## 4 Discussion  
Midtreatment panoramic radiographs are commonly approved in clinical practice to evaluate tooth angulations and then to decide if brackets reposition or detailing bends are necessary. The present clinical retrospective study is based on the assumption made by the previous studies that CBCT is the gold standard in representing mesiodistal tooth angulation. Data from CBCT were compared to data from panoramic RX in order to understand how the latter distorted the mesiodistal angulation of the upper first and second premolars. A comparison between the variation of mesiodistal angulation measured on panoramic radiography and the variation of mesiodistal angulation and buccolingual inclination measured on CBCT was made for first and second premolars. There was a very low correlation between the mesiodistal root angulations shown on panoramic images and mesiodistal root angulations on CBCT for first and second premolars. Medium-high correlations were detected when panoramic radiography mesiodistal angulations were compared with CBCT buccolingual inclinations only for the first premolars. The results showed a similar trend only between the variation of mesiodistal angulation measured on panoramic radiography and the buccolingual inclination measured on CBCT for the first premolar. The correlation analysis showed a consistent correlation between them. No other trends were found, so data of second premolars were excluded from the study. On the basis of these results, it is strictly necessary to add a clinical intraoral evaluation to angulation shown on panoramic radiography in order to guarantee the most satisfactory clinical results. \begin{table}
\begin{tabular}{c c c} \hline \hline
**M-D Panoramic Radiography Angulation** & **CBCT** & **R Coefficient** \\ \hline \multirow{2}{*}{U4 right} & M-D & \(-\)0.46 \\ \cline{2-3}  & B-L & 0.70 \\ \hline \multirow{2}{*}{U4 left} & M-D & \(-\)0.13 \\ \cline{2-3}  & B-L & 0.59 \\ \hline \multirow{2}{*}{U5 right} & M-D & 0.18 \\ \cline{2-3}  & B-L & \(-\)0.03 \\ \hline \multirow{2}{*}{U5 left} & M-D & 0.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of Pearson _rho_ correlation analysis. Low or no correlations are shown among mesiodistal angulation in panoramic radiography and in CBCT for first and second premolars. Medium-high correlations are shown among panoramic radiography mesiodistal (M-D) angulation and CBCT buccolingual (B-L) inclination for the first premolars. Low correlations are shown among mesiodistal angulation in panoramic radiography and both mesiodistal angulation and buccolingual inclination on CBCT for second premolars. The present investigation works on the assumption that the canine-premolar is the most distorted region in the upper arch. Many authors have already reported that the representation of the actual mesiodistal root angulation in panoramic radiography is affected by errors. In particular, [PERSON] and [PERSON] [11] stated that the canine-premolar region of both arches expressed the greatest amount of angular distortion and variability in panoramic radiography. The same results were found by [PERSON] and [PERSON] [13] who showed that in most cases there was a statistically significant difference between the mesiodistal tooth angulations of panoramic images and the actual angle measurement determined on typodont dentition, as shown in the present study comparing panoramic radiography and CBCT. In particular, a panoramic radiograph tends to underestimate incisors and canine angulation and overestimate the angulation of premolar and molar, so posterior roots appear projected more distally than they actually are, with the effect of creating the illusion of exaggerated root divergence between canine and first premolar. This was also proved if panoramic images were compared with CBCT. Another study [12] showed similar results by analyzing images from four panoramic units, which indicated a definite trend in their overestimation and underestimation of the tooth angulations.