Sn eutectic melt was undercooled and spontaneously solidified in the encasement of a glass flux. Structure morphologies of the sample surface as well as inside the sample were systematically examined, and a critical undercooling of 130 K was clearly revealed for the alloy. Below the critical undercooling, coupled lamellar eutectics (a-Ni and b-Ni 3 Sn) dendritically grow in the undercooled melt. Beyond the critical undercooling, a-Ni dendrites first form during the early recalescence. b-Ni 3 Sn nucleates uniformly in the remaining liquid and then separately grows with a-Ni. Solidification of the remaining liquid into lamellar eutectics only occurs at the places in the sample surface layer where the space between the a-Ni dendrite arms is large enough. The finding that all the solidification structures at undercooling above 20 K comprise anomalous eutectics indicates that both coupled eutectic growth and decoupled dendritic growth in the rapid solidification can result in the anomalous eutectic formation. The results also indicate that it is feasible to measure the crystal growth velocity by observation of the recalescence front when undercooling exceeds 50 K for this alloy.

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Background/purpose Calcium hydroxide [Ca(OH) 2 ], a wildly used intracanal medicament, should be completely removed from the root canal before obturation to avoid negative effects on the treatment. This study evaluated the effectiveness of conventional needle irrigation (CNI), passive ultrasonic activation (PUI), photon-induced photoacoustic streaming (PIPS), XP-endo Finisher (XP) and EDDY for the removal of Ca(OH) 2 from S-shaped root canal. Materials and methods Eighty-four S-shaped root canals in resin blocks were prepared using Protaper Gold up to size #25/0.08 and filled with Ca(OH) 2 . Five groups were established according to the removal techniques (n = 16): CNI, PUI, PIPS, XP and EDDY group. The positive and negative control group (n = 2) were also established. Sodium hypochlorite 3% was used as the irrigant. Digital radiographs were used to measure the remaining Ca(OH) 2 . Statistical analysis of the data was performed by using the Kruskal–Wallis test, followed by Dunn's post hoc test with Bonferroni correction ( α = 0.05). Results All the tested techniques completely removed Ca(OH) 2 from the straight portion and coronal curve of the S-shaped root canal in 100% of cases. Regarding the apical curve, PUI, EDDY, PIPS and XP removed significantly more Ca(OH) 2 than CNI ( P < 0.05), with no significant differences among these four groups ( P > 0.05). The complete clearance of Ca(OH) 2 from the apical curve was observed in 75%, 62.5%, 56.3%, 43.8% and 0% of cases of PUI, EDDY, PIPS, XP and CNI group, respectively. Conclusion Irrigant activation enhanced Ca(OH) 2 removal from the apical region of the S-shaped root canal. CNI was significantly less effective than all activation techniques.

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Background/purpose Gold metal technology improves flexibility and the resistance to cyclic fatigue of the endodontic mechanical files. This study compared the performance of ProTaper Gold (PTG) multiple file system and WaveOne Gold (WOG) single file system in simulated S-shaped root canals, which represents one of the most challenging root canal morphology. Materials and methods Forty S-shaped canals (n = 20 canals/per group) in resin blocks were instrumented to an apical size of 0.25 mm using PTG and WOG Primary, respectively. The total amount of resin removal, canal transportation, centering ratio, and the degree of canal straightening were measured in Photoshop CS6 software. Statistical analysis was performed by using Mann–Whitney U-test ( α = .05). Results None of the files fractured during the instrumentation. The WOG group removed significantly less amount of resin at 0, 3, 6, 7 and 9 mm from the apex ( P < .05). The WOG group remained more centered in canals at 0 mm from the apex ( P < .05). The PTG group showed a better centering ability and less canal transportation at 4, 5 and 6 mm from the apex ( P < .05). In the coronal curvature portion, the use of WOG Primary significantly decreased curvature angle and increased radius compared with PTG instruments ( P < .05). There was no significant difference between the two groups in terms of the apical curvature angle and radius change ( P > .05). Conclusion The WOG Primary file has a less aggressive dentin cutting and more centered apical preparation. The PTG system is more advantageous in shaping the coronal curvature of S-shaped canal.