What Numbing Injection Do Dentists Use?

The numbing injection your dentist uses almost certainly contains an amide local anesthetic, most commonly lidocaine (also called lignocaine) or articaine. These drugs have been the backbone of dental pain control since the late 1940s, and they work by temporarily blocking nerve signals so you feel pressure but not pain during a procedure.¹ But the syringe your dentist picks up holds more than just one ingredient, and the choices made about which drug, which concentration, and which add-ins to use depend on what procedure you are having and your own medical history.

The Main Drugs in the Cartridge

A dental anesthetic cartridge is a small glass tube, typically 1.7 or 1.8 milliliters, pre-loaded with a local anesthetic solution. The most widely used agents fall into a handful of options:

Lidocaine: The most established dental anesthetic worldwide, usually delivered as a 2% solution. It has a long track record and remains the default choice in many practices.
Articaine: Increasingly popular, typically at 4% concentration. It penetrates bone and soft tissue more effectively than lidocaine because of its higher fat solubility, which can make it especially useful for procedures on back teeth or in areas where bone is thicker.²
Mepivacaine: Often chosen when a vasoconstrictor like epinephrine is not appropriate, since it works well on its own and wears off faster than lidocaine with epinephrine. That shorter duration is an advantage for quick procedures.
Prilocaine and bupivacaine: Less commonly used but still available. Bupivacaine is a long-acting anesthetic sometimes chosen for oral surgery where extended post-operative numbness is desirable.

All of these belong to the amide class of local anesthetics. An older class, the esters (like procaine, the original “novocaine”), has largely been phased out of injectable dental use because amides cause fewer allergic reactions and provide more reliable numbing. If someone tells you they are “allergic to novocaine,” they may be recalling an ester-type reaction that is unlikely to occur with modern amide anesthetics. A true allergy to amide local anesthetics is extremely rare.

Why Epinephrine Comes Along for the Ride

Most dental anesthetic cartridges include epinephrine (adrenaline) as an added ingredient, usually at a concentration of 1:100,000 or 1:200,000. Epinephrine is a vasoconstrictor, meaning it narrows blood vessels near the injection site. This serves two practical purposes: it keeps the anesthetic concentrated in the area where it is needed (rather than being washed away by blood flow), and it reduces bleeding during the procedure. The result is deeper, longer-lasting numbness.

Epinephrine is one of the most widely used vasoconstrictors in dental treatment, including in oral surgery where it may be applied directly into bone.³ For most healthy patients, the tiny dose of epinephrine in a dental cartridge has no noticeable systemic effect beyond a brief, mild increase in heart rate that some people notice. But for patients with certain heart conditions, uncontrolled high blood pressure, or hyperthyroidism, your dentist may choose a formulation without epinephrine or with a reduced concentration.

Going without epinephrine is a realistic option for shorter procedures. Research comparing epinephrine-free articaine and mepivacaine found that both provided adequate numbing for routine dental work, and patients benefited from a shorter period of post-procedure numbness.⁴ For a simple filling that takes twenty minutes, not being numb for three hours afterward is a real quality-of-life benefit.

How the Numbing Actually Works

Your nerves send pain signals by allowing sodium ions to rush through tiny channels in the nerve cell membrane, generating an electrical impulse that travels to your brain. Local anesthetics work by plugging those sodium channels from the inside of the nerve membrane, physically preventing the flow of sodium ions and stopping the electrical impulse from ever forming.⁵ No impulse, no pain signal, no sensation. The drug does not knock you out or affect your brain directly. It works only in the tissues where it is deposited.

The effect is temporary because your body gradually metabolizes and carries away the anesthetic molecules. Small nerve fibers (the ones that carry pain and temperature signals) are blocked before larger fibers (the ones that carry pressure and motor signals), which is why you can often still feel your dentist pressing on a tooth even though the sharp pain is gone. As the drug wears off, sensation returns in roughly the reverse order.

Injection Techniques and Where the Needle Goes

Not every numbing injection is the same procedure. The two most common approaches differ in where the anesthetic is deposited and how much of your mouth goes numb.

An infiltration injection places the anesthetic near the tips of the roots of individual teeth. The drug soaks through the bone to reach the nerves serving those specific teeth. Infiltrations work well in the upper jaw, where the bone is thinner and more porous, and increasingly on the lower jaw as well when using articaine, whose superior tissue penetration can cross thicker bone. The injection itself tends to be less uncomfortable because the needle goes into soft tissue near the tooth rather than deep into the mouth.

