Effects of ultrasmall platinum nanoparticles (PtNPs) on RAW264 cells were examined using cell viability assays, flow cytometry, and transmission electron microscopy (TEM). RAW 264 cells were exposed to the three concentrations of PtNPs with particle sizes of 4.4 nm (ultrasmall NPs) and 31.0 nm (large NPs). Cytotoxicity assays revealed no significant NP size-dependent differences in cell viability; however, both particle types caused a pronounced reduction in viability at higher concentrations compared with untreated controls.　TEM imaging showed receptor-mediated endocytosis for both ultrasmall and large PtNPs. Although exposure to PtNPs clearly reduced cell viability relative to the controls, distinguishing size-specific effects remains challenging. Further comprehensive studies are required to elucidate the various cellular responses toward ultrasmall PtNPs and their potential size-dependent mechanisms of action.

Pure titanium disks were fabricated and coated with silicon nitride using plasma chemical vapor deposition. Surface characterization was performed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Rat bone marrow cells (RBMCs) were cultured on the titanium disks, and the expression levels of osteogenesis-related genes, including alkaline phosphatase (ALP) and osterix (OSX), were analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). SEM analysis confirmed the presence of crystalline layers on the silicon nitride-coated titanium surfaces, and XPS analysis detected silicon, nitrogen, oxygen, and carbon molecules on the coated surfaces. RBMCs cultured on the silicon nitride-coated titanium surfaces exhibited higher expression levels of ALP and OSX compared to those cultured on uncoated titanium surfaces. These findings suggest that silicon nitride coating on titanium surfaces promotes the induction of early hard tissue differentiation in RBMCs at the genetic level. Further research is necessary to evaluate the potential clinical applications of this material in dental implants.

Surface wettability is important for obtaining osseointegration. Recently, the authors have applied various plasma treatments to pure titanium surfaces as a method of achieving superhydrophilicity, and found that these surfaces contributed to the initial adhesion of rat bone marrow cells and the ability to induce differentiation of hard tissues. The results suggest that the use of argon gas has a greater effect on the ability to induce hard tissue differentiation than the use of atmospheric pressure plasma alone. On the other hand, it has been reported that increasing the output of argon gas can have a greater effect. Therefore, we compared the effects of argon plasma treatments with different outputs on rat bone marrow mesenchymal cells. The results of this study showed that argon plasma treatment with higher output power had a higher ability to induce hard tissue differentiation in pure titanium.

This study investigated the potential of titanium nanotube (TNT)-containing collagen gels as novel bone graft materials for enhancing hard tissue differentiation in extensive bone defects. TNT was synthesized via low-temperature chemical methods and incorporated into a collagen gel modified with glycerol and pullulan. Characterization of the TNT-containing collagen gel confirmed the formation of nanoscale tubular structures and the presence of titanium. In vitro analysis of rat bone marrow cells (RBMCs) cultured with the TNT-containing collagen gel showed significantly higher cell adhesion, alkaline phosphatase (ALP) activity, and calcium deposition compared to the control and collagen gel groups. In vivo evaluation using a rat cranial defect model revealed increased bone volume and trabecular density in the TNT-containing collagen gel group, with histological observations indicating advanced calcified hard tissue formation. These findings suggest that the nanotubular structure of TNT promotes extracellular matrix formation and osteoblast activity, supporting bone regeneration. Although further investigation is needed to optimize TNT concentration and assess long-term effects, TNT-containing collagen gels demonstrate promise as next-generation bone graft materials for repairing extensive bone defects. The combination of TNT with glycerol- and pullulan-blended collagen gels may create a synergistic effect, enhancing both the mechanical and bioactive properties of the composite material for advanced bone tissue engineering applications.

The objective of this study was to clarify the effects of two different concentrations of oxalic acid on the microstructure and composition of the enamel surface. Enamel sections were prepared from bovine mandibular incisors. The control group did not react the enamel samples with the oxalic acid solution. The experimental group exposed tooth specimens to oxalic acid solutions at two concentrations (0.45 mg/mL and 12.6 mg/mL). The reaction time between the oxalic acid solution and the tooth specimens was set at 90 minutes. Visual inspection of the tooth specimen surfaces was performed, surface microstructure was observed using scanning electron microscopy, and elemental analysis was conducted using SEM-energy dispersive X-ray spectroscopy. In the experimental group, prismatic crystalline structures formed on the enamel surface under all conditions, and carbon and oxygen were detected from these structures. Oxalic acid formed large amounts of calcium oxalate crystals on the enamel surface in a concentration-dependent manner, with their morphology and size varying with concentration.

