1. Community and Preventive Dentistry Faculty of Dentistry; Universitas Gadjah Mada; Yogyakarta Indonesia
2. Center for Dentistry & Oral Hygiene; University Medical Center Groningen; University of Groningen; Groningen The Netherlands
3. Department of Health Sciences, Community and Occupational Health; University Medical Center Groningen; University of Groningen; Groningen The Netherlands