In the first case of the experiment, this study was done with each new curett in the following three experiment. Twelve new double-ended No. 11/12 Gracy curettes from three different manufacturers (A, B and C) was randomly selected from our stock at first test. They were weared by wear tester with fixed pressure and limited distance. This study measured the width of worn curettes'cutting edge.

The results were as follows;

1) In 50 times experiment, this study discoverd that each manufacturer's curette was appeared with different degree of wear (p<0.01)

2) In 100 times experiment, this study result similarly to the 50 times experiment(p<0.01).

3) In 150 times experiment, the result of this study were alike as the X50 experiment and X100 experiment.

In the second case of the experiment, the study was done with a curett of a manufacturer in the following three experiment. Two double-ended No. 11/12 Gracy curette from three different manufactures (A, B and C) was randomly selected from our stock at second test.

1) In 50 times experiment, this study discovered that each manufacturer's curette was appeared with different degree of wear (p<0.05).

2) In 100 times experiment, the result was same, compared with the 50 times experiment.

3) In 150 times experiment, this study also discovered that the result was same with the result of the upper two cases.

In conclusion, this study discovered that the two cases of experimental were shown with a same result.