Finite element analysis of dental implant neck effects on primary stability and osseointegration in a type IV bone mandible.

The purpose of this study is to investigate the effect of implant neck design and cortical bone thickness by means of 3-D linearly elastic finite element analysis and to analyze primary and secondary stability of clinical evidence based on micromotion and principal stress. Four commercial dental implants, comparable in size, for a type IV bone and mandibular segments were created. Various parameters were considered, including the osseointegration condition (non- and full bonded), force direction (vertical and horizontal) and cortical bone thickness (0.3, 0.5 and 1mm). The force was considered a static load applied at the top of the platform. The magnitudes of the vertical and horizontal loading direction were 500 N and 250 N. Micromotion and principal stresses were employed to evaluate the failure of osseointegration and bone overloading, respectively. The results show that Maximum stress of the peri-implant bone decreased as cortical bone thickness increased. The stress concentration regions were located at the implant neck between the cortical bone and cancellous bone. The micromotion level in full osseointegration is less than that in non-osseointegration and it also decreases as a increasing of cortical bone thickness. Consequently, cortical bone thickness is a key factor for primary stability.

Inducing occlusion effect in Y-shaped vessels using high-intensity focused ultrasound: finite element analysis and phantom validation.

High-intensity focused ultrasound (HIFU) surgery offers a truly non-invasive treatment method with no skin incision, but precise targeting of tumour tissues for thermotherapy. Clinical experience reveals that the efficacy of tumour destruction not only involves in coagulating necrosis, but also involves in damaging the tumour vessels, which play an important role in tumour progression. These vessels take the elevated temperature away by perfusion, resulting in uncertainty of the occlusion effect during HIFU treatment. In this study, a Y-shaped vessel model comprising common and tumour vessels and an indirect fabrication method are proposed. The physical properties of the fabricated vessel phantom are measured and compared with human tissue. Simulation is performed using finite element modelling according to the tissue parameter, perfusion rate of the tumour vessel and treatment parameters including power intensity and exposure duration. The phantom experiments are carried out with perfusion of egg white to validate the threshold time prediction obtained from the simulation results. Our findings reveal that the threshold time obtained from experiments is consistent with the simulated one.