From Volume 6, Issue 4, October 2013 | Pages 109-111
Treatment of patients with extensive hypodontia can present many difficulties in treatment planning for the multi-disciplinary team. Presented is an interesting case of non-syndromic hypodontia where the developmental absence of teeth is related to only one quadrant of the mouth. This unusual case of hypodontia appears to be sporadic with no familial or environmental history.
Hypodontia is defined as the developmental absence of one or more teeth and has a prevalence that varies between different populations and continents. A recent meta-analysis of dental agenesis reported that, in Caucasian European populations, the prevalence, excluding third molars, is 4.6% in males and 6.3% in females.1 The site of agenesis varies within the arch and is most frequently observed at the end of each dental series. The mandibular second premolar is the most commonly affected tooth (2.91–3.22%), followed by the maxillary lateral incisor (1.55–1.78%) and then the maxillary second premolar (1.39–1.61%).1 Unilateral agenesis is more frequent than bilateral agenesis of teeth and females are 1.37 times more likely to be affected than males. The developmental absence of teeth in the primary dentition, although less common than the permanent dentition, has a prevalence of 0.08–1.55%.2
The successional teeth of the permanent dentition (incisors, canines and premolars) develop from localized proliferations within the dental lamina of each deciduous tooth germ. The absence of the primary tooth germ therefore results in the absence of its permanent successor.
Severe hypodontia, or oligodontia, is defined as the developmental absence of more than six teeth, excluding the third permanent molars. It is rare, 0.14%,1 and may be associated with a recognized syndrome, or can be a non-syndromic form and so have a familial pattern or occur sporadically. Non-syndromic hypodontia can be autosomal dominant, autosomal recessive or sex-linked and may have varying degrees of expression.3
Presented is the case of a boy aged 10 years and 6 months who had been referred to the orthodontic department for treatment of his prominent maxillary incisor teeth. He had previously been seen in the paediatric dental department following a referral by his general dental practitioner at the age of 3 years and 8 months, for the absence of the lower left primary first and second deciduous molars.
He presented in the late mixed dentition with a Class II division 1 incisor relationship on a moderate Class II skeletal base and an asymmetry of the left side of the mandible. The lower centreline was shifted 7 mm to the left of the facial midline. There was ankyloglossia, with the lingual fraenum being deviated in association with the lower dental midline. The overjet measured 10 mm and the overbite was increased and incomplete. There was spacing in the lower labial segment and in the lower left quadrant, the canine, premolars and molars were all missing. The lower left primary canine had initially been present, but had exfoliated on eruption of the lower left permanent lateral incisor. (Figures 1, 2, 3 and 4).
An unknown in this case is the degree of growth that is to take place and the affect this might have on the asymmetry. Treatment is currently underway with a sectional upper fixed appliance in combination with a functional appliance, namely a Medium Opening Activator (MOA). The possibility of premolar transplants into the edentulous region has been rejected owing to the superficial position of the inferior alveolar canal. Instead, a definitive plan will entail complex multidisciplinary treatment of orthodontics and restorative dentistry.
The presentation of this case is unusual as only one quadrant of the mouth is affected. Teeth develop from two distinct embryonic cell types, oral ectoderm and cranial neural crest ectomesenchyme, with generation of the mature tooth being dependent upon complex and reciprocal molecular signalling between these two cell populations.4 The first genes to be associated with non-syndromic tooth agenesis in humans were MSX1 and PAX9.5,6 Both of these genes encode transcription factors, which are strongly expressed in the ectomesenchymal compartment of the developing tooth and are essential for odontogenesis to progress beyond the bud stage in mice.7,8 In humans, mutations in these genes are predominantly loss of function and are associated with oligodontia. For both genes, third molars, upper lateral incisors and lower incisors are vulnerable, however, PAX9 can also affect first and second molars, whilst MSX1 is more associated with second premolar and maxillary first premolar absence.9 AXIN2 encodes an intracellular antagonist of Wnt proteins, which represent a large family of signalling molecules also found to be essential for murine tooth development.10,11 How AXIN2 modulates this process is currently unclear, particularly as the AXIN2 mutant mouse has normal tooth development.
This case is interesting in that it demonstrates a lack of tooth development related to a single quadrant affecting six teeth and that does not follow any known genetic association with hypodontia. There is no reported family history of hypodontia or exposure to environmental factors such as trauma, medications or associated ante-natal or post-natal complications that could account for this unusual presentation. To date, we have been unable to find any case reports describing such extensive but localized hypodontia of this nature.
Presented is an unusual case of hypodontia localized to a single quadrant of the mouth and whose aetiology is unknown.
