Comparative assessment of efficacy of automated micromotor and endomotor in biomechanical preparation of primary and permanent teeth: an in vitro pilot study

Introduction

Pulpectomy is essential procedure, extending the life duration of pulpally involved primary teeth. Long-term success of this endodontic procedure depends on complete debridement of infection from complex root canal system, and thorough cleaning and shaping, obtaining fluid-tight apical and coronal seal after obturation. Schilder [1] emphasized and coined an axiom, “Whatever comes out is equally important as what is placed in”. He specified that the preparation of canals must not only depend on the anatomy of canal, but should also be according to technique and material of obturation to achieve, “Concept of flow that allows appropriate removal as well as filling of root canal space” [2].
Taper refers to the gradual and controlled reduction in the length of root canal from the coronal to apical portion, typically achieved during canal preparation [3]. Taper is an important factor in determining the final length of root canal, successively providing space for the cleansing action of irrigant. Biomechanical preparation increases apical dimension and taper of root canal. Tapered canal has advantages, such as enhanced cleaning ability, improved instruments apical control, and more reliable apical resistance form (apical seal) appropriate for all filling techniques [4]. Root canal can be prepared by various types of instrumentations, including manual instrumentation, automated, sonic, and ultrasonic preparations as well as preparation with laser systems [2].
In the eighteenth century, only conventional hand instruments were used for endodontic treatment. Later, in 1915, with the introduction of K-files, manual hand filling became the conventional method for endodontic procedures. These traditional root canal preparation techniques with hand instruments have multiple steps, which highly depends on clinician’s skills and are often very complex procedures. As the trend continues, efforts have been made to introduce automated systems to decrease the time and efforts involved in preparation of root canals [2].
Automated root canal preparation can be done using 2 types of systems, such as endomotor and micromotor, with the speed of automated instruments varying from 150 rpm to 40,000 rpm [5]. K-files can be employed in manual preparation as well as in automated preparation through micromotor handpieces. A rotary file prepares canal with a 0.04% or 0.06% taper, whereas a K-file prepares canal with a 0.02% taper [6].
Rotary files demonstrate significant advantages over hand files in terms of bacterial reduction, working time decrease, obturation quality, and postoperative pain. There is abundant literature on comparison of biomechanical preparation of manual and rotary filing, but no relevant literature is found comparing biomechanical preparation using two different automated techniques.

Objectives

The study aimed to compare and evaluate the biomechanical preparation of two automated systems, i.e., micromotor and endomotor, in deciduous and permanent molars.

