A Prospective Follow-up Study of 44 Mandibular Immediately Loaded Implants Using Resonance Frequency Analysis: Preliminary 1-Year Results

Purpose: This clinical study aimed to evaluate initial, 4-months, and 1-year stability of immediately loaded dental implants inserted according to a protocol of lower rehabilitation with prefabricated bars. Materials and Methods: The sample was composed of 11 edentulous patients. In each patient, 4 interforaminal implants were inserted. Immediately after implant installation, resonance frequency analysis (RFA) for each fixation was registered as well as after 4 months and 1 year with the prosthetic bar removed as it is a screwed system. Results: The clinical implant survival rate was 100%. The RFA showed an increase in stability after 4 months from 64.09 +/- 648 to 64.31 +/- 4.96 and I year, 67.11 +/- 4.37. The analysis of variance showed a statistically significant result (P = 0.015) among implant stability quotient values for the different periods evaluated. Tukey test results showed statistically significant differences between 1-year results and the initial periods but there was no statistically significant difference between initial and 4-month results (P > 0.05). Conclusion: These preliminary 1-year results indicate that immediate loading of mandibular dental implants using the studied prefabricated bars protocol is a reliable treatment as it is in accordance with the results described in the literature for other similar techniques. (Implant Dent 2009; 18:530-538)

Reliability of orbital fits for resonant extrasolar planetary systems: the case of HD82943

We perform a statistical study of the process of orbital determination of the HD82943 extrasolar planetary system, using the current observational data set of N = 165 radial velocity (RV) measurements. Our aim is to analyse the dispersion of possible orbital fits leading to residuals compatible with the best solution, and to discuss the sensitivity of the results with respect to both the data set and the error distribution around the best fit. Although some orbital parameters (e.g. semimajor axis) appear well constrained, we show that the best fits for the HD82943 system are not robust, and at present it is not possible to estimate reliable solutions for these bodies. Finally, we discuss the possibility of a third planet, with a mass of 0.35M(Jup) and an orbital period of 900 d. Stability analysis and simulations of planetary migration indicate that such a hypothetical three-planet system could be locked in a double 2/1 mean-motion resonance, similar to the so-called Laplace resonance of the three inner Galilean satellites of Jupiter.

Dynamics of two planets in co-orbital motion

We study the stability regions and families of periodic orbits of two planets locked in a co-orbital configuration. We consider different ratios of planetary masses and orbital eccentricities; we also assume that both planets share the same orbital plane. Initially, we perform numerical simulations over a grid of osculating initial conditions to map the regions of stable/chaotic motion and identify equilibrium solutions. These results are later analysed in more detail using a semi-analytical model. Apart from the well-known quasi-satellite orbits and the classical equilibrium Lagrangian points L(4) and L(5), we also find a new regime of asymmetric periodic solutions. For low eccentricities these are located at (delta lambda, delta pi) = (+/- 60 degrees, -/+ 120 degrees), where delta lambda is the difference in mean longitudes and delta pi is the difference in longitudes of pericentre. The position of these anti-Lagrangian solutions changes with the mass ratio and the orbital eccentricities and are found for eccentricities as high as similar to 0.7. Finally, we also applied a slow mass variation to one of the planets and analysed its effect on an initially asymmetric periodic orbit. We found that the resonant solution is preserved as long as the mass variation is adiabatic, with practically no change in the equilibrium values of the angles.

