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Bisphenol A (BPA) is a substance commonly used in dental materials with noxious properties. Monomers of this substance may be dissolved in the saliva and cause adverse effects. This study aimed to evaluate the amount of BPA released in the saliva after residual adhesive removal in orthodontic patients using an ultrasonic scaler (US) and tungsten carbide bur (TCB).This single-center randomized clinical trial was conducted on 40 subjects whose stainless-steel brackets were bonded directly with light-cured bonding and composite. The subjects were randomly divided into 2 equal groups (n = 20) of TCB or US according to the adhesive removal method. The salivary BPA level was determined using high-performance liquid chromatography-mass spectrometry. And adhesive cleaning time was measured by a stopwatch. Data were analyzed by SPSS using an independent t test and paired-samples t test (P 0.05).The mean salivary BPA level was significantly lower in the TCB method than in the US method. (1.008 ± 0.061 μg/mL and 2.83 ± 0.24 μg/mL, respectively) (P 0.001). The mean adhesive cleanup time was significantly shorter in the TCB method than in the US method (8.86 ± 0.83 minutes and 13.20±1.02 minutes, respectively) (P 0.001).According to the results, residual adhesive removal with TCB released less BPA in saliva and shortened the adhesive cleaning time than the US method.The trial was registered at the Iranian Registry of Clinical Trials (IRCT20200702047988N1).The protocol was not published before trial commencement.

Aim: Clinicians and researchers have always made every effort to achieve proper bonding between the surface of the tooth and the rebonded orthodontic brackets in order to prevent the re-fracture failure of orthodontic pressures throughout treatment. The aim of this study was to determine the bond strength of rebonded brackets by four adhesive removal methods. Materials and methods: Seventy-five orthodontic brackets were bonded to the extracted first premolar teeth and then debonded. Fifteen of these teeth were rebonded to new brackets after adhesive removal and were named as the control group. Sixty debonded brackets were divided into four groups by means of resin-removal: laser, burr, sandblast, and direct flame. These recycled brackets were re-bonded to the teeth with the same basic bonding methods. The shear bond strength (SBS) was measured at the speed of 0.5 mm/min and the data were analyzed using ANOVA and post hoc tests (α=0.05). Results: SBS was significantly different in all four groups compared to the control group (pp=0.99). Conclusions: 5W Er:YAG irradiation and direct flame due to relatively good bond strength can be recommended as proposed methods for orthodontic brackets recycling.

Conserved integrals and invariants (advected scalars) are studied for the equations of radial compressible fluid/gas flow in $n>1$ dimensions. Apart from entropy, which is a well-know invariant, three additional invariants are found from an explicit determination of invariants up to first-order. One holds for a general equation of state, and the two others hold only for entropic equations of state. A recursion operator on invariants is presented, which produces two hierarchies of higher-order invariants. Each invariant yields a corresponding integral invariant, describing an advected conserved integral on transported radial domains. In addition, a direct determination of kinematic conserved densities uncovers two "hidden" non-advected conserved integrals: one describes enthalpy-flux, holding for barotropic equations of state; the other describes entropy-weighted energy, holding for entropic equations of state. A further explicit determination of a class of first-order conserved densities shows that the corresponding non-kinematic conserved integrals on transported radial domains are equivalent to integral invariants, modulo trivial densities., Comment: 20 pages. Discussion of scaling properties and analysis applications of the new conserved integrals has been added

Symmetries and Casimirs are studied for the Hamiltonian equations of radial compressible fluid flow in n>1 dimensions. An explicit determination of all Lie point symmetries is carried out, from which a complete classification of all maximal Lie symmetry algebras is obtained. The classification includes all Lie point symmetries that exist only for special equations of state. For a general equation of state, the hierarchy of advected conserved integrals found in recent work is proved to consist of Hamiltonian Casimirs. A second hierarchy that holds only for an entropic equation of state is explicitly shown to comprise non-Casimirs which yield a corresponding hierarchy of generalized symmetries through the Hamiltonian structure of the equations of radial fluid flow. The first-order symmetries are shown to generate a non-abelian Lie algebra. Two new kinematic conserved integrals found in recent work are likewise shown to yield additional first-order generalized symmetries holding for a barotropic equation of state and an entropic equation of state. These symmetries produce an explicit transformation group acting on solutions of the fluid equations. Since these equations are well known to be equivalent to the equations of gas dynamics, all of the results obtained for n-dimensional radial fluid flow carry over to radial gas dynamics., Comment: 19 pages

In the title complex, [HgI(2)(C(12)H(12)N(2))], the Hg(II) atom has a distorted tetra-hedral coordination formed by two N atoms of the 6,6'-dimethyl-2,2'-bipyridine ligand and two terminal I atoms [N-Hg-N = 70.1 (2) and I-Hg-I = 130.59 (3)°]. The crystal packing features π-π contacts between the pyridine rings of adjacent mol-ecules [centroid-centroid distance = 3.773 (5) Å] and also between a pyridine ring of one mol-ecule and the five-membered chelate ring of an adjacent mol-ecule [centroid-centroid distance = 3.668 (4) Å].