Periodontal disease (PD) is a prevalent inflammatory disease in dogs and humans triggered by bacterial plaque in the periodontal tissue, ranging from early stages (gingivitis) to advanced stages (periodontitis). This study aimed to comprehend how the bacterial microbiome in the dog plaque shifts as PD advances. We profiled the bacterial communities in plaque samples from 48 dogs at various PD stages. We also examined the effects of a two-week tooth brushing treatment on bacterial microbiome in 9 dogs diagnosed with PD. We revealed that PD severity in dogs correlates with age. As PD severity increased, the prevalence of Porphyromonas, Fusobacterium, Treponema, and Moraxella rose, while Conchiformibius, Neisseria, Actinomyces, and Pasteurella declined. Linear discriminant effective size (LEfSe) analysis suggests that Conchiformibius may be linked to oral health, while Porphyromonas is associated with PD progression. Notably, brushing with a gel may reduce the prevalence of Porphyromonas. Further studies are warranted to explore PD prevention or treatment strategies.