Ray Nj

Effect of pre‐heating on the viscosity and microhardness of a resin composite

The effect of pre-heating resin composite on pre-cured viscosity and post-cured surface hardness was evaluated. Groups of uncured specimens were heated to 60 degrees C and compared with control groups (24 degrees C) with respect to viscosity and surface hardness. Mean (SD) viscosities of the pre-heated specimens (n = 15) were in the range of 285 (13)-377 (11) (Pa) compared with 642 (35)-800 (23) (Pa) at ambient temperature. There was a statistically significant difference between the two groups (P < 0.001). Mean (SD) Vickers microhardness (VHN) of the pre-heated group (n = 15) was 68.6 (2.3) for the top surface and 68.7 (1.8) for the bottom surface measured at 24 h post curing (specimen thickness = 1.5 mm). The corresponding values for the room temperature group were 60.6 (1.4) and 59.0 (3.5). There was a statistically significant difference between corresponding measurements taken at the top and bottom for the pre-heated and room temperature groups (P < 0.001). There was no significant difference between top and bottom measurements within each group. Pre-heating resin composite reduces its pre-cured viscosity and enhances its subsequent surface hardness. These effects may translate as easier placement together with an increased degree of polymerization and depth-of-cure.

Electronic properties and crystal structure of (2,2′-bipyridyl)-catena-µ-(oxalato-O1O2: O1′O2′)-copper(II) dihydrate and aqua(2,2′-bipyridyl)-(oxalato-O1O2)copper(II) dihydrate

The crystal structure of the title compounds [Cu(bipy)(C2O4)]·2H2O (1) and [Cu(bipy)(C2O4)(OH2)]·2H2O (2) have been determined by X-ray analysis. Compound (1) crystallises in the triclinic space group P with a= 9.673(3), b= 6.940(3), c= 9.103(3)A, α= 105.718(3), β= 110.347(3), γ= 97.539(3)°, and Z= 2. The six-co-ordinate CuN2O2O′2 chromophore of (1) involves an elongated rhombic octahedral stereochemistry involving a symmetrically co-ordinated bipy ligand (mean Cu-N 2.007 A) and unsymmetrically co-ordinated bridging oxalate groups (mean Cu-O 1.988 and 2.320 A). Compound (2) crystallises in the triclinic space group P with a= 10.565(3), b= 7.246(3), c= 10.806(3)A, α= 102.467(3), β= 62.119(3), γ= 98.134(3)°, and Z= 2. The CuN2O2O′ chromophore of (2) is basically square pyramidal with a symmetrically co-ordinated bipy ligand (mean Cu-N 1.989 A), and a symmetrically co-ordinated oxalate group (mean Cu-O 1.953 A) in the plane of the square pyramid, and a water molecule at 2.341 A out of the plane. The electronic reflectance spectrum of (1) involves main band at 14 500 cm–1 with a resolved broad band at 9 300 cm–1, while that of (2) involves a single broad band at 15 600 cm–1, a difference that is consistent with the structures and suggests an ‘electronic criterion of stereochemistry’ to distinguish these two structures.

Crystal structure and electronic properties of ammine[tris(2-aminoethyl)amine]copper(II) diperchlorate and potassium penta-amminecopper(II) tris(hexafluorophosphate)

The crystal structure of the title compounds [Cu(tren)(NH3)][ClO4]2(1) and K[Cu(NH3)5][PF6]3(2) have been determined by X-ray diffraction methods using three-dimensional diffractometer data; the structures were solved by heavy-atom techniques and successive Fourier synthesis. Compound (1) crystallises in a cubic unit cell, space group P213, with dimensions a= 11.626(3)A and Z= 4, and (2) crystallises in the orthorhombic unit cell, space group Imma with dimensions, a= 14.90(1), b= 11.79(1), c= 10.57(1)A, and Z= 4. The cation in (1) has a trigonal-bipyramidal molecular structure with strict C3 symmetry while that in (2) has a square-based pyramidal molecular structure with strict C2v symmetry. The polycrystalline and single-crystal electronic properties for these two σ-bonding CuN5 chromophores are reported and related to the one-electron energy levels for the two stereochemistries, using extended-Huckel molecular-orbital calculations, and correlated with earlier data on high-symmetry five-co-ordinate CuN5 chromophores.

