ObjectiveTo investigate the changes in the quantity of colonizing Streptococcus mutans(S. mutans) and Acti-nomyces on the root surface plaque before and after post-core crown restoration of the mandibular first molars in the elderly patients.Methods A total of 30 elderly patients, each with one post-core crown restoration of the mandibular first molar, were randomly chosen to participate in the studies. Patients with mandibular first molars with post-core crown restoration and those with healthy contralateral mandibular first molars were divided into the test and control groups, respectively. Root surface plaques of the two groups were collected before tooth preparation, 72 h after preparation, one week afterpreparation, and one month after restoration. S. mutans, Actinomyces naeslundii (A. naeslundii) and Actinomyces viscosus (A. viscosus), were identified using colony morphology, biochemical techniques, and polymerase chain reaction (PCR). Plaque count was measured usingmicrobial colony count.Results The number of S. mutans and A. viscosus and A. naeslundii in the test group, whichwas statistically significant (PConclusion The quantities of S. mutans, A. viscosus and A. naeslundii increase one week after preparation but decrease one month after restoration. The finding suggests that dentists shouldeducatepatientsabout plaquecontrol during the earlyperiod after tooth preparation.
