Tooth agenesis

Tooth agenesis is one of the most common developmental anomalies in man. The common
forms, in which one or a few teeth are absent, may cause cosmetic or occlusal harm, while
severe forms which are relatively rare require clinical attention to support and maintain the
dental function. Observation of tooth agenesis and especially the severe forms is also important
for diagnosis of malformation syndromes.

Some external factors like pollutants or cancer therapy may cause developmental defects and
agenesis in dentition. However, twin and family studies have shown the predominant role of
inheritance in the etiology of agenesis. Furthermore, studies on inherited tooth agenesis as
well as mouse null mutants have identified several of the genetic factors and helped to understand the molecular mechanisms of tooth development. However, so far success has onlybeen made in identifying the genes involved in syndromic or rare dominant forms of toothagenesis, while the genes and defects responsible for the majority of cases of tooth agenesis,especially the common and less severe forms, are largely unknown.

In this study, different types of tooth agenesis were studied. It was shown that a dominant
nonsense mutation in PAX9 was responsible for severe agenesis (oligodontia) affecting especially
permanent molars in a Finnish family. In a study of tooth agenesis associated with
Wolf-Hirschhorn syndrome, it was shown that severe tooth agenesis was present if the
causative deletion in the short arm of chromosome 4 spanned the MSX1 locus. A conclusion
from these studies was that severe tooth agenesis was caused by haploinsufficiency of these
transcription factors. During this work several other gene defects in MSX1 and PAX9 have
been identified by us and others, and according to an analysis of the associated phenotypes
presented in this thesis, similar but significantly different agenesis phenotypes are associated
with defects in MSX1 and PAX9, apparently reflecting distinctive roles for these two transcription factors during the development of human dentition.


The original aim of this work was to identify gene defects that underlie the common incisor
and premolar hypodontia. For this purpose, several candidate genes were first excluded. After
a genome-wide search with seven families in which tooth agenesis was inherited in an
autosomal dominant manner, a promising locus in chromosome 18 was identified for second
premolar agenesis in one family. This finding was supported by results from other families.
The results also implied existence of other loci both for second premolar agenesis and for
incisor agenesis.

On the other hand the results from this study did not lend support for comprehensive involvement of the most obvious candidate genes in the etiology of incisor andpremolar hypodontia. Rather, they suggest remarkable genetic heterogeneity of tooth agenesis.Despite the increasing knowledge of the molecular background of tooth agenesis, the pathologicaland developmental mechanisms of tooth agenesis have only become clarified in a few cases. The available evidence suggests that human tooth agenesis usually is a consequenceof quantitative defects which predispose to a failure to overcome a developmentalthreshold. However, the stages and causes may be different in the case of different genes.

More Information:

Plastic Surgery Before And After

Facial Cream