Material and methods

Study design and methodology

This in vitro pilot study was performed in the Department of Pediatric and Preventive Dentistry, Mahatma Gandhi Dental College and Hospital, MGUMST, Jaipur, India. Prior to the study, ethical clearance was obtained from the Institutional Ethical Committee (approval number: MGDCH/Dental/2022/121).
Primary molars extracted due to poor prognosis or over-retained teeth, and permanent molars extracted for orthodontic treatment or teeth with poor prognosis, were considered as samples. These extracted molars were stored immediately in 10% formalin solution at room temperature for 1 week before the study. Deciduous molars with at least 2/3rd or 8 mm of root length, with intact root showing normal morphology, and permanent molars with complete roots and fully formed apices were included [8]. Samples were divided into 15 primary and 15 permanent teeth. Thirty extracted molars were distributed into three groups as provided below:
• group A (n = 10, control-manual) – biomechanical preparation by manual filing:
• group A1 (n = 5): primary molar teeth prepared with manual filing,
• group A2 (n = 5): permanent molar teeth prepared with manual filing;
• group B (n = 10, micromotor handpiece) – biomechanical preparation by K-400 micromotor handpiece:
• group B1 (n = 5): primary molar teeth prepared with K-400 micromotor handpiece,
• group B2 (n = 5): permanent molar teeth prepared with K-400 micromotor handpiece;
• group C (n = 10, endomotor) – biomechanical preparation using endomotor:
• group C1 (n = 5): primary molar teeth prepared with endomotor,
• group C2 (n = 5): permanent molar teeth prepared with endomotor.
For each extracted molars, access opening was done using a round bur (large) #12 (Diaburs, Prime Dental Products, Mumbai, India). On approaching the pulp chamber, the roof of pulp chamber was removed for access into the root canals. The covering dentin was removed with round-nose, tapered, diamond bur #EX-24 (Diaburs, Prime Dental Products, Mumbai, India) to accomplish a straight-line access into the canals. Copious irrigation was performed with normal saline to remove the debris. A size 10 K-file was then used for each root canal to check the canals patency. Radiograph method was employed for working length determination with a #10 K-file inserted into the canal up to 0.5 mm short of radiographic apex.
Biomechanical preparation was performed in all the 3 groups as follows.
Group A1 and A2 (control-manual): instrumentation was done manually using K-files (Mani, Japan). A K-file was sequentially (20/.02, 25/.02, 30/.02) inserted into the canal till working length and motion of filing used was pushed and pulled. Prep Canal (Ammdent, India) was applied as lubricant while filing with K-files. During filing, copious irrigation was completed with 2.5% NaOCl solution.
Group B1 and B2 (micromotor handpiece): instrumentation was performed using automated system K-400 micromotor handpiece (Bombay Dental, India). A K-file (Mani, Japan) was attached to the hand piece and inserted into the canal till working length. Subsequently, micromotor was run in clockwise rotation of the K-file in the canal. Prep Canal (Ammdent, India) was applied as lubricant while filing with K-files. During filing, copious irrigation was completed with 2.5% NaOCl solution.
Group C1 and C2 (endomotor): instrumentation was performed with automated system endomotor (Unicorn DenMark Ltd., India). The first glide path was created using K-file #10, #15, #20, #25. Then, a Pedo-Flex (Waldent, India) rotary file was attached to endomotor handpiece and inserted into canal of primary teeth (group C1) sample till working length. Subsequently, endomotor was run in clockwise rotation of file. Filing was carried out sequentially using #20/.04, 25/.04, 30/.04. NeoEndo Flex rotary file (NeoEndo) was attached to endomotor handpiece and inserted into canal of permanent teeth (group C2) sample till working length. Then, endomotor was run in clockwise rotation of file. Filing was carried out sequentially using #20/.04, 25/.04, 30/.04. Prep Canal (Ammdent) was used as lubricant, and while filing with both these rotary files, copious irrigation was completed with 2.5% NaOCl solution, followed by last irrigation with normal saline in all the six group samples. After biomechanical preparation, an internal 3-dimensional shape of all canals was assessed by intra-canal impressions made from polysiloxane impression material (GC Flexceed, India). First, lubricant spray was placed in the canal and let it dry, followed by placement of light-bodied vinyl polysiloxane material into the pulp chamber on which, the heavy body impression material was placed to enable the movement of light-bodied impression material into the space of the root canal. In addition, heavy-bodied impression material acted as a provision for the coronal portion of impression, and to facilitate removal.

Evaluation criteria

A set impression of prepared canal was evaluated within twenty four hours and assessed using digital ca­mera (Figures 1-3), according to criteria reported by Naga­ratna et al. [7] as follows:
• flow: good flow – when continuous flow of the material from the root canal orifice to stop at apex; poor flow – when abrupt change in direction and presence of ledges give rise to poor flow characteristics,
• taper: good taper – when canal has a conical shape throughout the length, poor taper – when canal has an hourglass/cylindrical shapes.

Statistical analysis

Data were combined, and statistical analysis was done using IBM SPSS Statistics for Window, version 21.0 (Armonk, NY: IBM Corp., US) at 95% CI and 80% power. Descriptive statistics were analyzed in terms of frequency and percentage. Fisher’s exact test with Freeman-Halton extension was employed for the analysis of flow and taper in deciduous and permanent teeth of group A, group B, and group C. P < 0.05 was consi­dered statistically significant.

