This document outlines six principles of dental radiography: 1) use the smallest possible X-ray source to reduce image blurriness, 2) maximize the distance between the X-ray source and object, 3) minimize the distance between the object and receptor, 4) keep the receptor and tooth parallel, 5) direct the X-ray beam perpendicular to the receptor, and 6) avoid movement during exposure to prevent penumbra formation and blurring. It also defines the three parts of a shadow - the umbra, penumbra, and antumbra.

1. Principle One : X-rays should be emitted from the smallest
source of radiation as possible.
The smaller the focal spot area, the sharper the image. Larger the focal spot
area, the greater the amount of penumbra & loss of image sharpness.

2. Principle Two : The X-ray source-to-object distance
should be as long as possible.
A longer PID & target film distance results in less magnification

3. Principle Three : The object-to-receptor distance should
be as short as possible.
Diagram illustrating object film distance.
The closer the proximity of the tooth to the film , lesser the image enlargement.

4. Principle Four : The receptor & long axis of the tooth
should be parallel to each other.
If the tooth & the film are not parallel, an angular relationship is formed
& a distorted image results. In the above diagram the length of the image
that appears on the film is shorter than the actual tooth.

5. Principle Five : The X-ray beam should be directed
perpendicular to the receptor.
To limit distortion, the central ray of the X-ray beam must be
perpendicular to the tooth & the film.

6. Principle Six : There should be no movement of the tube, film or patient
during exposure.
( Given by Mason & Lincoln )
Diagram illustrating the influence of motion on film sharpness.
The image outline becomes blurred owing to penumbra formation.

7. PARTS OF SHADOW :
1) Umbra
2) Penumbra
3) Antumbra
1) Umbra :
 The umbra (Latin for “shadow”) is the innermost & darkest part of a shadow, where the
light source is completely blocked by the occluding body.
2) Penumbra :
 The penumbra (paene-almost,umbra-shadow) is the region in which only a portion of the
light source is obscured by the occluding body.
3) Antumbra :
 The antumbra (ante-before) is the region from which the occluding body appears entirely
contained within the disc of the light source.
GUIDED BY, PREPARED BY,
DR.BHUMI PATEL VISHAL,SHRUTI,
DR.JIGAR JOSHI NANCY,SHIVANGI