Probiotic Drink as a Double-edged Sword in Caries Prevention

Objective: There is insufficient clinical evidence validating the putative cariostatic mechanism and sustainability of probiotics despite growing interest in their application in caries prevention. To evaluate potential oral effects of a sweet probiotic drink in adults and their sustainability. Methods: 14 healthy volunteers (aged 21-40yrs) consumed Yakult^® once daily for a week. Subjects were screened thrice, the day before start of intervention (baseline), the day after cessation and two weeks after cessation. During each visit, subjects underwent biofilm collection from the buccal mucosa, tongue, palate, upper incisor and lower molar, and supragingival plaque pH characterization. Investigated pH parameters were area under Stephan curve (AUC), lowest pH reached and recovery time. Real-time quantitative PCR was performed on DNA extracts of biofilm samples with primers specific for Lactobacillus casei Shirota strain (LcS) and Streptococcus mutans. Wilcoxon signed rank tests were employed for statistical analysis. Results: 12 of 14 subjects met study requirements. Between visits 1 and 2, a subgroup (n=5), or “responders”, experienced reduced plaque acidogenicity (63.30% AUC decrease; P<0.05) while “non-responders” (n=7) had increased plaque acidogenicity (711.70% AUC increase; P<0.05). Both were not sustainable after intervention ended. Responders had significantly higher baseline AUC and recovery time (both P<0.05). Total bacterial load was higher in hard tissue biofilm than soft tissue biofilm in all visits (all P<0.05). Persistence of probiotic LcS was detected after cessation of intervention. A non-traditional association between lowered plaque acidogenicity and significant and/or larger-than-tenfold parallel increases in S. mutans and LcS colonization on teeth was observed (all P<0.05). Soft tissue co-colonization increase in washout period (both P<0.01) did not help sustain cariostatic effects in responders. Conclusions: Short-term probiotic consumption may be transiently cariostatic in individuals with higher baseline plaque acidogenicity, but cariogenic in lower-risk individuals. LcS cariostatic mechanism may be tissue-dependent and involve co-aggregation with biofilm S. mutans.