Nerve damage after the extraction of wisdom teeth

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What is a wisdom tooth?

A wisdom tooth is the common name given to the third molars. Wisdom teeth are also called ‘8’s’ because they are the eighth tooth in each quadrant (when counting from the centre/midline of the face).

Our wisdom teeth are right at the back of our mouths and usually come through around the age of 18, although they may be much later.

Why do wisdom teeth cause problems?

Whilst some people experience discomfort and recurrent infections with their wisdom teeth, many of us do not even know if we have them!

Problems with wisdom teeth occur when there isn’t enough room for them to develop and grow through the gum (erupt) into our mouth. As a result of this lack of space, they may develop at strange angles and/or get stuck in a position where they cannot grow through.

If the wisdom teeth get stuck half in-half out of the gum they are called ‘partially erupted’. Partially erupted wisdom teeth can cause recurrent infections in the surrounding gum and bone. These may happen more frequently if the teeth and gums around the back of our mouths are not kept clean. Sometimes, all that is needed is some preventive care and/or advice from our dentist or hygienist to help us learn how to keep the area around the wisdom tooth healthy.

In previous years, non-erupted and/or partially erupted wisdom teeth were almost routinely removed at the first sign of any infection and sometimes they were removed just in order to prevent problems. However, due to the location of nerves around the lower wisdom teeth, when extracting these teeth there is a specific increased risk of damaging these nerves.

As a direct result of the increased risk of nerve damage occurring when lower wisdom teeth are extracted, the current guidelines are that these teeth should be managed so to reduce their associated problems and extractions should be avoided wherever possible.

How does nerve damage occur?

At the back of our mouths, both in the upper and lower jaws, there are a number of blood vessels and nerves within a fairly small space. However, the risk of nerve damage is significantly higher when the lower wisdom teeth are extracted because they may be close to the nerves.

A nerve may be damaged when it is squashed, cut or traumatised by direct contact (which effectively bruises the nerve).

Nerve damage may occur when a wisdom tooth is extracted under local or general anaesthetic.

When lower wisdom teeth are extracted, the nerves that may be damaged are the lingual nerve and the inferior alveolar nerve (also called the inferior dental nerve). These are both sensory (feeling) nerves – they allow us to sense/feel things such as touch, temperature and taste.

We have two lingual nerves and two inferior alveolar/dental nerves, one on each side of the jaw. If, for example, the left lingual nerve is damaged, we will have altered sensation on that side – the undamaged right side will not be affected.

As well as altered sensation, the damaged nerve may also cause aching and/or throbbing pains.

The lingual nerve

The lingual nerve gives the sense of touch, temperature and taste to the tongue. It also gives sensation to the gums along the inside of the teeth (on the side nearest to the tongue) and to the mucosa (soft tissue) under the tongue.

The lingual nerve is located within the gum and soft tissues on the inside/tongue side of the jaw bone, roughly adjacent to the area around the wisdom teeth.

If a lingual nerve is damaged, we are not able to feel that side of our tongue properly – it may be totally numb or tingle, like ‘pins and needles’. We may also not be able to taste things properly – and may experience a burning sensation. Some foods may particularly exacerbate these abnormal sensations and so we may prefer to avoid eating them.

How is the lingual nerve damaged?

During a straight forward extraction, is would be very unusual for any lingual nerve damage to occur. This is because there is usually bone between the tooth roots and the area of soft tissue, which contains the lingual nerve – and this bone protects the lingual nerve from any damaging trauma.

However, if the wisdom tooth is at an angle it may be necessary to cut the gum and remove some bone (and maybe also cut the tooth into smaller pieces) in order to extract the tooth. This is called a surgical extraction.

When cutting bone and/or the wisdom tooth, it is essential to protect the lingual nerve from any risk of also being cut or otherwise traumatised. The risk of injury to the lingual nerve is well recognised and steps should always be taken to protect this nerve.

Preventing damage to the lingual nerve

The lingual nerve can easily be protected by placing an instrument (a ‘retractor’) between the jaw bone and the soft tissue, which contains the lingual nerve. In fact, it is so easy to protect the lingual nerve in this way that there is simply no excuse for not doing it.

