Journal of Indian Society of Pedodontics and Preventive Dentistry
Journal of Indian Society of Pedodontics and Preventive Dentistry
                                                   Official journal of the Indian Society of Pedodontics and Preventive Dentistry                           
Year : 2019  |  Volume : 37  |  Issue : 1  |  Page : 80--86

Comparative assessment of dentin removal following hand and rotary instrumentation in primary molars using cone-beam computed tomography


Prasad K Musale, Krutika R Jain, Sneha S Kothare 
 Department of Pedodontics and Preventive Dentistry, MA Rangoonwala College of Dental Sciences and Research Centre, Pune, Maharashtra, India

Correspondence Address:
Prof. Prasad K Musale
Department of Pedodontics and Preventive Dentistry, MA Rangoonwala College of Dental Sciences and Research Centre, Azam Campus, Hidaytullah Road, Camp, Pune - 411 001, Maharashtra
India

Abstract

Objective: Pediatric endodontics has witnessed many advances in recent years, thus facilitating a faster and efficient treatment option in root canal therapy in children. This in vitro evaluation aims to determine the amount of dentin removal in primary mandibular first and second molars instrumented with hand and rotary files using cone-beam computed tomography (CBCT). Materials and Method: Sixty primary mandibular molars were divided into two groups: Group I was prepared by manual instrumentation using K-type files and Group II was prepared with rotary instrumentation using 0.04 Hero Shaper Classics. Both these groups were further divided into two subgroups, namely (a) primary mandibular first molar and (b) primary mandibular second molar. All the root canals were prepared up to size 30 using the stepback technique. They were mounted on silicone-based impression material and subjected to CBCT scans for the evaluation of dentin removal before and after instrumentation. Dentin removal was calculated by superimposing images using the InVivo 5.1 Anatomage software. Data were statistically analyzed using independent samples t- test. Results: An average amount of dentin removed was found to be significantly higher in manual instrumentation compared to rotary instrumentation in both primary mandibular first and second molars (P < 0.001). Conclusions: Rotary technique serves as an efficient alternative to the traditional manual instrumentation by overcoming its shortcomings in terms of conservation of the remaining dentin thickness and the time required for its preparation.



How to cite this article:
Musale PK, Jain KR, Kothare SS. Comparative assessment of dentin removal following hand and rotary instrumentation in primary molars using cone-beam computed tomography.J Indian Soc Pedod Prev Dent 2019;37:80-86


How to cite this URL:
Musale PK, Jain KR, Kothare SS. Comparative assessment of dentin removal following hand and rotary instrumentation in primary molars using cone-beam computed tomography. J Indian Soc Pedod Prev Dent [serial online] 2019 [cited 2021 Oct 27 ];37:80-86
Available from: https://www.jisppd.com/text.asp?2019/37/1/80/252852


Full Text



 Introduction



Primary molars scheduled for total pulpectomy is a unique challenge to dental practitioners because of the tortuous and bizarre morphology of their root canal systems, as well as difficulty in patient management and isolation.[1] Cross sections at various levels for the primary molars exhibit thin ovoid canals, with mesial root canals wider buccolingually as compared to the distal canals.[2] When working on primary molars, it is generally recommended to maintain the original anatomic shape of the root canal, to preserve the maximum dentin thickness, and at the same time to effectively enlarge the root canal so as to remove its organic and inorganic contents.[3] The thickness of the remaining dentine following intraradicular procedures may be the most important iatrogenic factor that correlates to the fracture resistance of the root.[4]

Hand instruments such as K-files, reamers, and H-files were traditionally used to prepare the body of the canal. Because most of the hand preparation techniques are time consuming and have shown to cause iatrogenic errors (i.e., ledging, zipping, canal transportation, and apical blockage), much attention has been directed toward root canal preparation techniques with nickel-titanium (Ni-Ti) rotary instruments.[5] Instrumentation with motorized devices using rotary Ni-Ti instruments with various tapers has led to promising results, i.e., less straightening or decentralization of the canal and a rounder canal preparation even in severely curved root canals.[6],[7],[8] Ni-Ti rotary files with 4% taper instruments can provide more funnel-shaped canal desired for the ideal compaction of obturating material.[9]

As an alternative to manual instrumentation, rotary biomechanical preparation of primary teeth was first described by Barr et al.[10] using the Profile 0.04 taper rotary instruments, and they concluded it to be a cost-effective and efficient technique resulting in consistently uniform and predictable obturation. Considering that rotary files are more convenient to use and can facilitate quicker pulpal treatment, their application may be more appropriate in children with behavioral management problems.

