Yuqing Hao

Competition between yogurt probiotics and periodontal pathogens in vitro

Abstract Objective. To investigate the competition between probiotics in bio-yogurt and periodontal pathogens in vitro. Material and methods. The antimicrobial activity of bio-yogurt was studied by agar diffusion assays, using eight species of putative periodontal pathogens and a ‘protective bacteria’ as indicator strains. Four probiotic bacterial species (Lactobacillus bulgaricus, Streptococcus thermophilus, Lactobacillus acidophilus, and Bifidobacterium) were isolated from yogurt and used to rate the competitive exclusion between probiotics and periodontal pathogens. Results. Fresh yogurt inhibited all the periodontal pathogens included in this work, showing inhibition zones ranging from 9.3 (standard deviation 0.6) mm to 17.3 (standard deviation 1.7) mm, whereas heat-treated yogurt showed lower antimicrobial activity. In addition, neither fresh yogurt nor heat-treated yogurt inhibited the ‘protective bacteria’, Streptococcus sanguinis. The competition between yogurt probiotics and periodontal pathogens depended on the sequence of inoculation. When probiotics were inoculated first, Bifidobacterium inhibited Porphyromonas gingivalis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Porphyromonas circumdentaria, and Prevotella nigrescens; L. acidophilus inhibited P. gingivalis, A. actinomycetemcomitans, P. circumdentaria, P. nigrescens, and Peptostreptococcus anaerobius; L. bulgaricus inhibited P. gingivalis, A. actinomycetemcomitans, and P. nigrescens; and S. thermophilus inhibited P. gingivalis, F. nucleatum, and P. nigrescens. However, their antimicrobial properties were reduced when both species (probiotics and periodontal pathogens) were inoculated simultaneously. When periodontal pathogens were inoculated first, Prevotella intermedia inhibited Bifidobacterium and S. thermophilus. Conclusions. The results demonstrated that bio-yogurt and the probiotics that it contains are capable of inhibiting specific periodontal pathogens but have no effect on the periodontal protective bacteria.

Effects of Galla chinensis on inhibition of demineralization of regular bovine enamel or enamel disposed of organic matrix

OBJECTIVE This in vitro study was undertaken to assess the effects of Galla chinensis extract on inhibition of enamel caries-like demineralization and to elucidate the role of the organic matrix of enamel in this process. DESIGN Either regular or enamel disposed of its organic matrix both of bovine origin were exposed to a demineralizing solution for 3 days (pH 4.5). Specimes were additionally treated with either 4 g/L of G. chinensis extraction (GCE) or double distilled water (DDW) four times daily for 5 min each time. Regular enamel exposed accordingly to sodium fluoride (1g/L) during the demineralizing period served as positive control. After exposure mineral loss and lesion depth of all samples were analysed by transversal microradiography. One-way ANOVA and Student-Newman-Keuls test were used to compare the differences amongst groups. A factorial ANOVA was chosen to test the interaction between GCE and enamel organic matrix. RESULTS Mineral loss and lesion depth of specimens in the positive control group were significantly lower compared to all other groups. Regular enamel treated with GCE showed significantly lower values compared to regular enamel treated with DDW or to enamel disposed of its organic matrix (p<0.05). These three groups revealed similar values (p>0.05). Significant interaction between GCE and enamel organic matrix with respect to both outcomes could be observed (p<0.05). CONCLUSIONS G. chinensis inhibits enamel caries-like demineralization in vitro. However, its potential seems to be weaker compared to sodium fluoride. The organic matrix of enamel was shown to play a substantial role in the observed mechanism.

Measurement of hydroxyapatite density and Knoop hardness in sound human enamel and a correlational analysis between them

