We have examined the basic studies on the rotational performance of the air turbine handpieces by using the brake method. Once, we used the constant feed speed testing method in which the test bur was pressed to the brake block at a constant feed speed. In the case of this method, the load increases in inverse proportion to the rotational speed as the loading time increases. In this paper for analyzing on the problem of the brake block materials used to this testing method, we did the performance test of the usually used air turbine handpieces by using the glass and the supper alloy which were superior to the frictional resistance as the brake materials. Consequently, by the difference of these brake materials, the characteristics of handpieces are not influences. But, in the long loading times, the dynamic friction coefficient between the glass block and the test bur became the great values. Therefore, in the constant feed speed testing method, the measured values of normal loads on the test bur, are influenced with the dynamic friction coefficients in the high load levels. On the rapidly dropped phenomenon of the rotational speed of air turbine handpieces, we measured the moment values at the support of test bur. And then we discussed the relation between the rotational performance and the length of burs or points using for cutting instruments. On the basis of the theoretical and experimental investigations of air turbine's rotational performance, we measured and examined the maximum works of the various kinds of the handpieces used in clinical field. The characteristics of the four-type handpieces, such the standard, torque and miniature types and air bearing type, used in this studies, were influenced with the materials of the brake block as far as the bounds of the loads were high in the rotational performance tests.