# A Literature Review on the Uncommon Use of Extraoral Periapical Radiography
## 3 Results and Discussion
Some papers recommended horizontal positioning of the patient’s Frankfort plane (F) or occlusal plane (O). [PERSON] et al. (2020), [PERSON] et al. (2018), [PERSON] et al. (2018), [PERSON] et al. (2017), [PERSON] et al. (2016), [PERSON] et al. (2016), [PERSON] et al. (2015). [PERSON] et al. (2014), [PERSON] et al. (2014). [PERSON] et al. (2013), [PERSON] et al. (2013). [PERSON] et al. (2012), [PERSON] et al. (2012), [PERSON] et al. (2011), [PERSON] et al. (2011), [PERSON] et al. (2011), [PERSON] et al. (2011). [PERSON] et al. (2011), [PERSON] et al. (2011). [PERSON] et al. (2007), [PERSON] et al. (2003), [PERSON] et al. (2003). \begin{table}
\begin{tabular}{c c c c c c} \hline
**Ref.** & **First Author** & **Year** & **kV** & **mA** & **s** & **Image Receptor** \\ \hline
[27] & [PERSON] & 2020 & 70 & 7 & 0.18 & IO sensor \\ \hline
[28] & [PERSON] & 2018 & 65 & 6 & 0.9 & Film \\ \hline
[29] & [PERSON] & 2017 &? &? &? & IO sensor and film \\ \hline
[30] & [PERSON] & 2016 & 70 & 15 & 0.8 & IO sensor \\ \hline
[31] & [PERSON] & 2016 & 70 & 8 & 0.5 (mandible) and 1.5 (maximilla) & IO sensor and film \\ \hline
[32] & [PERSON] & 2015 & 70 & 8 & 0.7 & Film \\ \hline
[35] & [PERSON] & 2014 & 70 & 7 & 0.5 (mandible) and 1.0 (maximilla) & IO sensor \\ \hline
[36] & [PERSON] & 2013 & 65 & 10 & 0.45–0.55 & IO sensor \\ \hline
[37] & [PERSON] & 2013 & 65 & 10 & 0.50–0.55 & Film \\ \hline
[39] & [PERSON] & 2012 & 66 & 8 & 0.7 &? \\ \hline
[40] & [PERSON] & 2011 & 70 & 8 & 0.1 (IO sensor) and 0.6 (film) & IO sensor and film \\ \hline
[41] & [PERSON] & 2011 & 65 & 10 & 0.45–0.55 & IO sensor \\ \hline
[42] & [PERSON] & 2007 & 60 & 7 & 0.5 & IO sensor \\ \hline
[17] & [PERSON] & 2003 &? &? &? & IO sensor \\ \hline \end{tabular}
\end{table} 
Table 3: Exposure factors used by the 14 original articles on EOPA. One strength of this review was that it searched multiple major literature databases and manually searched the reference lists, similar to a recent review on a related topic on the comparison between paralleling and bisecting angle techniques [43]. Unfortunately, very few studies actually compared EOPA with IOPA. Many papers merely demonstrated the usefulness of EOPA. Without ample data to compare between the two, it would be a very bold statement to claim that EOPA was not inferior to IOPA. A particular concern was that the technique used across the studies was highly variable, especially with regard to whether a holder was used, the vertical angulation of the primary beam, and whether the mouth should be opened or closed during mandibular EOPA. This variability can lead to inconsistencies in the outcomes and make it challenging to draw definitive conclusions. It is recommended that future studies should be consistent in the technique used, so that consistent evidence/data can be accumulated for further evaluation. Standardization is critical to ensure that results are reproducible and comparable across different study sites. It would be beneficial for future studies to include larger sample sizes and diverse patient populations to ensure that findings are as generalizable as possible. Comparative studies that directly evaluate the diagnostic efficacy, patient comfort, and clinical outcomes of EOPA versus IOPA are particularly needed. These studies should also consider various clinical scenarios, such as assessing different types of dental pathologies besides merely checking the working length or tooth length, to provide a comprehensive evaluation of the two techniques. Without a certain degree of standardization, the term EOPA can only represent a broad concept that is not reproducible across study sites and cannot be readily followed by general dentists. The lack of interest from the general audience was similarly reflected by the low citation count of the papers reviewed in this work. None of them were cited 20 times or more, whereas four were cited 1 time and another four were cited 0 times.