OBJECTIVE The aim of this study was to measure the hydroxyapatite (HAP) density and Knoop hardness (KHN) of enamel slabs and to analyse the relationship between them. DESIGN Twenty enamel slabs (10 lingual sides and 10 buccal sides) were prepared and scanned with micro-CT. Tomographic images of each slab from dental cusp to dentinoenamel junction (DEJ) were reconstructed. On these three-dimensional (3D) images, regions of interest (ROIs) were defined at an interval of 50 microm, and the HAP density for each ROI was calculated. Then the polished surfaces were indented from cusp to DEJ at intervals of 50 microm with a Knoop indenter. Finally, the data were analysed with one-way ANOVA, Students t-test, and linear regression analysis. RESULTS The HAP density and KHN decreased from the dental cusp to DEJ. Both HAP density and KHN in the outer-layer enamel were significantly higher than those in the middle- or inner-layer enamel (P<0.05). The HAP density showed no significant difference between the buccal and lingual sides for enamel in the outer, middle and inner layers, respectively (P>0.05). The KHN in the outer-layer enamel of the lingual sides was significantly lower than that of the buccal sides (P<0.05); there was no significant difference between the lingual and buccal sides in the middle or inner layer. Linear regression analysis revealed a linear relationship between the mean KHN and the mean HAP density (r=0.87). CONCLUSION Both HAP density and KHN decrease simultaneously from dental cusp to DEJ, and the two properties are highly correlated.

Effect of compounds of Galla chinensis on remineralization of enamel surface in vitro

OBJECTIVE The aim of the study was to investigate the effect of chemical compounds of Galla chinensis on in vitro the remineralization of enamel surface. METHOD Bovine enamel blocks with in vitro produced initial lesions were used. The lesions were subjected to a pH-cycling regime for 12 days. Each daily cycle included 4x1 min applications with one of four treatments: Group A: 1000 ppm F aq. (as NaF, positive control); Group B: deionized water (DDW, negative control); Group C: 4000 ppm crude aqueous extract of G. chinensis (GCE); Group D: 4000 ppm gallic acid. The enamel specimens were analysed by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and X-ray microdiffraction (XRD). RESULTS The morphology of surface enamel was different in each group. The mineral composition was identified as similar to hydroxylapatite, but the crystallite sizes of enamel in different groups were significantly different. In addition, the Ca/P ratios were significantly lower in GCE group. CONCLUSION GCE could affect the mineral ions deposit on the surface layer and then modified the remineralization of initial dental caries. The mechanism seems to be different between GCE and gallic acid.

Defect of cell wall construction may shield oral bacteria's survival in bloodstream and cause infective endocarditis.

Infective endocarditis (IE) is a rare but life-threatening infection. Bacteremia with organisms known to cause IE occurs commonly in association with invasive dental origin. Despite daily oral activities as well as professional dental treatments inducing bacteremia and the dental bacteremia as a risk factor of IE, the details of dental bacteria in the pathogenesis of IE are far from elucidation to date. How do a few microorganisms survive host defenses or escape from antibiotic attacking to seed target organs and cause distant infections? Why are Gram-positive bacteria more frequently detected than Gram-negative bacteria in IE? Cell wall-deficient bacteria (CWDB) were traditionally defined as bacteria with altered morphology and consistent with damaged or absent cell wall structures identified by EM. A number of case reports and laboratory studies suggest that CWDB may be found in the peripheral blood of patients with IE, and may also be demonstrated in vegetations on the valves of patients with IE. CWDB, in vitro, are resistant to antibiotics that act on cell wall biosynthesis. Recent studies indicate that the Streptococcus mutans (S. mutans) strains, the major cariogenic bacterium, isolated from the infected valve were deficient in some wall-associated proteins which are main cariogenic virulence of S. mutans, and the deficient stains exhibited less susceptible to antibiotics that act on cell wall biosynthesis. Further, the cloned deficient mutans were less susceptible to phagocytosis by human polymorphonuclear leukocytes but to possess higher platelet aggregation properties than their parent strains. As outlined above, we hypothesize that defect of cell wall construction may shield oral bacterias survival in bloodstream and cause IE.

Effect of enamel organic matrix on the potential of Galla chinensis to promote the remineralization of initial enamel carious lesions in vitro

