Kyushu Dental University

This study aimed to evaluate the in vivo biocompatibility and bioactivity of gelatin hydrogel sponges incorporating bioactive glasses (BG), with or without impregnation of basic fibroblast growth factor (bFGF), as a potential scaffold for dentin-pulp complex regeneration. H.E. staining showed inflammatory cell infiltration in gelatin hydrogel sponges not incorporating BG (Gel-BG(0)) at 1 week, with blood vessels in the bFGF group (Gel-BG(0)-bFGF). Gelatin hydrogel sponges incorporating 10 wt% BG (Gel-BG(10)) and 50 wt% BG (Gel-BG(50)) retained their structure without inflammation. At 2 weeks, Gel-BG(0)-bFGF was no longer present, while Gel-BG(10) and Gel-BG(50) showed fragmentation and fibroblast infiltration. At 6 weeks, extracellular matrix-like structures were observed in Gel-BG(10) and Gel-BG(50). Masson's trichrome staining confirmed collagen deposition, and von Kossa staining revealed calcification. SEM-EDX analysis demonstrated Ca and P deposition throughout the implanted Gel-BG(10) and Gel-BG(50), with minimal Si and no co-localization of Ca and C. The co-localization of Ca and P indicates in vivo hydroxyapatite formation derived from BG. Gelatin hydrogel sponges incorporating BG and impregnated with bFGF demonstrated excellent biocompatibility, collagen matrix formation, and in vivo mineralization. These findings support their potential application in dentin-pulp regeneration and bone tissue engineering.

Sodium hypochlorite (NaClO) is widely used as a root canal irrigant because it is an effective antimicrobial agent; however, cytotoxicity to periapical tissues remains a clinical concern. Peracetic acid (PAA) is a well-established disinfectant, but its oral biocompatibility, particularly at low concentrations, and commercially formulated preparations have not been fully evaluated.

The antimicrobial efficacy and biocompatibility of a low-concentration PAA-based commercial disinfectant (Actril) were tested against representative oral pathogenic bacteria. Minimum inhibitory, bactericidal, and biofilm inhibitory concentrations were determined, and cytotoxicity toward gingival epithelial cells and periodontal ligament fibroblasts was assessed. Bactericidal activity against Enterococcus faecalis biofilms were evaluated using live/dead staining. Irrigation efficacy was further examined in E. faecalis-infected extracted human teeth using scanning electron microscopy and quantitative polymerase chain reaction.

Actril exhibited antimicrobial activity at PAA-equivalent concentrations markedly lower than those required for NaClO, with reduced cytotoxicity toward periodontal tissue-related cells. Live/dead staining demonstrated bactericidal effects within E. faecalis biofilms, although variability was observed at threshold concentrations. In extracted tooth models, Actril facilitated biofilm disruption and exposure of dentinal tubules within a clinically relevant irrigation time. Quantitative analyses confirmed significant reduction of bacteria compared with non-irrigated controls, comparable to the effects of NaClO.

Although PAA itself is not a novel antimicrobial agent, a low-concentration, commercially formulated PAA-based disinfectant demonstrated a favorable balance between antimicrobial efficacy and biocompatibility in oral biofilm models. These findings support the potential application of PAA as a low-toxicity antimicrobial strategy in endodontic environments.

Dental caries are caused by organic acids produced by cariogenic bacteria through carbohydrate metabolism. Suppression of acid production without disrupting the oral microbiome is a promising preventive strategy against dental caries. Surfactin, a naturally derived biosurfactant, has several biological activities. However, its effects on acid production by cariogenic bacteria remain unclear. In this study, the effects of surfactin on lactate production, growth, biofilm formation, and metabolic activity of Streptococcus sobrinus, were investigated.

In vitro assays were performed to distinguish surfactin-mediated suppression of acidogenic metabolism from its effects on bacterial growth or biofilm formation, combined with molecular and enzymatic analyses to explore the underlying regulatory mechanisms.

Surfactin significantly reduced lactate production in planktonic and biofilm-associated S. sobrinus, and it delayed environmental pH reduction in the presence of sucrose. Notably, these effects were observed without inhibition of bacterial growth or biofilm formation. There were no significant changes in the expression of lactate production-related genes, and lactate dehydrogenase activity was not inhibited by surfactin. In contrast, in the MTT assay, there was a transient reduction in metabolic activity, accompanied by delayed initiation of growth.

These findings indicate that surfactin selectively attenuates acidogenicity in S. sobrinus, without markedly affecting bacterial viability or biofilm architecture, which is consistent with an anti-virulence mode of action. Although further validation in more complex oral environments and comprehensive safety assessments are required, this study provides fundamental evidence supporting the potential of naturally derived biosurfactants as a basis for future preventive strategies for caries.