A nerve block targets a major nerve trunk before it branches out to multiple teeth. The most common version is the inferior alveolar nerve block, which numbs most of the lower jaw on one side, including the teeth, the lower lip, and part of the tongue. It requires placing the needle deeper in the back of the mouth near the jaw’s inner surface. A study comparing the two approaches during orthodontic extractions found that patients reported significantly less pain during the infiltration injection itself compared to the nerve block, while the numbing during the actual extraction was equally effective for both techniques.⁶

One underappreciated aspect of nerve blocks is that the needle occasionally enters a blood vessel during the injection. Research measuring this directly found that about 15% of inferior alveolar nerve block injections resulted in the needle entering a vessel.⁷ This is why your dentist aspirates (pulls back on the plunger slightly before injecting) to check for blood. If blood appears, they reposition the needle. Injecting anesthetic directly into a blood vessel could send the drug systemically rather than keeping it local, potentially causing a rapid heartbeat or other unwanted effects.

What Happens Before the Needle

If you have ever had a dentist dab something on your gums before the injection, that was a topical anesthetic. These come as gels, ointments, or sprays containing benzocaine or lidocaine at higher concentrations than the injectable form. The idea is simple: numb the surface tissue so the needle prick hurts less. A clinical trial in children found that topical anesthetics do have both a real pharmacological effect and a psychological one, reducing the discomfort of needle penetration into the oral mucosa.⁸

Researchers have also been exploring microneedle patches, which are adhesive patches covered in tiny, barely visible needles that create micro-channels in the gum tissue, allowing a topical anesthetic to penetrate more deeply than a simple gel.⁹ This technology is still in early clinical evaluation, but the concept of making the injection itself painless is a real focus of dental research because fear of the needle is one of the biggest barriers keeping people out of the dentist’s chair.

Buffered Anesthetics and Faster Onset

One of the quieter innovations in dental anesthesia is buffering. Anesthetic cartridges are manufactured at a low pH (acidic) to keep the drug stable on the shelf. That acidity is part of what stings when the solution is injected. Adding a small amount of sodium bicarbonate (baking soda) to the cartridge just before injection raises the pH closer to neutral, which does two things: it reduces the burning sensation during injection, and it allows more of the anesthetic to cross nerve membranes in its active form, speeding up the onset of numbness.

A systematic review and meta-analysis of buffered local anesthetics in pediatric dental procedures found a significant reduction in pain during injection compared to unbuffered solutions, along with a promising trend toward faster onset.¹⁰ Another study specifically measuring the onset of a jaw nerve block found that the buffered solution kicked in at roughly a minute and a quarter, compared to about a minute and forty-five seconds for the unbuffered version.¹¹ That difference sounds small in isolation, but dentists report that the cumulative effect of less sting and faster numbness makes a noticeable difference in patient cooperation, especially with children and anxious adults.

Buffering does require an extra step at chairside (mixing the bicarbonate in right before use), and dedicated buffering systems have been developed to make this convenient. Not all dental offices use buffered anesthetics yet, but the practice is growing.

Computer-Controlled Delivery Systems

Part of the pain from a dental injection comes not from the needle itself but from the pressure of fluid being pushed into tissue too quickly. Computer-controlled local anesthetic delivery devices address this by regulating injection speed with a small motor, delivering the solution at a slow, constant rate that the tissue can absorb without building up painful pressure.¹² These devices often look less like a traditional syringe and more like a pen, which can help reduce anxiety in needle-phobic patients. The most well-known brand is the Wand, though several systems are on the market. They are particularly useful for palatal injections (the roof of the mouth), which are notoriously painful with a traditional syringe because the tissue there is tightly bound and has little room to accommodate rapidly injected fluid.

When the Numbness Wears Off, and How to Speed That Up

After most dental procedures using lidocaine with epinephrine, you can expect soft tissue numbness (lip, cheek, tongue) to linger for two to five hours, depending on the amount injected and your individual metabolism. That lingering numbness is the most common patient complaint after dental work. It makes eating, drinking, and talking awkward, and it creates a real risk of accidentally biting your lip or cheek, especially in children.

A product called OraVerse (phentolamine mesylate) was FDA-approved specifically to reverse this lingering numbness. It is a vasodilator injected at the same site as the original anesthetic after the dental procedure is done. By widening blood vessels, it speeds up the removal of the residual anesthetic from the tissue, cutting the duration of numbness roughly in half.¹³ It is especially useful for patients who need to return to work, public speaking, or eating immediately after an appointment. The main reason it is not used universally is cost: it requires an additional injection and a separate cartridge, and insurance coverage varies.

Side Effects and Safety Concerns

For the vast majority of patients, dental local anesthetics are remarkably safe. The most common “side effect” is simply prolonged numbness, which is annoying but harmless. A racing heart sometimes occurs from the epinephrine component, and it passes within minutes. Temporary soreness at the injection site is normal and resolves on its own.

