In order to study the expression of the strength of phosphate cement, 60% aqueous solution of various phosphoric acid compounds and 60% orthophosphoric acid aqueous solutions contained 13 group elements were mixed with the powder of commercial phosphate cement. As a result, the compressive strength of the hardened cements mixed with the diphosphoric and polyphosphoric acid solution increased 2.5 and 4.6 times, respectively, in comparison with that of orthophosphoric acid. The compressive strengths of the hardened cements mixed with the orthophosphoric acid solutions containing 13 group elements were higher than that of the orthophosphoric acid without Al³⁺, and the order of the strength was Al>In>Tl. From the powder X-Ray diffraction analysis of the hardened cements, the increase of the strength of the phosphate cement seems to be the formation of the amorphous aluminum phosphate salts, and it is not neutralization reaction of zinc oxide and phosphoric acid.

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The purpose of this study was to examine the changes in mechanical properties and the necessary heat treatment time for forming orthodontic Ni-Ti alloy wires using direct electric resistance heat treatment equipments. In this study, twenty-three different types of commercial orthodontic Ni-Ti alloy wires (size: 0.016×0.022 in) were examined using 5 wires from each type. We examined the necessary heat treatment time for forming, and change in mechanical properties by heat treatment. As a result, we found that heat treatment time required for the formation into required shapes for all samples were 2.4〜15.1 seconds. In terms of the changes in the mechanical properties, we sorted the wires into increased, decreased and minimal change loads in the super-elastic regions. Furthermore, the equipment utilizing electric resistance of the various Ni-Ti alloy wires had an complex effect, stress hysteresis, and stiffness. From the results above, we found that it is important to understand the bending properties of each wires when forming with electric resistance heat treatment equipments.

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