Results

Comparing primary teeth in three groups, namely group A1 (manual), group B1 (micromotor), and group C1 (endomotor) for taper of prepared canal, the percentage of good taper observed in group C1 (100%) was the highest, followed by group B1 (80%) and group A1 (40%). No statistically significant difference was observed in taper among primary teeth in group A1, group B1, and group C1, respectively, with p > 0.05 (Table 1).
Comparing permanent teeth in three groups, namely group A2 (manual), group B2 (micromotor), and group C2 (endomotor, for taper of prepared canal, the percentage of good taper observed in group C2 (endomotor, 100%) was the highest, followed by group B2 (micromotor, 60%) and group A2 (manual, 40%). There was no significant statistical difference seen in taper among permanent teeth in group A1, B1, and C1, respectively, with p > 0.05 (Table 2).
Comparing three primary teeth groups, namely group A1 (manual), group B1 (micromotor), and group C1 (endomotor), the comparable flow was achieved in group B1 (100%) and C1 (100%). However, the least flow of material was assessed for group A1 (60%). There was no statistical significant difference when compared group B1 and C1, respectively (Table 3). Comparing three permanent teeth groups, namely group A2 (manual), group B2 (micromotor), and group C2 (endomotor), the comparable flow was achieved in group B2 (100%) and C2 (100%). However, the least flow of material was assessed for group A2 (40%). There was a statistically significant difference observed in flow in permanent teeth, with p < 0.05 (Table 4).

Discussion

The success of endodontic treatment is based on biomechanical and chemical cleaning and shaping of root canal. Bizarre hand complex root canal and physiological resorption of roots of deciduous teeth, present negotiation and, thorough instrumentation, a challenge for pulpectomy [9]. Detection of additional canals, curvatures of the canals, isthmus, lateral, and accessory canals play a significant role in the successful root canal treatment in permanent teeth [10]. The important objective in preparation of root canals of primary teeth is to prevent instrument penetration past the apical end, avoid damage to successor tooth bud, using resorbable obturating material, and to prevent extrusion of obturating material [11]. Objectives for biomechanical preparation of permanent teeth were described by Schilder [1] as follow: uninterruptedly tapered funnel from the apical end to access cavity, width should be narrower at every point from access cavity to apical end, preparation must follow the original shape of canal, apical foramen should persist in its original position, and the apical opening must be as small as practical [2]. These objectives can be accomplished by using biomechanical preparation. A preparation that provides continuously tapered canal will preserve the integrity along with apical preparation of the canal to achieve an adequate cleaning efficacy [4].
Practically, pulpectomy procedure for deciduous dentition should be fast and simple, with minimal number of appointments, providing effective debridement without weakening the structure of the tooth, or compromising the succedaneous teeth to restore and maintain function of the tooth [12]. The rotary instrumentation technique was found to be more effective for pulpectomy in deciduous molars, benefiting with reduced treatment time and better cleaning efficiency when compared with the conventional manual preparation technique. Automated preparation using rotary files and endomotor is currently in use, and has various advantages, such as quick and easy removal of tissue and debris, reduced time of instrumentation, and funnel-shaped prepared canals resulting in a more even fill of obturation material [13]. Limitations of rotary filing include increased cost of endomotor and rotary files, cyclic fatigue of endodontic instruments, and files being more prone to breakage [7]. Challenges faced through endomotor and rotary files can be solved with micromotor handpiece K-400 (Bombay Dental). Instead of using special rotary files, K-hand file is attached to this handpiece, which can be applied as micromotor or chair air motor. The ideal speed of a micromotor is 3,000 to 4,000 rpm, while K-400, an oscillating K-file handpiece, works at a speed of 300 to 400 rpm, and it is built with gear ratio of 10 : 1. This new automated instrument overcomes a disadvantage of more instrumentation time in manual filing, maintaining the 0.02% taper obtained through K-file [14].
Clean root canal is achieved by preparation of apical portion as small as possible while increasing taper of the root canal, which will allow greater deposition of irrigant and improved dentin removal from the walls of the canal [15]. In our study, when comparing the taper of canal after biomechanical preparation with micromotor handpiece having 0.2% taper K-file attached, and endomotor handpiece, to which 0.4% taper rotary files was attached, we found the highest percentage of good taper providing conical shape to the canal in endomotor-driven preparation, followed by micromotor-driven, with the least value achieved by manual preparation. These results were similar for both deciduous and permanent teeth, showing no significant difference between both automated systems. Boutsioukis et al. [16] in their study reported that an increase in taper improved irrigant replacement and wall shear stress while reducing the risk for extrusion of the irrigant. Albrecht et al. [17] noticed hand files resulting in more apical debris extrusion than ProTaper and Kedo-S files. In a study by Nagaratna et al. [7], better quality of taper was seen more significant using Profiles, while contradictory results were demonstrated by Thompson and Dummer [18], concluding that K-files demonstrated better taper qualities than Profiles in the prepared canals due to canal transportation in apical aspect with rotary files.
According to Schilder [1], biological objective of biomechanical preparation is to create sufficient space for intra-canal medicaments. Smooth preparation allows constant flow of obturating material from root canal orifice to apical end, whereas abrupt variation in direction and presence of ledge create hindrance to the flow. In our study on comparing the flow through prepared canal between two automated preparations, comparable flow was achieved in both micromotor-driven and endomotor-driven preparation in both deciduous and permanent teeth. These results were better when compared with manual preparation. Moudgalya et al. [19] conducted a study to compare the efficacy of rotary files and manual files, and concluded that rotary files showed a significant decrease in count of bacteria, reduced instrumentation time, better obturation quality, and reduced patient pain. Musale and Mujawar [20] evaluated the effectiveness of rotary and manual K-files in cleaning and shaping ability, instrumentation time, and distortion of the instrument in primary molars, and concluded that rotary files preparations were better in conical canals of primary teeth than using conventional manual instruments. Souza et al. [21] conducted a study to assess the cleaning ability and instrumentation time using pediatric rotary files, and compared them with other files; they concluded that rotary instrumentation showed better results in relation to root canal deviation and amount of dentin thickness, with reduced time of instrumentation. Shivang et al. [14] compared postoperative pain using automatic reciprocating files and continuous rotary instrumentation with laser irradiation, and concluded that both the systems resulted in lesser postoperative pain and more patient comfort. Dafalla et al. [22] found both Profile and K-file with unacceptable results for smoothness of the canal walls and flow of material, but K-files showed better canal tapering. According to Nagaratna et al. [7], Profile files resulted in better taper, smoothness, and flow compared with manual K-files. Babu and Kavyashree [23] in their study assessed time for instrumentation, time for obturation, quality of obturation, and clinical and radiolographic success of pulpectomy using rotary and manual file systems; they concluded that the rotary file systems took less time for instrumentation and obturation than the manual NiTi files.

