Periodontal debridement is most important procedure in periodontal treatment, because periodontal disease is the biofilm infection. The use of ultrasonic instrument has many clinical advantages compared to classical hand instrument. The introduction of newly developed ultrasonic scaler tips made the use of ultrasonic scaler popular. However the study of tooth substance removal according to the working parameters of ultrasonic scaler with newly developed tips is not sufficient. The purpose of this study is to evaluate the effects of working parameters of piezoelectric ultrasonic scaler with curette tip on casting gold removal. The working parameters was standardized by the sledge device which controls lateral force(0.5 N, 1.0 N, 2.0 N) and power setting was adjusted 2, 4, 8 in P mode and S mode and instrumentation time was 5 seconds. The defect depth and width were measured with profile meter and defect surface was examined by SME. The depth of defect was significantly large in S mode(39.58 +/-19.35micrometer) compared to P mode(8.37 +/-6.98micrometer). There was significant decrease of depth of defect between 1.0N(32.87 +/-27.18micrometer) and 2.0N(14.86 +/-15.04micrometer). The area of defect was also significantly large in S mode(4482.42 +/-3551.71micrometer2) compared to P mode (922.06 +/-960.32 micrometer2). There was significant decrease of area of defect between 1.0N(3889.12 +/-3936.00micrometer) and 2.0N(974.66 +/-986.01micrometer). The change of mode did not effect on the width of the defect. The change of power setting did not effect on the depth, width, and area of defect. In spite of limitation of this study it could be concluded that the use of piezoelectric ultrasonic scaler with curette tip on S mode could make significant tooth substance loss.