2.1

Ethical considerations

The research protocol was approved by the Institutional Ethics Committee. The guidelines provided by the World Medical Association’s Declaration of Helsinki on Ethical Principles for Medical Research was followed to conduct the research. Throughout the different stages of this research, we adhered to the CONSORT guidelines for planning and reporting clinical trials in Pediatric Endodontics ( Fig. 1 ). This research was derived from secondary data of a clinical trial that evaluated the clinical efficacy of pediatric rotary and hand files systems and has been published [ ].

CONSORT flow char followed during clinal trial.

2.2

Sample size calculation

The sample size was calculated using G Power analysis, considering previously published studies with 95% power [ , ]. The estimated sample size was 22, which was rounded off to 25.

2.3

Selection of study participants

This study was a treatment clinical trial, randomized controlled, parallel, and with four arms. The study population was composed of normal, healthy, and cooperative children aged between 4 and 7 years who sought endodontic treatment at our department. This age group of children were selected considering the lack of cooperation of younger children less than four years and the status of physiological root resorption in elder children [ ].

The objectives, the clinical procedures, treatment outcomes, risk and benefits (possible complications) of the procedure were explained to the parents or caretakers of the participating children. Their informed, written consent was obtained after clarifying all questions raised by them. Assent was obtained from the children aged more than 6 years.

Each participating child was given an identification number to maintain confidentiality, and their records were kept by the principal investigator alone. Intraoral examinations were performed and standardized intraoral periapical radiographs were taken for teeth with possible indications for pulpectomy. Primary molars with necrotic pulp, sinus tract, irreversible pulpitis symptoms, radiolucent areas in the furcation or periapical region, and at least two-thirds of each root remaining were included [ , ]. Primary molars with structures inadequate for restoration, perforated pulpal floor, swelling (intraoral or extraoral), internal or external pathological root resorption, and excessive mobility were excluded [ , ]. Additionally, children requiring special health care needs, with limited or lacking cooperative abilities, or requiring sedation/general anaesthesia for behaviour management and allergy to local anaesthetics and any other drugs were not included [ , ].

2.4

Randomization

The selected one hundred primary molars were randomly allocated to one of the 4 treatment groups (Group PF, KS, BG and HF) using block randomization technique of varying block sizes using computer generated sequence. It was provided by an independent researcher not involved in the study. The allocation was done using serial numbered concealed envelopes opened just after working length determination by a person other than the operator. Block randomization ensures equal chance of selection without any allocation bias and also the sample size remain equally distributed at any given point of time [ ].

2.5

Interventions

The injection site was dried with gauze and topical anaesthetic agent was applied with cotton. Following, local anaesthesia (2% lignocaine, Lignox, Bangalore, India) was administered to the indicated tooth. An inferior alveolar nerve block for mandibular teeth and infiltration for maxillary teeth was done. Dental caries and overhanging enamel were removed using a #330 high-speed bur under a water spray. A #8 round bur was used to access the coronal pulp, and the entire roof of the pulp chamber was removed. The pulp tissue was removed from the pulp chamber using a sterile sharp spoon excavator (2 mm, EXC31W, #41 Round, 31 W Endo Excavators, Hu-Friedy HFg. Co., LLC). Straight-line access was obtained and pulp tissue was extirpated from the root canal using H-files (Mani, Inc., Tochigi, Japan). The patency of the root canal was assessed using a #10 K-file (Mani, Inc., Tochigi, Japan), and the working length was determined by superimposing an endodontic instrument over the preoperative radiograph and keeping it 1–2 mm short of the radiographic apex [ ].

The randomization process determined the type of endodontic files for root canal instrumentation to be performed for each child and was performed by a blinded assistant for the study. All the root canal instrumentation was performed by a single trained operator. The cleaning and shaping of the root canals in the Group PF, KS, BG and HF were carried out with Pedo-Flex pediatric rotary files (Waldent Innovation Pvt Ltd), Kedo-SG pediatric rotary files (Reeganz Dental Care Pvt. Ltd., India), Pro AF Baby Gold pediatric rotary files (Kids-e-Dental, India) and hand NiTi K-files (Dentsply, Switzerland), respectively. In Group PF, KS and BG, the root canals were first instrumented up to the coronal one-third using a coronal-enlarging file (Endoflare-Micromega, Geneva, Switzerland), then enlarged to working length according to the sequence recommended by the manufacturer. The rotary file systems used for Groups PF, KS, and BG were operated with an endodontic motor (X-Smart, Dentsply Maillefer, OK, USA) at 300 rpm and 2.2-Ncm torque with a lateral brushing motion [ ]. To prevent unexpected lateral perforation, especially in severely curved root canals, each rotary file was not entered into the root canal more than twice [ ]. In Group HF, the root canals were instrumented using hand NiTi K files. The initial file was determined as the minimum-size file that provided resistance for intracanal placement until the working length was reached. The root canals were then enlarged up to three times the size of the initial file and cleaned and shaped using a pullback motion [ ]. A single pediatric dentist with adequate knowledge and experience of rotary and hand instrumentation techniques performed the pulpectomy under stringent aseptic conditions in a single visit.

