Frank Lobbezoo1, Jari Ahlberg2, Daniele Manfredini3. 1. Department of Oral Kinesiology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, The Netherlands. 2. Department of Oral and Maxillofacial Diseases, University of Helsinki, Helsinki, Finland. 3. School of Dentistry, University of Siena, Siena, Italy.