Why did the anesthetic not work at my dental appointment

Listed below are a few of the most common causes of local dental anesthetic failure:

1. Delivery Technique

Placement of the local anesthetic

The most common cause of not getting numb is when the dentist has missed the spot where he/she intended to deposit the local anesthetic.

Not waiting long enough for the local to work

The tooth has not been allowed enough time to go numb.

Giving the local too fast

Some local anesthesia techniques may not work as well if the local is given too quickly.

Choice of local anesthetic

Lidocaine or Septocaine with epinephrine works best for most situations. But if for some reason it does  not work for you, a different  anesthetic can be used.
If you have certain medical problems, an epinephrine-free solution might be preferred, such as Carbocaine.

Not giving enough local anesthetic

Sometimes it just takes a greater amount of local anesthetic to achieve profound numbing.

2. Anatomical Variation

Local anesthetic is usually effective if it is given in the right spot and has enough time to take effect. It works by blocking the nerve supply to the area being treated. 

However, there is huge anatomical variation between people. Some people have such an unusual anatomy that the “standard” dental injection does not work.

3.Infection/Inflammation

Local anesthetic is very pH sensitive. It requires a basic pH in which to work properly. Any time there is an area of acute infection and/or inflammation the pH drops and the environment becomes acidic, causing the anesthetic to not work well.

4.Fear/Anxitey

When a person is fearful or anxious, the local anesthetic may not work as well as when you’re relaxed. The hormones related to anxiety can prevent local anesthetic from working properly in some people. The actual neurophysiological mechanism by which stress hormones prevent the anesthetic from working properly is still unclear.