radiograph. Control samples were devoid of any dentinal defects, so it was concluded that sectioning done with IsoMet Saw did not lead to any dentinal defects. This study is in accordance with Adorno et al.[11] who had used a similar method of sectioning. PDL was simulated by coating samples with silicone impression material, and then samples were placed in acrylic blocks to dissipate the stresses during biomechanical preparation of the root canal.

3%NaOCl, 17% EDTA, SmearClear, and 2% CHX were used in the study as these irrigants are routinely available.

Maximum number of dentinal cracks was seen in canals irrigated with 17% EDTA. This is in accordance with previous studies as EDTA decreases the microhardness of dentin which is due to its chelating property.[1213] The results of this study are in confirmation of our previous study in which comparison of dentinal defects in samples prepared with hand files using different irrigants was evaluated.[14]

When comparison was done between the control and 3% NaOCl group, statistically significant difference was found. The results are in sink with the studies done by Slutzky-Goldberg et al.[15] and Ari et al.[16] who concluded that the microhardness of dentin is significantly reduced with the use of NaOCl which is due to its organic dissolving property.

Significantly more dentinal defects were found in root canals irrigated with 2%CHX than the control group. This is in simulation with the result of a previous study which showed the microhardness of dentin is significantly decreased with the use of 2% CHX.[17]

The composition of SmearClear is 17% EDTA solution containing cetrimide and two surfactants, polyoxyethylene and iso-octylcyclohexyl ether.[18] Surfactants reduce calcium removal effectiveness of EDTA.[19]

More dentinal defects were observed as compared to the previous study as in the study samples were prepared with Hyflex CM rotary Ni-Ti files.

Larger sample size studies seem to be required to further investigate the influence of root canal irrigants on dentinal cracks.

CONCLUSIONS

From the above study, we can conclude that 2% CHX is a mild irrigant and causes a smaller number of dentinal defects as compared to 17%EDTA. This should be kept in mind during endodontic procedures.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.