Discussion

The presence of a tooth in the nasal cavity or maxillary sinus is unusual. The cause of such supernumerary nasal teeth is unclear. One theory suggests that the supernumerary nasal tooth is created either from a thin tooth bud that arises from the dental lamina near the permanent tooth bud, or the tooth germ undergoes a dichotomy.^{Reference Dhingra and Gulati5} Another theory is that their development is a reversion to the dentition of extinct primates, which had three pairs of incisors.^{Reference Dhingra and Gulati5,Reference Liu7} The hyperactivity theory suggests that supernumerary nasal teeth are formed as a result of local, independent hyperactivity of the dental lamina.^{Reference Liu7} The role of epithelial mesenchymal interaction has also been suggested.^{Reference Ray, Singh, Das and Roy8}

The formation of supernumerary nasal teeth can also result from: the presence of any obstruction at the time of tooth eruption due to a crowded dentition, persistent deciduous teeth or exceptionally dense bone; developmental disturbances, such as a cleft palate; rhinogenic or odontogenic infection; and displacement as a result of trauma or cysts.^{Reference Moreano, Zich, Goree and Graham9} Rege et al.^{Reference Rege, Shal and Marfati10} described osteomyelitis of the maxilla as a cause of nasal teeth and reported three ectopic nasal teeth following osteomyelitis of the maxilla.

None of the four patients in the present study had a history of odontogenic infection, or osteomyelitis of the maxilla or cleft palate, and the number of teeth in the arch was normal. However, they did have a history of repeated rhinogenic infection. We speculate that supernumerary nasal teeth could be related to a rhinogenic infection.

Supernumerary nasal teeth are usually misdiagnosed because they are asymptomatic or the symptoms are atypical. Here, we presented four patients with supernumerary nasal teeth, three of whom had previously been misdiagnosed. Supernumerary nasal teeth are commonly misdiagnosed as rhinopolyps, nasal cavity angioma, chronic rhinitis, hypertrophic rhinitis, epistaxis and so forth. This is due not only to the inexperience of the clinician, but also to the features of the supernumerary nasal tooth.

The number of teeth in the arch was normal in all four patients in the present study. In addition, the supernumerary nasal tooth was completely covered by nasal mucosa, and surrounded by granulation tissue and necrotic debris. The supernumerary nasal tooth stimulated the adjacent nasal mucosa or injured the nasal mucosa, thereby resulting in hypertrophy and proliferation of granulation tissue as it gradually increased in size. The inferior nasal conchae and septum were also extruded by the supernumerary nasal tooth, resulting in deviation of the septum. Thus, hyperactivity of supernumerary nasal teeth may cause a series of clinical symptoms. When a supernumerary nasal tooth as an ivory white mass is not covered or is only partly covered by the hypertrophic nasal mucosa or granulation tissue, a misdiagnosis of a foreign body, rhinolith, osteoma, calcifying odontogenic cyst, or malignant tumour, such as chondrosarcoma and osteosarcoma, may be made.^{Reference Mittal and Sultan11,Reference Kumar, Namdev, Bakshi and Dutta12}

The diagnosis of supernumerary nasal teeth mainly depends on signs within the nasal cavity and radiological examination findings. Dental panoramic tomographs would be helpful in outlining the exact relationship and orientation of the supernumerary or ectopic tooth with respect to the existing dentition. However, some authors have suggested that conventional radiological examination may not be able to confirm supernumerary nasal teeth precisely, as panoramic radiographs only provide information on the state of dentition and help determine if a tooth is supernumerary, which may not be sufficient to identify intranasal teeth off the midline.^{Reference Mittal and Sultan11,Reference Kumar, Namdev, Bakshi and Dutta12}

Nevertheless, CT is useful for identifying the exact position of the supernumerary nasal tooth, and will help in deciding whether the tooth can be removed through an intraoral or transnasal approach. Although the differential diagnosis of an intranasal white mass includes a foreign body, odontoma, osteoma, calcifying odontogenic cyst, and malignant tumours, such as chondrosarcoma and osteosarcoma, the CT findings of tooth-equivalent attenuation and a centrally located cavity are highly discriminating features.^{Reference Iwai, Aoki, Yamashita, Omura, Matsui and Maegawa13–Reference Vinothkumar, Kandaswamy, Arathi, Ramkumar and Felsypremila15}

In order to avoid misdiagnosis of supernumerary nasal teeth, clinicians need to increase their awareness of supernumerary nasal teeth; in addition, conventional CT and dental panoramic tomographs should be performed in patients with neoformation of the nasal cavity. Treatment is not difficult, and the supernumerary nasal tooth can be removed under endoscopic guidance.