Microbiological Diagnosis for Periodontal Diseases

Periodontitis, an infectious disease caused by bacteria, brings about destructive changes leading to loss of bone and connective tissue attachment (Williams, 1990). Several oral bacteria are considered to be possible pathogens in periodontitis (Darveau et al., 1997). In particular, the black-pigmented, Gram-negative anaerobic rods Porphyromonas gingivalis and Tannerella forsythia have been implicated as major pathogens in the etiology of this disease. These two species are frequently isolated together, implying the existence of an ecological relationship between these organisms (Darveau et al., 1997). Treponema denticola, a helical oral spirochete, has also been considered as a major pathogen in periodontitis (Darveau et al., 1997). Mixed infection with these three bacteria in periodontal sites is correlated strongly with the severity of adult periodontitis (Socransky & Haffajee, 1998). Socransky named this combination the “red complex” and found that these bacteria were most crucial for the progression of this disease (Socransky & Haffajee, 1998). Thus, the detection of these organisms provides essential information about the severity of periodontitis. Aggregatibacter actinomycetemcomitans is suspected to be the most probable causal factor for aggressive periodontitis in adolescents (Darveau et al., 1997). Although we cannot completely rule out the possibility of exogenous infection, periodontitis is thought to be primarily an endogenous infection caused by oral bacteria. Various systems for the detection of oral pathogens have been reported, but most are qualitative (Yoshida et al., 2005a; Yoshida et al., 2005b). Because periodontal pathogens exist not only in infected pockets but also in the healthy sulcus, qualitative detection is not suitable for the diagnosis of periodontitis. For this purpose, we have developed a quantitative detection system that uses real-time polymerase chain reaction (PCR) methodology (Yoshida et al., 2003a; Yoshida et al., 2003b ). The best time for the detection of oral bacteria remains unclear. When during the periodontal treatment process should a diagnostic system be used? Can a quantitative detection system be used for the initial diagnosis of periodontitis? Furthermore, periodontitis is influenced by multiple factors such as genetic, environmental, and lifestyle-related factors that complicate the determination of a microbial cut-off value for disease onset. The use of microbiological detection for the initial diagnosis of periodontitis is thus likely to be of limited value. Nevertheless, microbiological diagnosis is meaningful in evaluating the effects of periodontal therapy. During periodontal therapy, factors