Microhardness of resin composite materials light-cured through fiber reinforced composite

OBJECTIVES To compare polymerization efficiency of resin composite basing materials when light-cured through resin composite and fiber reinforced composite (FRC) by testing microhardness. METHODS Simulated indirect restorations were prepared by application of resin composite (Clearfil AP-X) or FRC (EverStick) to nylon rings with 1.5mm thickness and 8mm diameter, followed by light-curing. Resin composite basing material (Clearfil Majesty Flow or Clearfil AP-X) was applied to identical rings and light-cured through the simulated indirect restorations with exposure times of 20, 40, or 60s. Light-curing though a ring without resin material (=no indirect restoration) served as control. For each combination of basing material and indirect restoration 10 specimens were prepared for each exposure time. Top and bottom surface Vickers microhardness numbers (VHNs) of basing materials were recorded after 24h. RESULTS After 60s exposure time, VHNs with indirect FRC were not different from control VHNs, while VHNs with indirect resin composite were significantly lower (p<0.001). Linear regression analysis revealed that resin composite basing material used had the greatest effect on top and bottom VHNs (p<0.001). The presence of an indirect restoration resulted in decreased VHNs (p<0.001), with resin composite resulting in lower VHNs when compared to FRC. Moreover, a longer exposure time resulted in increased VHNs (p<0.001). SIGNIFICANCE Results suggest that polymerization of resin composite basing materials is more effective when light-curing through an FRC than through a resin composite indirect restoration. Prolonging of exposure time, however, is necessary when compared to light-curing without presence of indirect restoration material.

Crystal structure of bis(2-aminoethyl)amine(di-2-pyridylamine)zinc(II) nitrate and the electronic properties of the copper(II)-doped system

The crystal structure of the title compound [Zn(dien)(bipyam)][NO3]2 has been determined by X-ray crystallographic analysis using photographic data. The complex crystallises in the monoclinic space group P21/c, with a= 12.34(5), b= 16.26(5), c= 9.92(5)A, β= 92.0(5)°, and Z= 4. The zinc(II) ion is five-co-ordinate with a distorted trigonal-bipyramidal stereochemistry, the mean out-of-plane and in-plane Zn–N bond distances being 2.20 and 2.09 A respectively. The e.s.r. and electronic spectra of 1% copper-doped [Zn(dien)(bipyam)][NO3]2 have been determined using polycrystalline samples and single-crystal techniques and the results interpreted to suggest that the stereochemistry of the doped CuN5 chromophore corresponds closely to that observed in the isomorphous [Cu(dien)(bipyam)][NO3]2 complex, rather than to the stereochemistry of the ZnN5 chromophore of the host lattice. Caution is expressed over the use of the Zn–N distances and N–Zn–N angles to describe the stereochemistry of the CuNx chromophore when doped into isomorphous zinc(II) complexes as host lattices and the use of the electronic reflectance spectra of copper(II)-doped zinc(II) complexes as a criterion for comparable stereochemistries is advocated. A comparison of the g and A factors and one-electron orbital energies is made with other very distorted copper(II) systems.

Endodontic access cavity simulation in ceramic dental crowns

OBJECTIVES It is proposed that a non-uniform rational B-spline (NURBS) based solid geometric model of a ceramic crown would be a flexible and quick approach to virtually simulate root canal access cavities. The computation of strain components orthogonal to surface flaws generated during the drilling would be an appropriate way of comparing different access cavity configurations. METHODS A μCT scan is used to develop a full 3D NURBS geometric solid model of a ceramic crown. Three different access cavity configurations are created virtually in the geometric model and there are then imported into proprietary finite element software. A linear analysis of the each crown is carried out under appropriate in vivo loading and the results are post-processed to carry out a quantitative comparison of the three configurations RESULTS The geometric model is shown to be a flexible and quick way of simulation access cavities. Preliminary indications are that post processed strain results from the finite element analysis are good comparators of competing access cavity configurations. SIGNIFICANCE The generation of geometric solid models of dental crowns from μCT scans is a flexible and efficient methodology to simulate a number of access cavity configurations. Furthermore, advanced post-processing of the primary finite element analysis results is worthwhile as preliminary results indicate that improved quantitative comparisons between different access cavity configurations are possible.

