The purpose of this study was to analyze the validity of different anatomic variations and pathologies of the maxillary sinus found in 2D panoramic radiography by comparing them to those initially detected on CBCT images. Additional aims were the evaluation of inter- and intra-examiner differences on panoramic-radiograph-driven evaluation of the maxillary sinus.
Differences between CBCT- and panoramic-radiograph-driven evaluations of the maxillary sinus
There is a moderate risk for false diagnosis of the maxillary sinus if only panoramic radiography rather than CBCT is used. In the present study, comparing 2D to 3D imaging, solely maxillary bone cysts penetrating into the sinus were frequently detected differently. Maestre-Ferrin et al. compared the efficacy of panoramic radiography, computed tomography (CT), and 3D CT in the diagnosis of mucosal thickening, mucous cysts, or complete opacity when using implant-planning software and showed that panoramic radiography was comparatively inferior . Maestre-Ferrin et al. [14, 15] also showed that panoramic radiography led to false-positive and false-negative findings in the visualization of maxillary sinus septa in almost half of their cases, and Krenmair et al.  observed the same inaccuracy of panoramic radiography in detecting antral sinus septa in 13 out of 61 cases. Our study demonstrated no significant differences between 2D and 3D imaging methods in the detection of basal septa.
The inter-observer disagreement between the two resident groups (first-year vs. last-year residents) examining 2D panoramic images was significant in the detection of the basal septa. As mentioned above, Maestre-Ferrin et al. have already indicated that panoramic radiography is insufficient for the detection of sinus septa , which complements to Shahbazian et al.’s finding that even though panoramic radiography provides a broad view of the sinus floor, it is unsuitable for detecting small lesions, due to low spatial resolution . A similar observation was obtained by Dreiseidler et al. who confirmed superior visualization of all important high-contrast structures for CBCT compared to panoramic radiography with a focus on presurgical implant planning .
There was only little intra-observer variation. The literature shows that the intra- and inter-examiner variation in the interpretation of radiographs may exceed the variation of imaging techniques and diagnostic yield [12, 18, 19]. That some variations may not be eliminated despite observer training has already been indicated by Kullman et al. . Their study analyzed inter- and intra-observer differences in assessing panoramic radiographs with regard to radiographic bone height at two assessments several weeks apart. Both outcomes of two observers were described as reliable but not excellent though both raters were experienced.
One limitation of the latter and also of the present study may be the relatively small number of raters. Another limitation of this study may be the prevalence imbalance of different findings in the maxillary sinus resulting in a negative impact on our statistical calculation. This might include not only the low prevalence of maxillary bone cysts penetrating into the sinus but also the high prevalence of basal septa, an imbalance former studies have already demonstrated [15, 21, 22].
An explanation for our reported findings may be that, due to the superimposition of different structures, low spatial resolution and visual loss of cortical plates or undulating concavities, precise evaluation of a maxillary sinus finding is difficult in 2D panoramic radiography [5, 11]. Moreover, this difficulty might express that, as a consequence, the shown inter- and intra-observer variation in the interpretation of 2D radiographs may exceed the diagnostic yield .
Undiagnosed sinus conditions may be associated with chronic orofacial pain that is one of the most common reasons why patients consult physicians . Moreover, precise assessment of the maxillary sinus by obtaining information on bone characteristics, on condition of Schneiderian membrane, on the presence of septa, and on the lateral sinus wall is mandatory prior to any lateral or internal sinus floor elevation [7, 8]. Currently, different radiographic means are used for preoperative tooth and bone-site and implant-site assessment. Clinicians commonly use 2D or 3D radiography. Both options imply advantages and disadvantages . CBCT is used primarily to evaluate bony anatomy and to screen for overt pathology of the maxillary sinuses prior to dental implant treatment [24, 25]. However, prior to any radiographic imaging, especially for young patients, its benefit must be to weigh against its risk, with highest attention to the ALARA principle (as low as reasonably achievable) . This study indicates that panoramic radiography provides a sufficient view of the maxillary sinus for basic diagnostics, and it may be an adequate imaging method especially in the initial diagnostic phase. A precise assessment of different conditions of the maxillary sinus may only be possible using CBCT.