Both intraoral and panoramic x-rays machines have the following exposure factor controls: milliamperage, kilovoltage and time. The primary difference between the two types of quipment is the control of exposure parameters. Intraoral x-ray units usually have fixed mA and kVp controls while the exposure is altered by adjusting the time for specific intraoral projections. Panoramic unit exposure is controlled by adjusting complimentary parameters; the exposure time is fixed while the kVp and the mA are adjusted according to patient size, stature and bone density. Although the principles of operation are identical, the exposure control panel is more complex in its format.
- Milliamperage (mA) Control – regulates the low voltage electrical supply by adjusting the number of electrons flowing in the electrical circuit. Altering the milliamperage setting influences the quantity of x-rays produced and image density or darkness. A 20% difference is required to visibly alter image density.
- Kilovoltage (kVp) Control – regulates the high voltage electrical circuit by adjusting the potential difference between the electrodes. Altering the kilovoltage setting influences the quality or penetration of the x-rays produced and image contrast or differences in density. A 5% difference is required to visibly alter image density.
- Time Control – regulates the period of time over which electrons are released from the cathode. Altering the time setting influences the quantity of x-rays and image density or darkness in intraoral radiography. The exposure time in panoramic imaging is fixed for a specific unit and the entire exposure cycle ranges from 16 to 20 seconds in length.