Talon cusp can be seen in:
Talon cusp is an additional cusp that is usually located on the lingual surface of anterior teeth. It extends atleast half the distance from the cemento-enamel junction to the incisal edge. It is composed of normal enamel and dentin and contains a horn of pulp tissue.
It is seen in: 

Mohr syndrome
Rubinstein Taybi syndrome
Sturge-Weber syndrome
Mohr syndrome
Rubinstein Taybi syndrome
Sturge - Weber syndrome
All of the above