Several methodologies have been described to evaluate these instrumentation parameters, including serial sectioning, radiographs, microscopic analyses, silicone impressions, muffle system, endodontic cube, multislice computed tomography, and cone-beam computed tomography (CBCT).[11]

CBCT has been proven to show the exact location and anatomy of the root canal system and is sanctioned as a tool to explore root canal anatomy. It has been successfully used for measurements before and after instrumentation of root canals and for determining the amount of dentin removed during cleaning and shaping of root canals.[12],[13]

The available literature on root canal preparation in primary teeth does not quantify the amount of dentin removal from the root canal walls by manual and rotary techniques and ascertain its consequences. Therefore, this in vitro study aims to evaluate the action of manual and rotary endodontic instruments on root canal walls of primary teeth, focusing on dentin removal in the primary mandibular first and second molar teeth using CBCT.

 Materials and Methods



The present study was conducted in the Department of Pedodontics and Preventive Dentistry of M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, India. It was approved by the Ethical Committee of Maharashtra Cosmopolitan Education Society, Pune, India in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

Criteria for tooth selection and storage

Human primary mandibular first and second molars were collected from rural public health centers run by the Government of Maharashtra, India, where pulpectomies are not performed and extraction is the only treatment of choice. Other teeth were extracted due to questionable prognosis, for orthodontic treatment, or overretention beyond the age of exfoliation.

Collection, storage, sterilization, and handling of the extracted teeth followed the Occupational Safety and Health Administration guidelines and regulations.[14]

All teeth were selected after macroscopic examination with the help of magnifying glasses and artificial light, according to certain predetermined criteria which included mandibular molar teeth with a minimum of 7-mm root length measured from cementoenamel junction (CEJ) without any evidence of external/internal resorption and having minimum curvature with angulation <30°. Canal curvature standardization with angles (10°–20°) and radii (8 mm) were determined with preoperative CBCT images.[15]

Teeth with <7-mm root length, extreme root canal curvatures, calcified canals, or bifurcated/trifurcated root evident on preoperative buccolingual and mediodistal radiographs were excluded from the study.

The selected teeth were washed under running water and stored in 0.5% sodium hypochlorite solution for a week.

Sample size calculation and distribution

A sample size of 60 was derived using power calculation considering the previously published studies which yielded 80.0% power ([Type II error = 0.20] and 5% Type I error probability [α = 0.05]) in detecting the true statistically significant difference between manual and rotary instrumentation for each tooth across the four study groups. These selected teeth were serially numbered and allocated to the four study groups of 15 teeth each the online randomization software used was www.randomiser.org.

Mounting of teeth

The teeth were mounted on four circular putty indices made up of silicone-based high-viscosity impression material (Speedex putty impression material, Coltene/Whaledent AG, Switzerland), with thirty teeth in each block, in such a way that standardization of the specimens for the tomography images before and after root canal instrumentation was maintained. The roots were not separated, and the coronal portion was kept to simulate the position of the instruments inside the root canal.[16]

Imaging

Each putty index was then submitted to CBCT examination (i-CAT equipment; Imaging Science International, Hatfield, PA, USA), using the image protocol for the teeth, with the following exposure parameters: voxel size: 0.125 mm, beam diameter: 16 cm × 4 cm, and scan time: 26.9 s.

Preparation of teeth

The biomechanical preparation of the selected teeth was carried out by a single calibrated operator following standardized technique under the guidance of a postgraduate teacher with a clinical experience of more than 15 years.

Endodontic access was obtained by taking a drop with a sterile, round diamond bur #6, and access was defined with a safe ended bur (SS White, NJ, USA).

The canals were located using a DG16 instrument (Hu-Friedy, IL, USA). After copious irrigation of the pulp chamber with 1% sodium hypochlorite (UPS Hygienes Pvt. Ltd., India), #10 K-file (MANI INC, Japan) was introduced into the root canal until just visible at the apical foramen. The final working length was set at 1 mm short of this initial length.

