1 Oral and Maxillofacial Surgery and Maxillofacial Prosthetics, University of Groningen and University Medical Centre Groningen, Groningen, The Netherlands. Electronic address: n.vosselman@umcg.nl.
2 Oral and Maxillofacial Surgery and Maxillofacial Prosthetics, University of Groningen and University Medical Centre Groningen, Groningen, The Netherlands.