O Coleman1, T W M Walker2, A Kerai3, R van der Valk4, S J Thomas2. 1. Guy's Dental Hospital, Great Maze Pond, London, SE1 9RT. 2. Dept. of Oral and Maxillofacial Surgery, Bristol Royal Infirmary, Dental Hospital and Children's Hospital, University Hospitals Trust, Bristol NHS Foundation Trust, Lower Maudlin Street, Bristol, BS12LY. 3. Dept. of Oral and Maxillofacial Surgery, Oxford University Hospitals NHS Foundation Trust, Headley Way, Oxford, OX3 9DU. 4. Dept. of Oral and Maxillofacial Surgery, Ground Floor, Dental Institute, Denmark Hill, SE5 9RS.