A Comparative Evaluation Of The Apical Foraminal Deformation Caused By Three Rotary File Systems: An In Vitro Study

Keywords

Apical Deformation; Foraminal Deformation; Protaper Gold; Profit S3; Hyflex CM; Stereomicroscope.

Introduction

The primary goal of endodontic treatment is to obtain adequate disinfection of the root canal space in order to prevent recurrence of apical periodontitis [1, 2]. This involves chemo-mechanical preparation of the root canals followed by a three-dimensional root canal filling. An important step in this process is determining the working length of the canal. According to the endodontic glossary, ‘Working length’ is defined as the distance from a stable coronal reference point to the point at which root canal preparation and obturation must terminate [3]. Numerous authors have discussed their opinions on this subject and have come to conclusions as to what must be the ideal working length. Ingle (1973) stated that the WL must be 0.5mm short of the external root surface; Weine (1982) stated that it must be 1mm short of the radiographic apex; Guldener (1985) stated that for necrotic teeth it must be 0.5mm short of the tooth length while it should be 1mm short for vital teeth; Frank (1988) stated that it must be 0.5- 1mm short of the apex; etc [4]. Langeland et al [5] stated that root canal preparation and obturation must end at the apical constriction irrespective of the vitality of the tooth. On the other hand, some authors advocated penetration of the foramen to or beyond the radiographic apex. Schilder et al [6] declared his aim was to debride and fill up to the apex, as well as fill the lateral canals and apical ramifications.

In cases of apical periodontitis especially in necrotic teeth, recognizing the presence of microorganisms in the apical portion of the canal has contributed to the acceptation of larger apical preparations [7, 8] and cleaning, debridement, and enlargement of the apical foramen [9] during root canal instrumentation since it can overcome the potential limits of irrigation in the apical area, optimizing root canal disinfection [10, 11]. Achieving a larger apical diameter during foraminal enlargement, however, might lead to apical transportation. This transportation of the apical foramen can lead to complications in subsequent cleaning and filling procedures [12].

With the advent of nickel-titanium instruments in endodontics, root canal preparations have become easier and more predictable. Nickel-titanium files are known for their elasticity and resistance to torsional fatigue when compared to hand stainless steel files [13]. Several types of thermal treatments have been developed with the aim of optimizing the mechanical properties of NiTi alloy [14, 15]. Some of them include M wire technology, R-phase, controlled memory, gold files, blue files, etc. They are known to have better flexibility, fracture resistance, resistance to cyclic fatigue, etc.

Protaper Gold is a heat-treated file with advanced metallurgy and a progressively tapered design. Hyflex CM is manufactured based on the controlled memory technology and is claimed to be highly flexible. ProFit S3 (PS3) is a new endodontic file system manufactured using new heat-treated technology and having a titanium oxide coating.

Mesial root canals of mandibular first molars are reported to be curved both in buccolingual and mesiodistal directions [16]. Maintaining a centered preparation with minimal apical deformation is difficult and hence these teeth are more prone to ledging and canal transportations.

Since no previous study has compared the apical foramen deformation caused by these three rotary systems, the aim of this study was to compare and evaluate the apical foramen deformation caused by Protaper Gold, Profit S3, and Hyflex CM rotary file systems in mandibular molars.

Previously our team has a rich experience in working on various research projects across multiple disciplines [17-31] Now the growing trend in this area motivated us to pursue this project.

Materials And Methods

Thirty mesial root canals in Vertucci’s Type IV configuration in fifteen extracted mandibular molars with fully developed roots were included in the study. The teeth exhibited no defects, their root canals were not calcified, showed no internal or external root resorption, no prosthetic crowns or dental posts, no signs of prior endodontic treatment, and no aberrant canal morphology. Only teeth with apical curvature between 20 and 40 degrees were included. Preoperative stereomicroscopic images were taken at 100X magnification and the apical foramen dimensions were assessed (A0).

Access cavities were prepared using Endo Access bur, 21 mm size 2 (Dentsply Maillefer, Swiss made) and K-file (Mani, Utsunomiya, Tochigi, Japan) of size #10 hand files were used to achieve the initial patency of the canal to full working length (WL), visible at the apical foramen, and the WL was established at this length. The canals were randomly divided into 3 groups (n=10) : Group 1 - Protaper Gold (PTG); Group 2 - ProFit S3 (PS3); Group 3 - Hyflex CM (HCM). Instrumentation was done using the file systems of the respective groups up to file size #25/0.06. Postoperative assessment of the apical foramen dimensions was done using the stereomicroscope (A1).

Apical foraminal deformation produced by instrumentation was calculated for each canal using the formula:

Apical deformation = A1-A0

According to this formula, a result of ‘0’ indicates no apical deformation. The data were evaluated statistically using SPSS software (Version 23.0) by one-way analysis of variance (ANOVA) followed by the post hoc Tukey test to explore apical foraminal deformation in each group. The level of significance was set at 0.05.

Results And Discussion

Table 1 represents the mean preoperative as well as postoperative apical foramen areas for each group. The mean area of apical foramen, postoperatively, was 0.01804mm for Protaper Gold , 0.01046mm for Profit S3 and 0.01476mm for Hyflex CM systems. There was no significant difference between the preoperative AF areas. There was a significantly lower postoperative AF deformation after using Profit S3 compared to the Protaper Gold system. There was a significantly lower postoperative AF deformation after using Profit S3 compared to Hyflex CM system. Profit S3 system showed the least AF deformation compared to Protaper Gold and Hyflex CM systems.

