Dental Agenesis
From bonepath
This is a general term describing the absence of one or more teeth due to failure to form (a.k.a. hypodontia). Some form of dental agenesis of the permanent dentition (not including the third molar) affects anywhere from around 2 – 11% of the general population (Peck et al. 1994, Vastardis 2000, De Coster et al. 2009), compared with less than 1% for the deciduous dentition (Vastardis 2000).
Dental agenesis is often a symptom of ectodermal dysplasias, oral-facial-digital syndromes, and orofacial clefting (though none in the Ford Collection exhibit the latter). The most commonly missing teeth are upper lateral incisors (I2s) when 1-2 teeth are missing, and fourth (a.k.a. second) premolars are most commonly absent when more than 2 teeth are missing (Vastardis 2000). In addition, agenesis is often accompanied by tooth rotation. For example, Baccetti (1998a-b) found a significant association between premolar rotation and incisor agenesis (and vice versa). Peck and colleagues (1994) report an association between tooth agenesis, and both palatally displaced permanent upper canines and transposed canines and premolars. Garib and colleagues (2009) further found an association between dental agenesis and microdontia.
Such associations indicate a genetic basis for agenesis and other anomalies, and some of these bases are beginning to be understood. For example, Witkop Syndrome is characterized by dental agenesis and nail growth issues, and is caused by a nonsense mutation of the Msx1 gene (Jumlongras et al. 2001, Alappat et al. 2003). Another example is Hypohydrotic Ectodermal Dysplasia, the commonest form of ectodermal dysplasia, which is due to mutation of the EDA gene (De Coster et al. (2009). Other genes implicated in dental agenesis include TGFA, AXIN2 and FGFR1. The genetic basis of commonest form of hypodontia (agenesis of a few incisors or premolars), however, remains obscure (De Coster et al. 2009). Moreover, the fact that the most commonly agenetic teeth are at the ends of their respective morphogenetic fields hints that spatial constraints may underlie agenesis in some cases.
References
Alappat S, Zhang ZY, Chen YP. 2003. Msx homeobox gene family and craniofacial development. Cell Research 13:429-42.
Baccetti T. 1998. A controlled study of associated dental anomalies. The Angle Orthodontist 68:267.
Baccetti T. 1998. Tooth rotation associated with aplasia of nonadjacent teeth. The Angle Orthodontist 68:471-4.
De Coster PJ, Marks LA, Martens LC, Huysseune A. 2009. Dental agenesis: genetic and clinical perspectives. Journal of Oral Pathology and Medicine 38:1-17.
Garib DG, Peck S, Gomes SC. 2009. Increased occurrence of dental anomalies associated with second-premolar agenesis. The Angle Orthodontist 79:436-41.
Jumlongras D, Bei M, Stimson JM, Wang WF, et al. 2001. A nonsense mutation in MSX1 causes Witkop syndrome. American Journal of Human Genetics 69:67-74.
Vastardis H. 2000. The genetics of human tooth agenesis: new discoveries for understanding dental anomalies. American Journal of Orthodontics and Dentofacial Orthopedics 117:650-6.
