A good definition of commensal microflora and an understanding of its relation to health are essential in preventing and combating disease. We hypothesized that the species richness of human oral microflora is underestimated. Saliva and supragingival plaque were sampled from 71 and 98 healthy adults, respectively. Amplicons from the V6 hypervariable region of the small-subunit ribosomal RNA gene were generated by PCR, pooled into saliva and plaque pools, and sequenced by means of the Genome Sequencer 20 system at 454 Life Sciences. Data were evaluated by taxonomic and rarefaction analyses. The 197,600 sequences generated yielded about 29,000 unique sequences, representing 22 taxonomic phyla. Grouping the sequences in operational taxonomic units (6%) yielded 3621 and 6888 species-level phylotypes in saliva and plaque, respectively. This work gives a radically new insight into the diversity of human oral microflora, which, with an estimated number of 19,000 phylotypes, is considerably higher than previously reported.

A direct comparison of quantitative microradiography and microhardness profiles was made using artificial caries-like lesions in human enamel. Tooth crowns with lesions were cut in half through the center of the lesions and opposing halves were assessed by one of the techniques, from the anatomical surface, across the lesion, and into the underlying enamel. A linear relationship was found between volume percent mineral determined by microradiography and the square root of the Knoop Hardness Number assessed by microhardness testing in the mineral range of 40–90 volume percent. The relationship also holds for sound dentine. It is concluded that either technique can be used to measure mineral profiles through carious lesions as a result of demineralization and presumably remineralization.