Final answer:
A developmental elevated projection on the lingual surface of a newly erupted incisor is known as a tubercle. It's a normal feature and usually wears down with use.
Step-by-step explanation:
The developmental elevated projection on the lingual surface of a newly erupted incisor is called a tubercle. This structure is common on the back (lingual) surface of the incisors. It should not be confused with a cusp, which is a pointed area on the crown of a tooth such as a cuspid (or canine), typically used for tearing and shredding food. A developmental feature such as a tubercle on an incisor is normal and usually wears down with time.
A tubercle is noted for being an extra cusp, typically occurring on the permanent incisors. Comparing this to other structures, a ridge refers to a linear elevation on a tooth and is not isolated like a tubercle, and a fossa is a depression or hollow area on the surface of a tooth.