PADI4 and rheumatoid arthritis: After excluding the keywords “rheumatoid arthritis” and “arthritis,” the top 10 keywords identified were P. gingivalis PD inflammation expression peptidylarginine deiminase (PAD) gut microbiota gingival crevicular fluid (GCF) antibody Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) and T cells (Figure 6).