1. Department of Orthodontics, Glasgow Dental Hospital and School, 378 Sauchiehall street, Glasgow G2 3JZ, U.K.
2. Department of Dental Materials Science, Newcastle Dental School, Framlington Place, Newcastle upon Tyne NE2 4BW, UK.
3. Department of Child Dental Health, Newcastle Dental School, Framlington Place, Newcastle upon Tyne NE2 4BW, UK.