Nickel-titanium rotary files have a number of advantages over the stainless steel hand files including good flexibility, improved fracture resistance, improved torsional and cyclic fatigue, increased speed of canal preparation, etc. Protaper Gold files were developed with advanced metallurgy and have a progressively tapered design that is claimed by the manufacturer to enhance cutting efficiency and safety. These files have a convex triangular crosssection and a progressive taper, hence the name ‘Protaper’. The manufacturer claims that this property helps in navigating challenging curves in the apical region of the canal while giving a proper shape to the canal. The file also has a feature of a shorter handle for improved accessibility to the teeth [32].

‘Hyflex CM’ is a NiTi rotary file system made using the novel “controlled memory” technology. Controlled memory wire (CM wire) is manufactured by a unique process that controls the material’s memory, making the files extremely flexible, but without the shape memory that is typical of other NiTi files. The file maintains the shape of the canal even after its removal. This prevents canal straightening and hence it is widely used in curved canals [33].

ProFit S3 (PS3) is a new endodontic file system introduced in the year 2019. It is a blue file manufactured using new heat-treated technology. This rotary system has a titanium oxide coating and hence the blue color. It has a variable taper design, which varies between 4% and 8%, with a rectangular cross-section. In crosssection, the file makes a two-point contact with the canal walls, thereby reducing the apical extrusion of debris. PS3 has good shape memory, flexibility, and increased resistance to fracture [34]. The cross-section of PTG files is convex triangular, PS3 is offset rectangular and Hyflex CM is double fluted. All the files have a non-cutting tip. The PS3 and PTG both have a variable taper and both are heat-treated file systems, the difference is that PTG has a sequence of instruments to be used and whereas PS3 is a single file system [34].

Apical enlargement and deformation post instrumentation may be clinically correlated with debris or irrigant extrusion and post operative pain experienced by the patient [35]. Hence foraminal enlargement must be kept to a minimum during instrumentation. In our study, PTG showed the highest apical deformation post instrumentation, followed by Hyflex CM and Profit S3. The higher apical deformation of the Protaper gold system may be due to its higher taper (8%) in the apical 3 mm. Also, Hyflex CM and Profit S3 have 2 point contact that reduces aggressiveness of file and hence apical foramen enlargement and deformation.

Our study was in agreement with previous studies that have proved that major apical foramen deformation is present when instrumentation is done upto the apex or beyond the apex [36-38] A previous study done by Frota et al in 2017 assessed the apical foramen deformation that occurred during root canal preparation with different reciprocation systems: Reciproc, WaveOne (MWire), and ProDesign R (Shape Memory Technology Wire) at two different working lengths (WLs): 0.0 and 1.0 mm beyond the AF. they concluded that AF deformation was dependent on the alloy as well as the taper; and PDR showed the lowest AF deformation values at both WLs [39].

Another study by Silva Santos et al in 2018 compared the foraminal deformation caused by rotary and reciprocating motions using scanning electron microscope. They concluded that the kinematics did not play a role in the apical foramen deformation as both the motions caused similar deformation [36].

Gustavo et al concluded that manual stainless steel and mechanical NiTi patency manuverers produced similar apical foramen deformation [40].

The results of the present study suggest that instrumentation at the apex promoted major apical foramen deformation in all three systems. The alloy, taper, and cross-section of the file may play an important role in the degree of deformation produced. However, findings of an in vitro study should be carefully evaluated before being clinically considered. Further studies evaluating the influence of foraminal enlargement on cleaning efficacy and root canal filling ability are suggested. Moreover, clinical studies are paramount to assess outcomes of treatments performed with instrumentation at or beyond the apex.

Our institution is passionate about high quality evidence based research and has excelled in various fields [21, 41-50].

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Figure 1:

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Figure 1: Demonstrating mandibular molar teeth used for the study.

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Figure 2:

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Figure 2. Representing a bar graph representing the mean apical area of deformity of the different groups pre and post instrumentation. Statistically significant difference observed between PTG and PS3 as well as PS3 and HCM groups (p<0.05).

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Figure 3:

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Figure 3: Showing the pre and post instrumentation stereomicroscopic images of the apical foramen.

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Table 1:

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Table 1. Representing the mean and standard deviation of the preoperative and postoperative apical foramen areas.

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Table 2:

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Table 2: Showing the inter-group comparisons of apical deformation. Statistically significant difference observed between PTG and PS3 as well as PS3 and HCM groups (p<0.05) by ANOVA and posthoc Tukey tests.

Conclusion

Within the limitations of this study, it can be concluded that the Profit S3 system showed the least apical foramen deformation compared to the Protaper Gold and Hyflex CM systems. The alloy, taper, and cross-section of the file may play an important role in the degree of deformation produced. Further in vitro as well as clinical studies are recommended to assess the debris extrusion, micro-crack formation, cleaning efficacy and root canal filling ability as well as post-operative pain caused after instrumentation with these systems.

Acknowledgement And Declarations

The authors would like to acknowledge the institution and all the staff members of the Department of Conservative Dentistry and Endodontics for their support towards completion of this research. The authors deny any conflicts of interest associated with this paper.