[1] Univ Hosp Hamburg Eppendorf, Dept Prosthet Dent, Ctr Dent & Oral Med, D-20246 Hamburg, Germany
[2] Univ Bern, Inst Social & Prevent Med, CH-3012 Bern, Switzerland
[3] Graz Univ, Graz, Austria
[4] Univ Zurich, Zurich, Switzerland
[5] Univ Bern, Dept Fixed Prosthodont, Sch Dent Med, CH-3010 Bern, Switzerland
[6] Univ Med Ctr Hamburg Eppendorf, Dept Prosthet Dent, Ctr Dent & Oral Med, D-20246 Hamburg, Germany