In hereditary cases, evidence of dental germ developing after surrounding tissues have closed the space required for development may be a large contributing factor, as well as such genetic disorders as Down syndrome, ectodermal dysplasia, cleidocranial dysplasia, and cleft lip and cleft palate. MSX1
MSX1 (muscle segment homeobox 1) is involved in condensation of ectomesenchyme in the tooth germ. Among the members of homeobox genes, MSX1 and MSX2 are crucial in mediating direct epithelial-mesenchymal interactions during tooth development by expressing in regions of condensing ectomesenchyme in the tooth germ. MSX1 mutations have been identified as a contributing factor in missing second premolars, third molars, and a small percentage of first molars. MSX1 is less likely to cause anterior agenesis.Heterozygous mutations in PAX9 (paired box gene 9) could arrest tooth morphogenesis as it plays a role of transcription the gene expressed in tooth mesenchyme at the bud stage during tooth development. A study showed that single nucleotide polymorphisms in PAX9 were highly associated with missing upper lateral incisors. AXIN2
The AXIN2 (AXIS inhibition protein 2) gene is a negative regulator of the Wnt signalling pathway, which is important in regulating cell fate, proliferation, differentiation and apoptosis. Its polymorphic variant may be associated with hypodontia such as missing lower incisors or in a more severe form of agenesis like oligontia (lack of six or more permanent teeth). EDA
EDA provides instructions for making a protein called ectodysplasin A. It encodes transmembrane protein that is part of TNF (tumour necrosis factor) family of ligands.
Management of retained primary teeth
When there is a case of hypodontia of the permanent premolar teeth, the primary molar teeth would often remain in the mouth beyond the time they are meant to be lost. Therefore, with a presence of healthy primary teeth in the absence of a permanent successor, retaining the primary teeth can be a feasible management of hypodontia. The primary molars present also functions as a space maintainer, prevent alveolar bone resorption and delays future prosthodontic space replacement by acting as a semi permanent solution going into adulthood Previous studies also shown a good prognosis of retained primary molars going into adulthood. However, leaving the primary teeth in place may run the risk of tooth infraocclusion where the occlusal surface is below that of adjacent teeth.Despite this, the retention of primary teeth, particularly molars, are more susceptible to occlusal wear, over-eruption of opposing teeth and the loss of inter-occlusal space. Orthodontic space closure
Orthodontic space closure is a way of using orthodontics in order to close spaces in the mouth where the teeth are missing. The ideal age for definitive orthodontic treatment is early adolescence but it is important to consider the patients age, severity of hypodontia, patient expectations and their commitment to treatment. It can be an option for hypodontia management in the case of missing maxillary lateral incisors through the reshaping, and mesial re-positioning of the adjacent canine.