Vital microorganisms in early supragingival dental plaque and in stimulated human saliva.

The aim of this study was to compare the percentage of vital microorganisms (= microbial vitality) of saliva with that of supragingival plaque both collected at various times during the early phases of de novo plaque formation. Between intervals of optimal oral hygiene, 14 healthy participants refrained from all oral hygiene measures for periods of 1, 4, 8 and 72 h. Stimulated whole saliva was collected at the beginning (= baseline) and the end of each period. Vestibular plaque was removed from teeth 13-16, and 23-26. Analysis of the pooled plaque (p) and saliva (s) samples comprised the total number of bacterial counts and colony-forming units to estimate the percentage of viable microorganisms (PEp; PEs). The microbial vitality (VFp; VFs) was determined by using a fluorescence staining to differentiate vital from dead bacterial cells. The bulk of the PEs values reached 5-30%. At baseline VFs ranged between 70% and 90%. The VFs values recorded at baseline or in the presence of 1 h and 4 h-old plaque, were significantly (alpha = 0.05) higher than the corresponding VFp values ranging from 5% to 30%. It was concluded that there is a considerable discrepancy between the microbial vitality of a very early dental plaque and that of whole surrounding saliva sampled at the same time. Unfavourable local environmental conditions prevailing at cervical tooth surfaces are suggested to restrain the survival of the majority of the first bacteria adhering to a particular tooth area during the early phases of supragingival plaque formation.