Effect of short implant crown-to-implant ratio on stress distribution in anisotropic bone with different osseointegration rates.

OBJECTIVE: This study aimed to provide evidence for the clinical application of single short implants by establishing an anisotropic, three-dimensional (3D) finite element mandible model and simulating the effect of crown-to-implant ratio (CIR) on biomechanics around short implants with different osseointegration rates. METHODS: Assuming that the bone is transversely isotropic by finite element method, we created four distinct models of implants for the mandibular first molar. Subsequently, axial and oblique forces were applied to the occlusal surface of these models. Ultimately, the Abaqus 2020 software was employed to compute various mechanical parameters, including the maximum von Mises stress, tensile stress, compressive stress, shear stress, displacement, and strains in the peri-implant bone tissue. RESULTS: Upon establishing consistent osseointegration rates, the distribution of stress exhibited similarities across models with varying CIRs when subjected to vertical loads. However, when exposed to inclined loads, the maximum von Mises stress within the cortical bone escalated as the CIR heightened. Among both loading scenarios, notable escalation in the maximum von Mises stress occurred in the model featuring a CIR of 2.5 and an osseointegration rate of 25%. Conversely, other models displayed comparable strength. Notably, stress and strain values uniformly increased with augmented osseointegration across all models. Furthermore, an increase in osseointegration rate correlated with reduced maximum displacement for both cortical bone and implants. CONCLUSIONS: After fixing osseointegration rates, the stress around shorter implants increased as the CIR increased under inclined loads. Thus, the effect of lateral forces should be considered when selecting shorter implants. Moreover, an implant failure risk was present in cases with a CIR ≥ 2.5 and low osseointegration rates. Additionally, the higher the osseointegration rate, the more readily the implant can achieve robust stability.

Three-dimensional finite element analysis of stress distribution on short implants with different bone conditions and osseointegration rates.

OBJECTIVE: This experiment aimed to investigate the effects of bone conditions and osseointegration rates on the stress distribution of short implants using finite element analysis and also to provide some reference for the application of short implants from a biomechanical prospect. MATERIALS AND METHODS: Anisotropic jaw bone models with three bone conditions and 4.1 × 6 mm implant models were created, and four osseointegration rates were simulated. Stress and strain for the implants and jaws were calculated during vertical or oblique loading. RESULTS: The cortical bone area around the implant neck was most stressed. The maximum von Mises stress in cortical bone increased with bone deterioration and osseointegration rate, with maximum values of 144.32 MPa and 203.94 MPa for vertical and inclined loading, respectively. The osseointegration rate had the greatest effect on the maximum principal stress in cortical bone of type III bone, with its value increasing by 63.8% at a 100% osseointegration rate versus a 25% osseointegration rate. The maximum and minimum principal stresses under inclined load are 1.3 ~ 1.7 and 1.4 ~ 1.8 times, respectively, those under vertical load. The stress on the jaw bone did not exceed the threshold when the osseointegration rate was ≥ 50% for Type II and 100% for Type III. High strain zones are found in cancellous bone, and the maximum strain increases as the bone condition deteriorate and the rate of osseointegration decreases. CONCLUSIONS: The maximum stress in the jaw bone increases as the bone condition deteriorates and the osseointegration rate increases. Increased osseointegration rate reduces cancellous bone strain and improves implant stability without exceeding the yield strength of the cortical bone. When the bone condition is good, and the osseointegration ratio is relatively high, 6 mm short implants can be used. In clinical practice, incline loading is an unfavorable loading condition, and axial loading should be used as much as possible.

Proximal Online Gradient Is Optimum for Dynamic Regret: A General Lower Bound.

In online learning, the dynamic regret metric chooses the reference oracle that may change over time, while the typical (static) regret metric assumes the reference solution to be constant over the whole time horizon. The dynamic regret metric is particularly interesting for applications, such as online recommendation (since the customers' preference always evolves over time). While the online gradient (OG) method has been shown to be optimal for the static regret metric, the optimal algorithm for the dynamic regret remains unknown. In this article, we show that proximal OG (a general version of OG) is optimum to the dynamic regret by showing that the proved lower bound matches the upper bound. It is highlighted that we provide a new and general lower bound of dynamic regret. It provides new understanding about the difficulty to follow the dynamics in the online setting.

Combined treatment of glibenclamide and CoCl2 decreases MMP9 expression and inhibits growth in highly metastatic breast cancer.

BACKGROUND: To observe the influence of combination treatment with glibenclamide and CoCl(2) on the growth and invasiveness of TA2 breast cancer, and to detect the protein and mRNA expression of MMP9. METHODS: 50 adult female TA2 mice were randomly divided into 5 groups including DMSO control, CoCl(2), glibenclamide, CoCl(2) + glibenclamide and paclitaxel. All of these mice were inoculated with TA2 spontaneous breast cancer cells in the left groin. Nine days after inoculation the tumor could be palpated. Different treatments for each group were then subcutaneously administered near the tumors on the 9th and 14th days after injection. Tumor size was measured to determine the growth curve. All mice were sacrificed on the 18th day after initial inoculation and tumor tissues were collected. Some fresh tissues without necrosis were stored at -80°C for mRNA detection and the other tumor tissue was fixed with 10% formalin for H&E and immunohistochemical staining. RESULTS: The growth rate of tumor cells in the CoCl(2) + glibenclamide group was lower than that seen in the other groups. On the 14th day, the average volume of tumor in the CoCl(2) + glibenclamide group was the lowest and the difference has statistical significance (P < 0.05), while the differences among the CoCl(2), glibenclamide and paclitaxel had no statistical significance. The mean percentage of cells expressing MMP9 and PCNA was the lowest in the CoCl(2) + glibenclamide group (P < 0.05). MMP9 mRNA expression paralleled MMP9 protein expression in these groups (P < 0.05). CONCLUSIONS: Combined treatment with glibenclamide and CoCl(2) inhibits TA2 spontaneous breast cancer growth and invasiveness with effects similar to paclitaxel.

