When does tooth J come in and fall out?
The upper baby second molars usually come in at 25–33 months and fall out at 10–12 years (ADA). The AAPD chart gives 20–30 months to come in and 9–12 years to fall out.
In the ADA chart, they are among the last to come in, and they are among the last to fall out, along with the upper baby canines and the lower baby second molars.
Tooth J is replaced by tooth 13, the upper left second premolar, which usually comes in at 10–12 years (ADA). Under the gum, tooth J starts to harden in the 4th month of pregnancy and is fully formed by about 36 months (AAPD).
The adult molar behind tooth J
In up to 3% of children, the adult first molar behind this tooth comes in tilted and gets caught under it (ectopic eruption). It is more common in the upper jaw, and about 71% free themselves by age 9.
When it doesn't correct itself, a dentist may wedge the teeth apart with small separators, or use wires or springs to tip the molar back, so this baby molar isn't lost early.
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.
The same tooth on the right side, tooth A, has its own section on nerve treatment and crowns for deep decay.
Where is tooth J?
Tooth J is in your child's upper jaw on their left side. It is the fifth tooth from the middle: start at the gap between the two top front teeth and count 5 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 J is on your right.
In front of it (toward the middle) is tooth I, the upper left baby first molar. Behind it, the adult first molar (tooth 14) usually comes in at 6–7 years without replacing any baby tooth.
Its mirror twin on the right side is tooth A. The tooth in the same spot in the lower jaw is tooth K, the lower left baby second molar.
Dental charts show the patient's right side on the left, so tooth J sits at the far right end of the top row. The letters continue across the top: upper left teeth run from F (the front tooth) to J (the back molar).
What does the upper baby second molar do?
The upper baby second molar is the biggest baby tooth in the upper jaw and does much of a young child's chewing. It looks like a smaller version of the adult upper first molar that will come in right behind it.
Upper baby second molars are usually the last baby teeth to come in (25–33 months, ADA). By about age 3, all 20 baby teeth are usually in.
How many roots does tooth J have?
3 roots. Baby molar roots are thin and spread wide apart. The premolar that will replace the baby molar forms in the space between them.
Common problems with upper baby second molars
- 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.
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. These are typical problems for this kind of tooth, not a diagnosis.
Tooth J in FDI and Palmer notation
| System | Tooth J is written | What it means |
|---|---|---|
| Universal (ADA, used in the US) | J | Baby teeth are lettered A–T around the mouth, starting at the upper right back molar. |
| FDI / ISO 3950 (international) | 65 | First digit 6 = upper left quarter (baby teeth use 5–8); second digit 5 = fifth baby tooth from the middle. Said "six-five". |
| Palmer | └E (often typed ULE) | The └ bracket marks the upper left quarter; E = fifth baby tooth from the middle. |
Palmer stops at E. Palmer letters only run from A to E in each quarter, so a "J" can only be a Universal letter.
FDI baby teeth start with 5 to 8. The first digit 6 marks the upper left baby quarter, so FDI 65 can't be mixed up with an adult tooth.
Letters and numbers don't line up. J is letter 10 of the alphabet, but baby tooth J is replaced by adult tooth 13, not tooth 10.
All baby teeth in the upper left quarter
From the front of the mouth to the back:
| Universal | FDI | Palmer | Tooth |
|---|---|---|---|
| F | 61 | └A (ULA) | Baby central incisor |
| G | 62 | └B (ULB) | Baby lateral incisor |
| H | 63 | └C (ULC) | Baby canine |
| I | 64 | └D (ULD) | Baby first molar |
| J | 65 | └E (ULE) | Baby second molar (this tooth) |
The Tooth Number Chart & Converter converts any tooth between the three systems.
Tools for tooth J
- 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
What tooth is letter J?
When does tooth J come in?
When does tooth J fall out?
What if the adult molar gets stuck under tooth J?
Sources
- American Dental Association (MouthHealthy). Permanent Tooth Development (eruption chart). 2012. Accessed October 26, 2026.
- American Dental Association (MouthHealthy). Primary Tooth Development (eruption chart). 2012. Accessed October 26, 2026.
- American Academy of Pediatric Dentistry. Dental Growth and Development (chronology after Logan & Kronfeld 1933, adapted 2003). Accessed October 26, 2026.
- 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.
- World Health Organization. Oral health surveys: basic methods, 5th edition (tooth notation after ISO 3950). 2013. Accessed October 26, 2026.
- Nelson SJ. Elsevier. Wheeler's Dental Anatomy, Physiology and Occlusion, 11th edition. 2019.
- American Dental Association. ADA Dental Claim Form (tooth designation systems). Accessed October 26, 2026.
- Dentalcare.com (continuing education course CE500). An Overview of Dental Anatomy: Permanent Dentition. Accessed October 26, 2026.
- Dentalcare.com (continuing education course CE500). An Overview of Dental Anatomy: Primary Dentition. Accessed October 26, 2026.
- American Dental Association (MouthHealthy). Tooth Decay with Baby Bottles. Accessed October 26, 2026.
Last reviewed by the Dental Health Time editorial team, against the sources above. How we review.