 Clinical measurements The following clinical parameters are assessed at six sites per tooth mesiobuccal, midbuccal, distobuccal, distolingual, midlingual, mesiolingual at baseline, 12, and 24 months after surgery: Gingival Index GI, Plaque Index PI, PD and CAL-V to the nearest 0.5 mm using a straight manual periodontal probe PCPUNC 15, Hu Friedy, Chicago, IL, USA. As reference for the CAL-V measurements, the cemento-enamel junction CEJ is used. If the CEJ is destroyed by a restoration the restoration margin RM serves as reference. 