The Development of an Inherited Tooth Defect in the Mouse

Absence of third molars occurs in some inbred strains of mice (CBA and A) in which these teeth are small, and in the mutant Crooked-tail (Cd/Cd) in which all the molars and the lower incisors are reduced in size. Both in CBA and in Cd/Cd mice, the teeth which will later be absent are represented by tooth germs at first. On the 6th and 5th day after birth respectively, these tooth germs are arrested in the ‘cap’ stage or a little before. They do not invaginate to form a ‘bell’ and ultimately regress. The mechanism of this regression has not been elucidated.