Crowding

Why it happens

Crowding is a mismatch between the size of the teeth and the size of the arch holding them. Both are largely inherited, and they are inherited independently — which is how a child ends up with one parent's jaw and the other parent's teeth. Contributing factors include early loss of baby teeth allowing neighbours to drift, a narrow upper jaw, and teeth that are simply larger than average.

Why it worsens

Late lower incisor crowding affects people who never had orthodontic treatment as well as those who did. Several forces contribute: continued slow forward and upward growth of the lower jaw into adulthood, the natural mesial drift of teeth toward the front of the mouth, and soft tissue pressure from the lips. Wisdom teeth are commonly blamed and the evidence for them being the main driver is weak.

The practical consequence is that a mild crowding problem at twenty is usually a moderate one at thirty-five. Waiting rarely improves the situation.

Why it is worth correcting

Beyond appearance, crowded teeth are harder to clean, so plaque accumulates between overlapped surfaces and both decay and gum inflammation follow. A tooth pushed outside the bone that houses it can develop recession. And severely rotated teeth wear unevenly.

Creating space

• Expansion of a narrow upper jaw, most effective in a growing patient.
• Interproximal reduction — a fraction of a millimetre of enamel between teeth, recovering a few millimetres in total.
• Moving the back teeth backwards, often using anchorage devices.
• Extraction where crowding is severe.

Which applies depends on how many millimetres are missing, the position of the front teeth relative to the face, and the bone available around the lower incisors. That is measured from records rather than estimated by eye.