Correlation between Mesio-Distal Angulation and Bucco.-Lingual Inclination of First and Second Maximly Premolars Evaluated with Panoramic Radiography and Cone-Beam Computed Tomography  
[PERSON]  
1 Department of Medicine and Surgery, University of Insubria, 21100 Varese, Italy; [EMAIL_ADDRESS] (M.F. ); [EMAIL_ADDRESS] (R.F. ); [EMAIL_ADDRESS] (P.A.Z.) 1 Department of Biomedical Sciences, Dentistry and Morphological and Functional Imaging, University of Messina, Via Consolare Valeria 1, 98122 Messina, Italy; [EMAIL_ADDRESS] (R.N. ); [EMAIL_ADDRESS] (A.M.). 2 University of Illinois, Chicago  
just before debonding [5; 6; 7]. Despite a relatively low radiation dose for patients, its convenience, and a rapid procedure, panoramic radiography has the remarkable disadvantage of providing a radiographic projection produced by a nonparallel beam that gives a distorted and magnified image [8; 9]. The parallelism among object and film to one another and the orientation of the X-ray beam at a right angle (90\({}^{\circ}\)) is the only way to obtain images consistent with reality [10]. Unluckily, large beam deviations from the perpendicular to the object and the film are necessary to generate a panoramic image, and this creates a geometric distortion in the vertical and horizontal dimensions, and magnification in tooth position and inclination [10], especially in the premolar area [10; 11; 12; 13; 14; 15; 16]. Errors are due to the process of image capturing in terms of incorrect focal trough size, shape, and X-ray beam orientation, and also to image processing, which produces ghost imaging, summation images, and static distortion [17; 18]. Eventually, head positioning and patient movements affect the panoramic image quality [19]. For all these reasons, panoramic radiography actually does not provide an accurate representation of the true mesiodistal root angulations [19; 20; 21; 22; 23; 24; 25; 26; 27]. Indeed, a panoramic radiograph depicts variations of buccolingual inclination as changes in mesiodistal angulation, producing a wrong perception of root parallelism [11; 20] because the distortion depends on the position along the object and object depth [27]. One study [20] stated that a lingual root orientation results in apparent increase of mesial root inclination on panoramic radiographies, whereas a buccal root orientation results in an apparent increase of distal root inclination. Another study [12] showed that when the canine has buccal root orientation and the premolar has lingual root orientation, the root mesiodistal parallelism is projected on film as root convergence. Using panoramic radiography to understand correct root parallelism is possible only if the clinician is aware of the amount of distortion and knows how the distortion affects the images. Since it is very difficult, it is recommended to clinically examine teeth alignment just before debonding [20]. Cone-beam computed tomography (CBCT) has recently been suggested as a valid way to assess actual occlusion and root angulations in three planes of space [14; 15]. CBCT is also recommended in cases of skeletal malocclusions [28], dental anomalies [29], temporomandibular joint disorders [30; 31], evaluation of maxillofacial growth and development [32], anatomical assessment before temporary anchorage devices (TADS) insertion [33], and evaluation of endodontic lesions [34], and it may also be used during orthodontic treatment planning in order to assess tooth inclination and root positions [35]. In order to overcome limits related to radiation levels and optimize radiological risk to diagnostic needs, different Computer Tomography CT and CBCT low-dose protocols have been proposed during the last few years [36; 37]. The aim of this retrospective clinical study was to evaluate the reliability of the measurement of the mesiodistal angulation of the first and second premolar on orthopantomographic radiography.