Dental anaesthetics - can they fail?
77It doesn't have to hurt
Almost everyone has had experience of pain during dental work. They have an injection of anaesthetic and the dentist starts work a few minutes later after checking that the numbing has worked and then, ouch! Something has gone wrong, it hurts!
The nerves in the jaws which feed the teeth are typically numbed by injection into the gum but there are differences between top and bottom sets of teeth. In the lower jaw, the nerve is inside dense bone, so normally the dentist will anaesthetise the main nerve, right at the back. This anaesthetises the half of the jaw including the tongue and lips.
But the top jaw is much more spongy, and the nerves travel close to the surface before dipping down into each tooth. Dentists will inject close to the tooth in order to anaesthetise the surface nerve. They will also use a technique called infiltration to place the anaesthetic down the side of the tooth to get at the nerve.
For the top jaw, they may miss the nerve altogether or only partially anaesthetise it and they won't know until you howl! They can quickly re-inject and numb the tooth. If they use infiltration, it is quite possible for the anaesthetic not to reach the nerve and therefore have no effect. For the lower jaw, each person is slightly different and the canal the nerve travels in may be in a different place. It is possible, though uncommon, for the dentist to miss the main nerve.
In the case of root canal work on back lower jaw teeth, the sheer physical difficulty of placing the anaesthetic in the hard tissue explains the common complaints of pain in patients.
Adrenalin and stress
Adrenalin is often called the "fight or flight" hormone because when it is released it causes the blood vessels to tighten restricting blood flow, it increases muscle tone, and raises the body's awareness. Consequently, you feel more pain more quickly.
Adrenalin is often added to dental anaesthetics in low concentrations to restrict the local blood vessels which keeps the anaesthetic available and effective for longer. But the adrenalin caused by anxiety can counter the effect of the anaesthetic. Instead of the anaesthetic working better, your heightened awareness of pain overcomes the anaesthetic effect. You experience more pain, more anxiety, release more adrenalin, experience more pain, and so on.
Relaxation and sedatives
In reducing anxiety, the adrenalin effect is also reduced and so long as the patient remains calm, the anaesthetic will be more effective. To assist with this, mild sedatives can improve the effectiveness and there is some evidence that nitrous oxide, "laughing gas" also improves the effectiveness of dental anaesthetics.
Taking ibuprofen or codeine before visiting the dentist will also reduce sensitivity to pain thereby reducing the likelihood of an anxiety reaction.
Dentist reactions
Sometimes the dentist will explain that others have work done without any anaesthetic at all, the implication being that the patient really should just put up with the pain. Or else they will cajole the patient to hang on for just for another minute or two and continue working.
But this is very poor patient care. The patient need not be subjected to pain. Anaesthetics can and do work under the right conditions. Far too many dental patients are subjected to unnecessary pain and often do not understand the causes. In turn, dentists who have patients suffering from pain during treatment need to listen to them and take them seriously. Whatever the explanation offered, the patient needs pain-free treatment.
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Thanks for the comment Paul.
Depending on whether it is the upper or lower jaw, the dentist may have used a different method to apply the anaesthetic as well. For the upper jaw, since the nerves run over the surface and are harder to locate, they sometimes use the infiltration method which is essentially dripping the anaesthetic down towards the roots of the tooth.
In practice, this method relies on the anaesthetic reaching the root in sufficient quantity to properly anaesthetise the tooth. If there is plaque around the base of the tooth, or if insufficient anaesthetic gets down there, there will still be pain. It's cheaper and easier to use the infiltration method but it doesn't always work.
If it was the lower jaw, the nerve at the back of the jaw will have been numbed and failure of the anaesthetic is less common. But the adrenalin effect is well-documented even if some dentists don't generally take much notice of it.
You should certainly tell your dentist about the pain and that you understand the adrenalin effect and ask them what they propose to do about it. There's no reason to put up with pain at the dentist.
Paul 18 months ago
The points made on adrenalin and relaxation have made me sit up and think - perhaps my recent problem of still feeling the pain of the drilling, after local anaesthetic, is from nervousness during the injection causing the vessels to constrict and not absorb completely. Thank you!