Group I (n = 30): The root canals were manually prepared with stainless steel (SS) 21-mm K-files (MANI INC, Japan) in a stepback manner through size #30 by quarter-turn-pull techniqueGroup II (n = 30): The root canals were instrumented with rotary 21-mm Hero Shaper 0.04 file (Micro-Mega, Besancon, France) as per the manufacturer's recommendation. The root canals were shaped in a stepback manner through size #30 Hero Shaper files with a gentle pecking motion. All rotary files were activated by an X-Smart IQ™ motor handpiece (Dentsply Maillefer, Ballaigues, Switzerland) at 250 rpm with constant low torque setting as per the manufacturer's instructions.

Root canals were irrigated with 1% sodium hypochlorite followed by normal saline after each file use. For each tooth, approximately 10 ml of sodium hypochlorite was used during the entire biomechanical preparation. The files were lubricated with ethylenediaminetetraacetic acid gel (RC-Prep, Premier Dental Products, USA) each time they were used for preparation. Each time after removal from the canal, the files were inspected for unwinding or distortion of flutes with a handheld illuminated magnifying glass under ×3 magnification. Such distorted files were discarded. The files without any deformation were discarded after six uses.[17] After complete preparation, the canals were cleaned and dried using paper points.

At any one time, only five teeth were instrumented by the primary investigator to overcome any bias in the preparation due to operator fatigue.[18]

All the teeth were scanned with CBCT; the remaining dentin thickness was measured postoperatively.

Evaluation of dentin removal

Following instrumentation, pre- and post-operative scans were superimposed using the InVivo 5.1 Anatomage software (Anatomage, CA, USA), and the amount of dentin removed was measured at three standardized reference points (1 mm/apical site, 4.5 mm/middle site, and 8 mm/coronal site) and at four locations, namely mesial, distal, buccal, and lingual.[19] Canal center was determined using voxel measurement. After superimposing pre- and post-instrumentation images, distances from the internal aspect of the canal to the external aspect of the root were measured. The assessment of the CBCT scans was performed by a previously calibrated examiner (blinded).

Statistical analysis

The entire data were analyzed statistically using the Statistical Package for the Social Sciences (SPSS) version 11.5 (SPSS Inc., Chicago, IL, USA) for MS Windows. P < 0.05 was considered statistically significant. The statistical significance of the amount of dentin removed between manual and rotary instrumentation was tested using independent samples t- test after confirming the underlying normality assumption.

 Results



Distribution of actual dentin thickness and remaining dentin thickness and the amount of dentin removed from all the teeth by manual and rotary instrumentation are summarized in [Table 1].{Table 1}

The manual versus rotary statistical comparison of the amount of dentin removed showed that the average amount of dentin removed was significantly higher in manual instrumentation compared to rotary instrumentation for primary mandibular first and second molars at all sites and all locations combined (P < 0.001) [Table 2].{Table 2}

Furthermore, the average amount of dentin removed was found to be significantly higher in manual instrumentation compared to rotary instrumentation for all canals, at coronal [Table 3], middle [Table 4], and apical sites [Table 5] and at all locations combined, for primary mandibular first and second molars (P < 0.001).{Table 3}{Table 4}{Table 5}

The percentage change after dentin removal for the primary mandibular first molar and primary mandibular second molar was observed to be 37.54% and 38.06% with manual and 20.88% and 20.76% with rotary instrumentation, respectively [Table 6].{Table 6}

 Discussion



Current advances in pulpectomy procedures indicate a paradigm shift in root canal treatment for primary teeth. The uses of rotary Ni-Ti files are at the forefront of advances in the endodontics of primary teeth.[1] Biomechanical preparation of the root canal system in primary teeth has evolved from the times of Groter,[19] advocating no instrumentation to the introduction of rotary instruments by Barr et al. in 1999.[10]

The Ni-Ti files have two to three times the elastic flexibility of SS files. The superior resistance of Ni-Ti files to torsional fracture and their inherent ductility make these instruments more practical in the preparation of curved root canals.[20] Studies showed that the Ni-Ti instruments have exerted less force on the canal wall during preparation, as compared to their SS counterparts.[21] This feature allows Ni-Ti instruments to negotiate fine curved root canals while maintaining the original path.[22]