Mesenchymal stem cells (MSCs) are essential for the regeneration of dentine or alveolar bone. Although cells obtained from rat femoral bone marrow (rBMCs) have generally been used for odontogenesis, MSCs in dental pulp cells (DPCs) may be a superior option. However, the number of MSCs in dental pulp tissue is extremely low. A long period is required for MSCs in DPCs to differentiate into odontoblasts. Dexamethasone (Dex) induces the differentiation of MSCs into blast cells. We herein propose use of a novel chemical substance to replace or act as a co-factor for Dex to realize more prompt differentiation of MSCs, and vitamin B₆ (VB₆) was examined as one. rBMCs were used in the present study. The effects of VB₆ on the mineralized nodule formation were estimated by measuring Ca²⁺ levels. It was shown that Dex is an essential factor for MSCs to differentiate and mineralized nodule formation, and also that VB₆ acts as a co-factor for Dex.

Various cultured cell lines have been employed in cytotoxicity assays that evaluate the safety of chemical substances for human use. ISO 10993-5 and domestic medical device guidance documents both stipulate the use of mouse-derived L929 cells, Balb/c 3T3 clone A31 cells, and V79 cells as standard cell lines. Numerous other cultured cells have also been selected in various cytotoxicity studies. However, the extent to which test results vary when using alternative cultured cells has not been sufficiently investigated. In the present study, we compared the cell viability of NCTC clone 1469 cells, mouse liver–derived cells exhibiting stable proliferation, with that of standard Balb/c 3T3 clone A31 cells following exposure to seven metal ions: Ag, Au, Cu, Pd, Sn, Ti, and Zr. The results obtained showed that changes in cell viability following exposure to most metal ions were generally similar between the two cell lines. These results suggest that the use of cultured cells derived from various organs, in addition to the standard cell lines widely employed in cytotoxicity testing, provides valuable information for elucidating the mechanisms of action of various chemical substances, including materials used in regenerative medicine.

This study investigated the cleaning efficacy and optimal blasting pressure of agar particles when used to clean polymethyl methacrylate (PMMA) denture surfaces. PMMA discs coated with bovine serum albumin (BSA) as a simulated contaminant were cleaned using a sandblaster with agar particles which are micro-sized particles at five different pressures (0.1, 0.2, 0.3, 0.4, and 0.5 MPa). Stereomicroscopy and scanning electron microscopy (SEM) were used to observe surface changes. Elemental analysis, arithmetic mean surface roughness (Ra), and cross-sectional profiles were also evaluated. Residual BSA was clearly observed at 0.1 and 0.2 MPa, whereas no residue remained at ≥0.3 MPa. However, at 0.4 and 0.5 MPa, flaws distinct from polishing marks were detected. Elemental analysis revealed nitrogen (indicative of BSA) at 0.1 and 0.2 MPa but not at higher pressures. Ra increased significantly at all pressures except 0.3 MPa, and cross-sectional curves showed no changes at 0.3 and 0.4 MPa. These findings indicated that agar particle blasting at 0.3 MPa effectively removes contaminants without damaging the PMMA surface, suggesting its potential as a safe and effective novel denture-cleaning method.

Particles with diameters below 4 µm were isolated from cobalt–chromium alloy (Co-Cr) powders used in 3D additive manufacturing, and their effects on Balb/c 3T3 mouse fibroblasts were evaluated after four days of exposure. Cytotoxicity was evaluated using the MTT and neutral red uptake (NR) assays, and cell morphology was examined by scanning electron microscopy (SEM).

The MTT assay revealed a modest reduction in cell viability in the Co-Cr-exposed group compared with the particle-free control group, and comparable findings were obtained with the NR assay. However, in both assays the reduction in cell viability was minimal, indicating the absence of marked cytotoxicity. In contrast, SEM observations revealed surface irregularities and intracellular particle uptake, indicating morphological changes at the cellular level.

These findings suggest that Co-Cr microparticles of several micrometers in size can influence cell morphology while exerting only limited effects on cell viability. The biological behavior and in vivo impact of such particles remain poorly understood; nevertheless, even micron‑sized particles, similar to nanoscale or submicron powders, may pose potential biological risks in dental laboratory environments where Co-Cr alloy powders are handled, highlighting the importance of appropriate protective measures.