Background: Development of a standardized set of topic-specific outcomes known as a Core Outcome Set (COS) is important to address issues of heterogeneity in reporting research findings in order to streamline evidence synthesis and clinical decision making.

Aim: The aim of the current international consensus study is to identify "what" outcomes to include in the Core Outcome Set for Endodontic Treatments (COSET). Outcomes of various endodontic treatments (non-surgical root canal treatment, surgical endodontics, vital pulp treatment and revitalization procedures) performed on permanent teeth were considered.

Methods: A standard validated methodology for COS development and reporting was adopted. The process involved identification of existing outcomes through four published scoping reviews. This enabled creation of a list of outcomes to be prioritized via semi-structured patient interviews, e-Delphi process and a consensus meeting with a range of relevant global stakeholders. Outcomes were prioritized using a 1-9 Likert scale, with outcomes rated 7-9 considered critical, 4-6 are important and 1-3 are less important. Outcomes rated 7-9 by ≥70% and 1-3 by <15% of participants were considered to achieve consensus for inclusion in the COS. The outcomes that did not achieve consensus in the first round were considered for further prioritization in the second Delphi round and consensus meeting. Final decisions about the outcomes to include in COSET were made by voting during the consensus panel meeting using the Zoom Poll function.

Results: A total of 95 participants including patients contributed to the COS development process. The consensus panel recommended, with strong consensus, eight outcomes shared across all treatment modalities for inclusion in COSET: pain; signs of infection (swelling, sinus tract); further intervention/exacerbation; tenderness to percussion/palpation; radiographic evidence of disease progression/healing; function; tooth survival; and patient satisfaction. Additional treatment specific outcomes were also recommended.

Discussion: Many of the outcomes included in COSET are patient reported. All should be included in future outcomes studies.

Conclusion: COSET identified outcomes that are important for patients and clinicians and validated these using a rigorous methodology. Further work is ongoing to determine "how" and "when" these outcomes should be measured.