Title:
Three-dimensional ultrashort echo magnetic resonance imaging of orthodontic appliances in the natural dentition.

Abstract:
The purpose of this study was to determine whether ultrashort echo time magnetic resonance imaging technology could be used to image teeth with orthodontic appliances in place.
High-resolution 3-T ultrashort echo time magnetic resonance imaging was performed on 60 extracted premolars with fixed ceramic orthodontic appliances (Clarity, 3M Unitek, Monrovia, Calif; Radiance, American Orthodontics, Sheboygan, Wis; and Ice, Ormco, Glendora, Calif). The teeth were collected from the orthodontic clinic at the University of Alabama at Birmingham, and the institutional review board of the University of Alabama at Birmingham approved the study. Linear measurements of tooth morphology and orthodontic bracket dimensions were acquired with calipers and compared with virtual digital magnetic resonance imaging. The spin echo and high spatial resolution multi-slice turbo spin echo were only used for visual comparison with the ultrashort echo time slices. Both the caliper and the ultrashort echo time magnetic resonance imaging measurements were highly reliable and accurate. Comparisons between the 2 methods showed no statistically significant differences in any bracket or tooth dimensions, with a P value of >0.05. In general, the differences in the values ranged from -0.01 to 0.06 mm. A visual evaluation scale was used to assess the quality of the ultrashort echo time magnetic resonance images when assessing the delineation of dental hard tissues.
The visual evaluation scale of the images showed that enamel, dentin, pulp, and ceramic orthodontic appliances could be subjectively delineated at a high level with the ultrashort echo time magnetic resonance imaging.
The following conclusions can be drawn from this prospective study. Ceramic orthodontic appliances, without metal components, cause no dental image distortions and are readily visible on the ultrashort echo time magnetic resonance imaging scans. The measurements comparing linear tooth measurements with virtual digital magnetic resonance images demonstrated that magnetic resonance imaging has statistically and clinically significant accuracy on external tooth and bracket measurements. Visual evaluation of the images showed that enamel, dentin, pulp, and ceramic orthodontic appliances could be subjectively delineated at a high level with ultrashort echo time magnetic resonance imaging. Metallic slots in ceramic appliances cause severe image distortions. These distortions are localized and should not affect surrounding tissues in full-volume magnetic resonance imaging.