The present study investigated the molecular presence of 4 species of pathogenic periodontal bacteria (Porphyromonas gulae, Porphyromonas gingivalis, Tannerella forsythia, and Treponema denticola) using quantitative real-time polymerase chain reaction (PCR) in 230 household dogs with or without gingivitis, dental plaque and/or calculus. Overall, T. forsythia was most frequently present (77.8%), followed by P. gulae (50.9%), T. denticola (38.7%), and P. gingivalis (34.8%). A higher percentage of these bacteria was associated with factors such as age, grade of gingivitis, and an increase in dental plaque and/or calculus that indicated poor oral cleanliness. Even without a direct relation to gingivitis and plaque and/or calculus, these 4 species were consistently found not only in older dogs but also in younger ones. The results suggest that these bacteria are commonly present in household dogs, which puts them at risk of developing periodontal disease. Considering that 3 species of bacteria, excluding P. gulae, have zoonotic potential, it emphasizes the need for caution to prevent transmission between dogs and humans. Regarding overall bacterial DNA copy numbers, there was a wide range, with P. gulae having the most, followed by T. forsythia, P. gingivalis, and finally, T. denticola. The copy numbers did not always correlate with prevalence. The DNA copy numbers of T. forsythia were significantly lower in cases of higher-grade gingivitis and when there was poor oral cleanliness. These findings highlight the complexity of the interplay between bacterial type, prevalence, DNA copy numbers, and the oral health of household dogs.