How to control the exposure time of the dental film machine

Both intraoral and panoramic X-ray machines have the following exposure factor controls: milliamps (mA), kilovolts (kVp), and time. The main difference between the two machines is the control of exposure parameters. Typically, intraoral X-ray devices typically have fixed mA and kVp controls, while exposure is varied by adjusting the timing of specific intraoral projections. The exposure of the panoramic X-ray unit is controlled by adjusting complementary parameters; the exposure time is fixed, while the kVp and mA are adjusted according to the patient’s size, height, and bone density. While the principle of operation is the same, the format of the exposure control panel is more complex.
Milliampere (mA) Control – Regulates low-voltage power supplies by adjusting the amount of electrons flowing in a circuit. Changing the mA setting affects the number of X-rays produced and the image density or darkness. Significantly changing the image density requires a 20% difference.
Kilovolt (kVp) Control – Regulates high voltage circuits by adjusting the potential difference between electrodes. Changing the kV setting can affect the quality or penetration of the X-rays produced and differences in image contrast or density. To significantly change the image density, a 5% difference is required.
Timing Control – Regulates the time at which electrons are released from the cathode. Changing the time setting affects the number of X-rays and the image density or darkness in intraoral radiography. The exposure time in panoramic imaging is fixed for a specific unit, and the length of the entire exposure period is between 16 and 20 seconds.
Automatic Exposure Control (AEC) is a feature of some panoramic X-ray machines that measures the amount of radiation reaching the image receiver and terminates a preset when the receiver receives the required radiation intensity to produce an acceptable diagnostic image exposure. AEC is used to adjust the amount of radiation delivered to the patient and to optimize image contrast and density.