Ectopic third molars in the sigmoid notch: etiology, diagnostic imaging and treatment options

Background The etiology of ectopic third molars located in the sigmoid notch of the mandible is unclear. Only a few cases have been reported. The aim of this article is to discuss the etiology as well as treatment options and diagnostic imaging techniques. Methods A PubMed and Medline search of the literature from 1965 to 2015 to ectopic third molars in the mandibular notch was performed. Furthermore, a clinical case provided by the authors is reported. Results Among the eight reviewed cases, two male and six female patients were affected that ranged from 25 to 62 years of age (mean 48.4). Pain and swelling in the preauricular region or trismus but also the absence of symptoms was reported. Only in two of the summarized articles an extra-oral access for the removal of the tooth was used. The etiology seems to be individually different, however dentigerous cysts and chronic inflammation seem to play an important role in their appearance. While previous diagnostic reports described two-dimensional diagnostic imaging, currently the three-dimensional imaging is common for preoperative surgical planning with respect to removing ectopic molars. Conclusions Ectopic third molars in the mandible are a rare condition. The etiology seems to be individually different. Nowadays, three-dimensional imaging is common for preoperative surgical planning.


Background
Ectopic molars in the mandible are rare cases and the etiology of this condition is still unclear [1]. Ectopic third molars of the mandible have been described in the condylar region, the coronoid process, the ascending ramus and the sigmoid notch. A review by Wang et al. indicated only 13 reported cases in the literature depicting ectopic molars in the ramus region during a period of 30 years [2]. The surgical excision of third molars is one of the most common outpatient surgeries [3], whereas the removal of ectopic molars seem to be an unusual surgical intervention. Preoperative diagnosis is based on clinical findings and diagnostic X-ray examination [4]. In the present paper, we review the literature of all cases describing ectopic third molars found in the mandibular sigmoid notch region, which have been reported over a period of 50 years from 1965 to 2015. Subsequently, we add to this summary our own experience by presenting a new case with an ectopic third molar in the sigmoid notch.

Methods
A clinical case provided by the authors is reported. Furthermore, a literature search in PubMed and Medline databases was achieved by using the following MeSH terms: "sigmoid notch" OR "mandibular notch" AND "ectopic tooth" OR "third molar". Inclusion criteria were international cases of ectopic third molars in the sigmoid notch, which have been reported in English or native language from 1965 to 2015.

Results
From 1965 to 2015 only eight cases with ectopic third molars that occurred in the sigmoid notch of the mandible have been reported. In addition to six case reports which were written in English language [5][6][7][8][9][10], two cases that were presented in native language by an Italian and a Japanese group [11,12], respectively, were also included. Clinical and radiological features of these eight cases are summarized in Table 1.

Gender and age prevalence
Six female patients and two male patients were diagnosed with ectopic molars in the sigmoid notch. The age ranged from 25 to 62, with an average age of 48.4 years.

Clinical symptoms
As clinical symptoms the eight reported cases describes pain [8], swelling [7], trismus [5], discomfort of the mucosa [10] as well as combinations of these symptoms [11,12] or no symptoms [6,9]. The clinical features of the eight reported cases are summarized in Table 2.

Treatment
Treatment was described in all cases except one [8]. Granite et al. reported periodic radiographic examination [6], Giordano et al. indicated denied treatment by the patient [11] whereas three authors referred their patients to intraoral access and extraction of the ectopic molar under general anesthesia [7,9,10]. Only two cases described extra-oral surgical access for the extraction of the ectopic molar [5,12]. In detail, submandibular access was selected in both reports.
Adachi et al. also reported encircling radiolucency which was diagnosed pathologically as granulation tissue [10]. One report referred to an area of sclerotic bone surrounding the tooth [6] whereas Balan did not describe any cystic lesion or other abnormalities which could be detected in the radiologic image [8].

