G Schmalz1, D C Watts2, B W Darvell3. 1. Department for Conservative Dentistry and Periodontology, University Hospital Regensburg, Regensburg, Germany; Department of Periodontology, University of Bern, Bern, Switzerland. Electronic address: gottfried.schmalz@ukr.de. 2. School of Medical Sciences, Division of Dentistry, University of Manchester, UK. 3. Dental Materials Science, University of Birmingham, UK.