Essential Principles of Dental Radiography Physics and Technique

Fundamental X-ray Characteristics

X-rays behave similarly to light.
X-ray changes occur in cells and tissues. (True)
The tube of a dental X-ray machine is a hot-filament tube. (True)
Cooling in some devices is achieved through the circulation of air or oil. (True)
X-rays are absorbed by any form of matter (solids, liquids, gas). (True)

The silver halide crystals of the emulsion in the film are mainly bromides suspended in oil. (False) (They are typically suspended in gelatin.)
Light photons do not activate the silver crystals. (True)
The action of developing agents on continually exposed silver crystals causes the precipitation of silver. (True)
The *latent image* is formed when silver halide crystals absorb X-ray photons, creating a lacy silver stain in each crystal. This image is stored in the film and becomes visible upon development.
Film speed is determined by the size of the silver grains.

In posterior teeth, X-rays penetrate approximately 8mm. (True)
A small amount of enamel can absorb the same amount of radiation as a large amount of soft tissue. (True)
To produce tough, fast plates, more radiation and filters are used, resulting in less exposure time.
If urgent attention is needed when processing an X-ray, moisture can be removed from the developer solution.
The presence of fingerprints on the film is due to mishandling of the film.
Distorted diagnostic radiographs are often due to errors in the principles of screening geometry.
A revealing solution that is too cold will result in retarded development.
When making sequential X-rays, the minimum time between shots should be one minute.
For patient placement when taking X-rays of maxillary (top) pieces, we draw an imaginary line from the tragus lobe to the ala (lobe) of the nose.
The interpretation of the film serves as a diagnostic aid.

What happens when a photon of radiation directly interacts with an atom?
Two things can happen: the photon moves, but the atom must replace the electron that was displaced (ionization).
How are X-rays produced?
X-rays are produced when the filament is red-hot due to the passage of electric current, causing electrons to accelerate and collide with the target.
What is the use of X-rays in medicine?
Uses include diagnosing fractures of all kinds, whole bowel examinations, skull films, etc.
What is the function of the copper stem in the target?
It serves to carry heat, produced by the target, out of the X-ray tube.
Why do we still need hard X-rays?
Hard X-rays have higher penetration, allowing us to visualize all the hard tissues of the mouth.
What is the purpose of the vacuum in the X-ray tube?
The vacuum allows the electrons produced by the filament to advance quickly and unobstructed, ensuring they collide hard and fast with the target to produce X-rays.
Of what material is the focal point made?
It is a tungsten target.

What image do we seek in a Bitewing radiograph?
We seek the superior crown and the area below, looking for proximal caries or periodontal problems to determine the degree of destruction.
What image do we seek in a Periapical radiograph?
We seek a complete picture of the tooth, including the presence of cavities (depth, location) and pulp problems.
How many radiographs are minimally required for endodontic treatment?
Three radiographs are typically required:
1. The first is to know the direction, size, and shape of the roots.
2. The second is for pulp search and crown/root canal measurement, determining the final root size.
3. The third is to verify the final shutter speed (or final fill/obturation).
How many X-rays will we take in practice and what are they?
We typically take 10 X-rays: 6 periapical radiographs, 2 bitewing, and 2 occlusal.

What is primary radiation?
Primary radiation is the penetrating X-ray beam that originates from the Anode Target and exits through the tube head, constituting the primary or useful beam.
What occurs in the patient’s tissues when X-rays are absorbed?
Ionization occurs. This is the basic phenomenon that provokes change. Ionizing radiation is dangerous, but the danger is variable. It acts in living tissue through a process that causes stable atoms and molecules to become electrically unstable.
What is the role of the vacuum in the X-ray tube?
The vacuum facilitates the propagation of the electron cloud, allowing the electrons to reach the target more strongly and produce X-rays.
What happens if an X-ray is not fixed properly?
It will eventually clear (fade or wash away).