Errors in dental radiographs
Dental radiographs are an essential adjunct in the diagnosis of many oral conditions. In addition to a comprehensive clinical examination, good quality dental radiographs can provide essential diagnostic information when accurately interpreted.
In order to limit the radiation dose given to a patient for diagnosis of a dental condition, practitioners are encouraged to provide relevant radiographs with referrals to Dundee Dental Hospital. This local retrospective audit of an anonymised bank of referral radiographs analysed 50 intra-oral and 50 panoramic radiographs for common errors.
The aim of this audit was to analyse and highlight common errors in the radiographs provided with referrals to Dundee Dental Hospital.
Audit results would then be used to provide feedback to referring practitioners on radiograph errors.
In accordance with the National Radiological Protection Board Guidance Notes for Dental Practitioners4, no more than 30 per cent of dental radiographs should have one or more errors present. We therefore set our audit target that 70 per cent of images should be devoid of common radiographic errors.
This local retrospective audit involved a review of an anonymised bank of referral radiographs sent in to Dundee Dental Hospital. A sample of 50 intra-oral and 50 panoramic radiographs were assessed.
After an initial assessor calibration stage, a spreadsheet data collection tool was used to collect the data for each type of radiograph. Only specific intra-oral subtypes and panoramic radiographs were included in our audit.
Lateral oblique, occlusal and CT radiographs were excluded. The standards we used to assess these radiographs were related to the Faculty of General Dental Practitioners’ three-point grading scale of dental radiographs2 and our assessment criteria included:
- The image should be unaffected by collimation
- Image contrast should be such that images are clearly visible
- Horizontal angulation should be such that the inter-proximal surfaces of teeth can be identified
- Vertical angulation should be such that there is no elongation or foreshortening of the image
- Images should be devoid of artefacts including; scratches, evidence of delaminated plates and evidence of cracked sensors.
- Image contrast should be such that images are clearly visible
- Patient positioning should be such that the anterior teeth are not too wide or narrow
- Patient positioning should be such that the occlusal plane is correctly aligned (Frankfort plane horizontal)
- Patient positioning should be such that, where appropriate, the left and right sides are similar in orientation and magnification (patient not rotated)
- There should be no air shadows obscuring areas of interest
- Jewellery should not be visible on the image
- Patient should be positioned such that the intra-pupillary line is parallel to the floor (no evidence of tilting of the image).
In our sample of intra-oral radiographs, 84 per cent of the images had at least one common radiographic error present. This falls well short of our target of 70 per cent of images being devoid of common radiographic errors. The most common error was a ‘contrast’ error. As the images were digitally transferred to Dundee Dental Hospital, it was impossible to say if the contrast issues were due to an exposure error or post image capture alteration. Conversely, post image capture alteration may also have been used in these images to camouflage incorrect exposure.
Other significant errors included vertical or horizontal image angulation discrepancies. These were identified due to image elongation/foreshortening or the presence of avoidable overlap between adjacent teeth respectively. This may be due to failure to use commonly accepted methods of capturing accurate images, e.g. the use of beam aiming devices. This finding may open up the potential future project to lead and assess image capture methods utilised by referring practitioners.
Of the panoramic radiographs, 92 per cent were found to contain errors in exposure, patient positioning,
radiograph equipment or image processing/transfer. This, again, was well below our target of having 70 per cent of images devoid of common radiographic errors.
Evidence of air shadows was the most common radiographic error identified on panoramic images. In the sample population, 60 per cent of images were found to have an avoidable air shadow, i.e. patient not positioning their tongue against their palate present on the image and detracting from the information yielded.
Errors in the positioning of the patient’s Frankfort plane were found also to be common, with 32 per cent of patients being positioned ‘chin down’ and 24 per cent of patients being positioned ‘chin up’. This resulted in an increased or reduced angle of the occlusal plane on the image.
Additionally, 54 per cent of patients were found to be tilted when the panoramic images were assessed. This was identified through different reference markers on each side of the image appearing higher or lower than their contralateral counterpart, most commonly the condyle was used for assessment. Rotation (patient rotation upon positioning) and contrast errors were also found in significant numbers in our sample.
During the planning stage of the audit, the radiographs were to initially be scored according to the three-point scoring scale from the FGDP guidelines2. During the calibration stage, the audit team independently scored the radiographs using errors present on the image. It became evident that the subjective nature of this scoring system caused an inability for the assessors to come to an agreement on individual image scoring. This may be, in part, to assessors not knowing the purpose the radiograph was taken for, instead assessing it on a set of predefined standards. It was therefore decided to assess the images based on errors present and not score each individual radiograph. This is an interesting finding and may present a future opportunity to examine the subjectivity of the FGDP three point scoring system for dental radiographs.
From our results, we were able to highlight the proportion of images in which errors could be identified. This will enable us to provide practitioners motivation to audit their own images in order to improve the quality of radiographs taken.
Furthermore, in highlighting the incidence of certain types of common radiographic errors, our results will provide practitioners with information on which specific issues to address with regards to their radiographs/ radiographic technique.
About the author
Andrew MacInnes BDS (hons) MFDS RCPS (Glasg) is a senior house officer in the restorative department at Dundee Dental Hospital. Donald Thomson BDS, FDS
RCSEd DDR RCR is a consultant oral and maxillofacial radiologist at Dundee Dental Hospital. Alison Menhinick is a superintendent radiographer at Dundee
1V.E. Rushton, K. Horner, H.V Worthington, Factors influencing the selection of panoramic radiography in general dental practice, Journal of Dentistry 1999
(27, 8), 565-571 2Faculty of General Dental Practitioners, Selection Criteria for Dental Radiography 2nd Ed. 3K. Horner, P.N.Hirshmann, Dose reduction in
dental radiography, Journal of Dentistry1990, (18, 4), 171-184 4National Radiological Protection Board (NRPB), 2001. Guidance Notes for Dental
Practitioners on the Safe Use of X-ray Equipment. Chilton, Oxford: NRPB. Available from: https://www.hparadiationservices.org.uk/dxps/resources/