Effect Of Post Type And Restorative Techniques On The Strain And Fracture Resistance Of Flared Incisor Roots

Restoring flared endodontically treated teeth continues to be a challenge for clinicians. This study evaluated the effect of post types and restorative techniques on the strain, fracture resistance, and fracture mode of incisors with weakened roots. One hundred five endodontically treated bovine incisors roots (15 mm) were divided into 7 groups (n=15). The two control groups were (C) intact roots restored with Cpc (cast posts and core) or Gfp (glass fiber posts). The five experimental groups were (F) flared roots restored with GfpAp (Gfp associated with accessory glass fiber posts), GfpRc (anatomic Gfp, relined with composite resin), and GfpRcAp (anatomized Gfp with resin and accessory glass fiber posts). All teeth were restored with metal crowns. Mechanical fatigue was performed with 3x10 5/50 N. Specimens were loaded at 45°, and the strain values (μS) were obtained on root buccal and proximal surfaces. Following that, the fracture resistance (N) was measured. One-way ANOVA and Tukey's HSD tests (α=0.05) were applied, and failure mode was checked. No significant difference in strain values among the groups was found. Cpc presented lower fracture resistance and more catastrophic failures in flared roots. Gfp associated with composite resin or accessory glass fiber posts seems to be an effective method to improve the biomechanical behavior of flared roots.223230237Coelho, C.S., Biffi, J.C., Silva, G.R., Abrahão, A., Campos, R.E., Soares, C.J., Finite element analysis of weakened roots restored with composite resin and posts (2009) Dent Mater J, 28, pp. 671-678Teixeira, C.S., Silva-Sousa, Y.T., Sousa-Neto, M.D., Bond strength of fiber posts to weakened roots after resin restoration with different light-curing times (2009) J Endod, 35, pp. 1034-1039Zogheib, L.V., Pereira, J.R., do Valle, A.L., de Oliveira, J.A., Pegoraro, L.F., Fracture resistance of weakened roots restored with composite resin and glass fiber post (2008) Braz Dent J, 19, pp. 329-333Marchi, G.M., Mitsui, F.H., Cavalcanti, A.N., Effect of remaining dentine structure and thermal-mechanical aging on the fracture resistance of bovine roots with different post and core systems (2008) Int Endod J, 41, pp. 969-976da Silveira, T.C., Santos, F.M.C., Silva-Sousa, Y.T., de Sousa-Neto, M.D., Interfacial evaluation of experimentally weakened roots restored with adhesive materials and fibre posts: An SEM analysis (2008) J Dent, 36, pp. 672-682Moosavi, H., Maleknejad, F., Kimyai, S., Fracture resistance of endodontically-treated teeth restored using three root- reinforcement methods (2008) J Contemp Dent Pract, 9, pp. 30-37Bonfante, G., Kaizer, O.B., Pegoraro, L.F., do Valle, A.L., Fracture strength of teeth with flared root canals restored with glass fibre posts (2007) Int Dent J, 57, pp. 153-160Santos, A.F., Meira, J.B., Tanaka, C.B., Xavier, T.A., Ballester, R.Y., Lima, R.G., Can fiber posts increase root stresses and reduce fracture? (2010) J Dent Res, 89, pp. 587-591da Silva, N.R., Raposo, L.H., Versluis, A., Fernandes-Neto, A.J., Soares, C.J., The effect of post, core, crown type, and ferrule presence on the biomechanical behavior of endodontically treated bovine anterior teeth (2010) J Prosthet Dent, 104, pp. 306-317Silva, N.R., Castro, C.G., Santos-Filho, P.C., Silva, G.R., Campos, R.E., Soares, P.V., Influence of different post design and composition on stress distribution in maxillary central incisor: Finite element analysis (2009) Indian J Dent Res, 20, pp. 153-158Santos-Filho, P.C., Castro, C.G., Silva, G.R., Campos, R.E., Soares, C.J., Effects of post system and length on the strain and fracture resistance of root filled bovine teeth (2008) Int Endod J, 41, pp. 493-501Soares, C.J., Castro, C.G., Santos, F.P.C., Soares, P.V., Magalhaes, D., Martins, L.R., Two-dimensional FEA of dowels of different compositions and external surface configurations (2009) J Prosthodont, 18, pp. 36-42Macedo, V.C., de Faria, S.A.L., Martins, L.R., Effect of cement type, relining procedure, and length of cementation on pull-out bond strength of fiber posts (2010) J Endod, 36, pp. 1543-1546Leitune, V.C., Collares, F.M., Werner, S.S.M., Influence of chlorhexidine application at longitudinal push-out bond strength of fiber posts (2010) Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 110, pp. 77-81Novais, V.R., Quagliatto, P.S., Bona, A.D., Correr-Sobrinho, L., Soares, C.J., Flexural modulus, flexural strength, and stiffness of fiber-reinforced posts (2009) Indian J Dent Res, 20, pp. 277-281Marchi, G.M., Paulillo, L.A., Pimenta, L.A., de Lima, F.A., Effect of different filling materials in combination with intraradicular posts on the resistance to fracture of weakened roots (2003) J Oral Rehabil, 30, pp. 623-629Soares, C.J., Pizi, E.C., Fonseca, R.B., Martins, L.R., Influence of root embedment material and periodontal ligament simulation on fracture resistance tests (2005) Braz Oral Res, 19, pp. 11-16Huysmans, M.C., Peters, M.C., van der Varst, P.G., Plasschaert, A.J., Failure behaviour of fatigue-tested post and cores (1993) Int Endod J, 26, pp. 294-300Soares, P.V., Santos-Filho, P.C., Gomide, H.A., Araujo, C.A., Martins, L.R., Soares, C.J., Influence of restorative technique on the biomechanical behavior of endodontically treated maxillary premolars. Part II: Strain measurement and stress distribution (2008) J Prosthet Dent, 99, pp. 114-122Kishen, A., Kumar, G.V., Chen, N.N., Stress-strain response in human dentine: Rethinking fracture predilection in post-core restored teeth (2004) Dent Traumatol, 20, pp. 90-10