The amount of dentin removal indicates the aggressiveness of the instrument. In the present study, there was a statistically significant difference (P = 0.001) in the amount of dentin removal at all sites in all canals [Table 2]. This is similar to the findings of Zameer.[9] Lateral forces result in high stress concentrations in radicular dentine at the coronal one-third of the root. Most of the applied force is concentrated around the circumference of the tooth where the crown diameter is the smallest, corresponding to the cervical region of the tooth at the CEJ. There is a direct correlation between the root thickness and the fracture resistance of the tooth.[23] Lim and Stock have suggested that the minimum thickness of canal walls that should remain after canal preparation should be 0.3 mm, which allows adequate resistance against lateral and occlusal forces.[24]

In general, preparation of narrow curved canals by SS files is time consuming, difficult, and requires the limitation of apical enlargement to relatively small sizes, thus reducing the efficacy of irrigation and hindering obturation.[25] This is of utmost importance while dealing with the anatomical complexities of the deciduous teeth. The use of greater tapers should allow more apical deposition of the irrigant, facilitating a thorough removal of pulp tissue, necrotic debris, bacteria, and dentin filings by the combined cleaning effect of physical instrumentation and chemical irrigation.[26],[27],[28] Because SS is relatively inflexible, this feature has been shown to contribute to the development of furcal thinning, a critical limitation in the attempt to create deep radicular shape.[29]

In the current study, maximum dentin removal by manual instrumentation was observed in distobuccal canals of primary mandibular first molar. This may be explained by the tendency of the operator to perform more intensive instrumentation at the side opposite to the most favorable support. Maximum dentin removal by rotary instrumentation was observed in the distolingual canal of primary mandibular first molar (mean 0.20 mm). This could be owing to the resorption pattern of primary molars, which takes places lingually. Hence, we advise a cautious use of rotary instrumentation for all the mesiolingual and distolingual canals in these teeth. Despite the claim that Ni-Ti files have a sharper cutting edge because of their triangular cross section, they did not remove a significantly greater amount of dentine from the root canal than SS instruments.[30]

In a study by Kummer et al.,[16] manual instrumentation technique produced more dentin removal at the coronal and middle thirds of all roots in all groups of teeth compared with rotary instrumentation, which is in agreement with the results of this study. Canoglu et al.[18] in their study concluded that preparation with Profile 0.04 ISO Ni-Ti instruments could be a viable alternative to manual instrumentation in primary teeth due to their better centering ability and lesser incidence of canal transportation as compared to SS hand files. They also compared the amount of dentin removal from the inner and outer curvatures of the canal walls and found no significant difference between the two techniques.

Currently, the application of three-dimensional (3D) assessment was added in the list of evaluation methodology, such as CBCT.[31] 3D visualization of specimen is made possible through the noninvasive scanning process without any damage to the specimen; hence, the specimen could be preserved for further analysis. All the shortcomings of two-dimensional radiography and any sectioning techniques were solved. Previous research studies by Musale and Mujawar[17] and Selvakumar et al.[32] have successfully used CBCT for measurements before and after instrumentation after cleaning and shaping of the root canals and have proved it to be a nondestructive, reproducible tool for root canal assessment.

The effective CBCT slices used in this study provided a practical and nondestructive technique for the assessment of canal morphology before and after shaping. All the parameters were evaluated at three levels from the apex to the CEJ of the canal at equal intervals [Figure 1], [Figure 2], [Figure 3]. The results show that CBCT scanning is an accurate and efficient method of the assessment of root canal instrumentation techniques. Along with the mesiodistal direction, the buccolingual direction has also been assessed which cannot be verified using other radiographic techniques.{Figure 1}{Figure 2}{Figure 3}

Limitations of the study

Limitations of this study include that only mandibular molars were considered for the study; hence, further studies considering the maxillary molars and anteriors must be carried out with a bigger sample size. This being an in vitro study, the results must be interpreted with caution when using clinically.

 Conclusions



Within the experimental conditions of the present study, the following conclusions can be drawn:

The average amount of the remaining dentin thickness is significantly higher after rotary instrumentation as compared to manual instrumentation for all canals at coronal, middle, and apical sites and at all locations for primary mandibular first and second molarsThe average amount of dentin removed is significantly higher after manual instrumentation as compared to rotary instrumentation for all canals at coronal, middle, and apical sites and at all locations for primary mandibular first and second molars.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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