When does tooth A 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 A is replaced by tooth 4, the upper right second premolar, which usually comes in at 10–12 years (ADA). Under the gum, tooth A starts to harden in the 4th month of pregnancy and is fully formed by about 36 months (AAPD).
Nerve treatment and crowns for tooth A
Cavities. The AAPD advises repairing decayed baby teeth when possible, rebuilding each tooth to its original shape so it keeps its place until the adult tooth is ready.
When decay reaches deep into a baby molar, dentists can treat the nerve (pulp) instead of pulling the tooth: capping it, removing the top part (pulpotomy), or cleaning out the whole pulp (pulpectomy). A Cochrane review of 87 trials found that failures were uncommon with all of them.
Crowns for baby molars. Preformed crowns, usually stainless steel, are recommended for baby molars that are very decayed, badly broken down or have had nerve treatment. In a Cochrane review, crowns were less likely than fillings to fail badly or cause pain over the long term.
The same tooth on the left side, tooth J, has its own section on the adult first molar getting caught under it.
Where is tooth A?
Tooth A is in your child's upper jaw on their right 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 right side.
"Left" and "right" always mean the child's own sides, so when you face your child, tooth A is on your left.
In front of it (toward the middle) is tooth B, the upper right baby first molar. Behind it, the adult first molar (tooth 3) usually comes in at 6–7 years without replacing any baby tooth.
Its mirror twin on the left side is tooth J. The tooth in the same spot in the lower jaw is tooth T, the lower right baby second molar.
Dental charts show the patient's right side on the left, so tooth A sits at the far left end of the top row. Baby teeth use letters in the same path as adult numbers: upper right teeth run from A (the back molar) to E (the front tooth).
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 A 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 A in FDI and Palmer notation
| System | Tooth A is written | What it means |
|---|---|---|
| Universal (ADA, used in the US) | A | Baby teeth are lettered A–T around the mouth, starting at the upper right back molar. |
| FDI / ISO 3950 (international) | 55 | First digit 5 = upper right quarter (baby teeth use 5–8); second digit 5 = fifth baby tooth from the middle. Said "five-five". |
| Palmer | E┘ (often typed URE) | The ┘ bracket marks the upper right quarter; E = fifth baby tooth from the middle. |
Palmer letters mean something else. In Palmer notation the letters A–E count out from the middle in each quarter, so a Palmer "A" is always a baby central incisor, not this tooth. In Palmer, tooth A is E┘ (URE).
FDI baby teeth start with 5 to 8. The first digit 5 marks the upper right baby quarter, so FDI 55 can't be mixed up with an adult tooth.
Letters and numbers don't line up. A is letter 1 of the alphabet, but baby tooth A is replaced by adult tooth 4, not tooth 1.
All baby teeth in the upper right quarter
From the front of the mouth to the back:
| Universal | FDI | Palmer | Tooth |
|---|---|---|---|
| E | 51 | A┘ (URA) | Baby central incisor |
| D | 52 | B┘ (URB) | Baby lateral incisor |
| C | 53 | C┘ (URC) | Baby canine |
| B | 54 | D┘ (URD) | Baby first molar |
| A | 55 | E┘ (URE) | Baby second molar (this tooth) |
The Tooth Number Chart & Converter converts any tooth between the three systems.
Tools for tooth A
- 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 A?
When does tooth A come in?
When does tooth A fall out?
What is a baby root canal on tooth A?
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.
- Innes NP et al. Cochrane Database of Systematic Reviews, CD005512. Preformed crowns for decayed primary molar teeth. 2015. Accessed October 26, 2026.
- Smaïl-Faugeron V et al. Cochrane Database of Systematic Reviews, CD003220. Pulp treatment for extensive decay in primary teeth. 2018. Accessed October 26, 2026.
Last reviewed by the Dental Health Time editorial team, against the sources above. How we review.