Actinomyces oris (A. oris), an early colonizer in oral microbiota, possesses two antigenically distinct fimbriae types. Oral bacteria-derived membrane vesicles (MVs) contain diverse bacterial components and are associated with dental caries; however, their role in A. oris-mediated biofilm interactions remains unclear. This study investigated the effects of A. oris-derived MVs on early biofilm formation by Streptococcus mutans (S. mutans), a notable cariogenic bacterium. Biofilm formation was evaluated in salivacoated 96-well plates using MVs from A. oris MG-1 (wild type, WT) and fimbriae A mutant (ΔfimA) in Tryptic Soy Broth (TSB) without dextrose, supplemented with 0.25% sucrose. S. mutans growth was quantified by absorbance at 595 nm. Biofilm formation was measured by safranin staining at 492 nm; representative images were obtained by phase-contrast microscopy. A. oris-derived MVs exhibited no statistically significant effect on the early growth of S. mutans WT or the glucosyltransferases B and C (GtfB and GtfC) mutants (ΔgtfBC). Both MVs also showed no statistically significant effect on early S. mutans WT biofilms. A. oris WT-derived MVs significantly and dose-dependently promoted early biofilm formation of S. mutans ΔgtfBC, whereas A. oris ΔfimA-derived MVs showed no statistically significant effect. Visual observation revealed biofilm formation at 7.81–125 μg/mL in the presence of only A. oris WT-derived MVs. This difference proposed structural variation in MVs associated with fimbriae. Scanning electron microscopy (SEM) analysis revealed that WT-derived MVs were significantly larger than ΔfimA-derived MVs. These findings indicate that FimA-containing A. oris MVs promote insoluble glucan-independent S. mutans biofilm formation.

Saliva is an important body fluid and hyposecretion of saliva impairs various oral functions. To understand the mechanisms of salivary gland dysfunction and recovery, we established a system for primary culture of parotid acinar cells. Previous work reported that the isolation from the parotid glands and culture of acinar cells altered gene expression, leading to dedifferentiation. When the Src kinase inhibitor PP1 was added during culture, changes in gene expression were suppressed, and the acinar cell properties were maintained for a longer period. In this study, we compared microRNA (miRNA) expression profiles of cells isolated in the absence and presence of PP1, and cells culture for 1 day in the absence and presence of PP1. The effect of PP1 on changes in miRNA expression was compared with the changes in miRNA levels during the 1-day culture. We found that the changes in miRNA levels due to 1-day culture were partially suppressed by the addition of PP1. KEGG pathway analysis was performed using five miRNAs that were altered by 1-day culture and whose changes were reversed by the addition of PP1. The analysis suggested pathways related to the TGF-ϐ signaling, cell cycle, and regulation of stem cell pluripotency. These results imply a role of miRNAs in the injury response and tissue repair of the salivary glands.

The ability to assess ingestion, mastication, and swallowing sequentially is critical for evaluating oral function in older adults. While acoustic analysis of chewing sounds has shown possibility in younger populations, its reliability and applicability in older dentate and edentulous individuals remain unclear. The current study aimed: 1. To examine the intra- and inter-day reliability of chewing sound measurements in older adults: 2. To confirm that the chewing sounds reflect the hypothesized differences in masticatory function resulting from distinct oral environments between dentate and edentulous older adult groups, group differences have been assessed by comparing chewing sounds between dentate and denture-wearing edentulous older adults. Twenty-eight older adults were recruited based on their oral status: 14 dentate individuals with natural teeth (D group) and 14 edentulous individuals wearing complete dentures (CD group). Participants chewed almonds freely while oral sounds were recorded using a high-performance sound level meter positioned at the laryngeal region. Acoustic energy during the first 10 seconds of chewing was calculated as the equivalent continuous A-weighted sound pressure level (L_Aeq,10s). Measurements were conducted three times in each of two sessions, one week apart. The study demonstrated that chewing sounds recorded during the initial 10 seconds of mastication exhibit excellent intra- and inter-day reliability in both groups. The group differnces between dentate and edentulous groups showed significant differences with edentulous individuals generating higher L_Aeq,10s values than dentate participants. These findings support the feasibility of acoustic analysis as a sequential, non-invasive tool for evaluating ingestion, mastication, and swallowing functions in older adults.

In Japan’s super-aged society, maintaining oral function is essential for supporting healthy life expectancy and quality of life. Mastication and swallowing are continuous processes, yet most conventional assessments of masticatory function require expectoration of food and do not capture the entire sequence leading to swallowing. Acoustic analysis of mastication may enable a continuous evaluation of oral function. This study compared 1) the time required from food intake to swallowing and 2) the acoustic characteristics of mastication during the first 10 seconds of mastication between dentate (D) older adults and complete denture (CD) wearers. Fifteen dentate and 15 edentulous participants wearing complete dentures were enrolled. Acoustic data during almond mastication were recorded three times using a sound level meter placed near the laryngeal region. Root mean square (RMS), amplitude, flatness, alpha index, and mastication-to-swallowing duration were included as exploratory parameters for evaluation. Appropriate parametric or non-parametric tests were used for comparisons, and time-series correlations among acoustic features were analyzed. Entire duration was significantly longer in the CD. The CD alsoexhibited significantly larger amplitude mean values, whereas the D showed significantly steeper amplitude slopes. Time-series analysis demonstrated significant correlations in amplitude, flatness, and alpha index only in the CD, and the correlation coefficient for flatness differed significantly between the two. These findings indicate that denture wearers require longer mastication and demonstrate distinct acoustic features compared with dentate individuals. Acoustic analysis may serve as a practical method for continuous evaluation of oral function in older adults.

The mechanical properties of stereolithography (SLA)-printed materials are influenced by printing parameters. This study examined the effects of printing orientation and layer thickness on the surface and flexural mechanical properties of two chemically distinct SLA resins. Specimens were fabricated from two photopolymer resins: Model Resin V3 (MR) and Surgical Guide Resin V1 (SR) which are identified as methacrylate-based photopolymers. For each resin, specimens were printed at two layer thicknesses (50 and 100 μm) and in five printing orientations. Dynamic micro-indentation and three-point bending tests were performed to evaluate surface and flexural mechanical properties. Printing orientation was the most influential factor governing flexural properties, and the 0-I orientation consistently produced the lowest values for both resins. A smaller layer thickness (50 μm) generally improved mechanical properties, with a more pronounced effect in SR than in MR. Resin type showed a combined influence with the fabrication parameters; the relative performance of the two resins varied according to printing orientation. The mechanical properties of SLA-printed components are highly sensitive to printing parameters, particularly printing orientation. The 0-I orientation should be avoided when high flexural performance is required. Although a smaller layer thickness is generally advantageous, the results suggest a combined impact of material selection and fabrication parameters. Optimal fabrication therefore requires coordinated consideration of resin type, printing orientation, and layer thickness.