Endothelialization and in-stent restenosis on the surface of glycoprotein IIIa monoclonal antibody eluting stent.

Since the percutaneous transtuminal coronary angioplasty was introduced into China in 1984, this procedure has become widely accepted as an important step in coronary revascularization. This study shows the effect of the monoclonal antibody (mAb) on the platelet glycoprotein IIIa receptor during endothelialization and in-stent restenosis by implanting the mAb-eluting stents into iliac arteries of rabbits. The hard tissue cross sections of the stent-implanted arterial segments were made by polymethylmethacrylate embedding. Arterial intima proliferation was observed and analyzed. The endothelialization of the stent surface was observed using scanning electron microscope, whereas the ultrastructure of the neointima was observed using transmission electron microscope. After one month of stent implantation, the surfaces of both groups were covered by intact endothelial layers, but the neointimal areas and the ratio of stenosis were significantly lesser in the mAb-eluting stent group (p < 0.01). After 3 months, the ratio of stenosis in the mAb-eluting stent group was 14.67 ± 0.79, whereas that of the bare stent group was 21.58 ± 1.76 (p < 0.01). Therefore, the mAb eluting from the stent surface has the potential to accelerate endothelialization, prevent thrombosis formation due to the interaction of stent with blood, and decrease the stenosis ratio by inhibiting neointima proliferation.

Heparinized poly(vinyl alcohol)--small intestinal submucosa composite membrane for coronary covered stents.

To develop a novel coating material for coronary covered stents, we prepared a kind of composite membrane which contains polyvinyl alcohol (PVA) and porcine small intestinal submucosa (SIS) powders crosslinked and heparinized by N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The amount of immobilized heparin increased with increasing ratios of EDC:heparin, and the maximum amount was approximately 60 microg heparin per milligram SIS powder at a weight ratio of EDC:heparin of 2. Uniaxial tensile and balloon inflation testing suggested that the composite membrane crosslinked by lower EDC concentration is more flexible and elastic. The clotting time (APTT and PT) of the heparinized PVA-SIS membrane was longer than that of the unheparinized membrane. The number of adherent platelets on the heparinized PVA-SIS composite membrane was about 25% of the unheparininzed, and there was no sign of accumulation and almost no pseudopodium was observed. The endothelial cells were amicable with the heparinized and unheparinized PVA-SIS composite membranes. In in vivo implantation tests, we observed a thin capsule formed by several layers of fibroblasts surrounding the implants. These results showed that the heparinized PVA-SIS composite membrane has potential biomechanical and biological properties as a coating material for coronary covered stent.

[In vitro study of platelet glycoprotein monoclonal antibody eluting stents].

In order to prove the feasibility of preparation of the drug-incorporated stent by immersing stent wires in the monoclonal antibody (mAb) solution, fluorescence stain and image analysis were used to evaluate the L-PLA-coated stent. Absorption was measured using a radioisotope technique after preparing the mAb-incorporated stent, and the absorption curve was determined from the absorption data. In an in vitro perfusion circuit, the antibody was eluted from the stent matrices, and the related influence factors were evaluated based on the release data.

[Development of drug coating on drug eluting stents].

Researches on drug-eluting stents are now focusing on three main aspects: the stent materials, the coating matrix material and the selection, adhesion and controlled release of the biological agents. The current development progresses of the coating materials, their characteristics, and the coating method for metallic stents are reviewed in this paper.

Microbial desulfurization of gasoline in a Mycobacterium goodii X7B immobilized-cell system.

Mycobacterium goodii X7B, which had been primarily isolated as a bacterial strain capable of desulfurizing dibenzothiophene to produce 2-hydroxybiphenyl via the 4S pathway, was also found to desulfurize benzothiophene. The desulfurization product was identified as o-hydroxystyrene by gas chromatography (GC)-mass spectrometry analysis. This strain appeared to have the ability to remove organic sulfur from a broad range of sulfur species in gasoline. When Dushanzi straight-run gasoline (DSRG227) containing various organic sulfur compounds was treated with immobilized cells of strain X7B for 24 h, the total sulfur content significantly decreased, from 227 to 71 ppm at 40 degrees C. GC flame ionization detection and GC atomic emission detection analysis were used to qualitatively evaluate the effects of M. goodii X7B treatment on the contents of gasoline. In addition, when immobilized cells were incubated at 40 degrees C with DSRG275, the sulfur content decreased from 275 to 54 ppm in two consecutive reactions. With this excellent efficiency, strain X7B is considered a good potential candidate for industrial applications for the biodesulfurization of gasoline.