The healthy group exhibited significantly lower plaque index (PI), gingival index (GI), and probing depth (PD) scores compared with both periodontitis groups, and these differences reached statistical significance (<i>p</i> < 0.001).The median salivary apelin level in the periodontitis + DM group was significantly reduced relative to the healthy group (<i>p</i> = 0.009). Here, APLN is linked to periodontitis.