INTERPRETING INTRAORAL DENTAL
RADIOGRAPHS AN INTRODUCTION
BY AMANDA LOUGHLIN , MARK VINER , SARAH BOURNE OF BARTS & THE LONDON SCHOOL OF MEDICINE AND DENTISTRY , QUEEN MARY COLLEGE , UNIVERSITY OF LONDON
I n this , the first of a series of articles looking at intra-oral radiography we will take a look at the factors that affect image quality and give an introduction to image interpretation .
Intraoral radiographs are a common special investigation carried out in general dental practice . While these can greatly aid dentists in their ability to form an accurate diagnosis for a wide range of oral conditions , this is dependent on the clinicians ability to extract the relevant information from the radiograph . This ability relies upon the understanding of how a radiograph is produced , the key factors influencing the image and knowledge of “ normal ” anatomical appearance as well as knowledge of how disease processes may appear on radiographs .
Key factors affecting the image quality ( This excludes film processing errors ) mAs- current ( mA ) and time ( s ) have an effect on the volume of x-ray photons produced . An increase in the current or the length of time for which the current flows in the filament of the x-ray tube results in a greater volume of photons interacting with the image receptor . The greater the number of photons interacting with the receptor ; the greater the degree of darkening of the image . ( Fig 1 )
kV- The kilovoltage ( kV ) applied across the x-ray tube determines the energy of the photons produced . A higher kV increases the penetrating power of the photons . Low energy photons have a higher likelihood of being absorbed . Therefore , images produced at a low kV will appear very black and white- high contrast , whereas those produced at a higher kV will appear very grey- low contrast . ( Fig 2 )
Positioning - in intraoral periapical radiography and bitewing radiography , the aim is for the x-ray beam to be perpendicular to the long axis of the tooth / teeth imaged . ( Fig 3 )
Angulation errors - Excessive horizontal angulation will cause overlapping of the contact points of the teeth and therefore difficulty determining interproximal pathology . Excessive vertical angulation will cause distortion in the length of the tooth with images appearing either foreshortened or elongated . ( Fig 4 , 5 )
A
B
Figure 3 . A well-positioned radiograph . The central ray is perpendicular to the long axis of the teeth . There is no foreshortening or elongation of the roots and no overlap . There is no cone-cutting and no artefacts on the image .
Figure 1 . The effect of current and time on the final image . With an increase in mAS , the image looks darker . ( B ) A : 60 kVp B : 70 kVp
Figure 2 . The effect of increasing kV on the final image . As the kV increases- the image appears greyer- there is lower contrast . ( B )
Figure 4 . OVERLAPPING - Overlapping of dentition due to incorrect horizontal angulation . There is also evidence of a collimation error .
46 Dental Practice Magazine