Additional facts on the distance of mandibular posterior teeth to the inferior dental canal

I read with interest the excellent and comprehensive article entitled ‘Trigeminal nerve injuries related to restorative treatment’ by Professor Tara Renton (Dent Update 2018; 45: 522–540). In Table 2, Professor Renton summarizes the findings of several researches that studied the relationship between mandibular premolar apices and the mental foramen, highlighting the close proximity of the mental foramen with the first premolar apex and the second premolar apex.^1,2,3 One example of overextrusion of root canal filling material involving the premolar is shown in Figure 3. My personal experience with the Asian population has shown that, because of the variability in the location of the foramen relative to the apex, there seems to be no ‘absolute safety zone’ in the premolar region if accidental extrusion of endodontic files and materials occurs.⁴ I share with you the observation of the apex of a second premolar that literally ‘sits’ on top of the inferior dental canal (IDC) just next to the mental canal (Figure 1).