The Index of Orthodontic Treatment Need (IOTN) was used to assess the need for orthodontic treatment before and after treatment, on a systematic sample of 1225 cases. On the whole, full upper and lower fixed appliances brought about a greater improvement in Aesthetics and Dental Health Components compared to other appliance techniques, and were less likely to make the occlusion worse. It was found that certain occlusal traits were more likely to be successfully treated than others. A common problem resulting from treatment was the development of a cross-bite.