Use of an Orthodontic Bracket as a Fiduciary Marker for Digital Subtraction Radiography

Abstract

Radiography is an essential diagnostic technique for the detection of hard tissue changes over time. Digital subtraction radiography allows a significant improvement in the ability to detect subtle changes in hard tissues and has been used for many applications including assessment and monitoring of root resorption, caries, periodontal disease, periapical disease and implants. Subtraction radiography requires two identical images taken at different times. The subtracted image is a composite, representing the changes in density. The ability to accurately detect changes is dependent on the reproducibility of the projection geometry between images and the ability to register or superimpose those images. Historically, this has been difficult to achieve and clinical application of this technique has been limited. Many approaches have been suggested to address this problem. To date, no investigators have used an orthodontic bracket as a fiduciary marker for digital subtraction. The purpose of the study was to investigate the use of an orthodontic bracket with and without additional fiduciary markers for digital subtraction radiography. The hypothesis is that, by virtue of its geometry and stable position, an orthodontic bracket will provide more accurate subtractions than controls using anatomic reference points. This laboratory study examined digital subtraction images obtained from human mandibular incisors with and without brackets. Direct digital images of forty teeth were taken at no angulation and 10 and 15 degrees of labial and lingual tip. The images were reconstructed and subtracted using the Emago/Advanced v3.5 program. The standard deviations of the subtraction histograms were evaluated with an ANO VA model to test the null hypothesis of no significant difference in the accuracy of digital subtractions between groups. An exploratory analysis of the length and width of the reconstructed images was also performed. Ten teeth were randomly selected to have their reconstructions repeated to assess intra and inter operator repeatability with this method. Subtractions performed using the brackets alone or the brackets with additional fiduciary markers were significantly more accurate than those performed with anatomic landmarks (p < 0.05). Reconstruction length of the no bracket group was closer in length to the reference images while length of the bracket groups were closer to the reference image length for labial tipping and closer to the tipped image for lingual tipping. Differences in width between groups were negligible. Improving the accuracy of digital subtraction by using orthodontic brackets as fiduciary markers will assist in research applications of interest to orthodontists, particularly root resorption, and may contribute to the improvement of clinical applications, such as monitoring patients genetically susceptible to root resorption. The use of an orthodontic bracket provides another tool to facilitate the application of digital subtraction radiography.