# A Literature Review on the Uncommon Use of Extraoral Periapical Radiography
###### Abstract
For cases that are unlikely to obtain images with acceptable diagnostic value by IOTA, extraoral modalities such as extraoral periapical radiography (EOPA) may be more suitable. EOPA is thought to be applicable to numerous clinical situations, such as patients with mental disorders, dental phobia, severe gag reflex, large tongue, or trismus [16]. EOPA was not a mainstream concept and hence seldom mentioned in oral and maxillofacial radiology textbooks. It is believed that [PERSON] and [PERSON] first introduced the concept of EOPA in 2003 [17] by reporting two cases: one endodontic case with intraoperative and post-operative imaging, and another case with a lower third molar assessment. Basically, EOPA places the image receptor on the face of the patient, buccal to the tooth to be imaged. It can be used without a receptor holder, as the patient can hold the image receptor against their face with their fingers. Before that, [PERSON] reported the visualization of the third molar region by placing an occlusal film (size 4) extraorally [18]. That was not a periapical radiograph, as [PERSON] indeed took an IOTA for the patient, but decided to take that additional extraoral image in order to visualize the impacted upper third molar and the associated radiolucency high above the second molar. Another related work was published by [PERSON] et al., who reported the extraoral placement of an occlusal film in the parasagittal plane to visualize the anterior jaw region and obtain diagnostic information from the bucco-lingual dimension [19]. The advantages of EOPA over IOTA are a superior comfort level and applicability. Since no image receptor is placed inside the patient's mouth, EOPA must be more comfortable than IOTA. Moreover, patients with special needs, a sensitive mouth, or trismus can use EOPA when IOTA is not applicable. One alternative to EOPA is panoramic radiography, but EOPA might be more useful to communities with limited access to panoramic radiography. EOPA can be taken with standard dental radiological armamentarium with little modifications (Figure 1). Basically,the simplest way to perform EOPA is to instruct the patient to place the image receptor on the side of their face ipsilateral to the tooth under investigation. Then, the X-ray tubehead should be positioned such that the primary X-ray beam can penetrate the tooth under investigation and reach the image receptor without passing through the dentition of the contralateral side. Another way to perform EOPA is to reassemble the standard parts of IOPA receptor holders, so that there will be a ring to aim the X-ray tubehead, a plastic block to hold the image receptor close to the face, and a long metal arm that connects the ring and the plastic block. Besides the relatively simple set-up method, periapical radiography also allows for a much clearer assessment of the periapical status of the teeth compared to panoramic radiography [20], such allowing for the ability to detect root dilacerations and other abnormal shapes [21], and apical periodontitis [22]. Due to the complex image acquisition mechanism of panoramic radiography, vertical measurements made on panoramic images are particularly less reliable than horizontal measurements [23]. There are few opinion/perspective papers on promoting the use of EOPA, but there was one recent literature review that focused on the use of EOPA in determining working length during endodontics. Hence, this narrative review aimed to review the dental literature on the use of EOPA, irrespective of a particular dental specialty, to reveal the results of comparisons between EOPA and any other dental imaging modalities.