Solitary median maxillary central incisor: A case report of a rare dental anomaly.

The solitary median maxillary central incisor (SMMCI) syndrome is a rare dental anomaly and has an incidence of 1:50,000 live births. In SMMCI, there is only one central incisor present, and it develops exactly at the midline. SMMCI occurrence has been described with growth hormone deficiency or other structural anomalies in the midline of the body. In this case, the 8-year-old female patient reported a single median maxillary central incisor with missing maxillary and mandibular frena, with apparently no other abnormalities. Early diagnosis and recognition of SMMCI are important for all practicing Orthodontists, as it may be a sign of other severe congenital or developmental abnormalities.

The absence of upper central incisors was first reported by Scott in 1958. The solitary median maxillary central incisor (SMMCI) syndrome or SMMCI is a rare dental anomaly and has an incidence of 1:50,000 live births.[1] It is characterized by the absence of a maxillary central incisor in both the primary and permanent dentition. Rappaport et al.[2] in 1976 introduced the term “mono superocentro incisivodontic dwarfism” to describe the association between a single maxillary central incisor and isolated growth hormone deficiency. A single maxillary central incisor has also been reported as an isolated finding.[3]

The SMMCI is unique in that it develops precisely in the midline, and it is the sole central incisor present (with the crown and root size the same as that of a normal central incisor). In contrast, a mesiodens is a conical usually asymmetric, permanent series tooth, which while it may erupt in the midline between two normal central incisor teeth, develops to the right or left side of the midline. SMMCI was first described as an isolated defect in a 6-year-old girl.[1] Since then, SMMCI has been reported both as an apparently isolated dental finding and with a variety of midline developmental defects, holoprosencephaly, and/or pituitary dysfunction.

To accurately describe the characteristic tooth present, it is necessary to specify:

Solitary: The tooth present exists as the only central incisor tooth in the maxilla

Median: The tooth is present precisely in the midline of the maxillary alveolus (a single central incisor tooth present to one or other side of the midline indicates that the contra lateral tooth has been lost from trauma or disease, or did not continue to develop beyond the cellular stage, the tooth germ being resorbed)

Maxillary: This characteristic tooth occurs in the maxilla and not in the mandible

Central Incisor:The tooth is a central incisor tooth although of unusual crown form and is not a supernumerary tooth (mesiodens).

Hence the acronym SMMCI.[4]

Case Report

We report a case of an 8-year-old female, who reported to our orthodontic office with her parents. Her chief complaint was that of an unaesthetic appearance due to the presence of a single large upper front tooth, the median maxillary central incisor. Medical and dental history revealed that she was born full term, her father was 30 years old and the mother 25 years old at time of her birth. Her mother had an uneventful pregnancy. She had a single median deciduous maxillary central incisor. Which was followed by the permanent SCMMI. On examination she was in the mixed dentition, the maxillary and mandibular arches were symmetrical. Notably there was an absence of the maxillary and mandibular labial frena [Figures 1 and 2].

Figure 1

Intraoral photograph showing the presence of solitary median maxillary central incisor

Figure 2

Radiographic evidence of solitary median maxillary central incisor

Discussion

The SMMCI tooth is unique in that both crown and root are symmetrical. It develops precisely in the midline and is the sole central incisor present with the crown and root size the same as that of a normal central incisor. The clinical and radiological findings and absence of any history of trauma confirmed that this patient had an SMMCI tooth. The mechanism leading to the formation of an SMMCI tooth is unknown, although Hall et al.[1] have postulated that a critical absence of or reduction in lateral growth from the midline, on or around gestation days 37 or 38, results in premature fusion of the epithelial dental lamina, thus preventing the formation of two complete and separate central incisor teeth. One tooth consisting of two normal distal halves of central incisors develops from the fused enamel knots and subjacent mesenchyme of these tooth germs.

The patient had a single median maxillary central incisor with missing maxillary and mandibular frena, with apparently no other abnormalities. She was referred to a pediatrician to rule out the presence of any other medical abnormalities. This is a case of an isolated SMMCI. It is imperative to identify a SMMCI as it is most often associated with other serious abnormalities. Cases of SMMCI with simultaneous choanal atresia and pyriformaperture stenosis in a neonate[5] andoromandibular limb hypogenesis syndrome type 1[6], have been reported.

Early diagnosis of SMMCI is important as it may be a sign of other severe congenital or development abnormalities. Referral to a pediatrician for further investigations is important. The child with SMMCI syndrome may require long term comprehensive care by a multidisciplinary team, which includes several specialists working in tamdem. A patient with isolated SMMCI is most often likely to approach an orthodontist to correct the unaesthetic appearance. The orthodontist could expand the maxilla in the permanent dentition, providing sufficient room for the SMMCI tooth to be moved electively to one side of the midline. This would provide sufficient room for an artificial central incisor in the contra lateral side.[4] The SMMCI could then be recountoured using a labial veneer to create the anatomic form of the appropriate side. Hence it is imperative for the practicing orthodontist to be aware of this rare dental anomaly.