Influence of pH on inhibition of Streptococcus mutans by Streptococcus oligofermentans

Streptococcus oligofermentans is a novel strain of oral streptococcus that can specifically inhibit the growth of Streptococcus mutans. The aims of this study were to assess the growth of S. oligofermentans and the ability of S. oligofermentans to inhibit growth of Streptococcus mutans at different pH values. Growth inhibition was investigated in vitro using an interspecies competition assay. The 4‐aminoantipyine method was used to measure the initial production rate and the total yield of hydrogen peroxide in S. oligofermentans. S. oligofermentans grew best at pH 7.0 and showed the most pronounced inhibitory effect when it was inoculated earlier than S. mutans. In terms of the total yield and the initial production rate of hydrogen peroxide by S. oligofermentans, the effects of the different culture pH values were as follows: pH 7.0 > 6.5 > 6.0 > 7.5 > 5.5 = 8.0 (i.e. there was no significant difference between pH 5.5 and pH 8.0). Environmental pH and the sequence of inoculation significantly affected the ability of S. oligofermentans to inhibit the growth of S. mutans. The degree of inhibition may be attributed to the amount of hydrogen peroxide produced.     

Effect of pH on dentin protease inactivation by carbodiimide

A water‐soluble crosslinking agent, 1‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide (EDC), has been used as a pretreatment of acid‐etched dentin to inactivate matrix‐bound endogenous dentin proteases. The aim of this study was to evaluate the effect of pH on the inactivation capacity of EDC. Demineralized dentin beams (1 × 2 × 6 mm) were divided into six groups (n = 8 per group). Then, EDC (0.3 M) was solubilized in distilled water with pH of 2, 4, 6, 7, 9, or 11. Control EDC was solubilized in 0.1 M 2‐(N‐morpholino) ethanesulfonic acid (MES) buffer and its pH was adjusted to 6. The dentin beams were pretreated for 1 min with EDC at each pH or with EDC in MES buffer at pH 6.0 and then incubated in 1 ml of simulated body fluid (pH 7.2) for 1, 3, 7, or 14 d. Untreated beams served as controls. At each study time‐point, the dry mass of dentin beams was assessed and the incubation media were analyzed for carboxyterminal telopeptide of type‐I collagen (ICTP) and C‐terminal telopeptide of type I collagen (CTX) using specific ELISAs. Data were subjected to repeat‐measures anova . The results of the study indicated that specimens pretreated with EDC in MES buffer showed the lowest collagen degradation in terms of mass loss and release of telopeptides, while specimens pretreated in alkaline media showed the highest collagen degradation. This study indicates that the pH of the EDC solution plays an important role in the stability of dentin protease inactivation.     

Candida–streptococcal mucosal biofilms display distinct structural and virulence characteristics depending on growth conditions and hyphal morphotypes

Candida albicans and streptococci of the mitis group form communities in multiple oral sites, where moisture and nutrient availability can change spatially or temporally. This study evaluated structural and virulence characteristics of Candida–streptococcal biofilms formed on moist or semidry mucosal surfaces, and tested the effects of nutrient availability and hyphal morphotype on dual‐species biofilms. Three‐dimensional models of the oral mucosa formed by immortalized keratinocytes on a fibroblast‐embedded collagenous matrix were used. Infections were carried out using Streptococcus oralis strain 34, in combination with a C. albicans wild‐type strain, or pseudohyphal‐forming mutant strains. Increased moisture promoted a homogeneous surface biofilm by C. albicans. Dual biofilms had a stratified structure, with streptococci growing in close contact with the mucosa and fungi growing on the bacterial surface. Under semidry conditions, Candida formed localized foci of dense growth, which promoted focal growth of streptococci in mixed biofilms. Candida biofilm biovolume was greater under moist conditions, albeit with minimal tissue invasion, compared with semidry conditions. Supplementing the infection medium with nutrients under semidry conditions intensified growth, biofilm biovolume and tissue invasion/damage, without changing biofilm structure. Under these conditions, the pseudohyphal mutants and S. oralis formed defective superficial biofilms, with most bacteria in contact with the epithelial surface, below a pseudohyphal mass, resembling biofilms growing in a moist environment. The presence of S. oralis promoted fungal invasion and tissue damage under all conditions. We conclude that moisture, nutrient availability, hyphal morphotype and the presence of commensal bacteria influence the architecture and virulence characteristics of mucosal fungal biofilms.     

Estimation of the costs of smoking‐related oral disease: a representative South Korean study

Objectives: The objectives of this study were to estimate the socioeconomic and psychological costs associated with smoking‐related oral disease (SROD) with the aim of generating objective data that could be used in smoking cessation counselling by dental care providers and could also serve as data with which to set standards and criteria for use in dental health insurance. Methods: Patients were sourced from the 11 dental hospitals associated with dental schools in South Korea. A total of 1,288 of 10,080 patients with SROD were selected to participate in the study for a period of 2 years from January 2009 to March 2011. Data collected were analysed using spss Version 17.0. Results: Among the SRODs, the most common was periodontal disease (40.7%). Periodontal disease accounted for the highest social and economic costs. Mouth cancer accounted for the highest psychological cost. Conclusions: In order to reduce associated socioeconomic and psychological costs, dental care providers and government should provide more proactive and more efficient smoking cessation programmes.     

World Workshop on Oral Medicine VII: What participants perceive as important

Our objective was to identify which aspects of World Workshop on Oral Medicine (WWOM) participation were perceived as significant for participants’ professional development. Online survey was sent to previous WWOM participants. Qualitative analysis of participants’ responses to an open‐ended question was performed. Fifty‐two WWOM participants responded. Nearly three quarters of respondents (72.3%) felt that participation in the WWOM helped their career. A high percentage of respondents (67.3%) provided answers that fell under the domains of international collaboration, followed by personal academic benefits (48%). Overall, the results indicate that WWOM participation played an important role in individual's professional development. We identified aspects of WWOM involvement that the participants perceived as important. This information will be used for the development of an objective instrument for measuring impact of WWOM on participant's professional path.