1. Hannover Medical School; Prosthetic Dentistry and Biomaterials Science; Carl-Neuberg-Straße 1 Hannover Germany 30625
2. University Hospital Bonn; Department of Periodontology, Operative and Preventive Dentistry; Welschnonnenstr. 16 Bonn Germany 53113
3. UCL Eastman Dental Institute; Unit of Periodontology and International Centre for Evidence-Based Oral Healthcare; 256 Gray's Inn Road London UK WC1X 8LD
4. School of Dentistry, The University of Manchester; Cochrane Oral Health Group; Coupland III Building, Oxford Road Manchester UK M13 9PL