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.

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.

[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.

[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.

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.