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References

Fishel D, Buchner A, Hershkowith A, Kaffe I Roentgenologic study of the mental foramen. Oral Surg Oral Med Oral Pathol. 1976; 41:682-686
Phillips JL, Weller RN, Kulild JC The mental foramen: 2. Radiographic position in relation to the mandibular second premolar. J Endod. 1992; 18:271-274
Denio D, Torabinejad M, Bakland LK Anatomical relationship of the mandibular canal to its surrounding structures in mature mandibles. J Endod. 1992; 18:161-165
Ngeow WC Is there a “safety zone” in the mandibular premolar region where damage to the mental nerve can be avoided if periapical extrusion occurs?. J Can Dent Assoc. 2010; 76
Littner MM, Kaffe I, Tamse A, Dicapua P Relationship between the apices of the lower molars and mandibular canal – a radiographic study. Oral Surg Oral Med Oral Pathol. 1986; 62:595-602
Tilotta-Yasukawa F, Millot S, El Haddioui A, Bravetti P, Gaudy JF Labiomandibular paresthesia caused by endodontic treatment: an anatomic and clinical study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006; 102:47-59
Devine M, Yilmaz Z, Hirani M, Renton T A case series of trigeminal nerve injuries caused by periapical lesions of mandibular teeth. Br Dent J. 2017; 222:447-455

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

From Volume 45, Issue 7, July 2018 | Page 669

Authors

Wei Cheong Ngeow

Lecturer, Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Universiti Kebangsaan Malaysia (UKM), Kuala Lumpur, Malaysia

Articles by Wei Cheong Ngeow

Article

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).

Figure 1. A case where the second premolar ‘sits’ directly above the right inferior dental canal with part of it's apex in contact with the right mental canal. (a) Cross section view. (b) Right panoramic view. (c) Three dimensional view.

I noticed that Figures 2 and 4 showed overextrusion of filling material involving the first and second molars. However, the morphometric distance between the apices of these teeth and the IDC was not provided in Table 2. I believe it would be good to remind the readers that for the mandibular first molar, although 3.5–6.9 mm is the generally acknowledged range of distance,2,5 this distance in fact can be as little as 1 mm.6 Tilotta-Yasukawa et al6 reported that the second molar too can be less than 1 mm from the inferior dental canal. This, again, is in contrast with the range of 3.5–4.5 mm distance reported earlier by Denio et al3 and Littner et al.5 The risk of endodontic overextrusion will increase if these teeth have wide apical foramina or when the apical constriction has been destroyed during root canal preparation or by resorption. The loss of bony barrier between the IDC and apices, eg in cases where a pathological lesion such as periapical granuloma is present, will even make it riskier to perform safe root canal treatment.4 In fact, Professor Renton and her team had earlier shown that periapical lesions of mandibular teeth itself can cause trigeminal nerve injuries.7

I hope the additional information is useful.