## 3 Discussion  
The NaOCl accident is a rare event, estimated at least one case in the whole dentist's practice [7]. However, from 1975 to 2016, almost 52 cases were reported in peer-reviewed journals [10]. Nevertheless, the prevalence of such cases in clinical practice appears higher. Therefore, this work aimed to report four clinical cases of HAs that occurred in our research team over four years (2019-2022) and evaluate the causes of the reported hypochlorite accidents and the endodontic treatment prosecution in relation also to the operator's behaviour expanding the [PERSON] et al. template [10] adding to it the degree of severity (according to the topographical pattern of the lesions described by [PERSON] et al. [8] and modified by the authors), the presence of legal action against the first practitioner, and clinical information about endodontic treatment so to investigate the dentist's behaviour. Furthermore, for better management of the accident and considering the time to onset of some symptoms, such as swelling and ecchymosis, we improved [PERSON]'s template, adding a pharmacological therapy section in the post-operative extrusion management from day 1. From applying the standardised procedure to data reporting, we noted that four reports presented similar risk factors for the occurrence of the NaOCl accident: female gender (3/4) and dental elements in the maxillary site (4/4) [7]. Furthermore, the diffusion of sodium hypochlorite in soft tissues is facilitated by the lower bone density of female subjects and by the thickness of the cortex surrounding the vestibular roots of the maxillary teeth [7; 11]. In the third case, the CBCT exam, executed after the hypochlorite accident and addressed to evaluate the causes for HA, showed the apical fenestration as the probable origin of the HA. According to this, a recent quasi-experimental study [24] investigating the apical fenestration in a series of 13 HAs examined with CBCT analysis underlined the crucial role of the apical fenestration as a risk factor in the occurring of this kind of accident, so moving the attention from the use or not of NaOCl to its possible portal-of-exit. To this  
Figure 5: Cross section shows coronal stripping of vestibular root of element 14; axial sections show apical transportation. end, [PERSON] et al. recommended analysing the actual reasons for the HA without renouncing a priori to use NaOCI in the following steps aimed to conclude the endodontic treatment. The prevalence of apical fenestration varies significantly among general populations and dental elements with greater maxillary involvement, especially lateral incisive, canine, and first premolar [25; 26]. Specifically, analysing [PERSON] et al. results and focusing only on types I, IV, and VI of root fenestration (i.e., fenestration involving apex), we determined a presence of apical fenestration in 85% of analysed elements [25]. Furthermore, the apical foramen, the stripping, the apical transportation and the lateral canals could be considered portal of exit (POE) in the irrigant extrusion. As evidenced by the conventional radiological examination and the investigation executed using an intraoperative microscope, both reports excluded any perforation except for the last. Nonetheless, in the second case, the preoperative radiological examination showed the presence of a distal lateral canal near the calibrated needle's access, a possible POE for hypochlorite accident. Since the small diameter of the lateral canals should hamper the flow of NaOCI, involvement of the lateral canals in the occurrence of the hypochlorite accident could be possible, though rare [27]. When the aetiology of the accident is not well defined and the endodontic anatomy unclear, a CBCT exam should be performed.