Dental X-Ray Machine Components – Chapter 3

External components include the master switch, exposure buttons, and mechanisms to regulate the machine
Tube head positioning is facilitated from the external components

MILLIAMPERE SELECTOR (mA)
- Measures the amount of current passing through the wires of the circuit (amount of x-rays produced)
KILOVOLT PEAK SELECTOR (kVp)
- Measures the difference in current voltage across an x-ray tube
- Determines the speed of electrons traveling toward the target and their penetrating ability
TIMER
- Regulates the duration of the interval that the current will pass through the x-ray tube
EXPOSURE BUTTON
- Activates the x-ray production process

Allows for moving and positioning the tube head, so the x-ray source is brought to the area of imaging
Contains the wires connecting the base of the machine to the tube head
Allows the tube head to move _ and

Contains dental x-ray tube, insulating oil, and transformers
Protects the x-ray tube, grounds high-voltage components, prevents overheating of the x-ray tube, and absorbs non-contributing x-rays

Two circuits are used in producing dental x-rays:
- Filament circuit: Provides low-voltage to the filament to generate a source of electrons
- High-Voltage circuit: Provides high-voltage to accelerate the electrons from the cathode filament to the anode target

Located in the tube head
Required to decrease or increase the ordinary current entering the x-ray machine
STEP DOWN is for filament circuit – where electrons are produced (low-voltage)
STEP UP is to increase the voltage needed to propel the electrons toward the target (high-voltage)

Voltage is the electrical pressure between two electrical charges
Determines the speed of the electrons when traveling from cathode to anode
Speed is directly proportional to penetrating power or energy of the x-rays produced
Dental x-ray machines operate at very high voltage, expressed in kilovolt (kV) = 1,000 volts
Highest voltage the current rises to during an exposure is called Kilovolt Peak (kVp)
Dental x-ray machines typically operate with a range of 50 kVp to 100 kVp

Small rectangular area on the target of the anode to which the focusing cup directs the electron beam from the cathode
Size of the focal spot affects the sharpness of the radiographic image
Primary beam (useful x-rays) is the beam originating at the focal spot
Central ray is the x-ray in the center of the primary beam

Applied to the high-voltage circuit (between cathode and anode), boiled-off electrons are propelled from the cathode to the target on the anode, producing heat and x-rays
The 20-degree angle of the anode target directs most of the x-rays through the window toward the port opening
These x-rays make up the primary x-ray beam
The central ray is the x-ray in the center of the primary beam
A labeled diagram shows the relationships among:
- Cup, Focusing electron cloud, Tungsten target, Anode, X-ray, Cathode
- Low-voltage transformer, Oil, Copper stem, Filament, Window, Radiator, Vacuum, Filter, PID, X-rays, Port
- High-voltage transformer, Tube head, Collimator, Primary beam, Central ray, FILTER, COLLIMATOR

The X-ray beam has two aspects:
- Quantity: refers to the number of x-ray photons produced
- Quality: refers to the penetrating power or energy of the x-ray beam
INTENSITY: product of the quantity and quality
The beam is affected by:
- mA, kV, exposure time, and distance

$Q \propto \text{mA} \cdot t$

$E \propto \text{kVp}$

$I \propto Q \cdot E$

$I \propto (\text{mA} \cdot t) \cdot \text{kVp}$

Distance effect (inverse square law):
$I \propto \frac{1}{d^{2}}$

Therefore, the overall relationship (qualitative):
$I \propto \frac{\text{mA} \cdot t \cdot \text{kVp}}{d^{2}}$