THE DENTAL X-RAY MACHINE: COMPONENTS AND FUNCTIONS l Oral radiology MCQs

THE DENTAL X-RAY MACHINE: COMPONENTS AND FUNCTIONS l Oral radiology MCQs (multiple choice question) for dental students

 

Operation of the dental x-ray machine

1. Turn power on. A light on the control panel will indicate that the machine is ready to operate.
2. Unless preset by the manufacturer, select mA and kVp best suited for the exposure to be made.
3. Set timer for the desired exposure time.
4. Place the image receptor into the holding device and position in the patient’s oral cavity.
5. Utilizing the extension arm and yoke, adjust the tube head by aligning the PID so that the central beam of radiation is directed toward the center of the image receptor at the appropriate horizontal and vertical angulations.
6. Establish appropriate protected location from the tube head.
7. Depress exposure button and hold it down firmly until the exposure is completed. The audible signal and x-ray exposure indicator light will activate for the duration of the exposure.
8. Remove the image receptor and holder from the patient’s oral cavity after the exposure.
9. When the procedure is complete, fold the tube head support extension arm into the closed, neutral position.
10. Turn off the power to the x-ray machine.

REVIEW IN THE DENTAL X-RAY MACHINE: COMPONENTS AND FUNCTIONS

• All x-ray machines, regardless of size and voltage range, operate similarly and have the same components (control panel, extension arm, and tube head) and electrical parts (x-ray tube, low- and high-voltage circuits, and a timing device).

• The control panel may be integrated with the x-ray machine tube head support, or it may be remote from the unit, mounted on a shelf or wall. There are five major controls, some of which will be preset by the manufacturer or may be selected by the operator:

1. the line switch to the electrical outlet.
2. the milliampere selector.
3. the kilovoltage selector,
4. the timer.
5. the exposure button.

• A folding extension arm is a support from which the tube housing is suspended. The tube head is a tightly sealed heavy metal housing that contains the dental x-ray tube, insulating oil, and step-up and step-down transformers.

• Three conditions must exist to produce x-rays:

1. a source of free electrons,
2. high voltage to accelerate them.
3. a target to stop them.

• The dental x-ray tube creates these conditions. X-rays are produced only when the unit is turned on and a firm pressure is maintained on the exposure button. Electric current flows into the x-ray machine and proceeds either through the step-down transformer or the step-up transformer.

• The step-down transformer reduces the electric current from the wall outlet to heat up the filament inside the focusing cup of the cathode (negative) side of the tube. Thermionic emission results in freed electrons available to make x-rays. The step-up transformer increases the electric current to impart kinetic energy to the freed electrons to cause them to propel across the tube to strike the target (at the focal spot) on the anode (positive) side of the tube.

• The degree to which the filament is heated and, therefore, the quantity of electrons made available depends on the millamperage setting. Quantity refers to the number of x-rays in the beam. The higher the mA, the more electrons available. The penetrating ability or quality of the resultant x-rays is determined by the kilovoltage

• setting. The higher the kVp, the more penetrating the x-rays.

• The beam of radiation that exits the port seal of the tube head is the primary or useful beam. The polychromatic beam must be filtered to allow only x-rays with sufficient energy to reach the oral structures.

• The radiographer must be familiar with the operation of the machine, and the patient must understand the procedure and provide consent. To achieve consistent results, the radiographer should follow a systematic and orderly procedure.