Root Canal Pain and Anesthesia: Why Anesthesia Fails, Supplemental Injections, and Polarized Reviews

Is it normal for a root canal to hurt even with anesthesia?

Root canal treatment is done under local anesthesia, and when anesthesia takes full effect, pain during treatment is usually controlled [1][2]. However, anesthesia can work less well on a tooth with severe acute inflammation, so both the experience “it hurt even with anesthesia” and the experience “it didn’t hurt at all” can be true [2]. When DentStat analyzed 2,600 patient comments about root canal pain and anesthesia, the most frequently observed were confusion about which of the polarized reviews is right and expressions of fear before treatment [4]. This article explains where that difference comes from and what options exist when it hurts during treatment.

Why does it hurt even though I was anesthetized?

The biggest factor is the state of inflammation at the visit. Acutely inflamed tissue becomes more acidic, making it hard for local anesthetic to work, and even in the same person anesthesia may not take well when inflammation has progressed severely [2]. Also, in areas with dense bone such as lower molars, the anesthetic has difficulty penetrating, so supplemental anesthesia is sometimes needed [2]. In other words, pain during treatment is not only a matter of constitution; how far the inflammation had progressed when treatment started has a large effect [2][3].

Should I endure it if it hurts during treatment?

If you say so instead of enduring it, more anesthesia can be added [2]. When the standard anesthesia is not enough, supplemental anesthesia is used, such as an intraligamentary injection given directly into the ligament area that holds the tooth, or an intraosseous injection given inside the bone [2]. In the comment analysis, experiences of distrust were observed where pain was not relieved even after agreeing on a hand-raising signal [4], so confirming the pain signal and additional anesthesia steps before treatment starts helps manage anxiety.

Why are reviews so polarized?

Because the condition of the pulp (nerve tissue) differs from tooth to tooth. A tooth whose nerve has already died has less tissue to feel pain, so treatment is often close to painless, while a tooth whose nerve is alive with severe inflammation, as in acute pulpitis, is harder to numb and more likely to hurt [1][2]. A dull ache lasting a few days after treatment is a common part of recovery [1]. In the end, polarized reviews are less a matter of luck in treatment and more a reflection of differences in tooth condition [2][3].

I keep putting it off because I’m scared. Is there a way?

When anxiety is high, the option of combining conscious sedation (often called “sleep anesthesia” in Korea) is considered [2]. Even under sedation, local anesthesia is what blocks the pain, and the detailed conditions are covered in the sedation dentistry guide. Meanwhile, if inflammation progresses while you delay, the tooth can reach a state where anesthesia is even harder, so putting it off out of fear can end up leading to more painful treatment [1][2]. The comment analysis also repeatedly showed cases of people who delayed for a long time out of fear and visited only after symptoms worsened [4].

Common myths and facts

“Anesthesia always means no pain” is only half true: anesthesia can work less well when there is acute inflammation [2]. There is also a perception that “pain during treatment means the treatment was done wrong,” but many factors are involved in pain, including the degree of inflammation, the tooth location, and the shape of the canals [2][3]. The misunderstanding that “pain after it is finished means failure” also needs to be distinguished from the fact that a dull ache for a few days right after treatment is a common part of recovery [1].

For the overall root canal process, health insurance, and crown criteria, see the root canal treatment guide, and for dental clinics by region, see Find a Dentist.