Brazing characteristics of ZrO2 and Ti-6Al-4V brazed joints with increasing temperature / 대한치과보철학회지

PURPOSE: In this study, brazing characteristics of ZrO2 and Ti-6Al-4V brazed joints with increasing temperature were investigated. MATERIALS AND METHODS: The sample size of the ZrO2 was 3 mm x 3 mm x 3 mm (thickness), and Ti-6Al-4V was 10 mm (diameter) x 5 mm (thickness). The filler metal consisted of Ag-Cu-Sn-Ti was prepared in powder form. The brazing sample was heated in a vacuum furnace under 5 x 10(-6) torr atmosphere, while the brazing temperature was changed from 700 to 800degrees C for 30 min. RESULTS: The experimental results shows that brazed joint of ZrO2 and Ti-6Al-4V occurred at 700 - 800degrees C. Brazed joint consisted of Ag-rich matrix and Cu-rich phase. A Cu-Ti intermetallic compounds and a Ti-Sn-Cu-Ag alloy were produced along the Ti-6Al-4V bonded interface. Thickness of the reacted layer along the Ti-6Al-4V bonded interface was increased with brazing temperature. Defect ratios of ZrO2 and Ti-6Al-4V bonded interfaces decreased with brazing temperature. CONCLUSION: Thickness and defect ratio of brazed joints were decreased with increasing temperature. Zirconia was not wetting with filler metal, because the reaction between ZrO2 and Ti did not occur enough.

A study on the pattern of the root resorption following maxillary incisor retraction / 대한치과교정학회지

This study was carried out in order to find out the pattern of the root resorption following maxillary incisor retraction after maxillary 1st bicuspid extration in maxillary protrusion patients. For this study, thirty two patient who received orthodontic treatment were chosen. The results were as follows; 1. Of the total 192 teeth, 61 teeth(31.77%) showed no apical root loss, 64 teeth(33.33%) fell into the class "slight", 46 teeth(23.96%) fell into the class "moderate". Only 21 teeth(10.94%) were classified as "excessive". 2. No correlation was noted between the amount of apical root loss and the types of tooth movement of the maxillary central incisors. 3. The patients who were treated with standard brackets had more changes in tooth axis and less movement of root apexes, but the patients with straight brackets had less changes in tooth axis and more movement of root apexes. 4. Comparing the degree of root resorption between bracket types, patients who had used standard brackets showed more apical root loss than patients who had used straight brackets. 5. The most frequent degree of root resorption observed in standard bracket patients was second degree, followed by first degree and third degree. The most frequent degree of root resorption observed in straight bracket patients was zero degree, followed by first, second degree and third degree.