Co-crystal of suberic acid and 1,2-bis(4-pyridyl)ethane: A new case of packing polymorphism

The polymorphic behaviour of a co-crystal composed of neutral suberic acid and 1, 2-bis(4-pyridyl)ethane is reported. A multidisciplinary approach has been employed, using thermal analysis methods (differential scanning calorimetry and polarized light thermomicroscopy), spectroscopic methods (infrared spectroscopy) and X-ray single crystal and powder diffraction. Two new polymorphs, I and III; have been identified, and for one of them the crystal structure has been elucidated and compared to that of a known polymorph, form II, showing that the assembling of the molecules in chains via H-bonds is a common feature of both polymorphs. Polymorph II, obtained by crystallization from an aqueous or ethanol solution or by grinding, undergoes a solid-solid transition to polymorph I, which melts at 180.5 °C. Upon cooling from the melt, polymorph I is obtained, and a solid-solid transformation also occurs, to polymorph III''. Polymorph III was obtained serendipitously in an attempt to prepare a Nd(III) complex. The relative stability of the three polymorphic forms was established

Brane-world Quantum Gravity

The Arnowitt-Deser-Misner canonical formulation of general relativity is extended to the covariant brane-world theory in arbitrary dimensions. The exclusive probing of the extra dimensions makes a substantial difference, allowing for the construction of a non-constrained canonical theory. The quantum states of the brane-world geometry are defined by the Tomonaga-Schwinger equation, whose integrability conditions are determined by the classical perturbations of submanifolds contained in the Nash's differentiable embedding theorem. In principle, quantum brane-world theory can be tested by current experiments in astrophysics and by near future laboratory experiments at Tev energy. The implications to the black-hole information loss problem, to the accelerating cosmology, and to a quantum mathematical theory of four-sub manifolds are briefly commented.Comment: 14 pages, no figures, JHEP format, to appear in JHEP April 200

The Deformable Universe

The concept of smooth deformations of a Riemannian manifolds, recently evidenced by the solution of the Poincar\'e conjecture, is applied to Einstein's gravitational theory and in particular to the standard FLRW cosmology. We present a brief review of the deformation of Riemannian geometry, showing how such deformations can be derived from the Einstein-Hilbert dynamical principle. We show that such deformations of space-times of general relativity produce observable effects that can be measured by four-dimensional observers. In the case of the FLRW cosmology, one such observable effect is shown to be consistent with the accelerated expansion of the universe.Comment: 20 pages, LaTeX, 3 figure

