The effect of liquorice extract-containing starch gel on the amount and microbial composition of plaque

Our pilot experiments showed that acid production from a starch gel in interdental plaque can be inhibited by some plant extracts. From among these, liquorice was selected to study the clinical feasibility. Sixteen healthy volunteers (mean age: 30.4±6.9 y) used 6 g of either control (8% acid hydrolysed corn starch, 25% maltitol syrup, water, w/w) or liquorice gel (control + 2,5% liquorice extract), 3 times a day for 2 weeks. The gels were used in a random order with a 2 weeks’ wash-out period in between. Professional cleaning was carried out prior to the onset of each gel-period. At the end of each fortnight, plaque was allowed to accumulate for 2 days and all available plaque from the right side of the mouth was collected using dental curettes, weighed and transferred to transport medium. The plaque on the left side was dyed and photographed in a standardized manner. Mutans streptococci (MSB agar), total streptococci (MS agar) and facultative bacteria (blood agar) were assessed from the plaque using plate culturing techniques and expressed as log CFU. Plaque index (0-5) of incisors and canines on the left side was evaluated from the photographs. The weight of plaque after consumption of the liquorice gel did not differ from that of the control gel (p=0.268; t-test). No differences were found in the microbial counts (mutans streptococci, total streptococci and facultatives; p=0.438, p=0.301 and p=0.272, respectively), nor in the plaque index between the two gels (p=0.686; Wilcoxon). As no enhancement of plaque accumulation and no increase in the number of plaque mutans streptococci could be seen, it can be concluded that it might be possible to use both starch and liquorice extract in toothfriendly products.