Assessment of Root Dentin Defect during Retreatment Procedure using Various NiTi Hand and Rotary Retreatment Files: An In vitro Study.

Aim: The aim of the current study was to evaluate the radicular dentin defect during retreatment employed diverse NiTi hand and rotary retreatment file systems. Materials and
Methods: Eighty mandibular premolars with a single root and root canal that were recently extracted were gathered and stored. The premolars were subject to decoronation at cementoenamel junction (CEJ) beneath irrigation with water to attain a uniform radicular length of 16 mm. Gutta-percha cones were covered with sealer and introduced into the root canal up to the working length. Eighty teeth were allocated at random into four groups with each group consisting of 20 samples. Group I: Control, Group II: EdgeFile XR retreatment rotary files, Group III: ProTaper Universal retreatment files, and Group IV: MTwo retreatment files. Under constant water cooling, the roots were cut flat with a diamond disc at apical third (3 mm), middle third (6 mm), and cervical third (9 mm) points. Stereomicroscope was employed to visualize the sections below × 20 magnification.
Results: A statistically significant difference was noted among the groups with respect to the formation of radicular dentinal defects at 3 mm (P < 0.01) and 6 mm (P < 0.001), while the sections at 9 mm did not exhibit any statistically significant difference (P > 0.598).
Conclusion: Despite the limitations in this study, it was concluded that all the evaluated file systems efficiently eliminated root canal filling during the retreatment. In addition, it was noted that the EdgeFile XR group exhibited fewer root dentin defects in comparison with the MTwo and ProTaper Universal group of files. Copyright:

INTRODUCTION

In spite of a soaring success rate, endodontic treatment may sometimes not provide the required response and failure of the therapy may result. A retreatment by nonsurgical means necessitates full elimination of the previously existing endodontic restorative material to permit the removal of the necrotic tissues as well as the microbial populace. The most favorable retreatment by nonsurgical means requires secure and proficient exclusion of restorative materials from the root canals to bestow effectual cleansing, shaping, and filling of the root canals.[1]

Cracks in dentin may result from the quantity of dentin that has been taken out in the course of the root canal therapy and retreatment. In addition, multiple file systems might be deployed that include numerous tapers, blades for cutting, and differently configured tips which may employ manual, rotary, and reciprocal movement during the use. A large number of studies have shown that lesser number of cracks is generated when manual and reciprocating movement equipment are used as compared to rotary files.[23]

Owing to the superiority of NiTi rotary files as compared to the stainless steel file system, their fame has increased leading to wide usage of the NiTi file systems in endodontic treatment and retreatment. Although NiTi rotary files have multiple advantages, they have caused defects in dentin-like cracks during shaping of the canals and endodontic retreatment. Furthermore, it has been suspected that dentinal defects by widening may lead to unwanted sequel-like vertical fractures of the root.[456] Thus, this study was undertaken to evaluate the radicular dentinal defects that occur during retreatment with rotary files such as EdgeFile XR, NiTi hand, ProTaper Universal, and MTwo.

MATERIALS AND METHODS

Sample collection and preparation

Eighty mandibular premolars with a single root and root canal that were recently extracted for orthodontic treatment purposes were gathered and stored in normal saline after a 24 h immersion in chloramine-T solution till they were used for this study. The exclusion criteria were carious teeth, restored teeth, teeth with external cracks and defects, calcification of canals, and teeth with evidence of external or internal resorption.

The premolars were subject to decoronation at CEJ beneath irrigation with water to attain a uniform radicular length of 16 mm. The patency of the root canal was checked with a number 10 K-file which was then pulled back 1 mm to ascertain the working length and confirmed with radiographs. A marble jig that was made for this study was then used to mount all the samples. The teeth were then subjected to instrumentation with number 15 and 20 ISO size K-files (Dentsply Maillefer) to the working length that was established before creating a glide path. Universal rotary equipment were employed for the chemomechanical preparation utilizing a torque-controlled motor (X-smart, Dentsply Maillefer) up to the master apical file F3 (ProTaper Universal).

2 mL of 5.25% NaOCl was used to irrigate the root canals among instrument change. A lentulospiral was used to carry the resino-seal sealer (Amrit Chemicals and Minerals Agency, Punjab) into the root canal. Conventional F3 gutta-percha cones were covered with sealer and introduced into the root canal up to the working length. The samples were stored at 37°C temperature and humidity of 100% inside a humidified incubator for 10 h to permit the sealer to set entirely.

Retreatment procedure

Eighty teeth were allocated at random into four groups with each group consisting of 20 samples.

Group I: Control

Group II: EdgeFile XR retreatment rotary files

Group III: ProTaper Universal retreatment files

Group IV: MTwo retreatment files.

At the root canal opening, 0.2 mL RC solve was utilized to soften the gutta-percha in all the above groups. 1 mL 2.5% NaOCl irrigation of the root canals was performed during the retreatment because this showed better bactericidal action and a good tissue dissolution time. Retreatment was estimated to be complete if no gutta-percha or sealer was noticed on either the surface of the instrument or the walls of the dentin. Images were acquired after the retreatment and radicular dentin defects were evaluated with Barreto et al.[7] criteria as under:

Score 1 – No defect: the internal or external surface of the radicular dentin exhibited no lines or cracks.