The preparation and properties of [Cu(chelate)X2] complexes. Crystal structure and electronic properties of [bis(2-pyridyl)amine]dibromocopper(II)

The preparation and properties of a series of [Cu(chelate)X2] complexes are reported, where ‘chelate’= 1,10-phenanthroline (phen) and bis(2-pyridyl)amine (bipyam) and X = Cl– and Br–. The crystal structure of [Cu-(bipyam)Br2] has been determined; the crystals are monoclinic, space group C2, with a= 14.44(5), b= 7.92(3), c= 5.26(3)A, β= 94.7(5)°, and Z= 2. The structure has been solved using microdensitometer estimated photographic data using 509 reflections and refined to R 0.1022. The structure involves a distorted CuN2Br2 chromophore, with two-fold symmetry, and CU–N = 1.96, Cu–Br = 2.40 A, which from a consideration of the e.s.r. spectrum is best described as compressed, rather than elongated, tetrahedral. The electronic spectra of the [Cu(phen)X2] complexes are considered to involve an elongated rhombic octahedral CuN2X2X′2 chromophore stereochemistry.

The effect of variability in the powder/liquid ratio on the strength of zinc phosphate cement

Aim. To investigate (a) variability in powder/liquid proportioning and (b) effect of variability on diametral tensile strength (DTS), in a zinc phosphate cement. Statistical analyses (α = 0.05) were by Students t-test in the case of powder/liquid ratio and one-way ANOVA and Tukey HSD for pair-wise comparisons of mean DTS. The Null hypotheses were that (a) the powder-liquid mixing ratios would not differ from the manufacturers recommended ratio (b) DTS of the set cement samples using the extreme powder/liquid ratios would not differ from those made using the recommended ratio. Methodology. 34 dental students dispensed the components according to the manufacturers instructions. The maximum and minimum powder/liquid ratios, together with the manufacturers recommended ratio, were used to prepare samples for DTS testing. Results. Powder/liquid ratios ranged from 2.386 to 1.018. The mean ratio (1.644) was not significantly different from the recommended value of 1.718 (P = 0.189). DTS values for the maximum and minimum ratios were both significantly different from each other (P < 0.001) and from the mean value obtained from the recommended ratio (P < 0.001). Conclusions. Variability exists in powder/liquid ratio for hand dispensed zinc phosphate cement. This variability can affect the DTS of the set material.

The structure of monoaquabis(2-ethoxybenzoato)calcium(II)

ClsH20CaO7 is orthorhombic, space group P21212 t, with a - 6.61 (5), b -- 10.76 (5), c = 26.62 (5) A, U = 1893.31 A 3, z -- 4, d m -- 1.38 (2), d c -- 1.36 Mg m -3, F(000) = 806.57, #(Cu Ka) = 3.068 mm -1. The structure was solved by direct methods, using visually estimated integrated Weissenberg data, to give a final R = 0.104 for 1236 independent reflections. The Ca atom is eight-coordinate with a distorted bicapped trigonalprismatic geometry, and the molecular structure develops as a linear polymer, through the formation of four-membered Ca-O-Ca-O rings, to feature a tight packing of the metal ions along the chain axes. No hydrogen-bond interactions are present between adjacent chains and cohesion in this direction is limited to packing interactions.

Surface tarnishing in vitro of some commercially produced high-copper silver amalgams

Abstract The in vitro surface tarnishing of selected commercially produced high-copper silver amalgams is investigated by exposure to H 2 S/acetic acid vapour using metallographic techniques and colour photomicrography. In most cases, coloured reaction products are observed which may yield a general indication of the major dispersion of copper-rich material within the set amalgam. The experimental approach may be suitable for development as a simple tarnish test for high-copper amalgams.