Although hypodontia and supernumerary teeth are often considered as mutually exclusive conditions, this case report presents an unusual case of hypodontia and a supernumerary tooth occurring simultaneously. An adolescent male was referred to the local hospital department regarding upper arch crowding. Plain film radiographs confirmed the congenital absence of both lower lateral incisors in addition to an unerupted conical supernumerary tooth in the maxillary midline. This condition has been called hypo-hyperdontia and in this paper, we discuss the clinical findings and treatment planning considerations in relation to the limited number of previously reported cases. The case report raises awareness of concomitant hypo-hyperdontia and serves to highlight that concomitant anomalies should be excluded when hypodontia or supernumerary teeth are diagnosed. 1. Introduction Hypodontia and supernumerary teeth are often considered as two extremes of the same type of dental anomaly. They most commonly occur as mutually exclusive conditions, and each represents its own challenge in terms of treatment planning. On very rare occasions, hypodontia and supernumerary teeth can coexist with the condition termed “concomitant hypodontia and hyperdontia” [1], “oligopleiodontia” [2], or “hypo-hyperdontia” [3]. More recently, the term concomitant hypo-hyperdontia (CHH) has been used. Being an anomaly of extremes, CHH has been associated with conditions such as Ellis-van Creveld syndrome [4], Marfan syndrome [5], and Downs syndrome [6]. Nonsyndromic CHH is very rare with one epidemiological study finding an incidence of 0.3% in an orthodontic population [7]. It is therefore likely that the true incidence in the general population is significantly lower. The aim of this case report is to present a rare finding of CHH in a nonsyndromic adolescent who was referred as part of a routine orthodontic referral. The clinical presentation in relation to previously reported cases is discussed to raise awareness of the condition. 2. Case Report An 11-year-old, white male was referred to the Department of Child Dental Health, at the local University Dental Hospital for an orthodontic opinion from his general dental practitioner. The medical, dental, and social histories were unremarkable. 2.1. Extraoral Assessment The patient presented with a class I skeletal relationship with an average Frankfort-mandibular planes angle and lower facial height proportion. There was no significant asymmetry in the transverse plane. The lips were competent, and the nasolabial angle was slightly reduced. An
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