Despite advances in bone regenerative medicine, the relationship between stress-induced premature senescence (SIPS) in cells and bone regeneration remains largely unknown. Herein, we demonstrated that the implantation of a lipopolysaccharide (LPS) sustained-release gelatin sponge (LS-G) increases the number of SIPS cells and that the elimination of these cells promotes bone formation in critical-sized bone defects in the rat calvaria. Histological (hematoxylin–eosin and SA-β-gal) and immunohistological (p16 and p21 for analyzing cellular senescence and 4-HNE for oxidation) staining was used to identify SIPS cells and elucidate the underlying mechanism. Bone formation in defects were analyzed using microcomputed tomography, one and four weeks after surgery. Parallel to LS-G implantation, local epigallocatechin gallate (EGCG) administration, and systemic senolytic (dasatinib and quercetin: D+Q) administration were used to eliminate SIPS cells. After LS-G implantation, SA-β-gal-, p16-, and p21-positive cells (SIPS cells) accumulated in the defects. However, treatment with LS-G+EGCG and LS-G+D+Q resulted in lower numbers of SIPS cells than that with LS-G in the defects, resulting in an augmentation of newly formed bone. We demonstrated that SIPS cells induced by sustained stimulation by LPS may play a deleterious role in bone formation. Controlling these cell numbers is a promising strategy to increase bone regeneration.

The deterioration of human oral microbiota is known to not only cause oral diseases but also to affect systemic health. Various environmental factors are thought to influence the disruption and restoration of the oral ecosystem. In this study, we focused on the effect of nitric oxide (NO) produced by denitrification and NO synthase enzymes on dental plaque microbiota. Interdental plaques collected from 10 subjects were exposed to NO donor sodium nitroprusside (SNP) and then cultured in a specialized growth medium. Depending on the concentration of exposed SNP, a decrease in α-diversity and a continuous change in β-diversity in the dental plaque community were shown by sequencing bacterial 16S rRNA genes. We also identified eight operational taxonomic units that were significantly altered by NO exposure. Among them, the exposure of NO donors to Fusobacterium nucleatum cells showed a decrease in survival rate consistent with the results of microbiota analysis. Meanwhile, in addition to NO tolerance, an increase in the tetrazolium salt-reducing activity of Campylobacter concisus cells was confirmed by exposure to SNP. This study provides an overview of how oral plaque microbiota shifts with exposure to NO and may contribute to the development of a method for adjusting the balance of the oral microbiome.

Oral microbiome dysbiosis has important links to human health and disease. Although photodynamic therapy influences microbiome diversity, the specific effect of violet light irradiation remains largely unknown. In this study, we analyzed the effect of violet light-emitting diode (LED) irradiation on interdental plaque microbiota. Interdental plaque was collected from 12 human subjects, exposed to violet LED irradiation, and cultured in a specialized growth medium. Next-generation sequencing of the 16S ribosomal RNA genes revealed that α-diversity decreased, whereas β-diversity exhibited a continuous change with violet LED irradiation doses. In addition, we identified several operational taxonomic units that exhibited significant shifts during violet LED irradiation. Specifically, violet LED irradiation led to a significant reduction in the relative abundance of Fusobacterium species, but a significant increase in several species of oral bacteria, such as Veillonella and Campylobacter. Our study provides an overview of oral plaque microbiota changes under violet LED irradiation, and highlights the potential of this method for adjusting the balance of the oral microbiome without inducing antibiotic resistance.

The dentin bonding durability of a total-etch adhesive system (Prime & Bond^® NT) was investigated by tensile bond test using conventional and dumbbell-shaped specimens. Two bonding techniques were compared. After etching and rinsing, dentin surface was either blotted by cotton ball (wet-bonding) or air-dried (dry-bonding) before bonding agent was applied. The bond strength of wet-bonding specimens was significantly higher than that of dry-bonding for both conventional and dumbbell-shaped specimens after one day. The bond strength of wet-bonded conventional specimens did not decrease after two years of water immersion, but cohesive failure in demineralized dentin was observed after two years. Wet-bonded dumbbell-shaped specimens showed cohesive failure within demineralized dentin after only one day. The bond strength of drybonded conventional specimens decreased significantly after one year, and cohesive failure in demineralized dentin was confirmed after three months. As for dry-bonded dumbbell-shaped specimens, they showed cohesive failure in demineralized dentin after one month. The results of the present study showed that the bonding durability of dry-bonded Prime & Bond^® NT restorations was lower than that of wet-bonded restorations. Further, by using tensile bond test, cohesive failure in demineralized dentin was detected earlier in dumbbell-shaped specimens than in conventional specimens.

Silicon nitride (Si₃N₄) can facilitate bone formation; hence, it is used as a biomaterial in orthopedics. Nevertheless, its usability for dentistry is unexplored. The aim of the present study was to investigate the effect of Si₃N₄ granules for the proliferation and odontogenic differentiation of rat dental pulp cells (rDPCs). Four different types of Si₃N₄ granules were prepared, which underwent different treatments to form pristine as-synthesized Si₃N₄, chemically treated Si₃N₄, thermally treated Si₃N₄, and Si₃N₄ sintered with 3 wt.% yttrium oxide (Y₂O₃). rDPCs were cultured on or around the Si₃N₄ granular beds. Compared with the other three types of Si₃N₄ granules, the sintered Si₃N₄ granules significantly promoted cellular attachment, upregulated the expression of odontogenic marker genes (Dentin Matrix Acidic Phosphoprotein 1 and Dentin Sialophosphoprotein) in the early phase, and enhanced the formation of mineralization nodules. Furthermore, the water contact angle of sintered Si₃N₄ was also greatly increased to 40°. These results suggest that the sintering process for Si₃N₄ with Y₂O₃ positively altered the surface properties of pristine as-synthesized Si₃N₄ granules, thereby facilitating the odontogenic differentiation of rDPCs. Thus, the introduction of a sintering treatment for Si₃N₄ granules is likely to facilitate their use in the clinical application of dentistry.

Freeze-drying, also known as lyophilization, is widely used in the preparation of porous biomaterials. Nevertheless, limited information is known regarding the effect of gas permeability on molds to obtain porous materials. We demonstrated that the different levels of gas permeability of molds remarkably altered the pore distribution of prepared gelatin sponges and distinct bone formation at critical-sized bone defects of the rat calvaria. Three types of molds were prepared: silicon tube (ST), which has high gas permeability; ST covered with polyvinylidene chloride (PVDC) film, which has low gas permeability, at the lateral side (STPL); and ST covered with PVDC at both the lateral and bottom sides (STPLB). The cross sections or curved surfaces of the sponges were evaluated using scanning electron microscopy and quantitative image analysis. The gelatin sponge prepared using ST mold demonstrated wider pore size and spatial distribution and larger average pore diameter (149.2 µm) compared with that prepared using STPL and STPLB. The sponges using ST demonstrated significantly poor bone formation and bone mineral density after 3 weeks. The results suggest that the gas permeability of molds critically alters the pore size and spatial pore distribution of prepared sponges during the freeze-drying process, which probably causes distinct bone formation.