More serious but uncommon complications include paresthesia, a persistent altered sensation (tingling, numbness, or a “pins and needles” feeling) in the lip, tongue, or chin that lasts beyond the expected duration of the anesthetic. Paresthesia can result from direct needle trauma to a nerve, but the neurotoxicity of the anesthetic drug itself is a contributing factor that has historically received less attention. A review of the literature on this topic found that the risk is encountered with some regularity in dental clinics and called attention to the underappreciated role of the anesthetic’s own chemical effects on nerve tissue.¹⁴ Most cases of paresthesia resolve within weeks to months, but a small fraction become permanent. The risk appears to be somewhat higher with 4% concentrations (like articaine and prilocaine) compared to 2% solutions, though the evidence on this point is debated among dental researchers.

Fainting (syncope) is another concern, though it is more about the patient’s anxiety and physiological response than the drug itself. A systematic review found that dentists encounter roughly one fainting episode per year on average, and that dental fear was a strong predictor, increasing the risk more than threefold.¹⁵ Interestingly, the same review found that refusing local anesthesia in situations where it is normally used also dramatically increased fainting risk, which makes sense: the pain of an un-numbed procedure is a powerful trigger for a vasovagal response.

Tailoring the Choice to the Patient

Your dentist does not just grab whichever cartridge is closest. The choice of anesthetic, its concentration, whether it includes epinephrine, and the maximum safe dose all vary based on your medical profile. A comprehensive review of anesthetic selection for medically compromised patients concluded that agents like mepivacaine, lidocaine, and articaine are among the safest options across a range of systemic conditions, but that the specific choice and dose limits require adjustment for children, pregnant patients, and people with conditions like liver disease, heart failure, or uncontrolled hypertension.¹⁶

For pregnant patients, lidocaine with epinephrine is generally considered the safest option when anesthesia is needed, because it has the longest safety record in this population. Children receive lower total doses calculated by body weight, and their dentists often favor shorter-acting agents or epinephrine-free formulations to minimize the window during which a child might accidentally chew their numb lip. Patients on certain blood pressure medications (particularly non-selective beta blockers) need careful consideration before receiving epinephrine, because the interaction can cause a spike in blood pressure. If you take any medication for a heart condition, make sure your dentist knows before any injection.

Why “Novocaine” Still Gets Said in Waiting Rooms

Procaine, marketed as Novocain, was the first synthetic injectable local anesthetic and dominated dentistry for decades. It was an ester-type anesthetic, and it earned a reputation for occasional allergic reactions and inconsistent numbing. By the 1950s and 1960s, the amide anesthetics (led by lidocaine, which was first synthesized in 1943) had largely replaced it. Yet “novocaine” persists in everyday language the way “Band-Aid” stands in for adhesive bandage. If you ask your dentist for novocaine today, you will get lidocaine or articaine, and it will work better, last longer, and carry a lower allergy risk than the original ever did.

The persistence of the term occasionally causes real confusion. Patients who believe they are allergic to “novocaine” may delay or avoid dental care unnecessarily. A true allergy to amide local anesthetics is vanishingly rare. What patients often recall as an allergic reaction was usually a response to the epinephrine (heart racing, anxiety), an episode of fainting, or an actual allergy to the ester-class drug that is no longer used. If you have ever had a reaction during a dental injection, it is worth having a detailed conversation with your dentist about exactly what happened, because the odds are good that a different formulation can be used safely.

Articaine Versus Lidocaine

The most active debate in everyday dental anesthesia is whether articaine is genuinely better than lidocaine. Articaine has a unique chemical structure among the amide anesthetics: it contains a thiophene ring instead of the benzene ring found in the others, which gives it higher fat solubility and better ability to diffuse through tissue and bone. A split-mouth study where the same patients received articaine on one side and lidocaine on the other during upper premolar extractions found that articaine provided superior pain control, which the authors attributed to that enhanced tissue penetration.²

Articaine also breaks down faster in the blood than lidocaine (its thiophene ring is rapidly hydrolyzed), which in theory gives it a wider safety margin for repeated injections. On the other hand, its use at 4% concentration has attracted scrutiny around the paresthesia question mentioned earlier. Whether the higher concentration or the molecule itself is responsible for any increased nerve risk remains unresolved. In practice, many dentists now use articaine for infiltration on the lower jaw (where its bone-penetrating ability shines) and lidocaine for nerve blocks, combining the advantages of both.

For the patient in the chair, the difference between the two is often subtle. Both provide reliable numbness for the overwhelming majority of procedures. Your dentist’s choice is usually driven by the specific clinical situation and their own training and comfort level rather than one drug being categorically superior.