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Figure 5 . FORESHORTENING ( A ) ELONGATION ( B ) - Excessive vertical angulation leading to foreshortening and elongation of the roots on the lower and upper molars respectively .
Figure 6 . “ Cone cutting ” caused by failure to align the rectangular collimator correctly with the ring of the beam aiming device .
Figure 7 . Early caries - marked occlusal surface caries and interproximal enamel lesion . Figure 8 . Caries spreading along the DEJ .
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Figure 12 . Periodontal |
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ligament widening and |
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loss of lamina dura at the |
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apicies of the LR6 . The |
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surrounding bone appears |
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to have a more dense |
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trabecular pattern than |
Figure 9 . Caries under a restoration . |
Figure 10 . Multiple advanced
interproximal lesions .
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Figure 11 . Radiolucent area at the apicies of the
carious LR6 .
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the adjacent bone - this represents sclerosing osteitis . |
Coning / collimator use - Following the process of optimisation , radiation dose must be “ as low as reasonably practicable ”. In practical terms , this includes the use of collimation as this can reduce radiation exposure to the patient by up to 50 %. When aligning the x-ray tube head to the image receptor , care should be taken to prevent “ coning off ”. The use of beam aiming devices helps prevent positioning errors . ( Fig 6 )
We will be discussing intra-oral radiography technique in more depth in article 4 in this series .
Interpretation of Intraoral images The various tissues that make up the oral cavity produce images of differing radiodensity on a radiograph due to their ability to attenuate the x-ray beam . Restorations and enamel cause a high degree of attenuation meaning less x-ray photons are available to interact with the image receptor ( areas appear whiter on the final image ), whereas air and soft tissue causes relatively little attenuation resulting in an abundance of photons reacting with the image receptor ( blacker areas on the final image ).
Caries Carious lesions within the dental hard tissues change the relative attenuation of the beam ; therefore caries will appear more radiolucent than surrounding healthy enamel and dentine . It is important to note however that these radiographic images are two dimensional images of three dimensional structures , therefore a small carious lesion may not have enough effect on the attenuation of the beam to produce a visible change on the final image . Carious lesions will only appear on radiographic images once enough tooth substance has been affected to have an overall effect on the x-ray attenuation ( typically quoted as between 30-40 % demineralization in the approximal lesions ). ( Fig 7 )
Caries produce characteristic radiolucencies
in the teeth affected . The appearance of the radiolucency depends on the site and size of the lesion . Proximal surface- early caries appears as a triangle with the base at the tooth surface . When the demineralization front reaches the dentinoenamel junction ( DEJ ) a second triangle then begins to form with its base along the DEJ and apex towards the pulp- this triangle typically has a broader base than the enamel triangle . Proximal caries most commonly appears between contact points and the free gingival margin . ( Fig 8 )
Occlusal caries is more common in children and adolescents . It begins in the pits and fissures and progresses to the DEJ where it can be seen as a thin radiolucent line between enamel and dentine . As carious lesions progress into dentine , the margin between carious and non-carious tooth substance can be diffuse making detection difficult .
Caries under existing restorations can be very difficult and sometimes impossible to detect . Some restorative materials appear very radiopaque on radiograph - again , as the radiograph is a 2D image of a 3D structure it will not be possible to detect caries in any tissue obscured by this radiopaque restoration . Careful examination of the margins of restorations both clinically and on radiograph needs to be carried out to detect secondary caries .
Due to the difficulty of interpreting images , false positives and false negatives are very common and can lead to both overtreatment and damage of sound dentition , and delayed treatment of caries resulting in increased tooth substance damaged by caries . Caries progresses relatively slowly in most individuals therefore a conservative approach to caries diagnosis and treatment is often suggested- i . e . following careful history and examination and special investigations , identify suspicious lesion on radiograph , if there is no clinical sign of disease activity recall patient to take another radiograph after a suitable time period . The FGDP outlines the recommended frequency of radiographic assessment in patients with
varying caries risk statuses . ( Fig 9,10 )
Periapical inflammatory lesions Pulpal necrosis occurs secondary to bacterial invasion through the caries process or due to trauma to a tooth . An inflammatory response in the tissues surrounding the apical foramen occurs in response to the necrotic pulp . Inflammatory exudate accumulates in the periapical tissues- this initially appears on radiographs as widening of the periodontal ligament space .
As the inflammatory response continues to keep the invading bacteria from the necrotic pulp at bay , there is damage to the surrounding host tissues . This appears as resorption of the apical bony socket which on a radiograph will appear as a loss of the lamina dura .
Rarefying osteitis , periapical granuloma and periapical radicular cyst all appear as radiolucent areas around the apex of a nonvital tooth . ( Fig 11 )
Rarefying osteitis is loss of bone due to inflammation . A periapical granuloma and dental cyst appear as lucent areas typically centred on the apex of a non-vital tooth . These can only be distinguished from each other histopathologically ; however , typically a dental cyst appears as a larger lesion . When the contents of the necrotic pulp illicit an inflammatory response in the surrounding periodontal ligament and bone , the body may try to heal the apical area by stimulating the formation of granulation tissue - this gives rise to a periapical granuloma which on radiograph appears typically as a small radiolucency . If epithelial cells are entrapped in this , they may proliferate to form a radicular cyst . Both a periapical granuloma and radicular cyst are chronic conditions but may experience flare ups .
Sclerosing osteitis - In contrast to rarefying osteitis , chronic lesions may illicit an increase in bone deposition in response to inflammation . This gives radiolucent periapical areas a denser area of surrounding bone . ( Fig 12 ) u
Dental Practice Magazine
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