Risk of Porphyromonas gingivalis Recolonization During the Early Period of Periodontal Maintenance in Initially Severe Periodontitis Sites

Background: Porphyromonas gingivalis is considered a critical pathogen of periodontal diseases including recurrent periodontitis. The profound effects of active periodontal treatment (APT) on P. gingivalis elimination were previously demonstrated and revealed that the subsequent P. gingivalis‐free or ‐suppressed status seems to be maintained during early periodontal maintenance (PMT). The aim of the present study was to show the occurrence of microbial recolonization during this early PMT period. Methods: In total, 128 sites from 11 generalized chronic periodontitis patients and one generalized aggressive periodontitis patient underwent clinical and microbiologic examination at baseline (Exam‐I), after APT (Exam‐II), and in PMT (Exam‐III). Exam‐III was carried out an average of 4.5 ± 3.5 months after Exam‐II. Detection and quantification of putative pathogens were performed using a polymerase chain reaction–based method. Results: The PMT used was effective in maintaining the clinical conditions improved by APT. However, in microbiological examinations, Exam‐III showed higher detection frequency and levels of P. gingivalis than Exam‐II. This suggests that a P. gingivalis recolonization started in the early PMT period. P. gingivalis‐increased sites then showed significantly more severe signs of periodontitis in Exam‐I than P. gingivalis‐stable sites (bleeding on probing frequency: 76.7% versus 56.5%; suppuration frequency: 41.9% versus 12.9%). On the other hand, in Exam‐II, no significant differences of clinical parameters were noted between P. gingivalis‐increased and ‐stable sites. Conclusion: Severe periodontitis sites before APT seemed to place them at risk of P. gingivalis recolonization in the early PMT period, and this microbial restoration could be a cause of recurrent periodontitis.