Score 2 – Incomplete crack: a line that advanced into the dentin from the wall of the canal but did not reach the outer surface.

Score 3 – Complete crack: a line advancing to the outer surface of the root from the wall of root canals.

Score 4 – Craze lines: other lines not spreading to any radicular surface or advancing into the dentin from the outer surface, nevertheless reaching the wall of root canals.

Assessment of root dentin defect

Under constant water cooling, the roots were cut flat with a diamond disc along with water coolant at apical third (3 mm), middle third (6 mm), and cervical third (9 mm) points. The sections were viewed using a stereomicroscope (Olympus, Tokyo, Japan) at ×20 magnification. Photomicrography technique was used to take the digital pictures of the cracks.

Statistical analysis

The Statistical Package for the Social Sciences (SPSS) software version 20.0 was used to analyze the data thus collected. Each group was statistically analyzed using the Chi-square test. Statistical significance was set at P < 0.05.

RESULTS

As individual file systems were compared for the results attained at 3, 6, and 9 mm sections, a statistically significant difference was noted among the groups with respect to the formation of radicular dentinal defects at 3 mm (P < 0.01) and 6 mm (P < 0.001), while the sections at 9 mm did not exhibit any statistically significant difference (P > 0.598), as delineated by Tables 1-3.

Table 1

Comparative assessment of root dentin defect after retreatment at apical third (3 mm)

Retreatment groups	No defect, n (%)	Incomplete crack, n (%)	Complete crack, n (%)	Craze lines, n (%)	χ 2	P
Group I: Control	20 (100)	0	0	0	15.846	0.01
Group II: Edge File XR	19 (95)	1 (5)	0	0
Group III: ProTaper Universal	17 (85)	2 (10)	0	1 (5)
Group IV: MTwo	18 (90)	1 (5)	0	1 (5)

Table 3

Comparative assessment of root dentin defect after retreatment at coronal third (9 mm)

Retreatment groups	No defect, n (%)	Incomplete crack, n (%)	Complete crack, n (%)	Craze lines, n (%)	χ 2	P
Group I: Control	20 (100)	0	0	0	10.166	0.598
Group II: EdgeFile XR	18 (90)	1 (5)	0	1 (5)
Group III: ProTaper Universal	17 (85)	2 (10)	0	1 (5)
Group IV: MTwo	17 (85)	1 (5)	1 (5)	1 (5)

DISCUSSION

Periapical pathology in the root canal treated teeth arises from persisting microbial colonies within the complex root canal systems. Failed root canal treatment is best managed by nonsurgical means. The removal of old root canal filling, residual necrotic tissues and bacteria, reinstrumentation, canal disinfection, and obturation are the primary objectives of retreatment.[8]

Stainless steel hand files, NiTi files, ultrasonic files, and lasers have been used to remove the root canal fillings. The conventional file systems are arduous and time taking for operators, especially when an appropriately condensed filling material needs removal. Furthermore, this may also lead to endodontic mishaps. Several investigators such as Giuliani et al.,[9] Mittal and Jain,[10] and Joseph et al.[11] have noted that rotary files are more efficient in the removal of obturating materials than the hand file systems. This is in accordance with the findings of this study which also imply that the rotary file systems are more proficient in removing obturating material.

This study found that lesser radicular dentinal microcracks were noted with the EdgeFile XR group in comparison with the MTwo files group and ProTaper Universal group. Higher numbers of radicular dentin microcracks were seen with the ProTaper Universal file systems. This is consistent with the findings of Ashwinkumar et al.[12] and Al-Zaka[13] who also stated in conclusion that the ProTaper rotary files caused the highest number of dentinal microcracks. This can be attributed to the constant rotational forces and steady torque which occurs from the use of NiTi rotary files on the walls of the root canal. Furthermore, contributing to this are the equipment design characteristics such as design of the tip, cross-section geometry, flexibility, as well as taper.

The current research also depicted that rotary NiTi and EdgeFile XR equipment were significantly more valuable than other files. This is comparable to the study performed by Tomer et al.[14] who implied a superior performance of the EdgeFile XR equipment probably as they are prepared from annealed heat-treated NiTi alloy brand called the Fire-Wire™. This heat-treated Fire-Wire™ NiTi gives a performance enhancing durability which gives implausible flexibility along with much superior performance than the other file systems in the cyclic fatigue testing, which chiefly implies strength and durability of the file. EdgeFile XR improves and hastens the retreatment of root canals. Parabolic cross-section merges the qualities of being greatly competent and flexible while being highly secure and fracture resistant.

CONCLUSION

Despite the limitations in this study, it was concluded that all the evaluated file systems efficiently eliminated root canal filling during the retreatment. In addition, it was noted that the EdgeFile XR group exhibited fewer root dentin defects in comparison with the MTwo and ProTaper Universal group of files.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Table 2

Comparative assessment of root dentin defect after retreatment at middle third (6 mm)

Retreatment groups	No defect, n (%)	Incomplete crack, n (%)	Complete crack, n (%)	Craze lines, n (%)	χ 2	P
Group I: Control	20 (100)	0	0	0	11.562	0.001
Group II: EdgeFile XR	17 (85)	2 (10)	1 (5)	0
Group III: ProTaper Universal	15 (90)	2 (10)	2 (10)	0
Group IV: MTwo	17 (85)	1 (5)	1 (5)	1 (5)