Sample selection and preparation
teeth, calcification, caries
STERILE, CAVITY, CARIES
Eighteen freshly extracted primary molars were used in this study after obtaining ethical approval from the Research Ethics Committee (REC), Faculty of Dental Medicine for Girls, Al-Azhar University, Cairo, Egypt (Code: REC-PD-22-09). All methods were reported according to the Checklist for Reporting In Vitro Studies guidelines and regulations. Informed consent was obtained from patients’ guardians to use their teeth in this study.The collected teeth were washed under running water. Any remaining soft tissue fragments were removed from their root surfaces, and teeth were stored in a sterile saline solution.The selection of root canals was done on the bases of certain inclusion and exclusion criteria. The selected teeth should have at least two-thirds of their root length remaining without any signs of resorption, and there should be no evidence of calcification or internal resorption.The initial removal of caries was done first, then coronal cavity preparation was made using No. 2 round bur (Mani). K-files #15 (Mani) were used to measure the working length of all teeth by passing them through the apex and then subtracting 1 mm from the apex. All specimens were then randomly divided into 3 groups (n = 6 in each group) according to the rotary instrument used. A random sequence was generated using a random sequence generator website (To ensure the standardisation of pre- and post-CBCT scanning, each group of teeth was arranged on a rubber base (Zetaflow), which was horseshoe-shaped to accommodate the similarly shaped scanning tray of the CBCT machine (Genoray Papaya 3D). This custom-made rubber base was constructed with dimensions less than the field of view of the CBCT machine. Each group was then submitted to the CBCT examination at 75 kV and 15 mA to determine the canal shape before instrumentation. For each specimen, according to the distance from the cementoenamel junction, 3 tomographs were selected for the coronal, middle, and apical thirds (Photograph showing cone-beam computed tomography (CBCT) superimposition that ensures standardisation of pre- and post-CBCT scanning.Root canal preparation was performed using an endomotor (GeoSoft, EndoEst, Motor-Mini) with an apex locator. During the instrumentation procedure, 2 mL of 1.5% sodium hypochlorite was irrigated between each file, followed by 5 mL of 17% ethylenediaminetetraacetic acid as the final irrigating solution using a conventional syringe and a 30G needle placed 1 mm shorter than the working length. The data used and/or analysed during the current study are available from the corresponding author upon reasonable request.