1. Aarhus university; Department of Oral Epidemiology and Public Health; 9 Vennelyst Boulevard Århus Denmark DK-8000
2. University of Aarhus; Royal Dental College Library, Faculty of Health Sciences; 9 Vennelyst Boulevard Aarhus C Denmark DK-8000
3. Havana University; Odontology; Havana Cuba
4. School of Dentistry, The University of Manchester; Cochrane Oral Health Group; Coupland III Building, Oxford Road Manchester UK M13 9PL