Case presentation
A 51 year-old male was referred to our Clinic of Cranio-Maxillofacial Surgery by his dentist. The patient described pain in the preauricular region for a few days. The panoramic radiograph revealed lower right third molar being dislocated in the sigmoid notch associated with a radioluscent lesion (Fig. 1). In addition, the panoramic radiograph offered generalized periodontitis and an impacted third molar surrounded with a radioluscent lesion on the left side of the mandible. Unfortunately, no earlier radiographic images of the patient were available for comparing the development of the ectopic molar. Clinical intra-and extraoral inspection disclosed no further inflammation signs like swelling, trismus, fever or redness. Also signs of chronic inflammation like fistula did not appear. Cone beam scans (CT) showed the impacted tooth with cranial-dorsal directed roots and bone apposition in the sigmoid notch (Figs. 2, 3, 4). A radiolucent cystic lesion was extending from the pericoronary region of the tooth to the dental arch. The  [10] female 58 discomfort in the left buccal mucosa intraoral, general anesthetic CT, panoramic radiograph; radiolucent lesion mandibular canal was compressed but covered by a small sclerotic bone (Fig. 1). Under endotracheal general anesthesia, an intraoral access was selected by incising the anterior edge of the mandibular ramus. In order to expose the sigmoid notch, a subperiosteal dissection was done lingually. Because the tooth was completely osseously covered, bone was removed and the tooth was separated with a surgical drill. The cystic lesion was enucleated and sent routinely for pathological analysis to the Department of Pathology, University Hospital Muenster. Microscopic analysis of the specimen showed stratified epithelium, fibrous tissue with lymphocytic-, plasma cell-and granulocytic infiltration of neutrophilic type and chronic inflammation (Fig. 5). Furthermore, all second molars and the third molar on the left mandible have also been removed. No complications occurred in the postoperative phase. Antibiotics were not given during the entire therapy. Subsequently, periodontal therapy will be performed by the patient's dentist.

Discussion
Up to now, only a few reports of ectopic third molars located in the mandible were recorded in the literature. The etiology of this condition is still unclear but several causes were discussed. Capelli described a correlation between the lack of space between second molar and the ramus mandibulae leading to an ectopic position of the impacted third molar [13]. Also a relationship involving the growth of the coronoid process and the ectopic position was suspected whenever the base of the ectopic third molar was embedded in the bony-growth tissue of the coronoid process [14]. Moreover, deviant eruption patterns were also assumed as a primordial deviance of the germ leading to ectopic teeth [15]. These theories may apply to be causative for the individual ectopic molars illustrated in the case reports which were summarized in this review. For the case presented in this article, the theory reported by Thoma in 1958 [16] and several other authors like Stafne [17] seems to apply for the identified ectopic molar. Thoma suspected that the pressure of the cystic fluid was responsible for the    [5] Trismus and sporadic pain preauricularly Giardino et al. 1966 [11] (Article in Italian) Trismus, pain and swelling in preauricular region Nishijima et al. 1976 [12] (Article in Japanese) No symptoms Granite EL et al. 1985 [6] Slowly growing swelling for two years Metha DS et al. 1986 [7] Pain in the preauricular region Balan N. 1992 [8] No symptoms Fidink Y et al. 2015 [9] Discomfort in the left buccal mucosa Adachi M. et al. 2015 [10] migration of the tooth. In our reported patient, a dentigerous cyst surrounds the crown. In the panoramic radiograph a radiolucent area similar to a "path" that extended from the dental arch to the ectopic molar in the sigmoid notch, appeared. Possibly, this "path" represents the route of migration starting at the dental arch and ending at the sigmoid notch. As inflammations are known to be supporting the expansion of cysts, the periodontitis determined in our patient could serve as an additional factor for the expansion of the cyst, leading to migration of the tooth. The same theory was reported by Adachi et al. which describes "granulation tissue with chronic inflammation around the crown" being etiological to the process of retrograde migration and forcing up the tooth into an ectopic position [10]. In symptomatic patients surgical removal, after a careful preoperative planning, is the recommended treatment [18]. In the past, diagnostic X-ray examinations were mainly implemented by two-dimensional diagnostic imaging techniques like panoramic radiograph or lateral jaw projection. Reports about complications during or after the removal of ectopic molars in the sigmoid notch like nerve injury, damage of the mandibular joint, bleeding or infections were not described in the reviewed literature. Ghaeminia et al. illustrated in their study that threedimensional diagnostic imaging, compared to panoramic radiography, can contribute to optimal risk assessment and, as a consequence, allow better surgical planning [19]. Currently, three-dimensional diagnostic imaging techniques are established and can be beneficial in identifying position of the tooth, associated pathology and identifying the position of neurovascular structures [20]. Thus, preoperatively, the appropriate surgical method can be chosen [2].

Conclusions
Ectopic third molars in the sigmoid notch of the mandible are a rare condition with higher prevalence in women. The etiology seems to be individually different, however dentigerous cysts and chronic inflammation seem to play an important role in their appearance. For planning the surgical entryway, which is mostly selected from intraoral as well as the assessment of operativerisks, three-dimensional diagnostic imaging techniques should be a preoperative standard in diagnostics.