A Study on Removal of Cemented Dowels by Ultrasonic Apparatus. Part 3.

When removing cemented posts, the application of ultrasonic vibration is effective to reduce the retentive force of the posts. However, it is not clear which frequency of vibration moreeffective is.In this study, zinc phosphate, polycarboxylate, glass ionomer and adhesive resin cements wereused. After cementation, three lebels of vibration 25, 30, 42 kHz were added to the for cemented post, and the retentive force of posts were measured.Results were as follows:1. When used zinc phosphate, polycarboxylate and glass ionomer cements, the retentive forceof posts decreased clearly at each frequency of vibration for 3 minutes.2. When used adhesive resin cement, the retentive force of posts did not decrease at eachfrequencey of vibration.3. When used zinc phosphate cement, there was significantly no effective frequency. However, 25 kHz in polycarboxlate cement and 42 kHz in glass ionomer cement were hotably effective.