Paralleling Technique – Dental Radiology
Intraoral X-rays are vital in dentistry. Paralleling technique ensures optimal image quality, providing isometric and orthoradial images with minimal distortion. Proper settings reduce radiation dose and enhance diagnostics.
Table of contents
This article is based on an original article in Swedish which can be found here
BACKGROUND
In intraoral radiographic examinations, theoretical knowledge of projection theory and image acquisition is closely linked to our practical skills. Knowledge of radiation physics and projection is necessary to understanding and interpreting the images. Thus, we use specific methods for the imaging of teeth to ensure good diagnostics.
Intraoral radiographs are the most common radiographic examinations in dentistry and constitute an important diagnostic tool for general dentists (1). The effective radiation dose to the patient from a single intraoral image is low. Nevertheless, we should limit the number of radiographs to keep the patient's exposure as low as possible while maintaining diagnostic information (1, 2, 6). In all examinations involving ionizing radiation, the benefit we gain in terms of diagnostic information must outweigh the risk the radiation poses to the patient's health (1, 6). Each exposure must be justified and optimized (SSMFS2018:2, Chapter 3).
To limit the number of unnecessary exposures, it is of utmost importance that we have good knowledge of imaging techniques in order to obtain the diagnostic information we need.
PROJECTION THEORY
To begin with, we need knowledge of radiation physics and projection theory to interpret intraoral radiographs.
In mathematics, projection refers to the transformation of points in one plane onto another by connecting corresponding points with parallell lines. In intraoral radiography, this translates to how the tooth is depicted in the radiograph. This is influenced by the relationships between the direction of the radiation, the object being imaged, and the placement of the image detector. It is important to remember when interpreting the intraoral radiograph that it is a represenation of a three-dimensional structure on a two-dimensional surface, meaning several spatially distinct structures will appear to be located at the same point in the image.
The X-rays generated in our intraoral X-ray machines are not completely parallel. The rays diverge slightly from each other, consequently the objects being imaged will be depicted enlarged. Depending on their distance from the focus of the X-ray machine, the objects will have different degrees of magnification. This gives rise to distortion in the image.
