Comparison of Shaping Ability between Continuous Rotary and Comparison of Shaping Ability between Continuous Rotary and Manual Instrumentations in Pediatric Endodontics Manual Instrumentations in Pediatric Endodontics

Objective: The aim of this in vitro study was to evaluate the efficacy of rotary EndoArt Ni-Ti Gold Pedo Kit and K-files in shaping ability, canal transportation, centering ability and instrumentation time in primary molars. Methods: For the study total of 30 extracted primary molars root with minimum 7mm root length were selected. Shaping of root canals in primary molars were done using the two systems, and CBCT and specialized software were used for scanning and analysis of pre-operative and post-operative to evaluate the groups for their shaping properties, apical transportation and preparation time in primary root canals. Results: No differences were found in canal transportation measures and instrumentation time between the two groups (p>0.05). The EndoArt group removed more dentin compared to K-file in all sides of the root curvature. The statistical differences were significant for coronal and middle third of the root (p<0.05). Conclusions: Under the conditions of this study, rotary EndoArt Ni-Ti Gold Pedo Kit provided more conical canals than K-files in primary teeth.


INTRODUCTION
One of the most important objective in pediatric dentistry is to keep the tooth present in the dental arch until its physiological exfoliation. Early extraction of primary teeth leads to space loss, functional, aesthetical and psychological problems so, pulpectomy of primary teeth with irreversible pulpitis or necrosis should be considered as a treatment of choice. 1 The success of endodontic treatments depends on cleaning of debrise, shaping the root canals for providing a path for irrigants and suitable obturation materials, retaining the unity of radicular anatomy. 2 However, anatomic complexities of primary teeth such as accessory canals, anastomoses, thin and curved roots, close proximity to the succedaneous tooth germ and alterable resorbed root apex preclude the possibility of complete removal of all radicular pulp and can lead to undesirable complications. Additionally, difficulties in behavioural management of child patients making pediatric endodontics more challenging and increase the importance of time spent on treatment. 3,4 The hand files are commonly used for pulpectomy in primary teeth but manual preparation techniques have some limitations regarding time consumption and iatrogenic errors. 5,6 Due to limitations of hand files, rotary systems were introduced to pediatric endodontics. 7 Rotary systems for pulpectomy of primary teeth was affordable, fast, provide uniform shaping and filling and preserve the original anatomy of root canals. 6 However in a systematic review, it was found that the clinical and radiographic success rates of rotary systems and manual instrumentation were equivalent in primary teeth. 8 Also, it is reported that this systems leave unclean areas due to centred in root canals throughout rotation. 9 The vast majority of rotary systems are designed according to permanent tooth anatomy, therefore it is difficult to use for pediatric patients with limited mouth opening and it causes challenges in shaping root canals of primary tooth. So, special pediatric rotary file systems with modified taper, length, and tip size have been developed. 10,11 One of the new developed pediatric rotary system is EndoArt Ni-Ti Gold Pedo Kit (Incidental, Istanbul, Turkey) which was designed with modified length and taper introduced for pulpectomy of primary teeth. EndoArt Ni-Ti Gold Pedo Kit heat-treated NiTi rotary instrument system is made of a controlled memory wire. According to the manufacturer, this system has convex triangle cross-section design. This system contains three NiTi rotary files with a total length of 18mm. 12 There are no studies in the accessible literature evaluating the newly released EndoArt Ni-Ti Pedo Kit rotary file system. The aim of the present study was to compare the shaping ability and instrumentation time between stainless steel K-files and EndoArt Ni-Ti Gold rotary system in primary teeth.

METHODS
Ethics committee permissions were approved by the Local Ethics Committee (No: 2011-KAEK-2-2020/8). A total of 30 human primary molar teeth (15 maxillary, 15 mandibular) extracted either due to orthodontic treatment or those that have been over retained beyond the age of exfoliation. Teeth which have undergone pulpectomy, teeth with internal or extensive pathological root resorption were excluded from the study. Primary mandibular molar distal roots and maxillary molar palatal roots were preferred due to their generally large, curved, single canal. The roots were separeted for standardization with root length of 7 mm for the study. 13 The teeth selected for the inclusion into the study were stored in sterile water until the experimental time.
The #15 K-file (VDW GmbH, Munich, Germany) was advanced within the canal until the tip was seen through the major apical foramen and the working length was determined 1 mm shorter than this length. Roots were randomly distributed to one of two groups of 15 roots (8 distal roots of the mandibular teeth, 7 palatal roots of the maxillary teeth) each. All instrumentation procedures were performed by single operator. Each instrument was used in four canals, simulating a molar with four canals. A total of 10ml 2.5% NaOCl and 10ml distilled water were used for irrigation with a 30-G NaviTip needle (Ultradent Products Inc., South Jordan, UT, USA) between the use of each instrument in both groups.
The roots were mounted on a custom-made holder in which silicone boxes could be placed in the same position before and after instrumentation. For standardization, the roots were scanned at 13 mA, 90 kVp, 12 seconds and 6×8cm field of view with cone beam computed tomography (CBCT, GXDP-700, Gendex Dental Systems, Hatfield, USA). Invivo5 Anatomy Imaging Software (Anatomage, USA) was used for the measurements of root canal taper at the cervical, middle and apical third of the root. 13 The transportation was measured at 1 mm levels from the apical end of the root before and after instrumentation ( Figure 1). Mesiodistal transportation, buccolingual transportation were calculated with these formulas.
According to these formulas, 0 means no canal transportation 14

Measurement of instrumentation time
A digital chronometer was used for the measurement of inst r u ment ation time. T he time of active instrumentation, instrument changes within the sequence protocol and irrigation were include to the total instrumentation time.

