Trial registration and selective outcome reporting in Endodontic Research: Evidence over a 5-year period

To assess the prevalence of registration of clinical trials in endodontic research and to identify outcome reporting discrepancies between trial registration entries and respective final publications. Associations with publication characteristics, such as journal, year of publication, origin, number of centres and authors, funding and statistical significance of the findings, were also sought.

All reports of endodontic randomized controlled trials (RCTs) published in 4 endodontic specialty and 4 general dental journals from 1 January 2016 to 31 December 2020 were identified. Trial registration frequency patterns were assessed for the included RCTs, whilst for the ones registered, outcome reporting discrepancies were recorded. Article characteristics such as year of publication, geographic region, number of centres, authors participating in the publication, funding, type of registration and others were identified. Descriptive statistics and univariable/multivariable logistic regression were performed to examine the effect of study characteristics on identified registration practices.

One hundred and fifty-five RCTs were included, with the majority published in specialty journals (121/155; 78.1%). A total of 42.6% of the identified RCTs was registered (66/155), mostly retrospectively (38/66; 57.6%). There was strong evidence that each additional year for more recent publication accounted for 1.42 times higher odds of being registered (adjusted Odds Ratio = 1.42; 95%CI: 1.11, 1.80; p = .004). More than 1/3 of registered RCTs presented outcome reporting discrepancies (24/66; 36.4%), whilst such inconsistencies were almost evenly distributed between primary and secondary outcomes.

Trial registration policies in endodontic research should be reviewed and active endorsement of prospective registration practices should be prioritized for better clarity and transparency of the disseminated research. Outcome reporting discrepancies shall thus be eliminated, offering increased credibility in research findings and eliminating bias in this respect.