There are various factors which can affect the differentiation and development of ameloblasts, causing abnormalities to form within the tooth structure. One example is the BMP (bone morphogenetic protein,) which has an important role in ameloblast differentiation. When Follistatin, a BMP inhibitor, is over expressed in the epithelium of developing teeth, the ameloblasts do not differentiate and no enamel forms. Another example includes the conditional deletion of '"Dicer-1"' in the epithelium of developing teeth may cause impaired differentiation of ameloblasts which results in deficient enamel formation.