Primary maxillary central incisor: FDI 51 and 61
The two upper front baby teeth: short, wide crowns on long, slim roots, and the only primary incisors wider than they are tall.
Quick answer
- FDI 51 and 61, Universal E and F, Palmer URA and ULA.
- Primary maxillary central incisor erupts at 8 to 12 months.
The numbers on both sides
| Tooth | FDI | Universal | Palmer |
|---|---|---|---|
| Upper right central incisor | 51 | E | URA |
| Upper left central incisor | 61 | F | ULA |
In FDI the first digit is the quadrant and the second is the position counted from the midline. 51 is quadrant 5, position 1: the upper right primary central incisor. 61 is the same position in quadrant 6, on the upper left. 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 E on the upper right and F on the upper left. Palmer writes the letter for the position inside a bracket that shows the quadrant. In plain text that gives URA and ULA.
Crown surfaces: mesial, distal, labial (facial), lingual and incisal.
Development and eruption
| Stage | Age |
|---|---|
| Calcification begins | 14 weeks in utero |
| Crown completed | 1.5 months |
| Erupts | 8 to 12 months |
| Root completed | 1.5 years |
| Shed | 6 to 7 years |
Calcification starts at about 14 weeks in utero and the crown is complete by 1.5 months of age, so the tooth is formed long before it shows. It erupts at 8 to 12 months, and the root is complete at 1.5 years. Roots of primary teeth finish roughly 16 to 20 months after eruption, and about three years later they begin to resorb. 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); Salama and others, Anatomy of primary incisor and molar root canals, Pediatric Dentistry 14(2), 1992. Figures are usual values, and teeth vary from person to person.
Crown
The crown is the only primary incisor crown that is wider from side to side than it is tall. The other primary incisors have crowns taller than wide. Like all primary crowns it narrows sharply at the neck, and its enamel is about half as thick as permanent enamel, which gives the tooth its whiter, more opaque look.
On the back, a recognizable cingulum is bordered by distinct marginal ridges that enclose a shallow lingual fossa, much as on the permanent maxillary incisors. Deep grooves between developmental lobes are not typical, and the incisal edge has no mamelons.
Read on 24 October 2026. Sources: MolarPath note Primary tooth morphology (built on McDonald and Avery's Dentistry for the Child and Adolescent, 11th ed.); Chussid, Anatomy of Primary Teeth, Columbia University College of Dental Medicine lecture. Figures are usual values, and teeth vary from person to person.
Roots and canals
One long, slender, conical root carries the crown. The root is long compared with the short crown, so the root-to-crown ratio is greater than in a permanent incisor. The canal figures here come from Salama and colleagues, who cleared and examined 10 maxillary central incisors.
Every specimen had a single canal with no bifurcation or accessory canals and no clear boundary between chamber and canal. The canal measured 16.5 mm on average (range 16 to 17 mm), curved toward the lip in the apical third to half of the root, and varied from round to oval or triangular in cross-section. The sample was carious, unresorbed teeth, so a resorbing tooth can differ because dentin is laid down inside the canal as the root begins to resorb.
Read on 24 October 2026. Sources: Salama and others, Anatomy of primary incisor and molar root canals, Pediatric Dentistry 14(2), 1992; 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.
Neighbors and the tooth that replaces it
The lateral incisor beside it is narrower, with a crown taller than wide. The permanent successor is the maxillary central incisor, which arrives at 7 to 8 years, shortly after the primary tooth is shed at 6 to 7 years.
The germ of the permanent incisor lies lingual to the primary root, so resorption starts on the lingual root surface. Space matters: the permanent incisors are much wider than the primary ones. One published review gives an incisor liability of 7.6 mm in the upper arch, which is why a spaced primary arch is a favorable sign and a closed one predicts crowding.
Read on 24 October 2026. Sources: 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, so solution deposited in the fold diffuses to the pulp. Buccal infiltration is the usual approach for maxillary teeth.
Infiltration is preferred in young children because its effect is shorter and, in the lower jaw, it avoids a numb lip that a child may bite. Canadian labeling does not recommend articaine for children under 4 years.
Read on 24 October 2026. Sources: MolarPath note Mandibular techniques, local anesthesia (built on Malamed's Handbook of Local Anesthesia, 7th ed.); MolarPath note Maxillary 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
Trauma to a primary incisor can affect its successor. The AAPD advises suspecting ectopic eruption of a permanent incisor after trauma to a primary incisor, with a pulpally treated primary incisor, with asymmetric eruption or when a supernumerary tooth is found. It adds that a necrotic or over-retained pulpally treated primary incisor should be extracted in the early mixed dentition.
Ankylosis is common in anterior teeth after trauma such as avulsion, and the AAPD notes it can appear as late as five years after the injury.
Read on 24 October 2026. Sources: American Academy of Pediatric Dentistry, Management of the Developing Dentition and Occlusion in Pediatric Dentistry (2024 revision). Figures are usual values, and teeth vary from person to person.
Questions and answers
What are the numbers for the primary maxillary central incisor?
FDI 51 and 61, Universal E and F, Palmer URA and ULA.
When does it erupt and when is it shed?
The ADA chart gives 8 to 12 months for eruption and 6 to 7 years for shedding.
How many canals does it have?
One. Salama and colleagues found a single canal without bifurcation or accessory canals in each of 10 specimens.
Why is this the odd primary incisor?
Its crown is wider than it is tall. Every other primary incisor is taller than wide.
Read on 24 October 2026. Sources: American Dental Association, Tooth development charts (primary and permanent); Salama and others, Anatomy of primary incisor and molar root canals, Pediatric Dentistry 14(2), 1992; 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.
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