Yasutomo Yajima

Translucency and flexural strength of monolithic translucent zirconia and porcelain-layered zirconia

This study aims to investigate the effectiveness of monolithic translucent TZP with different colors and porcelain-layered TZP by evaluating their colors and strengths. Different mixing ratios of Zpex to Zpex-Yellow as translucent TZP, conventional opaque TZP (TZ-3YB-E) (Tosoh, Tokyo) as a control, and veneering porcelain (CERABIEN ZR, body porcelain, Noritake, Tokyo) with shade A3 as a typical shade. Disk-shaped specimens of 13 mm diameter and 1.5 mm thickness were prepared. These specimens were observed under reflected and transmitted light, and the translucency parameter (TP) values were measured. Strength was also evaluated with flexural strength in a biaxial bending test. The TP values of the monolithic TZP, Zpex100>Zpex70>Zpex50>TZ3YB, were larger in this order. The flexural strength of all the monolithic TZP showed approximately 1,000 MPa. It is suggested that colored translucent TZP is clinically useful when used as monolithic restorations.

Isolation of human salivary extracellular vesicles by iodixanol density gradient ultracentrifugation and their characterizations.

Diagnostic methods that focus on the extracellular vesicles (EVs) present in saliva have been attracting great attention because of their non-invasiveness. EVs contain biomolecules such as proteins, messenger RNA (mRNA) and microRNA (miRNA), which originate from cells that release EVs, making them an ideal source for liquid biopsy. Although there have been many reports on density-based fractionation of EVs from blood and urine, the number of reports on EVs from saliva has been limited, most probably because of the difficulties in separating EVs from viscous saliva using density gradient centrifugation. This article establishes a protocol for the isolation of EVs from human saliva using density gradient centrifugation. The fractionated salivary EVs were characterized by atomic force microscopy, western blot and reverse transcription polymerase chain reaction. The results indicate that salivary EVs have a smaller diameter (47.8±12.3 nm) and higher density (1.11 g/ml) than EVs isolated from conditioned cell media (74.0±23.5 nm and 1.06 g/ml, respectively). Additionally, to improve the throughput of density-based fractionation of EVs, the original protocol was further modified by using a fixed angle rotor instead of a swinging rotor. It was also confirmed that several miRNAs were expressed strongly in the EV-marker-expressing fractions.

Transmission of Periodontopathic Bacteria from Natural Teeth to Implants

PURPOSE Prevention of peri-implantitis is essential for the success of implant rehabilitation. Infection by periodontopathic bacteria is a major cause of peri-implantitis. The aim of the present study was to identify the source of peri-implant colonization by periodontopathic bacteria. MATERIALS AND METHODS Twenty-one patients with implants were enrolled in the study. Subgingival plaque samples from the adjacent, occluding, and contralateral natural teeth were collected prior to second-stage surgery. Samples from implant sulci were then obtained 2 weeks later. Detection of periodontopathic bacteria was performed by the polymerase chain reaction. RESULTS The detection rates for Aggregatibacter actinomycetemcomitans, Prevotella intermedia, Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, and Fusobacterium nucleatum in all subgingival samples from natural teeth were similar to that in the peri-implant sulci. Multiple logistic regression analysis revealed an association between the detection of A. actinomycetemcomitans, Prevotella intermedia, Porphyromonas gingivalis, Treponema denticola, and F. nucleatum in the gingival crevices of adjacent teeth and that of the peri-implant sulcus, but no association for Tannerella forsythia. CONCLUSIONS The present findings suggest that colonization by A. actinomycetemcomitans, Prevotella intermedia, Porphyromonas gingivalis, Treponema denticola, and F. nucleatum at the implant sulcus was affected by these microorganisms in the gingival crevice of adjacent teeth rather than those on occluding and contralateral teeth.

Alignment of biological apatite crystallites at first molar in human mandible cortical bone.

