The reproducibility of curet sampling of subgingival biofilms

Background: Because few studies have examined the critical issue of sampling reproducibility, the purpose of the present study was to examine the reproducibility of curet sampling of subgingival biofilms. Methods: Seven subgingival biofilm samples were taken successively, using a curet, from each of 80 sites and individually analyzed for their content of 40 bacterial species using checkerboard DNA-DNA hybridization. One healthy site was sampled in each of 20 periodontally healthy subjects, and one sulcus/pocket of <= 3, 4 to 5, and >= 6 mm was sampled in each of 20 subjects with chronic periodontitis. The significance of differences in counts and proportions of individual species at the seven successive samplings for each probing depth (PD) category was determined using the Kruskal-Wallis test. The reproducibility of species proportions at each PD category was measured using the coefficient of variation (CV), and the consistency of microbial profiles across samples was examined using the minimum similarity coefficient. Results: There was no significant difference in the mean proportions of the 40 test species in the seven successive samples in each of the four PD categories. The median CV for individual species in the same site was 0.79 (95% confidence interval [Cl]: 0.76 to 0.82) compared to 1.76 (95% CI: 1.69 to 1.82) in samples from different sites. The within-site mean minimum similarity coefficient ( +/- SEM) was 51.2% +/- 2.2%, and it was 27.9% +/- 0.3% between sites. Conclusion: The proportions of species remained consistent in successive curet samples, indicating that the use of curets provided a reliable and reproducible method to obtain subgingival samples.