1. Foundation for Oral Health and Parkinson’s Disease, P.O. Box 1155, 2340 BD Oegstgeest, Netherlands
2. Department of Neurology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, Netherlands
3. Department of Oral Kinesiology, Academic Centre for Dentistry Amsterdam (ACTA), University of Amsterdam and Vrije Universiteit Amsterdam, Gustav Mahlerlaan 3004, 1081 LA Amsterdam, Netherlands
4. Department of Dentistry, Radboud university medical center, P.O. Box 9101, 6500 HB Nijmegen, Netherlands