# A Literature Review on the Uncommon Use of Extraoral Periapical Radiography
## 2 Materials and Methods  
Although this is a narrative review, the existing literature was still collected and reviewed in a more systematic manner. The review question was what has been published in the literature regarding EOPA that could be a demonstration of its successful usage or a comparison with IOPA? In terms of PICO, the patient type (P) could be any patient or skull/phantom head; the intervention (I) should be using EOPA; a comparison (C) between EOPA and other imaging modalities should be recorded; and the outcome (O) could be any outcome.  
In October 2023, PubMed, Web of Science, and Scopus were searched to identify papers that reported on the use of EOPA. For PubMed, the search strategy was as follows: ALL = (\"extra-oral radiographic technique\" OR \"extra-oral periapical\" OR \"extraoral radiographic technique\" OR \"extraoral periapical\"). For Web of Science, the search strategy was as follows: \"extra5 oral radiographic technique\" OR \"extra5 oral periapical\" (Topic). For Scopus, the search strategy was as follows: TITLE-ABS-KEY (\"extra\"oral radiographic technique\" OR \"extra\"oral periapical\"). The search strings were slightly different between the databases due to the different wildcards available. Only papers written in English were considered. No filter was placed to limit the publication time frame, meaning that all papers indexed by the databases until October 2023 were considered. Manual reference tracing was performed to identify studies that were potentially missed. Google Scholar searches using each of the above search strings (i.e., extra-oral radiographic technique, extra-oral periapical, extraoral radiographic technique, or extraoral periapical)  
Figure 1: Set-up for extraoral periapical radiography (EOPA).  
were also performed, and the first 5 pages resulting from each search were checked to identify any omitted papers.  
A total of 70 papers were initially identified from PubMed, Web of Science, and Scopus. After manually removing duplicates by checking the paper title and authorship, 49 papers remained. The inclusion criteria were papers written in English that reported or reviewed the use of EOPA. Otherwise, they would be deemed irrelevant and excluded. As a result, 12 papers remained. Reference tracing identified 3 additional papers and the Google Scholar searches identified another 3. Hence, a total of 18 papers that reported or reviewed the use of EOPA were included (Figure 2).  
For each included paper, the following metrics were recorded: citation count from Scopus (retrieved from a cited reference search if the paper was not indexed by Scopus directly), journal impact factor and quartile (in the respective publication year), country of the affiliation of the first author, and document type (article or review/commentary). For articles, the study design was recorded (clinical study, case report/series/demonstration, or non-clinical study). The number of radiographic images taken and the type of teeth under investigation were noted. Then, comparisons with IOPA and any other imaging modalities were recorded. The following imaging parameters were noted: the horizontal angulation of the X-ray beam; any anatomical plane that needed to be maintained horizontally; whether the mouth should be opened or closed; whether a film/receptor holder was used; the kV, mA, and exposure time applied; and the receptor type: film, intraoral (IO) sensor, or phosphor plate. For clinical studies and case reports/series/demonstrations, the reasons for radiographic examination and the number and age of patients were recorded. A risk of bias assessment or quality assessment [24; 25; 26] of the reviewed literature is presented in Figure 3. The majority of the diagnostic studies had a relatively low risk of bias or high quality content compared to the narrative reviews and case series.  
Figure 2: Flowchart of the screening process.