The incisors are the front four teeth on both the upper and lower arches. There are 8 incisors in both the primary and permanent dentitions. Upper incisors are more different in appearance, while the lower incisors generally look about the same. They are named the central incisors and the lateral incisors, based on their location. The central incisors are closest to the midline (center) of the mouth, while the lateral incisors are the next set, closest to the canine teeth. Upper central incisors are more prominent than the others and have a slight curve toward the center of the mouth. They appear in both primary and permanent dentitions. Primary incisors generally begin erupting around 6 months of age, starting with the lower central incisors. The upper incisors follow, with the lower lateral incisors usually erupting last, closer to 16 months of age.
Incisors have one root and nerve canal. The root is approximately 1.5 times the length of the crown. The crowns have a single cusp and narrow biting edge, used to rip and tear food.
When permanent incisors erupt into the mouth they may have a few small scalloped projections on the biting edge of the tooth. These bumps are called mamelons and aid the tooth in the process of eruption. Over time the teeth are used and worn, wearing away mamelons, leaving a straight edge to the tooth.
Incisors are one of the most commonly injured teeth due to trauma or accident. Up to 90% of sports related injuries affect the upper incisors. (1) If the person suffers from an overjet, the teeth are at an increased risk of experiencing trauma. (2) Wearing a sports guard can help protect the teeth during activities where accident or injury could occur.
Sometimes the lateral incisors in the upper arch will appear very narrow. This is called a “peg lateral” and other than causing cosmetic concerns there is nothing anatomically wrong with the tooth.
As permanent incisors begin to erupt next to primary incisors, most parents notice a significant colour difference between the teeth. Typically permanent teeth have a more yellowish appearance due to the larger amount of dentin in the tooth (the tooth material under enamel). This is completely normal and is no reason to be concerned, but it is more significant in children that have mixed dentitions of both primary and permanent teeth.