Constraining the orbital orientation of eta Carinae from H Paschen lines

During the past decade, several observational and theoretical works have provided evidence of the binary nature of eta Carinae. Nevertheless, there is still no direct determination of the orbital parameters, and the different current models give contradictory results. The orbit is, in general, assumed to coincide with the Homunculus equator although the observations are not conclusive. Among all systems, eta Car has the advantage that it is possible to observe both the direct emission of line transitions in the central source and its reflection by the Homunculus, which is dependent on the orbital inclination. In this work, we studied the orbital phase-dependent hydrogen Paschen spectra reflected by the south-east lobe of the Homunculus to constrain the orbital parameters of eta Car and determine its inclination with respect to the Homunculus axis. Assuming that the emission excess originates in the wind-wind shock region, we were able to model the latitude dependence of the spectral line profiles. For the first time, we were able to estimate the orbital inclination of eta Car with respect to the observer and to the Homunculus axis. The best fit occurs for an orbital inclination to the line of sight of i similar to 60 degrees +/- 10 degrees, and i* similar to 35 degrees +/- 10 degrees with respect to the Homunculus axis, indicating that the angular momenta of the central object and the orbit are not aligned. We were also able to fix the phase angle of conjunction as similar to -40 degrees, showing that periastron passage occurs shortly after conjunction.

DETECTABILITY AND ERROR ESTIMATION IN ORBITAL FITS OF RESONANT EXTRASOLAR PLANETS

We estimate the conditions for detectability of two planets in a 2/1 mean-motion resonance from radial velocity data, as a function of their masses, number of observations and the signal-to-noise ratio. Even for a data set of the order of 100 observations and standard deviations of the order of a few meters per second, we find that Jovian-size resonant planets are difficult to detect if the masses of the planets differ by a factor larger than similar to 4. This is consistent with the present population of real exosystems in the 2/1 commensurability, most of which have resonant pairs with similar minimum masses, and could indicate that many other resonant systems exist, but are currently beyond the detectability limit. Furthermore, we analyze the error distribution in masses and orbital elements of orbital fits from synthetic data sets for resonant planets in the 2/1 commensurability. For various mass ratios and number of data points we find that the eccentricity of the outer planet is systematically overestimated, although the inner planet`s eccentricity suffers a much smaller effect. If the initial conditions correspond to small-amplitude oscillations around stable apsidal corotation resonances, the amplitudes estimated from the orbital fits are biased toward larger amplitudes, in accordance to results found in real resonant extrasolar systems.

Bone growth around silicon nitride implants - An evaluation by scanning electron microscopy

Silicon nitride has demonstrated to be a potential candidate for clinical applications because it is a non-cytotoxic material and has satisfactory fracture toughness, high wear resistance and low friction coefficient. In this paper, samples of silicon nitride, which were kept into rabbits` tibias for 8 weeks, and the adjacentbone tissue were analysed by scanning electron microscopy in order to verify the bone growth around the implants and the interaction between the implant and the bone. Bone growth occurred mainly in the cortical areas, although it has been observed that the newly bone tends to grow toward the marrow cavity. Differences were observed between the implants installed into distal and proximal regions. In the first region, where the distance between the implant and the cortical bone is greater than in the proximal region, the osteoconduction process was evidenced by the presence of a bridge bone formation toward the implant surface. The results showed that silicon nitride can be used as biomaterial since the newly bone grew around the implants. (c) 2007 Elsevier Inc. All rights reserved.

Tissue response around silicon nitride implants in rabbits

The chemical and dimensional stability associated with suitable fracture toughness and propitious tribological characteristics make silicon nitride-based ceramics potential candidates for biomedical applications, mainly as orthopedic implants. Considering this combination of properties, silicon nitride components were investigated in relation to their biocompatibility. For this study, two cylindrical implants were installed in each tibia of five rabbits and were kept in the animals for 8 weeks. During the healing time, tissue tracers were administrated in the animals so as to evaluate the bone growth around the implants. Eight weeks after the surgery, the animals were euthanized and histological analyses were performed. No adverse reactions were observed close to the implant. The osteogenesis process occurred during the entire period defined by the tracers. However, this process occurred more intensely 4 weeks after the surgery. In addition, the histological analyses showed that bone growth occurred preferentially in the cortical areas. Different kinds of tissue were identified on the implant surface, characterized by lamellar bone tissue containing osteocytes and osteons, by a noncalcified matrix containing osteoblasts, or by the presence of collagen III, which may change to collagen I or remain as a fibrous tissue. The results demonstrated that silicon nitride obtained according to the procedure proposed in this research is a biocompatible material. (c) 2007 Wiley Periodicals, Inc.

