Tooth Letter L: Lower Left Baby First Molar

When does tooth L come in and fall out?

The lower baby first molars usually come in at 14–18 months and fall out at 9–11 years (ADA). The AAPD chart gives 11–18 months to come in and 10–12 years to fall out.

In the ADA chart, they usually come in after the upper baby first molars (13–19 months) and before the upper baby canines (16–22 months), and they fall out at the same time as the upper baby first molars, after the lower baby lateral incisors (7–8 years) and before the lower baby canines (9–12 years).

Tooth L is replaced by tooth 21, the lower left first premolar, which usually comes in at 10–12 years (ADA). Under the gum, tooth L starts to harden in the 4th month of pregnancy and is fully formed by about 24–30 months (AAPD).

If tooth L is lost early: space maintainers

Losing it early. If a baby tooth is lost early to decay or injury, nearby teeth can drift into the room the adult tooth needs. Dentists sometimes fit a space maintainer, though the AAPD notes the evidence on how well they prevent crowding is limited.

A review of space maintainers for lost baby molars found that most types lasted no more than 2 years on average, usually because the cement came loose; a crown-and-loop design lasted longer.

Fused to the bone. Baby molars are the teeth most likely to fuse to the jawbone (ankylosis), which the AAPD reports in 7% to 14% of children. A fused tooth stops moving and can look like it is sinking as the teeth around it keep growing.

When a fused molar has to go. If a fused baby molar has an adult tooth under it, the AAPD says to keep it until it blocks that tooth or the teeth beside it start to tip or drift. Then it is removed, with a holding wire or other fixed appliance if needed.

The same tooth on the right side, tooth S, has its own section on crowns for decayed baby molars.

Where is tooth L?

Tooth L is in your child's lower jaw on their left side. It is the fourth tooth from the middle: start at the gap between the two bottom front teeth and count 4 teeth toward the back on their left side.

"Left" and "right" always mean the child's own sides, so when you face your child, tooth L is on your right.

In front of it (toward the middle) is tooth M, the lower left baby canine. Behind it is tooth K, the lower left baby second molar.

Its mirror twin on the right side is tooth S. The tooth in the same spot in the upper jaw is tooth I, the upper left baby first molar.

Dental charts show the patient's right side on the left, so tooth L sits on the right half of the bottom row. The letters then drop to the lower jaw: lower left teeth run from K (the back molar) to O (the front tooth).

What does the lower baby first molar do?

Baby molars do the grinding for young children, and they keep room for the premolars that replace them. Baby teeth matter even though they fall out: children need them to chew, speak and smile, and they help the adult teeth come in correctly.

How many roots does tooth L have?

2 roots, one at the front and one at the back. Baby molar roots are thin and spread wide apart. The premolar that will replace the baby molar forms in the space between them.

When to call a dentist about tooth L

If a baby tooth is knocked loose or out in a fall, or your child has swelling, fever or pain, call your dentist. Never put a knocked-out baby tooth back in (Knocked-Out Tooth Rescue explains why). Swelling that makes it hard to breathe or swallow is an emergency: call 911.

Tooth L in FDI and Palmer notation

Palmer stops at E. Palmer letters only run from A to E in each quarter, so an "L" can only be a Universal letter.

FDI baby teeth start with 5 to 8. The first digit 7 marks the lower left baby quarter, so FDI 74 can't be mixed up with an adult tooth.

Letters and numbers don't line up. L is letter 12 of the alphabet, but baby tooth L is replaced by adult tooth 21, not tooth 12.

All baby teeth in the lower left quarter

From the front of the mouth to the back:

The Tooth Number Chart & Converter converts any tooth between the three systems.

Tools for tooth L

• Teething Calculator: which baby teeth are due at your baby's age.
• Baby Teeth Tracker: log each tooth in and out.
• Kids Fluoride Calculator: how much toothpaste to use; the ADA says a rice-grain smear until age 3, then a pea-size amount.
• Tooth Fairy Calculator: what families give for a lost tooth.
• Dental Treatment Plan Decoder: plain English for treatment-plan shorthand like "#30 MOD comp".

Frequently asked questions

Sources

1. American Dental Association (MouthHealthy). Permanent Tooth Development (eruption chart). 2012. Accessed October 26, 2026.
2. American Dental Association (MouthHealthy). Primary Tooth Development (eruption chart). 2012. Accessed October 26, 2026.
3. American Academy of Pediatric Dentistry. Dental Growth and Development (chronology after Logan & Kronfeld 1933, adapted 2003). Accessed October 26, 2026.
4. American Academy of Pediatric Dentistry. Management of the Developing Dentition and Occlusion in Pediatric Dentistry (Reference Manual of Pediatric Dentistry). latest revision 2024. Accessed October 26, 2026.
5. World Health Organization. Oral health surveys: basic methods, 5th edition (tooth notation after ISO 3950). 2013. Accessed October 26, 2026.
6. Nelson SJ. Elsevier. Wheeler's Dental Anatomy, Physiology and Occlusion, 11th edition. 2019.
7. American Dental Association. ADA Dental Claim Form (tooth designation systems). Accessed October 26, 2026.
8. Dentalcare.com (continuing education course CE500). An Overview of Dental Anatomy: Types of Teeth and their Functions. Accessed October 26, 2026.
9. American Dental Association (MouthHealthy). Tooth Decay with Baby Bottles. Accessed October 26, 2026.

Last reviewed October 26, 2026 by the Dental Health Time editorial team, against the sources above. How we review.