Hypoexcitability precedes denervation in the large fast-contracting motor units in two unrelated mouse models of ALS

Hyperexcitability has been suggested to contribute to motoneuron degeneration in amyotrophic lateral sclerosis (ALS). If this is so, and given that the physiological type of a motor unit determines the relative susceptibility of its motoneuron in ALS, then one would expect the most vulnerable motoneurons to display the strongest hyperexcitability prior to their degeneration, whereas the less vulnerable should display a moderate hyperexcitability, if any. We tested this hypothesis in vivo in two unrelated ALS mouse models by correlating the electrical properties of motoneurons with their physiological types, identified based on their motor unit contractile properties. We found that, far from being hyperexcitable, the most vulnerable motoneurons become unable to fire repetitively despite the fact that their neuromuscular junctions were still functional. Disease markers confirm that this loss of function is an early sign of degeneration. Our results indicate that intrinsic hyperexcitability is unlikely to be the cause of motoneuron degeneration

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

Seismology of stars is strongly developing. To address this question we have formed an international collaboration OPAC to perform specific experimental measurements, compare opacity calculations and improve the opacity calculations in the stellar codes [1]. We consider the following opacity codes: SCO, CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large differences for Fe and Ni in equivalent conditions of envelopes of type II supernova precursors, temperatures between 15 and 40 eV and densities of a few mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar results and differ from OP ones for the lower temperatures and for spectral interval values [3]. In this work we discuss the role of Configuration Interaction (CI) and the influence of the number of used configurations. We present and include in the opacity code comparisons new HULLAC-v9 calculations [5, 6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data. Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences 201

Strategic review of enhancements and culture-based fisheries

Enhancements are interventions in the life cycle of common-pool aquatic resources. Enhancement technologies include culture-based fisheries, habitat modifications, fertilization, feeding and elimination of predators/competitors. Enhancements are estimated to yield about two million mt per year, mostly from culture-based fisheries in fresh waters where they account for some 20 percent of capture, or 10 percent of combined capture and culture production. Marine enhancements are still at an experimental stage, but some have reached commercial production. Enhancements use limited external feed and energy inputs, and can provide very high returns for labour and capital input. Moreover, enhancement initiatives can facilitate institutional change and a more active management of aquatic resources, leading to increased productivity, conservation and wider social benefits. Enhancements may help to maintain population abundance, community structure and ecosystem functioning in the face of heavy exploitation and/or environmental degradation. Negative environmental impacts may arise from ecological and genetic interactions between enhanced and wild stocks. Many enhancements have not realised their full potential because of a failure to address specific institutional, technological, management and research requirements emanating from two key characteristics. Firstly, enhancement involves investment in common-pool resources and can only be sustained under institutional arrangements that allow regulation of use and a flow of benefits to those who bear the costs of enhancement. Secondly, interventions are limited to certain aspects of the life cycle of stocks, and outcomes are strongly dependent on natural conditions beyond management control. Hence, management must be adapted to local conditions to be effective, and certain conditions may preclude successful enhancement altogether. Governments have a major role to play in facilitating enhancement initiatives through the establishment of conducive institutional arrangements, appropriate research support, and the management of environmental and other impacts on and from enhancements.<br /

Calibration of the length of a chain of single gold atoms

Using a scanning tunneling microscope or mechanically controllable break junctions it has been shown that it is possible to control the formation of a wire made of single gold atoms. In these experiments an interatomic distance between atoms in the chain of ~3.6 Angstrom was reported which is not consistent with recent theoretical calculations. Here, using precise calibration procedures for both techniques, we measure length of the atomic chains. Based on the distance between the peaks observed in the chain length histogram we find the mean value of the inter-atomic distance before chain rupture to be 2.6 +/- 0.2 A . This value agrees with the theoretical calculations for the bond length. The discrepancy with the previous experimental measurements was due to the presence of He gas, that was used to promote the thermal contact, and which affects the value of the work function that is commonly used to calibrate distances in scanning tunnelling microscopy and mechanically controllable break junctions at low temperatures.Comment: 6 pages, 6 figure