"Central incisors" refers to the two front teeth in the upper and lower jaw. They are the teeth that are most visible when a person smiles. Full definition
Some babies teeth early — around three months old, and some teeth later, granting exhausted parents a few extra nights of well - earned sleep which they may spend worrying about the fact that the baby has yet to teeth when everyone else at Mommy and Me has already gained the admirable but odd - looking lower central incisors that make baby grins look hilarious to people who don't have children. (parenttime.com)
These are followed by the two upper front teeth - the upper central incisors. (pregnancy-info.net)
This is followed by the second central incisor on the lower jaw. (stanfordchildrens.org)