OBJECTIVETo investigate the changes in the quantity of colonizing Streptococcus mutans(S. mutans) and Actinomyces on the root surface plaque before and after post-core crown restoration of the mandibular first molars in the elderly patients.

METHODSA 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 after preparation, 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 using microbial colony count.

RESULTSThe number of S. mutans and A. viscosus and A. naeslundii in the test group, which was statistically significant (P<0.05), increased 72 h after preparation. The quantities of S. mutans, A. viscosus, and A. naeslundii one week after preparation were significantly different (P<0.05). The plaque count of S. mutans, A. viscosus, and A. naeslundii in the test group decreased one month after restoration (P<0.05).

CONCLUSIONThe 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 should educate patients about plaque control during the early period after tooth preparation.