Unfortunately there can be times when a tooth will just not go numb. Usually additional numbing either in the same site or elsewhere, possibly of a different anaesthetic, will do the trick.
Some examples of more advanced dental injection techniques with dental equipment are mentioned. They are just examples – it would be beyond the scope of a web page to explain all the techniques for the reasons given below. Although the “standard” numbing techniques work most of the time for most people, numbing teeth isn’t just a case of putting local anaesthetic next to the tooth to be numbed. It’s somewhat more complex:
Some dentists are not very good at numbing but don’t think they have a problem or don’t care that they do. These dentists are best avoided. Others do care, but even the most experienced practitioner may not always be able to get you numb at the first attempt. Here are the reasons:
Placement of the local anaesthetic
The most common cause of not getting numb is when the dentist has missed the spot where s/he intended to put the local anaesthetic.
This problem usually arises when trying to numb lower teeth (especially lower back teeth) by blocking the nerve which supplies sensation to them (“inferior alveolar nerve block”). Your lips should be numb right to the midline (even though the numbing is given in the back). By putting the local into a slightly different spot, the numbing problem is usually solved. But some people have an unusual anatomy (see “anatomical variation” section below). So if this doesn’t do the trick, an alternative numbing technique should be used, such as the Gow-Gates technique or the Akinosi technique, with dental instruments, amongst others. These are considered “advanced” techniques and not every dentist knows how to do them.
Not waiting long enough for the local to work
The tooth has not been allowed enough time to go numb. This is unlikely with modern local anaesthetics, but in some people, anxiety delays the action of the numbing. The solution is to wait until you are completely numb.
Giving the local too fast
Some local anaesthesia techniques may not work as well if the local is given too quickly.
Choice of local anaesthetic
The usual anaesthetic solution used nowadays (lignocaine/lidocaine with adrenaline) works best for most situations. But if it should for some reason not work for you, a different LA solution (for example articaine) can be used.
If you have certain medical problems, an adrenaline-free solution might be preferred. Lignocaine/lidocaine without adrenaline isn’t ideal for this because it doesn’t numb the tooth well enough and wears off too quickly. Instead, carbocaine can be used.
Not giving enough local anaesthetic
Sometimes it just takes a greater amount of local anaesthetic to achieve profound numbing.