## 4 Discussion  
In recent years, multiple factors and parameters, such as mass flow rate, irrigant delivery time, shear stress, fluid flow velocity, turbulence, and shear wall stress showed to be crucial in altering the clinical irrigant flow rates [20]. Therefore, it should be of relevant importance to use a system that allows these parameters to be constantly controlled to obtain the best cleaning without the risk of being too invasive [13]. Then, the use of an automated root canal irrigation (AI) device was proposed. The AI device helps to deliver irrigants at a constant flow rate of 0.5 mL/min up to 12 mL/min. The fixation slots available in the device help in attaching various volume syringe barrels. The issues of cross-contamination are limited with the device as the separate barrels and irrigation tubes can be connected to the fixation slots during the usage of different irrigating solutions. The programmable modes are inbuilt into the device which helps in delivering the irrigant at a constant set flow rate [16]. Therefore, the potential benefit of using the AI device would be the reduced operator fatigue with enhanced irrigation, especially on using various irrigating solutions in the root canal system. The present study is the first study in the literature designed to assess root canal cleanliness after irrigation with an automated root canal irrigation device, employing a constant flow rate of 6 mL/min as already reported in the literature [12; 16], comparing its ability of smear layer and debrides removal with the most used technique for root canal irrigation, manual needle irrigation, and passive ultrasonic irrigation [12]. The current study showed a significant reduction (\(p<0.05\)) in smear and debris scores in passive ultrasonic irrigation as compared with the automated and manual needle irrigation groups. Pairwise comparison test also showed the passive ultrasonic irrigation group to be better compared to the manual and automated irrigation groups; however, the automated irrigation showed better results compared with the manual needle groups. This result is in contrast from what has previously been reported in the literature by [PERSON] et al. [16], that showed an insignificant difference by using manual irrigation or an automated root canal irrigation device. This difference in result could be explained by the oscillation of the needle at a frequency of 1 Hz and an amplitude of 3 mm during the course of irrigation as reported in the previous literature [21]. In the current study, authors decided to evaluate smear removal using a 30-gauge side-vented closed-ended needle, because the side-vented needles claimed to cause less irrigant extrusions and apical pressures with better shear wall stress compared to the other needle types [20]. Results demonstrate that smear formation is more significant at the apical one-third of the root canal, and it is quite challenging to clean and disinfect; this is mainly attributed to the inherent anatomical complexities [22] and canal diameter, and as a result there is a reduced irrigant flow in the apical aspect of the canal. Regardless of the use of various irrigant activation techniques, there still remains a smear layer at the apical one-third, hence the apical one-third is the most critical and difficult part to shape and clean [23], and it seems to improve the outcomes of root canal treatment [24]. Indeed, as reported in the result section of the present study, the recorded debris scores were higher at apical