Tooth 15 and the sinus
Sinus link. The roots of upper back teeth can reach up into the maxillary sinus, with only a thin layer of tissue between them. Because of that, a long-lasting infection at the root tip can sometimes spread into the sinus (odontogenic sinusitis).
The closest root. In a CBCT study of 652 upper molars, the front cheek-side root of the second molar sat closest to the sinus of all the molar roots. The distance was the same on the left and right, and it grew with age. The authors note this matters when planning a root canal, an extraction or an implant.
The same tooth on the right side, tooth 2, has its own section on sealants and keeping it clean.
Where is tooth 15?
Tooth 15 is in your upper jaw on your left side. It is the seventh tooth from the middle: start at the gap between the two top front teeth and count 7 teeth toward the back on your left side.
In a mirror, tooth 15 shows on the left side of your reflection. Someone looking into your mouth sees it on their right.
In front of it (toward the middle) is tooth 14, the upper left first molar. Behind it is tooth 16, the upper left wisdom tooth.
Its mirror twin on the right side is tooth 2. The tooth in the same spot in the lower jaw is tooth 18, the lower left second molar.
Dental charts show the patient's right side on the left, so tooth 15 sits on the right half of the top row. Universal numbers continue across the top: upper left teeth run from 9 (the front tooth) to 16 (the wisdom tooth).
When does tooth 15 come in?
The upper second molars usually come in at 12–13 years according to the ADA chart. The AAPD chart gives 12–14 years.
In the ADA chart, they usually come in after the lower second molars (11–13 years) and before the upper wisdom teeth (17–21 years). In the AAPD's 13-step order, from the first molars (step 1) to the wisdom teeth (step 13), they are step 12.
Under the gum, according to the AAPD chart, it starts to harden (calcify) at about 30–36 months, has a finished crown by 7–8 years and has a finished root by about 14–16 years, a few years after it comes into the mouth.
What does the upper second molar do?
Molars do the heavy grinding. Cleveland Clinic notes that about 90% of chewing happens on the molars. The upper second molar is a little smaller than the first molar in front of it, and its three roots are usually closer together.
It is also called the "12-year molar". Second molars are named for the age they usually arrive, about 12 years.
Adult molars don't replace any baby tooth. They come in behind the baby teeth as the jaw grows. Upper second molars usually complete the set of 28 adult teeth before any wisdom teeth arrive.
How many roots does tooth 15 have?
3 roots (two cheek-side, one palate-side), usually less spread out than the first molar's.
Common problems with upper second molars
- Treatment. Small cavities are fixed with a filling. If decay or an injury reaches the nerve, root canal treatment can save the tooth, often followed by a crown.
If tooth 15 hurts, feels loose, or the gum around it swells, the Dental Emergency Checker can help you decide how soon to see a dentist. Swelling that spreads to the eye or neck, or 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 15 in FDI and Palmer notation
| System | Tooth 15 is written | What it means |
|---|---|---|
| Universal (ADA, used in the US) | 15 | Adult teeth are numbered 1–32 around the mouth, starting at the upper right wisdom tooth. |
| FDI / ISO 3950 (international) | 27 | First digit 2 = upper left quarter; second digit 7 = seventh tooth from the middle. Said "two-seven". |
| Palmer | └7 (often typed UL7) | The └ bracket marks the upper left quarter; 7 = seventh tooth from the middle. |
"15" in FDI is a different tooth. Read as an FDI code, 15 means the upper right second premolar (tooth 4 in Universal). Charts and X-ray reports from outside the US often use FDI, so check which system is in use.
On a US chart, "27" is a different tooth. Universal 27 is the lower right canine (tooth 27), so "tooth 27" only means this tooth when the chart uses FDI.
Palmer needs the bracket. Every quarter of the mouth has a tooth 7 in Palmer notation; only the └ (or the letters UL) makes it this one.
All adult teeth in the upper left quarter
From the front of the mouth to the back:
| Universal | FDI | Palmer | Tooth |
|---|---|---|---|
| 9 | 21 | └1 (UL1) | Central incisor |
| 10 | 22 | └2 (UL2) | Lateral incisor |
| 11 | 23 | └3 (UL3) | Canine |
| 12 | 24 | └4 (UL4) | First premolar |
| 13 | 25 | └5 (UL5) | Second premolar |
| 14 | 26 | └6 (UL6) | First molar |
| 15 | 27 | └7 (UL7) | Second molar (this tooth) |
| 16 | 28 | └8 (UL8) | Wisdom tooth |
The Tooth Number Chart & Converter converts any tooth between the three systems.
Tools for tooth 15
- Adult Teeth Predictor: likely dates for your child's adult teeth.
- Dental Emergency Checker: how soon to see a dentist if it hurts or breaks.
- Dental Numbness Calculator: how long numbness lasts after a filling.
- Dental Insurance Calculator: what your plan may pay for a crown or root canal.
- How Long Does Dental Work Last?: how long fillings, crowns, veneers and implants usually last, from long-term studies.
- Dental Treatment Plan Decoder: plain English for treatment-plan shorthand like "#30 MOD comp".
Frequently asked questions
What tooth is number 15?
Is tooth 15 the same as tooth 27?
At what age does tooth 15 come in?
Is tooth 15 close to the sinus?
Sources
- American Dental Association (MouthHealthy). Permanent 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.
- 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: Types of Teeth and their Functions. Accessed October 26, 2026.
- Dentalcare.com (continuing education course CE500). An Overview of Dental Anatomy: Permanent Dentition. Accessed October 26, 2026.
- Cleveland Clinic. Teeth: Anatomy, Types, Function & Care. last updated January 26, 2023. Accessed October 26, 2026.
- Ordinola-Zapata R, Azevedo B, Tataryn RW, Versiani MA. Otolaryngologic Clinics of North America 57(6):927–939. Maxillary Dental Anatomy and Physiology: Endodontic and Periodontal. 2024. Accessed October 26, 2026.
- Pei J, Liu J, Chen Y, Liu Y, Liao X, Pan J. Journal of International Medical Research 48(6):300060520926896. Relationship between maxillary posterior molar roots and the maxillary sinus floor: Cone-beam computed tomography analysis of a western Chinese population. 2020. Accessed October 26, 2026.
Last reviewed by the Dental Health Time editorial team, against the sources above. How we review.