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Direct laryngoscopy with X-ray of the neck must be performed in every suspected case. Footnotes Competing interests: None. Patient consent: Obtained. Provenance and peer review: Not commissioned; externally peer reviewed.""A 10-year-old girl attended the OPD of the department of pedodontics and preventive SB431542 dentistry, for the treatment of carious teeth. On clinical examination a deep carious lesion was found in left primary second mandibular molar. A preoperative intraoral periapical radiograph was taken. The radiographic examination revealed an additional root both in left primary first molar and permanent first molar (figure 1). Second radiograph was then taken with 30�� mesial shift. The radiographs, at normal and 30�� angulation of right molar region were also taken to see the bilateral occurrence. The same findings of RE with primary and permanent first molars were observed in right-sided radiographs also (figure 2). Figure?1 Left mandibular primary and permanent first molars with radix entomolaris. Figure?2 Right mandibular primary and permanent first molars with radix entomolaris. Discussion RE can be present both with primary and permanent mandibular molars, occurring least frequently in primary first molars.1 Bilateral occurrence of RE on mandibular molars ranges between 50% and 67%.2 In this report, a case of RE was reported with bilateral occurrence on primary first molars and permanent first molars while primary second molars were not associated with RE. However, according to the literature primary second molars show higher prevalence of RE (27.8%) as compared to primary first molars (9.7%).1 The aetiology of development of RE is still unknown. In the literature some suggested the reason to be some external factors during odontogenesis or penetrance of an atavistic gene or racial genetic factors with high degree of genetic penetrance, as observed in some racial forms like Eskimos.3 The probability of presence of RE among molars was described by Field development theory,4 which states that permanent first molar is the key tooth or main site for field affecting genes for the posterior fields of the jaw. So the features present in permanent first molars have more chances of expression in the posterior field and also more the distant the tooth is from permanent first molar fewer are the features of the permanent first molar they exhibit. This may be the reason why the prevalence of RE is higher in primary second molar.5 The dimensions of RE may vary from a short conical extension to a mature root located distolingually with the normal root length and root canal, similar to mesial and distal roots of mandibular molars. Carlesen and Alexandersen, classified four different types of RE according to the location of cervical third of RE��in types A and B the cervical part is located distally with two normal components and single normal component, respectively.