Effect of three newer generation rotary files on smear layer removal using fumaric acid as an irrigant: A SEM study.

Background: To evaluate the efficacy of the smear layer removal with Fumaric acid when used in combination with new generation files Hyflex Electrical Discharge Machining (HEDM) file, Neoendo file, and Blueflex file. Materials and
Methods: Sixty extracted mandibular premolars with single-canal were selected for this study. Radiographs were taken to confirm the presence of single canal and absence of any type of calcifications, resorption, cracks, and fractures. The teeth were decoronated to a standardized length of 12 mm and working length was determined with ISO #15 K file. After this, teeth were randomly divided into 2 main groups - Control and Experimental group. In Control group, root canal instrumentation was performed with Neoendo, Blueflex, and HEDM files, respectively, along with 1 ml of 17% ethylenediaminetetraacetic acid (EDTA), and in Experimental group, root canal instrumentation was performed with Neoendo, Blueflex, and HEDM files, respectively, along with 1 ml of 0.7% fumaric acid for 1 min. Longitudinal grooves were prepared with slow-speed silicon carbide disc on the buccal and lingual surfaces of each root. Preparation for scanning electron microscope was done and phototmicrographs at ×3000 were taken. Statistical Analysis: The results were analyzed using ANOVA test for comparison of smear layer scores among various groups and Tukey's HSD test was used for paired comparisons of total smear layer scores. Conclusions: On the basis of the present study, Blue flex file along with fumaric acid was found to be best among the groups and Neo endo along with EDTA was the poorest. Copyright:

INTRODUCTION

The main purpose behind the endodontic treatment is to eliminate the micro-organisms from the infected root canal system and attain periapical tissue healing using biomechanical procedure with an antibacterial agent. Smear layer formation during root-canal procedure is an unavoidable process.[123] Smear layer averts the penetration of irrigating solutions, intracanal medicaments, and filling materials into the dentinal tubules and hampers their contact with the root canal wall so that it increases the risk of microleakage and bacterial infection.[4] Therefore, to enhance the success of endodontic treatment, it is very important to develop an instrument system which produces minimal amount of smear layer on the canal wall.[5] During the last decades, several nickel-titanium (NiTi) instruments have become popular because of their better cutting ability, flexibility, reliability, and efficiency against the hand-cutting instruments. It provides higher fracture resistance against cyclic and torsional fatigue with an exceptionally high root canal preparation.[6] Recently, a new generation NiTi file, Hyflex Electrical Discharge Machining (HEDM), has been introduced to improve the effectiveness of root canal irrigation as a supplementary technique. This new file system is also called as “Electrical Discharge Machining” which uses spark erosion. It influences the outcome of the subsequent phases of irrigation, disinfection, obturation. This rotary file stay centered in the curved root canal system so that it influences the overall success of root canal preparation.[7] Second, new generation file, Neoendo, utilizes a proprietary heat treatment which gives it a unique flexibility. It offers more rapid and more centered canal preparations. Third new generation file, Blue Flex file, the molecular structure of this files, has been altered by using a new type of heat treatment which gives blue color of a file and also increased the cyclic fatique resistance. Blue flex files offer better uncompromising cutting efficiency.[8] Revolutionary blue wire technology helps to reduce damage to dentine. In this study, we evaluated the smear layer removal efficacy of Fumaric acid when used in combination with new generation files which are HEDM file, Neoendo file, and Blueflex file.

MATERIALS AND METHODS

Sixty extracted mandibular premolar with single-canal were selected for this study. Radiographs were taken to confirm the presence single canal and absence of any type of calcifications, resorption, cracks, and fractures. Ultrasonic scaling was done to remove the calculus and soft tissues and kept in 0.1% thymol solution until use. Samples were randomly divided into control and experimental groups (n = 10 each).

Preparation of the root canal

The teeth were decoronated up to 12 mm and working length was determined with ISO #15 K file (Dentsply Maillefer, Ballaigues, Switzerland) until it was just visible at the apical foramen and then keeping it short by 0.5 mm. After this, teeth were randomly divided into two main groups:

Group I – Control group

Group II – Experimental group

Group I was further subdivided into three groups:

Subgroup A – Neoendo file + 17% ethylenediaminetetraacetic acid (EDTA)

Subgroup B – Blue Flex file + 17% EDTA

Subgroup C – HEDM + 17% EDTA

Group II was further subdivided into three groups:

Subgroup D-Neoendo file + 0.7% fumaric acid

Subgroup E– Blue Flex file + 0.7% fumaric acid

Subgroup F– HEDM + 0.7% fumaric acid.

In Control group (Subgroup A, B, and C), root canal instrumentation was performed with Neoendo (Orikam Healthcare India), Blueflex (DenMed, India) and (HEDM; Coltene/Whaledent, Altstatten, Switzerland) files, respectively, along with 1 ml of 17% EDTA irrigating solution individually after each instrument change for 1 min. Biomechanical preparation was done till rotary 25/4% shaping files in all the three subgroups. In Experimental group (Subgroup D, E, and F), root canal instrumentation was performed with Neoendo, Blueflex, and HEDM files, respectively, along with 1 ml of 0.7% fumaric acid irrigating solution individually after each instrument change for 1 min. Biomechanical preparation was done till rotary 25/4% shaping files in all the three subgroups. 0.7% fumaric acid was freshly prepared in the Department of Conservative Dentistry and Endodontics according to manufacturer instructions. The access cavity was sealed with sterile cotton pellet. Longitudinal grooves were prepared with a slow-speed silicon carbide disc on the buccal and lingual surfaces of each root. Each tooth was then carefully split into two halves using chisel and mallet and stored in distilled water until use. Preparation for scanning electron microscope was done and phototmicrographs at ×3000 were taken [Figure 1]. Scoring was done by two different observers using grids of (1 cm × 1 cm).

