. 2020 Sep 12;17(16):2531–2543. doi: 10.7150/ijms.46812

Table 1.

Classification of periodontitis severity

	Periodontitis Severity
Classification criteria*	Mild/Moderate	Severe
AL or/and PD²⁵, ²⁶	at least two teeth with interproximal AL ≥4 mm or at least two teeth with interproximal PD ≥5 mm	at least two teeth with interproximal AL ≥6 mm and at least one tooth with interproximal PD ≥5 mm
AL²⁶	>10% to <30% of examined sites (six sites on all teeth) having AL>3 mm	>30% of examined sites (six sites on all teeth) with AL>3 mm
ACH or/and tooth loss²⁰	whole mouth mean ACH ≥2mm to <3mm, or at least one site ACH ≥4mm, and no tooth loss due to periodontitis	whole mouth mean ACH ≥ 3mm, or at least two sites ACH ≥5mm, or tooth loss due to periodontitis

AL: attachment loss; ACH: alveolar crestal height; PD: probing depth;

*It can be considered as mild/moderate periodontitis by meeting any one of the criteria of mild/moderate. The same is true for severe.