The word crowding is used to describe the very common problem of irregular or overlapping teeth due to shortage of space.

Why do teeth become crowded?
The problem is we don't really know although there are plenty of theories.

• Our modern diet is less abrasive than in the past and this means we don't wear our teeth down as much as we used to. The effect was not just on the biting surfaces but also in between the teeth, making the teeth significantly less wide and therefore less crowded.
• The softness of our modern diet causes the jaw muscles to be lacking in proper exercise and this leads the jaws to fail to develop sufficiently to accommodate all the teeth.
• Air pollution didn't exist until the middle of the nineteenth century but is now said to cause inflammation of the lining of the nasal cavity, making children breathe through their mouths. This requires the lower jaw and tongue to drop a little to allow air to pass. It is the low tongue position that allows the upper jaw to become narrow and therefore more crowded.
• The combination of big teeth and small jaws. The separate genes that control the size of teeth and the size of the jaws are out of balance due, it is said, to population migrations in the last two hundred years leading to an inter mixing of the genetic pools. It is a statistical fact that people with large teeth are more likely to have crowded teeth

Take your pick! The first three theories are all environmental in nature and blame modern man's life style. Only the last theory has a genetic component. There is evidence that ancient man had crowded teeth, although less commonly, and the notion therefore that this is just a condition of modern man is incorrect. There are good arguments against all these theories, tending to indicate that crowding has several causes that are likely to be various combinations of both genetic and environmental influences.

Methods of treatment
There are five different ways in which crowding can be relieved. It is necessary to think of the teeth as arranged in the form of an arch, referred to as a dental arch. The first two options depend on reducing either the number or size of the teeth but without changing the size of the dental arch. The other three options rely on altering the dimensions of the dental arch whilst preserving the size and number of teeth.

• Extraction of teeth - This usually involves the removal of four permanent teeth halfway back in the mouth, one on each side from both top and bottom. The creation of these four spaces is very effective at relieving crowding. However, this should only be used when the crowding is severe.
• Enamel reduction - This entails the removal of tiny amounts of enamel from between the teeth. Of course, only a partial thickness of enamel is removed and the surface is subsequently polished. This creates a series of tiny spaces which then close spontaneously. However, cumulatively, sufficient space is made to relieve mild crowding. The process is painless and does not weaken the teeth or make them more vulnerable to decay.
• Widening the dental arches - As discussed in the page on orthopaedics, this technique has been used for over a hundred years. However, it is prone to relapse with a return of crowding at a later date, particularly when used for the lower teeth. Additionally, the amount of space created to relieve the crowding is quite small.
• Moving the front teeth forward - The lower front teeth can be guided forward towards the lip. This is more effective at creating space but is also prone to relapse with a return of crowding. There are exceptions as some types of bite can be treated in this way.
• Moving the back teeth further back in the mouth - This option is available for the upper teeth only and involves the patient wearing a headgear at night time. This can be very effective but it should be noted that it transfers crowding to the back of the mouth which may necessitate extractions at a later date.

These options are frequently used in combination. In borderline cases, there may be more than one treatment option. It is not possible to generalise, hence the need for individual assessment.

Extractions and the facial profile
It has been alleged that the extraction of teeth prior to orthodontic treatment leads to a flattening of the facial profile. However, many patients for whom no teeth were removed have lips that are set back at the end of treatment (because they always had a flatter profile). Conversely, many patients who have had four teeth removed have teeth and lips that are forward at the end of treatment. These paradoxes show that the issue is not black and white but much more complex. When the dentition is crowded, it is sometimes necessary to extract teeth to make space but, at other times, additional space can be created by widening the dental arch or guiding the front teeth further forward to accommodate the crowded ones.

The removal of premolars does have an effect on the profile, but less than might be expected. An interesting study was carried out by examining a sample of very similar patients who were borderline extraction cases. Half were treated with extractions and half without, and their profiles were compared 15 years later. The long term outcome was that the front teeth and lips of patients who had extractions were just 2mm further back than the non-extraction patients, the difference between the groups being no more than the thickness of a 10 pence coin. The teeth of the extraction group had also remained straighter over the 15 year period. An essential feature in this study is that both groups of patients were treated to high standards by specialists with fixed appliances.

When crowding is more severe, the extraction of teeth does not have any effect on the fullness of the lips. The facial profile is only harmed if extractions are undertaken following inadequate assessment and treatment planning or if the treatment is undertaken with insufficient control of the appliances.

What is the logical approach to extractions?
Clearly, each patient needs to be assessed individually. This is why Dr Kirschen and Dr Harris apply a process known as space planning which can identify all aspects of the dentition before treatment begins and the effects that corrective measures will have. This process can determine which cases need extractions and which don't.

We are aware that the extraction of teeth is an issue that can arouse strong emotional feelings. However, we pursue evidence-based clinical practice and recommend the extraction of teeth for the treatment of crowding only when absolutely necessary and use other space creation techniques in less severe cases .