Figure 1

Scanning electron microscopic image of Group A,B,C,D,E,F

On the basis of total quality score, the quality of various rotary endodontic files can be categorized into four groups [Table 1].

Table 1

Quality of various rotary endodontic files

Total score	Status
3.00-5.25	Very good
5.25-7.50	Good
7.50-9.75	Fair
9.75-12.00	Poor

Statistical analysis

The results were analyzed using ANOVA test for comparison of smear layer scores among various groups, and Tukey's HSD Test was used for Paired Comparisons of total smear layer scores [Table 2].

Table 2

Average smear layer scores among various groups for total area (C+M + A)

Groups	n	Mean±SD	Minimum	Maximum
Subgroup A	10	10±1.767	8	12
Subgroup B	10	8.5±1.366	8	12
Subgroup C	10	9.1±1.442	7	10
Subgroup D	10	9.4±1.678	8	10
Subgroup E	10	6.8±1.165	5	9
Subgroup F	10	7.8±1.278	6	11

SD: Standard deviation

OBSERVATION AND RESULTS

The mean remaining smear layer score was found to be minimum (6.8 ± 1.165) for Subgroup E followed by Subgroup F (7.8 ± 1.278). Hence, the quality of various rotary endodontic files according to mean smear layer removing score for the total area is found to be:

Subgroup E > Subgroup F > Subgroup B > Subgroup C > Subgroup D > Subgroup A.

DISCUSSION

The main purpose behind the root canal treatment is to shape root canals and to remove the pulp tissue, bacteria, and their by-products. To eliminate bacteria, instruments alone are not enough because it produces a large amount of smear layer along the root canal walls.[91011] Rotary instruments produced thicker smear layer in compare to hand instrumentation. The design of the flutes also affects the formation of the smear layer. Files with more land area produce less smear layer when compared to other files because more the land area more it can auger debris. When reciprocating files were used, a thicker smear layer was formed in the apical third when compared to continuous rotation files. Neoendo Flex file is a 3rd Generation Rotary File with 2 Files Shaping System undergone Gold Thermal Treatment which provides it extremely flexibility. HEDM is a 5th-generation NiTi rotary endodontic files fabricated with EDM technology, which hardens the surface of the NiTi file. This technology provides excellent flexibility and fracture resistance. The combination of flexibility, fracture resistance, and cutting efficiency makes it possible to reduce the number of files required during root canal therapy while preserving root canal anatomy. The built-in shape memory of HEDM files prevents stress during canal preparation by changing their spiral shape. Blue-flex files have double S cross-section which provides efficient removal of debris. This file has a variable pitch that increases from tip to handle to prevent locking, reduce ledge formation and apical extrusion and minimize canal transportation. Blue heat treatment provides higher flexibility and cutting efficiency. The goal of the irrigants is to increase mechanical debridement by flushing out debris, dissolving pulp tissue, and disinfecting the root canal system. In an urge to find a better irrigating solution, we have experimented 0.7% fumaric acid which is a trans isomer of maleic acid. 0.7% Fumaric acid was chosen in this study because 0.7% is the maximum amount of fumaric acid which is soluble in water at room temperature.[1213] 17% EDTA was used in this study because when it is used in higher concentration, they cause erosion of inter-tubular and peri-tubular dentin. In this study, Blueflex files used along with fumaric acid have shown significantly better smear layer removing property because of the molecular structure of the files. This has been altered using a new type of heat treatment, which increases the cyclic fatigue resistance of the files and gives the files a blue color and is the most important differentiating feature with other files.[1415] Fumaric acid has shown significantly better smear layer removal, may be due to the fact, two carboxylic groups are always opposite to each other in their three-dimensional orientation and can bind with more of Ca++ present in intraradicular dentin. Unlike EDTA, Fumaric acid demineralization depends on hydrogen ion concentrations as they are organic acids. After calculation, pH of 0.7% fumaric acid was obtained as 2.70. Since dentin demineralization occurs at pH 4–5 so fumaric acid can well demineralize and remove the smear layer.[13] At neutral PH, EDTA may not be efficient enough to remove the smear layer. Other contributing factor for the limited demineralization of EDTA may be due to its high molecular size than that of fumaric acid as larger molecules will bind to less number of Ca++ into the narrow canals. In the present study, Neoendo files used along with Fumaric acid and EDTA in Subgroup D and A, respectively, showed least efficiency in the removal of smear layer compared to other files.[16] It may be due to the fact that Neoendo Flex Files have a convex triangular cross-section and utilize a proprietary gold thermal treatment but had significantly higher debris and smear layer score at all the three levels of the canal.[17] The irregular geometry of the file design could be responsible for creating a nonuniform shape of root canal, which in turn could have prevented the flushing of debris and smear layer adequately. Fumaric acid is poorly absorbed after oral intake and is nontoxic, anticarcinogenic, anti-inflammatory, nonabsorbable, biocompatible and growth modulatory in action. That is why, fumaric acid was experimented as a root canal irrigant to remove smear layer in the field of endodontics.

CONCLUSIONS

Blue flex files along with fumaric acid showed the best smear layer removal when compared to other groups and Neoendo along with EDTA was the poorest.

The quality of various files according to ranks of smear layer removing was found to be:

Subgroup E > Subgroup F > Subgroup B > Subgroup C > Subgroup D > Subgroup A.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.