Stress distribution in orthodontic mini-implants

The objective of this study was to evaluate the stress distribution in the resin in contact with the spirals of cylindrical and conical mini-implants, when submitted to lateral load and insertion torsion. A photoelastic model was fabricated using transparent gelatin to simulate the alveolar bone. The model was observed with a plane polariscope and photographically recorded before and after activation of the two screws with a lateral force and torsion. The lateral force application caused bending moments on both mini-implants, with the uprising of fringes or isochromatics, characteristics of stresses, along the threads of the mini-implants and in the apex. When the torsion was exerted in the mini-implants, a great concentration of stress upraised close to the apex. The conclusion was that, comparing conical with cylindrical mini-implants under lateral load, the stresses were similar on the traction sides. The differences appear (1) on the apex, where the cylindrical mini-implant showed a greater concentration of stress, and (2) along the spirals, in the compression side, where the conical mini-implant showed a greater concentration of stress. The greater part of the stress produced by both mini-implants, after torsion load in insertion, were concentrated on the apex. With the cylindrical mini-implant, the greater concentration of tension was close to the apex, while with the conical one, the stresses were distributed along a greater amount of apical threads.

Synthesis, mechanism of formation, and molecular orbital calculations of arylamidoximes

A simple and easy synthesis of ten arylamidoximes from arylnitriles and hydroxylamine is described. The formation of the arylamides has been observed to a much lesser extent in the present work. A new mechanism for the formation of arylamidoximes, as well as arylamides, from arylnitriles and hydroxylamine is suggested. Quantum mechanical calculations have been carried out to support this mechanism. The enthalpy of formation in conjunction with atomic charges of the reactants and intermediates helped to understand more about the generation of the products.

Structural, electronic, and magnetic entropy contributions of the orbital order-disorder transition in LaMnO(3)

Measurements of X-ray diffraction, electrical resistivity, and magnetization are reported across the Jahn-Teller phase transition in LaMnO(3). Using a thermodynamic equation, we obtained the pressure derivative of the critical temperature (T(JT)), dT(JT)/dP = -28.3 K GPa(-1). This approach also reveals that 5.7(3)J(mol K)(-1) comes from the volume change and 0.8(2)J(mol K)(-1) from the magnetic exchange interaction change across the phase transition. Around T(JT), a robust increase in the electrical conductivity takes place and the electronic entropy change, which is assumed to be negligible for the majority of electronic systems, was found to be 1.8(3)J(mol K)(-1).

Dependence of Response Functions and Orbital Functionals on Occupation Numbers

Explicitly orbital-dependent approximations to the exchange-correlation energy functional of density functional theory typically not only depend on the single-particle Kohn-Sham orbitals but also on their occupation numbers in the ground-state Slater determinant. The variational calculation of the corresponding exchange-correlation potentials with the optimized effective potential (OEP) method therefore also requires a variation of the occupation numbers with respect to a variation in the effective single-particle potential, which is usually not taken into account. Here it is shown under which circumstances this procedure is justified.

Orbital-polarization terms: From a phenomenological to a first-principles description of orbital magnetism in density-functional theory

Phenomenological orbital-polarizition (OP) terms have been repeatedly introduced in the single-particle equations of spin-density-functional theory, in order to improve the description of orbital magnetic moments in systems containing transition metal ions. Here we show that these ad hoc corrections can be interpreted as approximations to the exchange-correlation vector potential A(xc) of current-density functional theory (CDFT). This connection provides additional information on both approaches: phenomenological OP terms are connected to first-principles theory, leading to a rationale for their empirical success and a reassessment of their limitations and the approximations made in their derivation. Conversely, the connection of OP terms with CDFT leads to a set of simple approximations to the CDFT potential A(xc), with a number of desirable features that are absent from electron-gas-based functionals. (C) 2008 Wiley Periodicals, Inc.