The dentist or dental surgeon should also only remove bone and/or tooth from the check (buccal) side of the wisdom tooth in order to keep the protective layer of bone between the tooth roots and the soft tissue, which contains the lingual nerve.

If lingual nerve damage occurs as a result of a surgical wisdom tooth extraction, it can only have happened because the lingual nerve was not adequately, if at all, protected.

In other words, in most cases, the presence of lingual nerve damage is, in itself, evidence of substandard care and dental negligence.

The inferior alveolar nerve (also called the inferior dental nerve)

These nerves are sometimes abbreviated and called the IA or ID nerve (or even the IAN and IDN). For ease, we will call them the ID nerves.

We have two ID nerves, one on the left and one on the right. Each ID nerve gives sensation to the teeth in the lower jaw on that side and the sense of touch and temperature to the gums on the cheek side of those teeth, the inside and outside of our lower lip and the area of chin below the lip on that side.

If an ID nerve is damaged, we may notice that our lower teeth on that side feel numb or a bit ‘fuzzy’. However, the most obvious sign of ID nerve damage is that our lip and chin will either be totally numb or will tingle, like ‘pins and needles’ on the affected side.

Although the right ID nerve gives sensation on the right side and the left ID nerve gives sensation on the left side, there may be some crossing over of the nerves in the centre of our lower lip and chin. Therefore, any altered sensation may seem less in the centre of our lower lip and/or chin as it is very unusual for both ID nerves to be damaged.

How is the inferior alveolar nerve/inferior dental nerve damaged?

The roots of a lower wisdom tooth may lie near, on or even around the ID nerve. Therefore, when the tooth is extracted, the nerve may be damaged by being squashed or bruised.

Unlike the lingual nerve, it is very unusual for the ID nerve to be cut during the extraction of a lower wisdom tooth extraction. The ID nerve is far more likely to be damaged by being squashed or bruised.

Although the ID nerve may be directly cut if the roots have developed around the ID nerve, this situation is rare and due to the very high risk of damage to the ID nerve, the decision to extract the wisdom tooth should be very carefully considered.

Preventing damage to the inferior alveolar nerve/inferior dental nerve

Unlike the lingual nerve, the risk of damaging the ID nerve can be minimised or even totally prevented by a careful and thorough pre-operative radiographic assessment.

It is essential to take a clear, good quality periapical x-ray of the wisdom tooth and its roots before even starting to plan the extraction procedure, especially if the wisdom tooth is unerupted or partially erupted. A careful review of a clear, detailed x-ray is the only way to make any assessment of the position of the tooth and its roots in relation to the ID nerve.

Although the ID nerve itself is not visible on an x-ray, the nerve travels through the lower jaw bone in a canal, and the sides of the canal are usually visible on an x-ray.

It is important to remember that an x-ray still only gives a 2-D image and cannot show the 3-D position of the wisdom tooth and/or its roots in relation to the ID nerve. However, an x-ray will at least show when there may be a greater risk of ID nerve damage occurring and this can be factored into your decision whether or not to go ahead with the extraction.

If an x-ray shows a greater risk of ID nerve damage, your dentist may refer you for specialist review and/or treatment.

If there is an increased risk of nerve damage as a result of a wisdom tooth extraction, it is even more important that you are told about these risks so that you can give full and informed consent to the procedure.

Will the damaged nerve recover?

The extent and duration of the nerve damage depends on the type of damage – a crushed or completely cut nerve is unlikely to recover although a bruised or partially damaged nerve may well make a very good, almost total recovery.

If the nerve has the capacity to recover, this will become obvious within a month or so of the injury. However, any recovery of sensation will be very gradual and it may take a few months before you are able to notice the difference.

Unfortunately, in some cases the damage to the nerve causes a permanent alteration or even loss of sensation.

If nerve damage does occur, you may be referred to a specialist who is experienced in attempting nerve repairs. These are surgical procedures and in some cases, the nerve repair is very successful and can vastly improve the unwanted symptoms of the nerve injury.

Sadly, sometimes even an attempt to surgically repair the nerve does not improve your symptoms of nerve damage. In this situation, a referral to a pain clinic may help you to manage and come to terms with the unwanted symptoms.

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