Limitations

This study was an in vitro study, hence it is difficult to fully replicate clinical conditions. Also, the sample size was relatively small. To enhance the validity of the results, future studies should consider clinical setting and larger sample sizes.

Conclusions

Preparation of root canal is a significant aspect in the success of endodontic therapy. Although our study found a statistically significant difference only in the flow of impression material in permanent teeth, the results suggest that automated systems may provide more favorable taper and flow characteristics compared with manual root canal preparation. It prevents the overzealous preparation, and helps in better cleaning efficacy and flow in obturating material. It can be considered as an advantage in endodontic treatment of primary and permanent teeth. More studies with increased sample and clinical application are needed to validate our findings. Incorporating advanced imaging techniques, such as micro CT or digital scanning, can provide more objective and reproducible assessments of root canal preparation, especially in anatomically complex teeth, such as molars.

Clinical significance

Biomechanical preparation is the critical step in endo­dontic procedure. Quality of obturation and success of the treatment depends on thorough debridement as well as cleaning and shaping of canals. Endomotor is being used over manual preparation, and micromotor can also be added to endodontic armamentarium. Special micromotor handpiece has been designed, which can provide good quality preparation of canals in less time.

Disclosures

1. Institutional review board statement: Ethical clearance was obtained from the Institutional Ethical Committee of the Mahatma Gandhi Dental College and Hospital, MGUMST, Jaipur, India (approval number: MGDCH/Dental/2022/121).
2. Assistance with the article: None.
3. Financial support and sponsorship: None.
4. Conflicts of interest: None.

References