The effect of periodontal therapy on the number of cariogenic bacteria in different intra-oral niches

Several publications have reported an increased susceptibility for root car ies after periodontal therapy. It has been suggested that newly exposed roo ts were less resistant to cariogenic species. This study examined the hypot hesis that the increased susceptibility could also be related to an intra-o ral microbial shift during the initial phase of the periodontal therapy fro m a perio-pathogenic to a more cariogenic flora. 10 patients with severe pe riodontitis were followed for 8 months after thorough scaling and root plan ing in combination with optimal plaque control. At baseline and after 4 and , 8 months, samples were taken from the saliva, the tongue dorsum and the s upragingival interdental spaces. These samples were cultured both aerobical ly and anaerobically in order to determine the total number of colony formi ng units (CFU) per sample as well as the number of CFU of Streptococcus mut ans and Lactobacillus species. Oral hygiene parameters were recorded at the same visits. Finally, at baseline and at the 8 months follow-up, changes i n caries activity and periodontal health were registered. Although the tota l number of aerobic and anaerobic CFU in samples from the tongue and the sa liva remained nearly constant over the entire observation period (variation s within 0.5 log), significant (p less than or equal to 0.05) increases in the number of S. mutans could be detected, especially at month. 8. The sign ificant decrease in the total number of anaerobic CFU in samples from the t eeth was not associated with a reduction in the number of S. mutans, so tha t also for this niche the relative proportion of the latter increased. The number of lactobacilli species for the different niches showed only negligi ble changes (within 0.5 log values), except for samples from the teeth for which a small (1 log), but statistically significant (p<0.01), reduction co uld be detected. The periodontal conditions improved for all patients, but the caries activity could not be arrested. These findings seem to indicate that the increased caries susceptibility after periodontal therapy might pa rtially be explained by a significant increase in, the number of S. mutans due to ecological changes within the oral cavity. The clinical consequence of this observation would be to advocate a more strict caries preventive pr ogram during initial periodontal therapy.