[Comparison of adhesive seal morphology between APC™ PLUS and APC™ Flash-Free Adhesive Coated brackets]. / Comparaison du joint de colle entre les attaches préencollées APC™ PLUS et les attaches APC™ Flash-Free.

INTRODUCTION: Does the new adhesive-coated APC™ Flash-Free bracket from the 3M Unitek® group simplify the bonding protocol without compromising precision? OBJECTIVES: The aim of this study was to compare the morphology of the adhesive joint between the classic APC™ PLUS adhesive-coated brackets and APC™ Flash-Free brackets. MATERIALS AND METHODS: In vitro bonding of esthetic brackets in the CLARITY™ ADVANCED range was performed to compare the morphology of the excess flash between APC™ PLUS and APC™ Flash-Free brackets. RESULTS: No statistically significant difference was found concerning the morphology of the excess flash between APC™ PLUS and APC™ Flash-Free brackets. A statistically significant difference was found regarding the thickness of the adhesive between the two types of bracket. The adhesive used for the APC™ Flash-Free brackets was significantly thicker than for the APC™ PLUS brackets (P=0.0001). Adhesive thickness was also more homogeneous on the APC™ Flash-Free brackets (P=0.001 for the relative difference). CONCLUSION: The adhesive is thicker but adhesive homogeneity is greater with APC™ Flash-Free brackets than with APC™ PLUS brackets.

[Is the shape memory effect a reality for 35° Copper Ni-Ti(®)? Study by means of differential scanning calorimetry]. / L'effet mémoire de forme est-il une réalité clinique pour le 35° Copper Ni-Ti(®) ? Étude par calorimétrie différentielle à balayage.

INTRODUCTION: Copper-nickel-titanium alloys are supposed to deliver a shape memory effect: when they are brought to a low temperature phase and subjected to a plastic deformation, they should recover their initial shape by simple heating. Nickel-titanium alloys can display different crystallographic phases: martensite, austenite and an inconstant intermediate R-phase. The shape memory effect is generally associated with the transition from martensite to austenite but it could also accompany the transition from R-phase to austenite. Since oral temperatures are not compatible with a fully martensitic alloy, this study aims, for 35° Copper Ni-Ti(®), to assess the R-phase presence at oral temperatures and to verify the possibility of using the R-phase shape memory effect under clinical conditions. MATERIALS AND METHODS: Thirty consecutive 35° Copper Ni-Ti(®) archwires from two different batches were examined by differential scanning calorimetry with partial cycles limited to temperatures encountered within the oral cavity (from 0 °C to 50 °C). The presence of an intermediate crystallographic phase was assessed on the thermograms. The transformation temperatures were determined and the two batches were compared using the Mann-Whitney U Test. RESULTS: Upon heating, all wires transformed directly from martensite to austenite. Af (mean  = 33.5 °C, SD  = 0.8 °C) was generally below the temperature stated by the manufacturer and a statistically significant difference (p ≤ 0.01) was found between the two batches. CONCLUSIONS: No R-phase was detected and transformation temperatures were not constant. This study questions the supposed shape memory effect displayed by 35° Copper Ni-Ti(®) wires under clinical conditions.

Torsional superelasticity of NiTi archwires.

OBJECTIVE: To reproduce and compare the intraoral torsional behavior of 10 commonly used preformed upper NiTi 0.017 x 0.025 archwires in 0.018-slot brackets at 20 degrees C, 35 degrees C, and 55 degrees C. MATERIALS AND METHODS: Ten upper preformed NiTi archwires were compared to a multibraided stainless steel wire. An original testing bench was used to reproduce palatal root torque applied onto an upper central incisor with a maximum value of 1540 g x mm. Ten samples of each wire type were tested at 20 degrees C, 35 degrees C, and 55 degrees C each. RESULTS: Loading and unloading at 20 degrees C revealed three categories of wires: a group of four NiTi wires of relative stiffness bereft of any superelasticity, a group of six NiTi wires displaying some horizontal plateau, and finally the stainless steel wire of lesser stiffness. Testing at the average oral temperature of 35 degrees C produced the same three categories of wires, with only 2 of 10 NiTi wires displaying a superelastic effect (Copper NiTi 35 degrees C and 40 degrees C). None of the NiTi wires was superelastic at 55 degrees C. Moments increased with temperature as the martensite was replaced by the more rigid austenite. CONCLUSION: This study showed that most NiTi wires did not exhibit in torsion the superelastic effect traditionally described in bending. The combination of straight-wire prescriptions and rectangular superelastic NiTi archwires did not provide optimal constant moments necessary to gain third-order control of tooth movement early in treatment. A braided stainless steel rectangular archwire displayed better torsional behavior at 35 degrees C than most NiTi archwires of the same dimensions.

Influence of relative humidity on electrical properties of alpha-Al2O3 powders: resistivity and electrochemical impedance spectroscopy.

The influence of humidity on the electrical properties of alpha-Al2O3 powders has been investigated using adsorption isotherms, DC resistivity, and electrochemical impedance spectroscopy. Samples of two alpha-Al2O3 particle sizes were examined, both individually and mixed together. The results show that the grain-bed resistivity decreases with humidity, whereas the grain capacitance is almost constant. The resistivity difference between the two particle sizes is of several orders of magnitude, while the capacitance values are not very different. These results are interpreted in terms of the layer-by-layer growth of water adsorbed on the grain surfaces. The first, more tightly bound adsorbed layer does not provoke the same effects as those layers adsorbed at higher relative humidity.