This study was conducted to determine if air pressure of 20 pounds per square inch (psi) was sufficient to operate disposable prophylaxis angles smoothly and efficiently without stalling.Five specimens of 15 types of disposable angles were evaluated by four dental hygienists to determine the minimum speed required for smooth operation. A fifth person operated the rheostat and increased the air pressure psi until signaled by the operators to stop once reaching a sufficient air pressure for operating the angle without stalling. Air pressure values were recorded for each test. Means and standard deviations were calculated for all raters for each angle. Data were analyzed using a two-way analysis of variance. Since there were no significant trends among raters, data for raters were combined for each angle and analyzed by a one-way analysis of variance. The Tukey-Kramer interval at a 0.05 significance level for comparisons among angles was determined.Study results showed that air pressure to achieve minimum speed required for smooth operation varied among the angles from 16.8 psi to 28.8 psi. The mean air pressure was 23.0 psi for angles with firm cups, 20.3 psi with soft cups, and 18.0 psi with regular cups. Some soft cup angles required air pressure greater than 20 psi while some firm cup angles required less than 20 psi. The regular flexibility of cup angles tested required less air pressure than 20 psi.The minimum air pressure psi required for smooth operation of disposable angles varied. Generally, air pressure greater than 20 psi was required to operate angles with firm cups, while less than 20 psi was required to operate angles with soft or regular cups.