There are many reasons teeth become crowded. Most of the time crowded teeth pose no problem to the heath of a person. Sometime crowed teeth may be due to periodontal disease, which causes bone loss and teeth lost bone support and become crowded. Loss of tooth structure from decay can also cause teeth to be crowded.
Modern orthodontic technique can correct many of these crowding problems. After teeth are aligned, flossing teeth can be easier and keep clean longer.