Hassanloo A, Watson P, Finer Y, Friedman S. Retreatment efficacy of the Epiphany soft resin obturation system. International Endodontic Journal, 40, 633-643, 2007. Aim To assess the efficacy of retreatment of canals filled with the Epiphany System with and without solvent, with particular reference to the extent of canal enlargement during retreatment. Methodology Sixty roots with canals prepared to apical size 45 were embedded in resin blocks and sectioned vertically. Digital micrographs of canal walls were captured. Roots were re-assembled and filled with Epiphany/Resilon (experimental) or gutta-percha/AH Plus (control). After 8 weeks, canals were retreated to size 45 with or without chloroform, and the time recorded. Roots were split, imaged, re-assembled, retreated to size 55, split and imaged. Root-filling residue, traced at three canal levels, was expressed as percentage of canal surface. Results Residue percentage was greater (t-test, P < 0.01) in the experimental group than in the control. Most residue in all specimens was in the apical third (anova, P < 0.01). Chloroform and enlargement to size 55 decreased residue in both groups (t-test, P < 0.01). Retreatment time was longer in the experimental group (P < 0.05), and reduced by chloroform in both groups (P < 0.05). Conclusions The Epiphany System was retreatable with and without chloroform, with lesser efficacy than gutta-percha and AH Plus sealer.

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Granular materials exhibit several regimes of behavior: plastic, inertial, fluidized, and entrained flow, but not all materials can pass through all of these states. Our concern is with the criteria that determine the transition from one regime to another and with the boundaries to the various flow regimes that these criteria define. Experimentally we have focused on fine, cohesive powders, where the interparticle cohesive force dominates over gravitational force and where entrained air can cause moving powder to become fluidized. [S0031-9007(98)08339-2] PACS numbers: 45.70.Mg, 81.20.Ev, 83.70.Fn The past decade has witnessed a strong interest in granular materials by the physics community, but there is an important class of granular materials that has been largely ignored in spite of its commercial importance; these materials can be classified as fine cohesive powders. In these powders, with particle diameters less than about 30 3 10 26 m, interparticle cohesive effects are dominant, and ambient gas plays an important role in the behavior of the powder. Granular materials display four different flow regimes: plastic behavior, inertial flow, fluidized flow, and entrained flow. Particle size, particle density, cohesivity, and gas flow determine which of these types of behavior occur.(i) The plastic regime is characterized by a small spacing between neighboring particles. Velocities are small or zero and the stresses are independent of velocity for simple geometries. Plastic behavior determines the stability of heaps and slopes and there is an extensive literature on the subject because of its importance in civil engineering.(ii) In the inertial regime the stresses are due to the transport of momentum by interparticle collisions. The spacing between particles is much smaller than the particle size but greater than in the plastic regime. In everyday life granular materials such as sand, sugar, and ground coffee exhibit the transition from plastic solid to inertial flow when the limit of plastic stability is reached. We note that the interstitial fluid plays no part in inertial flow.(iii) Powders are capable of being fluidized by gas flow provided their cohesivity is not too great. In this regime the interparticle distance is of the same order of magnitude as the particle size. The interstitial fluid is the agent of transfer of momentum between particles, and fluid velocity determines the stresses in the material. The best known example of this situation is the fluidized bed, in which gas is forced through a bed of particles and the gas flow causes a pressure drop across the powder. When the pressure drop is sufficient to support the weight of the powder and to overcome the interparticle cohesive forces, the bed expands and becomes fluidized. The powder then takes on many of the properties of liquid, its upper surface remaining horizontal when the container is tilted.(iv) A fourth regime is that of entrainment, or suspension of the particles by the gas. In this case the distance between particles is much greater ...

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