Statistical analysis
The statistical analysis of the data were done with IBM. SPSS statistics software package program (SPSS Inc., Chicago, Illinois, USA, Version 23.0). The Levene and Shapiro-Wilk tests were used for the determination of the homogenity of variance and normality. To find the significant difference between the groups, the unpaired t-test was used. For descriptive statistics, mean and standard deviation were used. Statistical significance was set at p<0.05.

RESULTS
The sample comprised 30 root canals of primary teeth (15 in each group). The canal transportation in the apical third results were shown in Table 1. No differences between the two groups were found (p> 0.05).
The mean instr umentation time obser ved for instrumentation with rotary EndoArt files is 4.868 min with a standard deviation of 1.157. The mean instrumentation time observed for instrumentation with K-file is 4.430 min with a standard deviation of 1.112. The mean instrumentation time between the two groups were not statistically significant (p>0.05). Table 2 shows the mean dentin removal after instrumentation. The EndoArt rotary file provided more conical canal taper compared with the K-file.
The EndoArt group removed more dentin compared to K-file in all sides of the root curvature. The statistical differences were significant for coronal and middle third of the root (p<0.05).

DISCUSSION
It is crucial to evaluate the effect of different instruments on root canal geometry in different roots for endodontic treatment in primary teeth. Therefore, the objective of this study was to evaluate pulpectomy of primary molar root canals with K type hand-files and EndoArt rotary files using CBCT analysis.
In accordance with the anatomical structure of the primary tooth and pediatric patients cooperation, special file systems for primary teeth are released to overcome the disadvantage of the existing rotary files, one of which was EndoArt Ni-Ti Pedo Kit. It has convex triangle cross-section design and consists of three NiTi rotary files with a total length of 18mm. In the accessible literature, no study has evaluated the comparison of shaping ability of EndoArt Ni-Ti Gold Pedo Kit and K-files. So, in this study canal transportation, centric ratio, mean dentin removal and instrumentation time were evaluated.
Various methods such as histological examination, serial sectioning, scanning electron microscope, radiographic comparisons, silicon modeling of instrumented teeth, microcomputer tomography have been used to evaluate the shaping capabilities of root canal file systems. In addition, CBCT is one of the methods used today to evaluate the shaping capabilities in examinations which ensured eloborate three-dimensional observation. 13 The most important advantage of this method is   that the tooth does not need to be cut before and after the procedure. 16,17 Additionally, CBCT provides images in both orthogonal and oblique planes so it is advantageous in terms of measuring centering ratio, apical transportation and dentin thickness. 18 In the present study, extracted primary molars used because of natural dentin provide more reliability of results compared with artificial resin canals. In addition, for simulating clinical situations minimum 7mm of root length were selected where at least twothirds of root length is considered to be necessary. Canal transportation is the iatrogenic change in the physiological pathway of the root canal and it occurs mainly because of the rigidity of endodontic files. 15 Physiological or pathological resorption in the apical and furcation areas, anastomoses, secondary canals and various anatomical variations of primary teeth increase the importance of canal transportation. 19 So, minimal canal transportation is required during endodontic treatment of primary teeth. The occurrence of up to 0.15mm of canal transportation has been considered to be acceptable. 20 In this study, there was no significant difference between the apical transportation values of EndoArt rotary and K files and value of canal transportation were seen in apical region was lower than 0.15mm. This result was consistent with the findings of a study that concluded that NiTi rotary files could be more effective in preparing canals with narrow apical diameters. 21 There is no definitive idea in the literature about the amount of dentin removal to provide the best disinfection of the root canal but, it is emphasized that the excessive dentin removal can increase the risk of perforations. [22][23][24][25] In this study, EndoArt rotary files removed more dentin compared to K-files in coronal and middle third of the root canals. This results was similar with the previous studies which reported greater dentin removal using a rotary files in primary teeth. 24,26 On the other side, some studies found that dentin removal was greater when using conventional hand files. 22,23,25 Barr et al. reported that the use of rotary files for root canal shaping has advantages such as more effective and faster removal of tissue and debris, easier access to canals, and conical shaped canals that allow a more effective canal filling. 7 In addition, EndoArt can effectively produce a well tapered root canal form than conventional K file.
In pediatric dentistry, the length of the treatment had an essential influence on the child patient's anxiety, so the instrumentation time during canal preparation is the topic of many studies. 11,[27][28][29] Most studies indicated shorter instrumentation time with rotary files compared with conventional hand files. 13,[28][29][30] But in the present study, the instrumentation time was found similar for the K file and EndoArt rotary file. The result may be related with the operator's experience and the tooth used in the previous studies being a primary or permanent tooth. 31,32 In authors' opinion, although the number of files is the same, the time spent in file change in the rotary file system is also a factor to be considered. The limitation of the study was the criteria of tooth selection. Among the primary tooth extraction indications, there are teeth that are too damaged for conservative or endodontic treatment, teeth with more than 1/3 radiolucency in their bifurcation and mobile teeth with extensive root resorption. It is difficult to find non-resorbed roots of extracted primary tooth so in previous in-vitro studies, different primary teeth were used. Especially, primary molar teeth were chosen. In present study, standardization has been tried to be achieved with the same root length, number of canals and curvature similar with the previous literature. 21,33,34 In future studies, resin teeth which are producted using three-dimensial technology can be chosen for the standardization but, the real canals of human primary teeth were selected for current study because of the similarity in canal cross-section, the dentin hardness and its surface texture to clinical condition.
Within the limitations of our study, according to the authors of this study, the use of EndoArt systems in primary teeth provides the shape of the root canal is more conical. As a result of the conical root canal, better quality root canal fillings can increase clinical success