Galla chinensis, a natural traditional Chinese medicine with main composition of tannic acid and gallic acid, is formed when the Chinese sumac aphid Baker (Melaphis chinensis bell) parasitizes the levels of Rhus chinensis Mill. Galla chinensis has shown the potential to enhance the remineralization of initial enamel carious lesion, but the mechanism is still unknown. This study was to investigate whether the enamel organic matrix plays a significant role in the potential of Galla chinensis to promote the remineralization of initial enamel caries. Bovine sound enamel blocks and non-organic enamel blocks were demineralized and exposed to a 12 day pH cycling. During the pH cycling, 30 specimens with the enamel organic matrix were randomly divided into three groups, and treated with 1 g L(-1) NaF (group A), 4 g L(-1) Galla chinensis extract (group B1) or double deionized water (group C1). Twenty specimens without the enamel organic matrix were randomly divided into two groups, and treated with 4 g L(-1) Galla chinensis extract (group B2) or double deionized water (group C2). The integrated mineral loss and lesion depth of all the specimens were analysed by transverse microradiography. The integrated mineral loss and lesion depth of group B1 were less than those of groups B2, C1 and C2, and there were no statistical differences among groups B2, C1 and C2. In conclusion, Galla chinensis can enhance the remineralization of initial enamel carious lesion, and the enamel organic matrix plays a significant role in this potential of Galla chinensis.

Activity of Nidus Vespae extract and chemical fractions against Streptococcus mutans biofilms

Aims:  To evaluate the effect of Nidus Vespae extract and chemical fractions on the viability and architecture of Streptococcus mutans biofilms.

Nanobacteria’s potential involvement in enamel repair in caries

Dental caries is the accumulation of numerous episodes of demineralization and remineralization, rather than a unidirectional demineralization process. Demineralization and remineralization occur constantly either simultaneously or alternately and whether a lesion will progress or be repaired depends upon the predominant process over periods. Even if fluoride has demonstrated the anti-caries effect by shifting the demineralization/remineralization balance favorably, little is known about non-fluoride action in favor of the balance and the effect of fluoride could not fully explain enamel repair in caries. Recently, in vitro experiments demonstrated enamel repair by synthetic apatite nanocrystals which showed the strong affinity, excellent biocompatibility, mechanical improvement, and a higher resistance to acids than apatite from teeth. This reminds us of a controversial microorganism called nanobacteria (NB) which form nanocrystalline apatite around themselves. Although NB have been detected in some pathological calcifications, epidemiologic literature suggests that they are widespread present in the healthy people blood. Considering the similarity of synthetic nanocrystalline apatite to that of NB and blood circulation communicating with saliva, we put forward a hypothesis that NB may act in enamel surface just like what the synthetic nanocrystalline apatite does in vitro to repair enamel in caries.

Polymerase chain reaction detection of Lactobacillus acidophilus in human oral cavity and fecal samples after 2-week consumption of yoghurt

Abstract Objective. To investigate whether short-term daily consumption of yoghurt leads to colonization by Lactobacillus acidophilus in a group of human subjects who were initially totally devoid of L. acidophilus in their oral cavities. Material and methods. Twenty-three volunteers consumed yogurt containing L. acidophilus during a 14-day trial stage. Oral and fecal samples were collected at the clearance stage and at the post-yoghurt intake stage until L. acidophilus was found. Standard polymerase chain reaction methods using specific primers were adopted for the detection and identification of L. acidophilus. Results. The isolation frequency decreased rapidly 72 h after stopping intake of yoghurt. After 1 week, L. acidophilus was absent in all oral samples. Non-significant differences were found between the survival rates of L. acidophilus in samples of saliva, plaque, tongue surface, and buccal mucosa. L. acidophilus was also found to remain in the gastrointestinal tract for longer than in the oral cavity. Conclusion. Allochthonous L. acidophilus is not likely to permanently colonize the oral cavity and intestine.

Effects of hydroxyapatite nanoparticle on remineralization of artificial root caries in vitro

An in vitro pH cycling model was used to evaluate the effect of nano-hydroxyapatite on the remineralization of artificial root caries. Sound human teeth fragments obtained from the cervical portion of the root were immersed in a demineralization solution for 96 h at 37°C to induce artificial root caries lesions. The demineralized samples were pH-cycled through treatment solutions, acidic buffer and neutral buffer for 8 days at 6 cycles per day. The samples were subsequently evaluated using a microhardness tester and scanning electron microscope (SEM). Nano-hydroxyapatite (nano-HA) and fluoride significantly increased the microhardness of the lesions (p ≪ 0.05) when compared to a control group. SEM revealed nano-HA adhered to the dentin surface densely and some of them even covered the openings of dentin tubules. We concluded that nano-HA positively affects the demineralization and/or remineralization processes of artificial root caries lesions and may be a promising agent for non-invasive root caries therapy.