Enzyme-catalyzed hydrolysis of dentin adhesive containing a new urethane-based trimethacrylate monomer

A new trimethacrylate monomer with urethane-linked groups, 1,1,1-tri-[4-(methacryloxyethylamino-carbonyloxy)-phenyl]ethane (MPE), was synthesized, characterized, and used as a co-monomer in dentin adhesives. Dentin adhesives containing 2-hydroxyethyl methacrylate (HEMA, 45% w/w) and 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane (BisGMA, 30% w/w) in addition to MPE (25% w/w) were formulated with H2O at 0 (MPE0), 8 (MPE8) and 16 wt % water (MPE16) to simulate the wet demineralized dentin matrix and compared with controls [HEMA/BisGMA, 45/55 w/w, at 0 (C0), 8 (C8) and 16 wt% water (C16)]. The new adhesive showed a degree of double bond conversion and mechanical properties comparable with control, with good penetration into the dentin surface and a uniform adhesive/dentin interface. On exposure to porcine liver esterase, the net cumulative methacrylic acid (MAA) release from the new adhesives was dramatically (P < 0.05) decreased relative to the control, suggesting that the new monomer improves esterase resistance

Molecular Toxicology of Substances Released from Resin–Based Dental Restorative Materials

Resin-based dental restorative materials are extensively used today in dentistry. However, significant concerns still remain regarding their biocompatibility. For this reason, significant scientific effort has been focused on the determination of the molecular toxicology of substances released by these biomaterials, using several tools for risk assessment, including exposure assessment, hazard identification and dose-response analysis. These studies have shown that substances released by these materials can cause significant cytotoxic and genotoxic effects, leading to irreversible disturbance of basic cellular functions. The aim of this article is to review current knowledge related to dental composites’ molecular toxicology and to give implications for possible improvements concerning their biocompatibility

Çok ölçekli elektromanyetik problemlerin hızlı ve verimli çözümü

Cataloged from PDF version of article.Includes bibliographical references (leaves 115-128).Frequency-domain surface integral equations (SIEs) used together with the method of moments (MoM), and/or its accelerated versions, such as the multilevel fast multipole algorithm (MLFMA), are usually the most promising choices in solving electromagnetic problems including perfect electric conductors (PEC). However, the electric-field integral equation (EFIE) (as one of the most popular SIEs) is susceptible to the well-known low-frequency (LF) breakdown problem, which prohibits its use at low frequencies and/or dense discretizations. Although the magnetic-field integral equation (MFIE) is less affected from the LF-breakdown, it is usually criticized for being less accurate, and being applicable only to closed surfaces. In addition, the conventional MLFMA which enables the solution of electrically large problems with an extremely large number of unknowns by reducing the computational complexity for memory requirements and CPU time suffers from the LF breakdown when applied to the geometries with electrically small features. We proposed a mixed-form MLFMA and incorporated it with the recently introduced potential integral equations (PIEs), which are immune to the LF-breakdown problem, to obtain an efficient and accurate broadband solver to analyze electromagnetic scattering/radiation problems from PEC surfaces over a wide frequency range. The mixed-form MLFMA uses the conventional MLFMA at middle/high frequencies and the nondirective stable plane wave MLFMA (NSPWMLFMA) at low frequencies (i.e., electrically small boxes). We demonstrated that the proposed algorithm is accurate enough to be applied for both open and closed surfaces. In addition, we modified and utilized incomplete tree structures in conjunction with the mixed-form MLFMA to have a novel broadband incomplete-leaf (IL) MLFMA (IL-MLFMA) for the fast and accurate solution of multiscale scattering/radiation problems using PIEs. The proposed method is capable of handling multiscale electromagnetic problems containing fine geometrical details in their structures. The algorithm is population based and deploys a nonuniform clustering that enables to use deep levels safely and, when necessary, without compromising the accuracy, and hence the error is controllable. As a result, by using the proposed IL-MLFMA for PIEs (i) the efficiency is improved and (ii) the memory requirements are significantly reduced (order of magnitude) while the accuracy is maintained.by Bahram Khalich

Kernel-based fast factorization techniques

This chapter has focused on MLFMA as a representative kernel-based fast factorization technique. To construct a basis for further discussion, we first considered the conventional MLFMA, which is based on the plane-wave expansion of electromagnetic waves, at a formulation level. To solve multi-scale problems involving dense (uniform or non-uniform) discretizations of electrically large objects, alternative MLFMA versions are needed since the conventional MLFMA suffers from a low-frequency breakdown. We listed a variety of ways to implement low-frequency-stable MLFMAs, such as based on multipoles, inhomogeneous plane waves, coordinate shifts, and approximation techniques. We showed how MLFMA implementations can be used to solve extremely large problems via parallelization, while they can be applied to complex structures with different material properties, including plasmonic and NZI objects. Examples were given for solutions of densely discretized objects to demonstrate how MLFMA can handle such complicated problems that possess modeling challenges. Finally, problems with non-uniform discretizations that naturally arise in multi-scale simulations were considered. A rigorous implementation for stable, accurate, and efficient solutions of these problems requires a well-designed combination of a suitable formulation/discretization, an effective solution algorithm (MLFMA version), and a carefully designed clustering mechanism

An Integral-Equation-Based Method for Efficient and Accurate Solutions of Scattering Problems with Highly Nonuniform Discretizations

© 2021 IEEE.We present a full-wave electromagnetic solver for analyzing multiscale scattering problems with highly nonuniform discretizations. The developed solver employs an elegant combination of potential integral equations (PIEs) with the magnetic-field integral equation (MFIE) to improve the iterative convergence properties of matrix equations obtained via method of moments, especially derived from highly nonuniform discretizations for which PIEs suffer from ill conditioning. A mixed-form multilevel fast multipole algorithm with incomplete tree structures is employed to efficiently and accurately solve the obtained matrix equations. The solver circumvents the well-known low-frequency problem originating from the breakdown of the conventional surface formulations and the standard MLFMA for highly nonuniform discretizations. The accuracy and efficiency of the proposed solver are demonstrated on canonical but challenging scattering problems

Near-Field-Based Preconditioning Technique in the Incomplete-Leaf MLFMA for Nonuniformly Discretized Electromagnetic Scattering Problems

© 2021 IEEE.The potential of incomplete tree structures, previously used in the context of the multilevel fast multi pole algorithm, on developing an effective preconditioning technique for multiscale electromagnetic problems is analyzed. The preconditioning technique is based on the sparse near-field matrix constructed by the near-field clustering definition of the incomplete tree structures for multiscale geometries. The proposed preconditioner is applied to solutions of matrix systems obtained via method-of-moments discretization of potential integral equations since the conditioning of the calculated matrices deteriorates as the problem size grows or the number of unknowns increases. The effectiveness and robustness of the preconditioning technique are demonstrated by numerical experiments on a complex target