Primary mandibular central incisor: FDI 71 and 81

The numbers on both sides

In FDI the first digit is the quadrant and the second is the position counted from the midline. 71 is quadrant 7, position 1: the lower left primary central incisor. 81 is the same position in quadrant 8, on the lower right. Universal gives baby teeth the letters A to T, from the upper right second molar around to the lower right second molar, which makes this tooth O on the lower left and P on the lower right. Palmer writes the letter for the position inside a bracket that shows the quadrant. In plain text that gives LLA and LRA.

Crown surfaces: mesial, distal, labial (facial), lingual and incisal.

Development and eruption

Calcification starts at about 14 weeks in utero and the crown is complete by 2.5 months. The tooth erupts at 6 to 10 months, the earliest of any primary tooth, and the maxillary central incisors follow a few months later. The root is complete at 1.5 years and the tooth is shed at 6 to 7 years.

Read on 24 October 2026. Sources: Human tooth development, tables citing Ash and Nelson, Wheeler's Dental Anatomy, Physiology and Occlusion (Wikipedia); American Dental Association, Tooth development charts (primary and permanent); MolarPath note Eruption sequence and chronology (built on McDonald and Avery, 11th ed., and Proffit's Contemporary Orthodontics, 7th ed.). Figures are usual values, and teeth vary from person to person.

Crown

Seen from the front, the crown is symmetrically flat. It is small and taller than it is wide, with a flatter lingual surface than the upper incisors and no mamelons.

The cervix is constricted and the enamel thin, like all primary crowns. The thin, less mineralized enamel makes the small lower incisor look lighter and more opaque than a permanent tooth.

Read on 24 October 2026. Sources: Chussid, Anatomy of Primary Teeth, Columbia University College of Dental Medicine lecture; MolarPath note Primary tooth morphology (built on McDonald and Avery's Dentistry for the Child and Adolescent, 11th ed.). Figures are usual values, and teeth vary from person to person.

Roots and canals

Anterior primary roots are narrower from side to side than the crown and conical, and they are long compared with the crown. The Salama root canal study did not include mandibular incisors, and the sources for this page give no canal count for the tooth, so none is stated here.

Read on 24 October 2026. Sources: Chussid, Anatomy of Primary Teeth, Columbia University College of Dental Medicine lecture. Figures are usual values, and teeth vary from person to person.

Neighbors and the tooth that replaces it

The lateral incisor beside it has a more rounded distoincisal angle. The permanent mandibular central incisor, the smallest permanent tooth, follows at 6 to 7 years.

The primary incisors are spaced in a growing arch, and the permanent lower incisors are wider in total, by about 6 mm for the four lower incisors in one set of figures. Eruption of the lower permanent incisors is the time to check arch length.

Read on 24 October 2026. Sources: Chussid, Anatomy of Primary Teeth, Columbia University College of Dental Medicine lecture; MolarPath note Primary tooth morphology (built on McDonald and Avery's Dentistry for the Child and Adolescent, 11th ed.); American Dental Association, Tooth development charts (primary and permanent). Figures are usual values, and teeth vary from person to person.

Local anesthesia

In children the cortical bone is thin and porous, which allows a buccal infiltration to diffuse to the pulp. A mandibular block is harder in a small child, the lip stays numb for a long time and the child may bite it. Infiltration avoids both problems.

The mandibular foramen sits low in young children, at or below the occlusal plane, which is another reason a block is harder to place.

Read on 24 October 2026. Sources: MolarPath note Mandibular techniques, local anesthesia (built on Malamed's Handbook of Local Anesthesia, 7th ed.). Figures are usual values, and teeth vary from person to person.

Clinical and exam points

A tooth present at birth is a natal tooth, and one that erupts in the first month is neonatal. Most are early primary incisors and should be kept when possible. Complications include feeding discomfort, tongue ulceration called Riga-Fede disease and aspiration of a mobile tooth.

A very loose tooth that risks aspiration is removed. Extraction is best delayed until about 10 days after birth to avoid bleeding from low vitamin K, and vitamin K is given first if it cannot wait.

Teething can bring drooling, irritable gums and a mild temperature, but a high fever points to another cause.

An eruption cyst is a soft tissue swelling on the ridge beside an erupting tooth. When the cavity around the crown holds blood, the swelling looks purple or dark blue and is called an eruption hematoma.

Read on 24 October 2026. Sources: MolarPath note Eruption sequence and chronology (built on McDonald and Avery, 11th ed., and Proffit's Contemporary Orthodontics, 7th ed.). Figures are usual values, and teeth vary from person to person.

Questions and answers

Read on 24 October 2026. Sources: American Dental Association, Tooth development charts (primary and permanent); MolarPath note Eruption sequence and chronology (built on McDonald and Avery, 11th ed., and Proffit's Contemporary Orthodontics, 7th ed.). Figures are usual values, and teeth vary from person to person.