These patient positioning procedures are discussed later. Before you make the exposure, position the patient, the film packet, and the tube head cylinder. Set the mA selector, the tube head selector (if necessary), the kVp selector, and the exposure time. Once the X-ray machine's operational readiness check has been completed, it is a simple matter to prepare it to take radiographs on a patient. Processing techniques will be discussed later in this chapter. If the processed film shows a light area where the penny was, the X-ray machine is working properly. After making the exposure, process the X-ray film.

Do not release the exposure switch until the selected exposure time is completed. This indicates that an exposure is being made. If the machine is working correctly, you will hear a click and the tone signal, and the 'X-ray' lamp on the control panel will glow. Exposure start is delayed approximately 1/2 second. Make the exposure by depressing the exposure button located on the control panel. WARNING: You must be behind a lead-lined shield or at least 6 feet from the tube head when making the exposure. When the tube head is correctly positioned, prepare to make the exposure. The tube head cylinder should be pointed down, 6 inches above and centered on the penny. Put a penny on top of the film packet and position the tube head. Place an unexposed packet of X-ray film on the seat of the dental chair. Check to see that the machine is emitting X-rays. To protect the patient from needless exposure to radiation, use the minimum exposure time necessary to produce the desired results. The time settings may be in fractions of a second or impulses. Check the X-ray film manufacturerВ’s recommended time setting for the type of film being used, the kVp and mA settings, and the film focal distance (FFD). Refer to the manufacturer's instructions for resetting procedures. NOTE: Some X-ray machines shut off automatically if the setting exceeds 90 kVp. The kVp setting will vary, depending on the patient's bonesize and density specific settings will be given later in this chapter. Adjust the kilovoltage (kV) until the desired kilovolt peak (kVp) is registered on the kilovolt meter. The depressed button and a lamp on the selected tube head will glow. Control panel for wall mounted X-ray machine.

Kv^5-6 exposure x rays