Comprehensive analysis of ectopic mandibular third molar: a rare clinical entity revisited

Abstract

Background: Ectopic mandibular third molar is a rare clinical entity with incompletely known etiology. Here, we sought to delineate its epidemiological, clinical and radiographic characteristics, and therapy by integrating and analyzing the cases treated in our institution together with previously reported cases.

Method: A new definition and classification for ectopic mandibular third molar was proposed based on its anatomic location on panoramic images. Thirty-eight ectopic mandibular third molars in 37 patients and 51 teeth in 49 patients were identified in our disease registry and from literature (1990-2016), respectively. These cases were further categorized and compared according to our classification protocol. The demographic, clinicopathological and radiographic data were collected and analyzed.

Results: These ectopic teeth were categorized into four levels, 33 in level I(upper ramus), 32 in level II (middle ramus), 15 in level III (mandibular angle) and 9 in level IV (mandibular body). The common clinical presentations included pain, swelling and limited mouth opening, although sometimes asymptomatic. Most teeth were associated with pathological lesions. Treatments included clinical monitor and surgical removal by intra- or extraoral approach with favorable outcomes. Clinical presentations and treatment options for these teeth were significantly associated with their ectopic locations as we classified.

Conclusions: Ectopic mandibular third molars are usually found in patients with middle ages and in upper and middle ramus of mandible. Surgery is preferred to remove these ectopic teeth and associated pathologies when possible.

Keywords: Ectopic tooth; Impacted third molar; Mandibular third molar; Panoramic radiography.

Fig. 1

Definition and classification of ectopic mandibular third molar based on panoramic images. a: diagram describing the definition and classification of ectopic mandibular third molar based on panoramic images. The line a was drawn from the occlusal plane of the mesial teeth such as the second and/or first molar. The intersection point between the line a and anterior mandibular ramus was defined as AMR (anterior mandibular ramus). The line b was extended from the root tips of the second molar or first molar when second molar was absent, which was also in parallel to the line a. The line c was perpendicular to line a and tangential through the distant contour of the mesial tooth. The line d was through the AMR point and parallel to the line c. Thus, the area surrounded by the four lines was defined as the physiological region (marked as the yellow area) for the third molar eruption. Therefore, four levels (I-IV) were defined as ectopic locations for the mandibular third molar. b: Any parts of the third molar which fall into the putative normal region as marked as the yellow area or contact with this area were defined as impaction rather than ectopic and excluded here. c-f: representative images of level I-IV ectopic third molar in mandible

Fig. 2

Patients screen and inclusion protocol

Fig. 3

Protocol of literature review and case selection