Primary mandibular lateral incisor: FDI 72 and 82
The lower second baby incisor: a rounder distal corner and a place in front of the lower primate space.
Quick answer
- FDI 72 and 82, Universal N and Q, Palmer LLB and LRB.
- Primary mandibular lateral incisor erupts at 10 to 16 months.
The numbers on both sides
| Tooth | FDI | Universal | Palmer |
|---|---|---|---|
| Lower left lateral incisor | 72 | N | LLB |
| Lower right lateral incisor | 82 | Q | LRB |
In FDI the first digit is the quadrant and the second is the position counted from the midline. 72 is quadrant 7, position 2: the lower left primary lateral incisor. 82 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 N on the lower left and Q on the lower right. Palmer writes the letter for the position inside a bracket that shows the quadrant. In plain text that gives LLB and LRB.
Crown surfaces: mesial, distal, labial (facial), lingual and incisal.
Development and eruption
| Stage | Age |
|---|---|
| Calcification begins | 16 weeks in utero |
| Crown completed | 3 months |
| Erupts | 10 to 16 months |
| Root completed | 1.5 years |
| Shed | 7 to 8 years |
Calcification starts at about 16 weeks in utero, the crown is complete at 3 months and the tooth erupts at 10 to 16 months. The root is complete at 1.5 years and the tooth is shed at 7 to 8 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). Figures are usual values, and teeth vary from person to person.
Crown
The lateral incisor is similar to the lower central incisor, with the crown taller than wide, a flat lingual surface and no mamelons. It differs in having a more rounded distoincisal angle, where the central incisor is symmetrically flat.
The primary tooth is thinner-enameled than its permanent successor, with a cervical constriction, and the pulp is relatively large with horns near the surface.
Primary enamel is roughly half as thick as permanent enamel and fairly even across the crown. It does not thicken toward the neck, and the dentin over the pulp is thin too.
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.); MolarPath note Pulp chambers and root canal morphology (built on Cohen's Pathways of the Pulp, 12th ed.). Figures are usual values, and teeth vary from person to person.
Roots and canals
The root is conical and narrow from side to side. As with the other lower incisors, the sources checked here give no canal count, so none is stated.
When the permanent successor approaches, the primary root is resorbed from its lingual surface, because the permanent incisor germ lies lingual to the primary root. The root-to-crown ratio of primary incisors is greater than that of permanent incisors.
Within a jaw, teeth erupt in a fixed order: incisors, then the first molar, then the canine and last the second molar. The lateral incisor follows the central incisor, usually in the second half of the first year or later.
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.
Neighbors and the tooth that replaces it
The central incisor next to it is symmetrical. The canine beside it is the longer, pointed tooth, and the lower primate space lies behind the canine, between the canine and the first molar.
The successor, the permanent mandibular lateral incisor, erupts at 7 to 8 years. It often comes in crowded, and the AAPD lists interproximal stripping of the mandibular primary canines as one way to make room for crowded lower lateral incisors.
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 Academy of Pediatric Dentistry, Management of the Developing Dentition and Occlusion in Pediatric Dentistry (2024 revision); American Dental Association, Tooth development charts (primary and permanent). Figures are usual values, and teeth vary from person to person.
Local anesthesia
Lower infiltration works well in children because the bone is thin and porous. The decision between infiltration and a block depends on age, as a block carries a longer numb lip.
Intraligamentary injection gives pulpal anesthesia of one or two teeth with little soft tissue numbness, but with a developing successor beneath, buccal infiltration avoids the pressure injury to the follicle that an intraligamentary injection risks.
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
The primary dentition is complete at about 2.5 to 3 years. A count far below 20 at age 3 should prompt a check for delayed eruption or missing teeth.
The AAPD notes that mandibular incisors have a high relapse rate for rotations and crowding, which is one reason the spacing of the primary incisors is watched. Ankylosis in anterior teeth is common after trauma such as avulsion.
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.); 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 mandibular lateral incisor?
FDI 72 and 82, Universal N and Q, Palmer LLB and LRB.
When does it erupt?
The ADA chart gives 10 to 16 months.
How do the two lower primary incisors differ?
The lateral has a more rounded distoincisal angle, and the central is symmetrically flat from the front.
Where does the primary root begin to resorb?
On the lingual surface, because the successor's germ lies lingual to it.
Read on 24 October 2026. Sources: American Dental Association, Tooth development charts (primary and permanent); 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.
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