Abstract The aim of this study was to quantitatively clarify the c-axis alignment of biological apatite (BAp) crystallites (hereafter referred to as BAp alignment) in the cortical bone of the human mandible first molar. Six mandible specimens were collected from the cadavers of six dentulous Japanese adults (mean age, 63.0±12.1 years) held at the Department of Anatomy, Tokyo Dental College. A microbeam x-ray diffraction system was used to determine BAp alignment in the mesiodistal direction. Bone mineral density (BMD) was also measured using 3-dimensional trabecular structure measurement software. The results showed that the degree of BAp alignment in the mesiodistal direction was low in the alveolar area and high at the base of the mandible, suggesting that BAp alignment in the alveolar area is affected by occlusal force. Moreover, it was observed that the correlation between BAp alignment and BMD was small, indicating that BAp alignment and BMD could be independent factors. Therefore, determining BAp alignment was important in the evaluation of bone quality, including bone strength.

Clinical evaluation of salivary periodontal pathogen levels by real-time polymerase chain reaction in patients before dental implant treatment.

Objective Periodontal pathogens in dental plaque are the main causative agents of periodontitis and peri-implantitis. Detection of the presence of such periodontal pathogens early would serve as a useful tool in the diagnosis and treatment of this disease. Therefore, the purpose of this study was to investigate whether the periodontal pathogen levels in saliva were correlated with the periodontal status of patients receiving implant treatment. Materials and Methods A total of 291 patients visiting Tokyo Dental College Chiba Hospital were divided into four groups: a no-periodontitis (np) group, a mild-periodontitis (mip) group, a moderate-periodontitis (mop) group, and a severe-periodontitis (sp) group. The levels of the following five periodontal pathogens in saliva were evaluated using real-time polymerase chain reaction: Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, Tannerella forsythia, Treponema denticola, and Prevotella intermedia. Results The levels of P. gingivalis and T. forsythia were significantly higher in mop group than in np group (P < 0.05). The levels of all periodontal pathogens tested except A. actinomycetemcomitans were significantly higher in sp group than in np group (P < 0.05). Conclusion The detection levels of the periodontal pathogens targeted in saliva samples were correlated with the periodontal status. This suggests that using saliva to screen for periodontopathic bacteria offers an easier-to-use clinical tool than the paper point method in the diagnosis and treatment of periodontitis and peri-implantitis.

Proliferation and osteogenic differentiation of human mesenchymal stem cells on zirconia and titanium with different surface topography.

The purpose of this study was to elucidate behavior of human mesenchymal stem cells (hMSCs) on yttria stabilized tetragonal zirconia polycrystals (TZP) and commercial pure titanium (CpTi) with different surface topography. Mirror-polished (MS), sandblasted with 150-μm alumina (SB150) and SB150 acid-etched (SB150E) were prepared on TZP and CpTi. Proliferation, osteogenic differentiation of hMSCs was evaluated. The scanning electron microscopy showed that micro- and nano-topographies were created on both TZP and CpTi SB150E surfaces. The proliferation ability, ALP activity, expression of Runx2 on the both SB150E specimens was significantly higher than those on the other specimens. These results suggested that creation of micro- and nano-topographies on TZP and CpTi by blast and acid-etching may offer a promising method for enhancing the proliferation and differentiation of hMSCs in clinical application.

Wear behavior of tetragonal zirconia polycrystal versus titanium and titanium alloy

The aim of this study was to clarify the influence of tetragonal zirconia polycrystal (TZP) on the two-body wear behavior of titanium (Ti). Two-body wear tests were performed using TZP, two grades of cp-Ti or Ti alloy in distilled water, and the cross-sectional area of worn surfaces was measured to evaluate the wear behavior. In addition, the surface hardness and coefficient of friction were determined and an electron probe microanalysis performed to investigate the underlying mechanism of wear. The hardness of TZP was much greater than that of Ti. The coefficient of friction between Ti and Ti showed a higher value than the Ti/TZP combination. Ti was more susceptible to wear by both TZP and Ti than TZP, indicating that the mechanism of wear between TZP and Ti was abrasive wear, whereas that between Ti and Ti was adhesive wear. No remarkable difference in the amount of wear in Ti was observed between TZP and Ti as the opposite material, despite the hardness value of Ti being much smaller than that of TZP.