The files in all the 4 groups were frequently inspected for flute unwinding or distortion. If observed, the files were discarded. Otherwise, in all four groups, each file was used on up to five teeth to maintain uniformity during root canal preparation [ ]. If a point of resistance was encountered, no attempt was made to go beyond it to lower the risk of instrument fracture [ ]. All root canals were prepared with intermittent irrigation using a standard 5-ml volume of normal saline. During root canal preparation, 17% Ethylenediaminetetraacetic acid gel (RC Help, Prime Dental Products, Pvt. Ltd.) was used to lubricate the root canal. After complete root canal preparation, final irrigation was carried out with saline and the root canals were dried with absorbent paper points.

In all the four groups, the root canals of the primary molars were obturated with zinc oxide eugenol cement (Zinc Oxide BP, Eugenol BP, Associated Dental Products Ltd.) using a Lentulospiral #25 mounted on a slow-speed handpiece. The selected Lentulospiral was cut to half its length with a pair of sharp scissors to facilitate handling [ ]. A homogenous mixture of zinc oxide eugenol was mixed in a powder: liquid ratio of 1:1 and carried into the root canal using a slow-speed handpiece rotating in a clockwise direction, which was then gently withdrawn from the root canal while still rotating. A rubber stopper was used to keep the Lentulospiral #25 1 mm short of the working length. This process was repeated five to seven times for each root canal until the canal orifice was filled with the paste [ ]. The pulp chamber was cleaned with a moist cotton pellet and then the access cavity was restored with type II glass ionomer cement (GC, India).

The pulpectomized teeth were restored with stainless steel crowns (3 M ESPE, St. Paul, MN, USA) within one week of pulpectomy. The crowns were placed in a second appointment because some younger children could not bear the long appointments and to standardized the procedures. As the final restoration of teeth that have undergone pulpectomy influences the outcome of endodontically treated teeth, stainless steel crowns were preferred. This is because they provide a hermetic seal that prevents microleakage and bacterial contamination of the root canals, which could lead to treatment failure [ ].

All participants were instructed to report any symptoms following the procedure, such as pain or swelling.

2.6

Evaluation of quality of obturation

After the procedure, immediate postoperative intraoral radiographs were taken using a dental X-ray unit operating at 60 kvp, 6 mA, 0.3 s, and 15 mm with exposure time of 200 ms for maxillary teeth and 120 ms for mandibular teeth. These radiographs were evaluated for the quality of obturation by two pediatric dentists who were blinded to the type of instrumentation used. A kappa test was performed for these examiners, producing scores of 0.88 and 0.95 for inter-examiner and intra-examiner agreement, respectively. The examiners graded each radiograph as underfilled, optimally filled, or overfilled [ , ]. In cases where there was disagreement between the examiners, a lower ranking was chosen.

2.7

Evaluation of outcome of pulpectomized teeth

Postoperatively the pulpectomized teeth were evaluated clinically and radiographically at three-month intervals over a period of two years. This frequent follow-up schedule was used to reduce participant dropout. Two independent blinded examiners, for the type of instruments, evaluated the outcome of the pulpectomized teeth. A kappa test was performed for these examiners, producing scores of 0.87 and 0.90 for inter-examiner and intra-examiner agreement, respectively. In cases where there was disagreement between the examiners, they jointly reviewed and discussed the radiographs in question until they reached an agreement. If the disagreement remained, the outcome was recorded as a failure. The pulpectomized teeth were judged clinically and radiographically successful/failure based on the modified criteria provided by Coll and Sadrian [ ]. A pulpectomy was considered clinically successful if there was no history of pain, tenderness to percussion, gingival swelling, sinus tract formation, or abnormal tooth mobility. Similarly, a pulpectomy was considered radiographically successful if there was no increase in the size of pre-operative radiolucency, development of new radiolucency on subsequent follow-ups, or development of pathologic root resorption (internal or external). The clinical success and radiographic success were determined independently, as not all radiographic failures are associated with clinical symptoms and vice versa [ ].

The participants, their parents, outcome assessors, and data analysts were blinded to the type of instrumentation used; however, the operator could not be blinded due to the recognizable characteristics of the rotary and hand files.

Further, all participants received the necessary treatment for other dental problems out of scope of this study. Those who refused for participation were not devoid from receiving the regular treatment of their dental problems.

2.8

Statistical analysis

Statistical Package for Social Sciences [SPSS] for Windows Version 22.0 Released 2013. Armonk, NY: IBM Corp., was used to perform statistical analyses.