New material for orthopedic implants: Electrochemical study of nickel free P558 stainless steel in minimum essential medium

Nickel, a component of stainless steels (SS) applied in orthopedic implants may cause allergic processes in human tissues P558 nickel free SS was studied to verify its viability as a substitute for stainless steel containing nickel Its performance is compared to ISO 5832-9 and F138 most used nowadays grades in implants fabrications, in minimum essential medium. MEM, at 37 degrees C. Potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and ""in vitro"" cytotoxicity were used as techniques. From the electrochemical point of view P558 SS is comparable to ISO 5832-9 SS in MEM It remains passivated until the transpassivation potential, above which generalized corrosion occurs F138 presents pitting corrosion at 370 mV/SCE. The cytotoxicity results showed that P558. ISO 5832-9 and F138 do not present cytotoxic character Therefore, these results suggest that P558 SS can be applied in orthopedic implants (C) 2010 Elsevier BV All rights reserved

New Relativistic Atomic Natural Orbital Basis Sets for Lanthanide Atoms with Applications to the Ce Diatom and LuF3

New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are inluded as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.

Crystal and molecular structures of three 2-sulphur-substituted cyclohexanones studied by X-ray crystallography and by ab initio molecular orbital calculations

The conformational features of three 2-sulphur-substituted cyclohexanone derivatives, which differ in the number of sulphur-bound oxygen atoms, i.e. zero (I), one (II) and two (III), were investigated by single crystal X-ray crystallography and geometry optimized structures determined using Hartree-Fock method. In each of (I)-(III) an intramolecular S center dot center dot center dot O(carbonyl) interaction is found with the magnitude correlated with the oxidation state of the sulphur atom, i.e. 2.838(3) angstrom in (I) to 2.924(2) angstrom in (II) to 3.0973(18) angstrom in (III). There is an inverse relationship between the strength of this interaction and the magnitude of the carbonyl bond. The supramolecular aggregation patterns are primarily determined by C-H center dot center dot center dot O contacts and are similarly influenced by the number of oxygen atoms in the molecular structures. Thus, a supramolecular chain is found in the crystal structure of (I). With an additional oxygen atom available to participate in C-H center dot center dot center dot O interactions, as in (II), a two-dimensional array is found. Finally, a three-dimensional network is found for (III). Despite there being differences in conformations between the experimental structures and those calculated in the gas-phase, the S center dot center dot center dot O interactions persist. The presence of intermolecular C-H center dot center dot center dot O interactions involving the cyclohexanone-carbonyl group in the solid-state, disrupts the stabilising intramolecular C-H center dot center dot center dot O interaction in the energetically-favoured conformation. (I): C(12)H(13)NO(3)S, triclinic space group P (1) over bar with a = 5.392(3) angstrom b = 10.731(6) angstrom, c = 11.075(6) angstrom, alpha = 113.424(4)degrees, beta = 94.167(9)degrees, gamma = 98.444(6)degrees, V = 575.5(6) angstrom(3), Z = 2, R(1) = 0.052; (II): C(12)H(13)NO(4)S, monoclinic P2(1)/n, a = 7.3506(15) angstrom, b = 6.7814(14) angstrom, c = 23.479(5) angstrom, beta = 92.94(3)degrees, V = 1168.8(4) angstrom(3), Z = 4, R(1) = 0.046; (III): C(12)H(13)NO(5)S, monoclinic P2(1)/c, a = 5.5491(11) angstrom, b = 24.146(3) angstrom, c = 11.124(3) angstrom, beta = 114.590(10)degrees, V = 1355.3(5) angstrom(3), Z = 4, R(1) = 0.051.