1. Department of Oral Medicine and Pathology, Guy's Hospital, King's College London, London SE1 9RT, UK
2. Department of Oral and Dental Science, University of Bristol, Lower Maudlin Street, Bristol, BS1 2LY, UK
3. School of Pure and Applied Biology, University of Wales, Cardiff, PO Box 915, Cardiff, CF1 3TL, UK
4. Department of Molecular Genetics, Forsyth Dental Center, Boston, MA 02115, USA