Inhibition of Streptococcus mutans by a commercial yogurt drink.

BACKGROUND/PURPOSE: Studies have been focused on using probiotics to prevent caries. The lactobacillus probiotic bacteria in Yakult® (LcY) has been shown to inhibit the growth or biofilm formation of Streptococcus mutans. However, sucrose in Yakult® raised concerns. The purpose of this study was to determine effects of Yakult® on the growth and adhesion of S. mutans. MATERIALS AND METHODS: S. mutans was grown in serial diluted Yakult®, filtered Yakult® or 20% heated Yakult®. S. mutans was co-cultured with LcY in media with or without diluted filtered Yakult®, or in LcY grown in media with or without sugars. Colony forming units and pH values of bacterial cultures were determined. SYTO 9-stained adhered bacteria were observed. RESULTS: Yakult® inhibited the growth of S. mutans. Filtering or heating Yakult® reduced its inhibitory ability against S. mutans. The inhibitory effect of LcY against S. mutans was enhanced when cultured in the presence of 20% filtered Yakult®. LcY cultured in sucrose media for 24 h inhibited the growth of S. mutans, but this effect was less evident when LcY was grown for 48 h. LcY grown in glucose or lactose media similarly reduced S. mutans growth. Culturing S. mutans with LcY grown in sucrose or glucose media reduced bacterial adhesion. However, co-culturing S. mutans with LcY grown in the lactose media did not decrease bacterial adhesion. CONCLUSION: Yakult® and its probiotic content may inhibit S. mutans growth and the effect may be moderated by the type of sugar added for LcY cultivation.

Optimal Er:YAG laser energy for preventing enamel demineralization.

OBJECTIVES: The purpose of this study was to identify the optimal laser energy range of Er:YAG laser irradiation for laser-induced caries prevention (LICP). METHODS: Twenty-one human non-carious molars were selected. The teeth were covered with nail varnish, except two 4 mm x 1 mm windows on both the buccal and lingual surfaces. The windows were randomly assigned to groups A, B, C and D, receiving no irradiation, 100, 200 and 300 mJ irradiation, respectively. The pulse width 10 pps (pulse per second) with a 1.0 mm spot size was used. After the laser treatment, each tooth was cut into two halves longitudinally. Then a two-day pH-cycling was performed, with an 18-hour demineralization followed by a 6-hour remineralization. Sections of 120 +/- 20 microm in thickness were obtained from each window. Lesion depth was measured using polarized light microscope coupled with an image analysis software. One-way ANOVA and post-hoc Tukey tests were used for evaluation of treatment effects. RESULTS: The laser treatments of 100 and 200 mJ have demonstrated significant protection of enamel demineralization (p = 0.01 and 0.001, respectively), but not the treatment with 300 mJ (p = 0.106). A smaller lesion depth was observed for the 200 mJ group (97.1 microm) than that of the 100 mJ group (105.6 microm). Compared with the control, a lesion reduction of 32.78 and 26.93% for the 200 mJ group and the 100 mJ group were obtained, respectively. CONCLUSION: Caries prevention may be achieved by using Er:YAG laser treatment if the optimal range of laser parameters for LICP can be employed.

Characterization of lipid in mature enamel using confocal laser scanning microscopy.

OBJECTIVE: To characterize the lipid components of organic matrix in mature human enamel using Confocal Laser Scanning Microscopy (CLSM) coupled with a hydrophobic fluorescent probe. METHODS: Twenty-four longitudinal sections of human enamel were fixed with 3.7% paraformaldehyde (PFA), partially decalcified with 0.5 M of EDTA, and labelled with a fluorescent probe (Nile red) before CLSM characterization. Based on the fluorescence spectra of Nile red in ethanol (1 microgram/ml), each enamel section was evaluated with 543 nm light source and with 590 nm long pass filter. Spectrophotometric analysis was carried out to characterize the autofluorescence and Nile red lipid fluorescence in mature enamel. Special optical parameters of the microscope were chosen to rule out the intrinsic fluorescence of the samples, and that induced by PFA. RESULTS: The intensity of autofluorescence and PFA-induced fluorescence were negligible above 565 nm; whereas the fluorescence of Nile red peaked at around 600 nm. Lipid material was identified in the cross-striations, the lines of Retzius, the Hunter-Schreger bands, inter-prismatic spaces, and inter-prismatic spaces in the mature human enamel. CONCLUSIONS: This technique successfully revealed the distribution of lipid components of organic matrix in mature human enamel and may be promising in assessing the changes of enamel organic elements in the developmental, pathological or experimental conditions.