Compton effect
The Compton Effect (also called Compton Scattering) is when only part of the dental x-ray is transferred to the electron and a new, weaker x-ray is formed and scattered in some new direction.
Radioactivity
the process whereby certain unstable elements undergo spontaneous disintegration in an effort to attain a stable nuclear state.
*Dental x-rays do not involve the use of radioactivity.
Decay
unstable isotopes are radioactive and attempt to regain stability through the release of energy.
X-ray machine components
control panel, extension arm, tube head.
Four functions of tube head:
- protects the x-ray tube from accidental damage
- Increases the safety of the x-ray machine by grounding its high voltage components to prevent electrical shock
- Prevents overheating of the x-ray tube by providing a space filled with oil, gas, or air to absorb the heat created during the production of x-rays
- Lined with lead to absorb any x-rays produced that do not contribute to the primary beam that exits through the port in the direction of the PID.
Transformer
electromagnetic device for changing the current coming into the dental x-ray machine.
Autotransformer
(located in the control panel) a voltage compensator that corrects minor fluctuations in the current flowing through the wires.
Amperage
measures the number of electrons that move through a conductor
3 requirements for acceptable radiographs
- All parts of the structures recorded must be imaged as close to their natural shapes and sizes as the patient’s oral anatomy will permit. Distortion and superimposition of structures should be kept to a minimum
- The area examined must be imaged completely, with enough surrounding tissue to distinguish between structures.
- The radiograph should be free of errors and show proper density, contrast, and definition.
High Contrast
short scale (60kvp) fewer shades of gray. Caries show up darker
Low Contrast
long scale (100kvp) more shades of gray. Perio
Direct Theory
x-ray photons collide with important cell chemicals and break them apart by ionization, causing critical damage to large molecules. One-third (1/3) of biological alterations from x-radiation exposure result from a direct effect.
Indirect Theory
based on the assumption that radiation can cause chemical damage to the cell by ionizing the water within it. Radiolysis of water.
Threshold Dose-Response Curve
indicates that there is a “threshold” amount of radiation, below which no biological response would be expected.
Nonthreshold Dose-Response Curve
indicates that any amount of radiation, no matter how small, has the potential to cause a biological response.
Protection Measures for the Patient
- Professional judgment-Use evidenced based selection criteria when determining which patients need radiographs
- Technical ability of the operator- Communication, working knowledge of radiographs, education (continuing education is important)
- Technique standards
- Equipment standards
- Optimum film processing
PID
8, 12, and 16 inches, circular or rectangular. The longer the PID, the less divergence of the beam creating smaller diameter of exposure.
Intraoral
- Bitewing- image coronal portion of both the maxillary and mandibular teeth and crestal bone on the same film. Used to detect proximal caries. #0,1,2,3
- Periapical- used to record a detailed examination of the entire tooth, from crown to root tip or apex. Used to examine periodontal ligament space and surrounding bone. #0,1,2
- Occlusal- image a larger area than periapical. Used for pathological lesions, root fragments, bone and tooth fractures, impacted and supernumerary teeth, for young children, and edentulous patients. Adult #4, child #2
Extraoral
panoramic packaged 25,50, or 100 to a box, sandwiched between black paper, needs to be manually loaded into a cassette. 5”x12” or 6”x12” in size.
