Tungsten carbide and steel bar are used intraorally for the removal of dental prostheses and for cutting teeth. Blades at the tip of the bar can often chip, leaving small fragments of blades inside one's mouth. Such small fragments of blades can remain inside the mouth even after rinsing, and can penetrate the soft intraoral tissues. To assess the safety of the small fragments of cutting bar in the human body, we used a tissue model made of 3D collagen gel to examine their cytotoxicity. Furthermore, these small fragments may be transported through the vascular system and induce developmental toxicity. Therefore, we examined their influence on cell differentiation using ES-D3 cells. Our results demonstrated that while steel bar exhibited little cytotoxicity, tungsten carbide cutting bar showed no cytotoxicity. However, both cutting bar reduced the differentiation of ES-D3 cells, indicating that the sharp edges of the fragments of blades can inhibit cell differentiation. Further studies are needed to investigate the influence of the shapes of cutting bar fragments on cell differentiation.
The risks of embryotoxicity of pure Ti and Ti alloys used as oral implant materials have not been sufficiently elucidated. The embryonic stem cell test (EST), which allows screening of the fetal teratogenicity of chemical substances, has already been demonstrated to show high predictability by international validation, mainly in Europe. We evaluated the embryotoxicity levels of constituent element ions (Ti, V, Al, Nb, Ta, and Zr) of implants using the EST. As a result, the V ion was found to be associated with some embryotoxicity risks, while the other metal ions showed no embryotoxicity. As previously demonstrated, the V ion shows marked cytotoxicity and carcinogenicity. Therefore, Ti alloys without V ions, such as Ti-6Al-7Nb, should be widely used as implant materials.
Subsequent to the orthodontic treatment, removal of residual colorless adhesives from tooth surfaces by cutting instruments with the lowest possible iatrogenic damage has been a long-standing challenge. Fluorescent imaging can be one of the most effective solutions. Y2O3:Eu3+ particles were synthesized by a homogeneous precipitation method and the subsequent calcination was performed at various temperatures. The particles had a narrow size distribution (200-300 nm) and showed sharp crystallinity independent of the calcination temperatures above 800 °C. In this study, 1,000 °C is confirmed to be the optimum calcination temperature. Although the reason for the decline in emission intensity of the 1,100 °C-calcined particles is still unclear, loss of spherical shape associated with excessive crystal grain growth and simultaneous sintering to each other by firing is a possible explanation. The emission from the phosphor-containing resins, intended for use in orthodontic adhesives, is appreciable although the emission intensity of the resins was weak even if their content was 20 wt.%. The decrease in emission intensity may be attributed to the scattering by the particles or cross relaxation processes. We conclude that the crystalline Y2O3:Eu3+ particles calcined at 1,000 °C could be applicable for further development of photoluminescent orthodontic adhesives.
Recent developments in regenerative medicine include the ability to transplant induced pluripotent stem (iPS) cells cultured in vitro into human patients. These iPS cells require scaffolds that are safe to use in humans and allow cell differentiation for 30 days. Collagen derived from fish, which is evolutionally distant from humans, is considered safe to use in humans. In the present study, we investigated the use of collagen extracted from the scales of tilapia, which inhabits tropical and subtropical regions, as a scaffold to enable long-term cell culture at 37°C. To establish the model of iPS cell culture, we used murine embryonic stem (ES) cells that require feeder cells, specifically EL M3 and ES-R1-EGFP B2/EGFP cells. We investigated whether differentiation of these cells could be maintained for 30 days.
Our results demonstrated that cell differentiation could be maintained in less than half of the two ES cell types. Differentiation was less efficient in ES-R1-EGFP B2/EGFP cells compared with EL M3 cells. Further investigations may include culturing for over 30 days or increasing the incubation temperature to determine the effects of thermal denaturation of collagen on cell differentiation.
In this study, nanoporous silica particles (NPS) were synthesized and their controlled drug-release behavior was investigated. The NPS were mixed with glass ionomer cement (GIC), which is a common dental material. Epigallocatechin gallate (EGCG) was charged into the samples as a model drug. Samples were immersed into distilled water; then, the supernatant was analyzed every day using a UV-visible spectrophotometer to observe EGCG-release behavior. GIC containing NPS can release EGCG for more than one week, whereas specimens without NPS released it for only a few days. This suggests that NPS has an excellent ability for sustained drug-release.
The safety of mixed materials for the body cannot be evaluated based on the mean of the safety data of the individual component materials in many cases, and the toxicity level may markedly vary when the mixture is influenced by a synergistic effect. Many recent commercial products are mixed with nanomaterials. Nanomaterials are incorporated into cells through special mechanisms, such as phagocytosis, but only a few studies have reported the evaluation of mixtures with nanomaterials. Thus, we investigated changes in the cytotoxicity levels of dental metals (Ag, Cu, and Pd ions) in a mixture with a very small non-toxic amount of nano titanium dioxide or nano zinc oxide by measuring the cell survival rate. The cytotoxicity levels slightly changed in the presence of a very small amount of nano titanium dioxide or nano zinc oxide compared with those in the absence of the nanomaterials, although the changes were not marked. Investigation from the perspectives of various fields including other nanomaterials is expected.