Wear behavior between zirconia and titanium as an antagonist on fixed dental prostheses.

The aim of this in vitro study was to investigate the wear behavior of the abrader when tetragonal zirconia polycrystal (TZP), cp-titanium (CpTi) and Ti-6Al-4V alloy (TiAlV) were used as the antagonist on fixed dental prostheses (FDPs). Both hemisphere abrader and flat substrate specimens were prepared using TZP, CpTi and TiAlV. Two-body wear tests were performed in distilled water, and the wear volume of the abrader specimen was measured to evaluate the wear behavior. In addition, scanning microscopic observation and an electron probe micro-analysis were performed to elucidate the underlying mechanism of the wear. The wear volume of CpTi and TiAlV abrader specimens was approximately 20 times larger than that of TZP abrader specimen against all substrate specimens. This is due to the differences in hardness between the ultra-hardness of TZP and the comparatively low hardness of CpTi and TiAlV. The wear volume of CpTi and TiAlV abrader specimens against the TZP substrate was significantly smaller than for the CpTi and TiAlV substrates despite the hardness of TZP being much larger than those of CpTi and TiAlV. This phenomenon may be based on the adhesive wear mechanism. Elements of Ti, Al and V originating in the TiAlV substrate were detected adhering to the abrader CpTi specimen. These results suggest that FDPs of CpTi and TiAlV are susceptible to wear against not only TZP but also CpTi and TiAlV in contrast to TZP FDPs.

Preferential capture of EpCAM-expressing extracellular vesicles on solid surfaces coated with an aptamer-conjugated zwitterionic polymer

Extracellular vesicles (EVs) collectively represent small vesicles that are secreted from cells and carry biomolecules (e.g., miRNA, lncRNA, mRNA, proteins, lipids, metabolites, etc.) that originate in those cells. Body fluids, such as blood and saliva, include large numbers of EVs, making them potentially a rich source of diagnostic information. However, these EVs are mixtures of vesicles released from diseased tissues as well as from normal cells. This heterogeneous nature therefore blurs the clinical information obtainable from EV‐based diagnosis. Here, we synthesized an EpCAM‐affinity coating agent, which consists of a peptide aptamer for EpCAM and a zwitterionic MPC polymer, and have shown that this conjugate endowed the surfaces of inorganic materials with the preferential affinity to EpCAM‐expressing EVs. This coating agent, designated as EpiVeta, could be useful as a coating for various diagnostic devices to allow concentration of cancer‐related EVs from heterogeneous EV mixtures.

Release properties of atelocollagen-gelatin complexes as carriers for local administration of fluvastatin

The aim of this study was to investigate properties of atelocollagen/gelatin complexes (AC/Gel) and their characteristics of sustained statin release, to assess the utility of AC/Gel. AC/Gel were prepared by changing the mixing ratio of AC (0 to 40% of AC). Analysis of spectra of fluvastatin (Flu), gelatin (Gel), and Flu with Gel complex using a Fourier transform-infrared spectrometer indicates that Flu was bound to Gel through a bond involving the carboxyl and amino groups. Evaluation of characteristics of sustained release of Flu from the AC/Gel using an ultraviolet-visible spectrophotometer showed that the release rate of Flu decreased with increasing the AC content. The histological evaluation using of Sprague-Dawley rats suggest that, unlike the pure Gel sponge, the AC/Gel was not absorbed in an early stage. Therefore, the present study showed that sustained Flu release can be controlled by using an AC/Gel, suggesting the utility of this composite material.