Figure 1 shows the α-diversity of the OC, PAI-1 and PAI-3 groups whose difference was statistically significant for all the metrics (p = 2e−6 observed, p = 2.4e−6 Chao1, p = 1.6e−6 Shannon and p = 2.3e−6  Simpson), indicating a diminished microbial diversity in lesioned tissues (PAI-1 and PAI-3) and a strong association between the loss of oral microbiota diversity and the progression of periodontitis, as previously reported [28,29]. The gene discussed is SERPINA5; the disease is periodontitis.