Tooth 4: Your Upper Right Second Premolar

Reviewed by the toothcheck Dental Team Independent dentist providing online second opinions.

If your dentist or an X-ray report mentioned "tooth 4" or "tooth #4," they were talking about one specific tooth: your upper right second premolar. It is a small but hard-working tooth, and it shows up on treatment plans more often than people expect, usually for a filling, a crack, or occasionally a crown.

This guide explains exactly where tooth 4 is, how it is numbered in the three common systems, what it does, and the problems that most often affect it. It also covers when a recommended treatment is genuinely urgent and when it is worth a closer look first.

Quick Answer

Tooth 4 (US Universal Numbering) is the upper right second premolar, also called the second bicuspid. In FDI notation it is tooth 15, and in Palmer notation it is the upper right 5. It sits just in front of your first molar and just behind your first premolar, on the upper right side of your mouth. It has two cusps and usually one root, sometimes two.

Where Tooth 4 Sits in Your Mouth

Picture your upper teeth from the front. The two front teeth (the central incisors) sit at the midline. Moving toward the upper right back of the mouth you meet the lateral incisor, the canine (the pointed "eye tooth"), then two premolars, then the molars. Tooth 4 is the second of those two premolars, so it is the fifth tooth from the midline.

Because the US system counts from the upper right back, tooth 1 is the upper right third molar (wisdom tooth) and the numbers climb toward the front and across to the left. That puts tooth 4 only three teeth in from the very back on the right. If you are new to the chart, our guide to dental tooth numbering explained shows the full layout, and how to identify tooth numbers on an X-ray helps you find it on your own films.

How Tooth 4 Is Numbered in Each System

Different countries and software use different codes for the same tooth, which causes a lot of confusion when records move between offices.

If a US dentist writes "#4" and a European clinic writes "15," they mean the same tooth. Only the US system uses a plain single number, so it is worth checking which system a report uses before comparing notes.

What a Premolar Does

Premolars are the transition teeth of your mouth. They sit between the canines, which tear, and the molars, which grind. A premolar does a bit of both.

• Tearing and holding: the pointed outer cusp helps break food into smaller pieces.
• Grinding: the inner cusp and the grooved top surface crush food before it reaches the molars.
• Supporting the bite: premolars help guide the way your jaws close and share chewing forces with the molars.
• Supporting the cheek and smile: upper premolars hold up the corner of the mouth and show when you smile broadly.

Tooth 4 typically has two cusps, one toward the cheek and one toward the palate. It usually has a single root, though some upper second premolars have two, or a single root with two canals inside. That detail matters if a root canal is ever needed, because extra canals make treatment more technical.

Common Problems with Tooth 4

Decay in the grooves

The chewing surface of a premolar has deep grooves where food and bacteria collect, and the contact between tooth 4 and its neighbors is a classic spot for decay to start between the teeth. These cavities often cannot be seen from the outside. They are usually found on bitewing X-rays. If you want to know what a flagged area looks like, see what a cavity looks like on an X-ray.

Existing fillings that wear or leak

Premolars often have fillings that were placed years ago. Over time the edges can break down, the filling can crack, or decay can form underneath. A dentist may recommend replacing it. That is sometimes necessary and sometimes a judgment call, especially if the old filling is still sealed and symptom-free.

Cracks and fractures

Because premolars have thin cusps and take real chewing force, they are prone to cracks, particularly when a large filling has weakened the tooth. Signs include sharp pain when you bite and release, or sensitivity to cold. Cracks do not always show on X-rays, so diagnosis often relies on your symptoms and a clinical exam.

Crowns

When a tooth has lost a lot of structure to decay or an old large filling, or has a crack, a dentist may recommend a crown to hold it together. A crown can be a good, protective choice, but it removes more healthy tooth than a filling does. Our article on crown versus filling and when you need a crown explains how to weigh the two.

Root canals

If decay or a crack reaches the nerve, the tooth can become painful, sensitive to heat, or develop an abscess. A root canal removes the infected tissue and saves the tooth. Upper second premolars are usually treatable this way, and many are then protected with a crown afterward.

Gum recession and sensitivity

Notches near the gumline on premolars are common, often from brushing too hard or from clenching and grinding. They can cause sensitivity to cold and are sometimes filled or treated with desensitizing products.

When a Problem on Tooth 4 Is Urgent and When It Is Not

Not every finding on tooth 4 needs immediate treatment. Rough guidance:

• See a dentist promptly for severe or throbbing pain, swelling in the gum or face, a pimple-like bump on the gum, or pain that wakes you at night. These can signal infection.
• Book a visit soon for sharp pain when biting, lingering sensitivity to hot or cold, or a broken filling.
• Usually not an emergency is a small area of early decay found on a routine X-ray with no symptoms. Early lesions in the enamel can sometimes be watched and managed with fluoride and good hygiene, while deeper ones are treated. The American Dental Association (https://www.ada.org/) publishes patient information on cavity prevention and treatment that explains the stages.

The key point is that a flagged cavity on tooth 4 is not automatically an urgent filling, and a recommended crown is not automatically the only option. Size, depth, symptoms and the condition of the rest of the tooth all matter.

Caring for Tooth 4

• Brush twice a day with fluoride toothpaste, paying attention to the back of the upper right.
• Clean between your premolars and molars daily with floss or interdental brushes, since this contact area is a common decay site.
• Ask about sealants or fluoride varnish if you are prone to grooves-and-fissure cavities.
• If you clench or grind, ask about a night guard to protect cusps and fillings.
• Get X-rays at the interval your dentist recommends, since between-teeth decay is hard to spot without them.

FAQ

What is tooth 4? The upper right second premolar, also called the second bicuspid. It is FDI 15 and Palmer upper right 5.

Is tooth 4 a premolar? Yes. It is the second of the two premolars on the upper right.

Where is tooth 4? On the upper right, just in front of the first molar and behind the first premolar.

Does tooth 4 always need a filling when a cavity is flagged? No. Very early lesions can sometimes be monitored, while deeper ones usually need treatment.

Can tooth 4 need a crown? Yes, when a lot of the tooth is missing or cracked. A smaller repair may be enough in less severe cases.

Final Thoughts

Tooth 4 is an ordinary but important tooth: a two-cusped premolar that helps tear and grind food and supports your bite on the upper right. Most problems with it are decay, an aging filling, or a crack, and most are very treatable when caught at a sensible stage.

If you have been told that tooth 4 needs a crown, a large filling, or a root canal and you are not sure it is the right call, a second look can help. With an online dental second opinion from toothcheck, a licensed dentist reviews your X-rays and treatment plan and gives you an independent written opinion in about 72 hours for 59 dollars. You can also read about our dental X-ray review to see what we look at.

Last medically reviewed: November 2026