**2. Methods**

#### *2.1. Study Protocol and Registration*

The Reporting Items preferred for Meta-Analysis and systematic Review (PRISMA) procedures (http://www.prisma-statement.org, accessed on 10 April 2022) were respected in this work. The current systematic review is registered in PROSPERO with the number CRD42021278968.

#### *2.2. Research Question*

Studies about assessment of root canal morphologies through microcomputed tomography were selected based on the "PICOS" (PRISMA-P 2016) technique:


#### *2.3. Search Strategies*

The electronic online databases search was conducted for research papers based on selected keywords, assessing root canal morphology using Micro-CT, published until March 2022. The number of studies obtained from each dataset is displayed in Table 1. The articles were searched using MeSH keywords and searched digitally on four specialty journal websites. The MeSH keywords were searched in PubMed and Scopus initially, as per our initial search criteria. Further, to add more scientific evidence related to the topic, the search was carried out in Cochrane. Furthermore, to include the latest articles up to the last search date published in the specialty journals as it may take some time for the articles to be included in the indexes after they are published, the search on websites of four endodontic specialty Journals were performed, including the Journal of Endodontics, the International Endodontic Journal, the Australian Endodontic Journal, and the Iranian Endodontic Journal.

**Table 1.** Information of sources and search strategies using MeSH keywords.


#### *2.4. Data Sources*

Two separate researchers (M.I.K and N.A.) performed an electronic literature search on 20 March 2022, using MeSH terms and keywords, as well as the Boolean operators "OR" and "AND" to compile relevant material using appropriate filters. The keywords used were "Tooth Root/anatomy and histology", "Tooth Root/diagnosis", "Tooth Root/diagnostic imaging", "Tooth root", "dental pulp cavity", "Micro-CT", and "X-ray Microtomography/methods". The required literature was then gathered using proper filters by combining these key terms with the Boolean operators "OR" and "AND" as shown in Table 1. Furthermore, a hand search was also conducted by two different reviewers using keywords such as "Root canal morphology," "Root canal configuration," "Root canal system," "Microcomputed tomography," "Micro-computed tomography," and "Micro-CT" from databases such as PubMed, Scopus, ScienceDirect, and Cochrane.

#### *2.5. Eligibility Criteria*

A literature search was performed to uncover studies that used Micro-CT to assess root canal morphology. Two reviewers used the PICOS approach to examine the entire texts of the remaining papers and set inclusion and exclusion criteria. The year of publication was not restricted in any way. On 20 March 2021, the final database search was accomplished. A third reviewer's decision was used to settle disagreements. Figure 2 illustrates the inclusion and exclusion criteria.

**Figure 2.** Inclusion and Exclusion Criteria.

#### *2.6. Study Selection*

The studies that examined the assessment of root canal morphology using the Micro-CT technique, which are published in various medical journals, were found through a random check of research papers from online sources. Two researchers evaluated relevant studies against previously defined inclusion and exclusion criteria to substantiate the search technique, as shown in Figure 2.

#### *2.7. Data Extraction*

Two reviewers (M.I.K and S.A.) assessed the titles and abstracts of the publications for the inclusion/exclusion criteria mentioned above, and "relevant" articles were chosen for a full-text reading. This procedure was carried out independently, with the help of a third researcher (NA), in the event of any questions or conflicts. A manual hand search was also carried out using different keywords, and studies were included based on selected criteria.

#### *2.8. Quality Assessment and Risk of Bias of Research Articles*

The papers were selected for inclusion and exclusion based on their titles, abstracts, and inclusion and exclusion criteria. Following the screening process, full-text articles were reviewed one by one, and the material's quality was evaluated. The articles were rated for allotment biases, preference biases, involvement integrity, allocation concealment, withdrawals and dropouts, confusion, data collection methods, and statistical analysis using internal and external validity guidelines. A total of 60 papers were screened for quality, with nine being rejected due to a lack of information about the processes, teeth, research nature, and outcomes.

The Joanna Briggs Institute (JBI) critical assessment checklist was used to appraise the quality of the included studies [35]. This checklist assessed nine items: (i) appropriate

sampling frame, (ii) proper sampling technique, (iii) adequate sample size, (iv) study subject and setting description, (v) sufficient data analysis, (vi) use of valid methods for the identified conditions, (vii) valid measurement for all the participants, (viii) use of appropriate statistical analysis, and (ix) adequate response rate. Answers such as yes, no, unclear, or not applicable are assigned to each item. The 'yes' response received a 1 score, whereas the 'no' and 'unclear' responses received ratings of 0. Finally, the average score for each item was computed. The quality of studies with scores below and above the mean was then classified as good or poor quality, respectively. The study was included or excluded based on the methodological quality assessment. (Supplementary Table S1).

Two researchers (M.I.K. and N.A.) oversaw scoring, and they used the JBI criteria to base their scores. After comparing the results of their individual questions, they resolved any discrepancies to arrive at an 'agreed score'. All of the 51 included studies individually had a total score of ≥70%. Hence, both the researchers (M.I.K and N.A.) showed agreemen<sup>t</sup> for most of the included studies and were given >70% scores, thus limiting the bias.
