Discussion
Anatomically, deciduous teeth have been considered more complex and challenging than their permanent counterparts, which makes chemomechanical preparation a crucial step.The present study aimed to evaluate the canal transportation and centring ability of different rotary endodontic files, where canal transportation refers to the post-instrumentation deviation in the axis comparable to the original pre-instrumentation axis. On the other hand, the centring ability is the ability of the file axis to be in line with the canal axis, thereby avoiding canal zipping, ledging, or perforation.Three root levels corresponding to cervical, middle, and apical thirds were chosen to be assessed. Several authors considered the root apex the reference point for evaluating canal centricity.The formula introduced by Gambill et al was used in several previous studies, as they assumed its effectiveness in measuring canal transportation and centring ability.The null hypothesis tested in the present study was that there is no difference in canal transportation and centring ability between regular and paediatric NiTi rotary files; it was accepted except for the results of canal transportation of group 1 in the MD direction at the cervical level, where ProTaper Next showed the lowest mean value (more canal transportation) compared to groups 2 and 3.The nonsignificant results of the centring ability in both directions, as well as canal transportation in the BL direction, could be attributed to several similarities amongst the 3 systems. They all worked in a crown-down manner with a rotational motion and an almost similar degree of taper of each system and terminated preparation with the same apical diameter (#30/0.07 for ProTaper Next and #30/0.06 for Fanta AF baby file and Kidzo Elephant file). Moreover, they are all made of heat-treated NiTi alloy, which improves the flexibility and shaping ability of the files, maintaining the original canal shape even in severely curved canals with a lower risk.On the other hand, the ProTaper Next regular rotary endodontic file produces more canal transportation cervically than the paediatric rotary files in the MD direction, which may be attributed to the rectangular cross-section of the ProTaper Next rotary file compared to a triangular cross-section of both paediatric files. Also, the file length may affect the authority over the file, as the regular ProTaper Next file measures 25 mm while the Fanta AF baby files and the Kidzo Elephant file measure 16 and 18 mm, respectively. Although the file size was standardised to be size 30, the taper of the ProTaper Next rotary file was 0.07 mm while that of the paediatric files was 0.06 mm, which means that the increase in diameter of ProTaper Next rotary file per millimetre will be more than that of both paediatric files at the same length.