Why Won’t My Upper Molar Stay Numb? What to Do If You Still Feel Pain

By Dr. Boris Zusin · Published October 12, 2026

If you have ever felt a zing during a filling even though your lip and cheek were completely numb, you are not imagining it and it is not your fault. Numbness in the lip, cheek, or gum does not guarantee that the nerve inside the tooth is numb. Upper back teeth (molars) are among the hardest teeth to numb fully with a single injection, and a tooth with deep decay is often inflamed, which makes numbing medicine work less well.

Why Upper Molars Can Be Hard to Numb

The injection is placed on the cheek side. For most upper teeth we place anesthetic next to the root on the cheek side and it soaks through the bone. Upper molars have a thicker bone plate and a root on the palate side that can sit farther away, so the medicine may not fully reach every root. Research has linked a more distant palatal root to a higher chance of numbing failure.

Inflamed nerves are harder to numb. Decay that is close to the nerve causes inflammation. Inflamed tissue is more acidic and its nerve endings are more easily triggered, so the same dose works less well. This is why a deep cavity can hurt even when a shallow one on the next tooth would not.

Timing matters. Upper-tooth numbing can take several minutes to reach the nerve, even after the lip feels asleep.

What We Do If You Feel It

Please raise your hand or tell us as soon as you feel anything. It is not a bother, and pushing through is never necessary. Depending on the situation we may:

• Wait a few more minutes and test the tooth again.
• Add an injection on the palate side near the root, or a small injection between the teeth.
• Give a second injection on the cheek side, sometimes with a different anesthetic such as articaine.
• Use a ligament injection, a small injection right around the tooth, as an extra step.

Most of the time one of these steps solves the problem within minutes.

What It Can Tell Us About the Nerve

Numbing that keeps failing despite extra injections can be a clue. It may mean the nerve is more inflamed than the X-ray suggested, and we may then re-check the tooth with cold and tapping tests and take an X-ray. Short, fleeting cold pain that fades quickly suggests the nerve can recover (reversible). Pain that lingers, wakes you at night, or comes on its own suggests the nerve is more deeply inflamed (irreversible) and may need a different treatment such as a pulp procedure or root canal. See our guide on reversible versus irreversible pulpitis.

When Pain Is More Than a Numbing Problem

Call us promptly, or seek urgent care, if a tooth hurts with throbbing pain, tenderness when you bite, or swelling. Fever, difficulty opening your mouth, swollen glands, or trouble swallowing can signal a spreading infection and should not wait. Antibiotics are not routinely needed for a painful tooth on their own; the usual treatment is dental treatment of the source.

If you have had trouble getting numb before, tell us at your next visit. We will plan for it. You can also read about tooth-colored fillings and root canal care.