The present study investigated how marginal bone level measurements of the second premolar in the upper and lower jaws differed between digital bitewing and panoramic radiographs. The chosen areas were related to the fact that the panoramic images in this particular sites usually show overlapping of teeth and marginal bone level, making it more difficult on diagnostics of caries and marginal bone levels. Our results found that measurements done on bitewing images were more consistent between and among observers than that on panoramic images. The consistency was, as expected, higher for intra-observer agreement than inter-observer agreement. Overall, the ICC was lower for measurements made on panoramic images, meaning that when only panoramic images are available clinically, marginal bone level measurements will differ to a higher extent than they would have if measured on bitewing images. Nevertheless, the reliability of the panoramic radiograph was within the range of moderate to good, and thus might be considered as clinically acceptable.
Difference in marginal bone level between the two image modalities was statistically significant in the mandibular premolar region. This finding is contradictory to some earlier studies using the analogue radiographic technique, in which they have shown that clinicians underestimated marginal bone loss in panoramic images [1, 4]. This discrepancy between the studies may be due to differences in digital and analogue technique where the measurement methods differ. Digital technology eliminates potential sources of analogue measurement error, where radiographic film is scanned, calibrated, and then magnified and measured with a ruler or slider. The distortion of vertical measurements on panoramic imaging results from the fact that the radiation source is normally 5°–10° upward from the lingual side. The inclinations of alveolar processes in maxillary and mandible at different region may also play a role. The mean difference in bone height was 0.27 mm in region of 35, whether this small difference had clinical significance that needs to be interpreted with caution.
The validity of both methods on assessment of marginal bone level could not be studied, since this is a retrospective clinical study and thus no “gold standard” could be achieved. Using bitewing as the reference method, we found no statistically significant difference on marginal bone measurement in the upper premolar region. To what extent patient treatment varies when applying these two radiographic methods have not been evaluated in this study. Periodontal diagnoses are based on various types of measurements, and choice of treatment is not decided on radiographic results alone. A comprehensive assessment of clinical and radiological appearance governs treatment choice.
The purpose of this study was to evaluate the method itself rather than observer ability. The number of observers can affect the evaluation of a method, thus several observers are required in studies such as this. Studies have found that more than six observers does not increase accuracy when assessing a method [11, 12]. Caries diagnostic studies have shown that the strength of the statistical calculation increases with the number of observers times the number of assessed areas, up to a certain limit. The number of observers in relation to the number of areas is inconsequential, as long as the total number of observations per method is the same [12, 13].
In bitewing images of high quality, the marginal bone level could be clearly distinguished, and all observers measured the bone level with a high degree of consistency. The observer consistency was somehow lower when panoramic images were applied. The observers experienced uncertainty marginal bone level measurement in 39% of the panoramic image, whereas the number was only 5%. This was expected since panoramic radiography has poorer resolution and more proximal overlaps, causing larger differences in marginal bone level measurements compared with bitewing images.
The observers were dental students in their final year with limited clinical experience in evaluating radiographic images, however, identifying ECJ and marginal bone level was considered more as pattern recognition than diagnostics. Intra- and inter-observer agreement of experienced general practicing dentists or specialists in oral and maxillofacial radiology might have been even better.