Supragingival plaque is collected from four sites per sample tooth. From the buccal and lingual sites samples are taken using Periotron© adapted to the tooth surface to collect dental plaque from the area near the gingival margin. Interproximal, supragingival plaque samples are collected by inserting a sterile paperpoint horizontally in buccal to lingual direction near the gingival margin. Samples from buccal/lingual and from interproximal sites are pooled respectively (two pooled samples from each subject per visit 2a, 3a, 4a) in a seperate transport tube containing 500 µl Ringer-Glycerin-Solution. The pooled samples are at once taken to the laboratory for analysis or stored in liquid nitrogen.