PAF1 and periodontitis: The prevalence of the four different initial periodontitis or subclinical periodontitis cases (the number of sites with probing depth (PD) ≥4 mm; PD1, PD2, PD3 and PD4) was quite high: 61.7% for PD1, 46.8% for PD2, 36.2% for PD3, and 34.0% for PD4.