Selective outcome reporting in randomized clinical trials of dental implants

Selective outcome reporting (SOR) is a type of bias that occurs when the primary outcome of a trial protocol is changed or omitted in the paper. The purpose of this study was to evaluate the prevalence of SOR in publications of randomized clinical trials (RCT) concerning dental implants.

Two reviewers independently screened protocols registered at ClinicalTrials.gov until February/2019. If the protocol met the eligibility criteria, the reviewers tried to identify the corresponding publication. Data extraction was carried out by the same reviewers. Primary and secondary outcomes were recorded for each trial and compared to outcomes previously described in protocols.

A total of 49 protocols were included. SOR was identified in 27 (55.1%) trials. The major discrepancies were as follows: protocol-defined primary outcome omitted in the publication (n = 6, 12.2%), new primary outcome introduced (n = 8, 16.3%), discrepancy in the primary outcome time frame (n = 17, 34.7%) and new secondary outcome introduced (n = 31, 63.3%). SOR was significantly associated with industry funding (p = 0.04) and timing of registration (p = 0.04).

Our results indicate a high rate of SOR in dental implants clinical trials. Use of registry data during the peer-review process may help decreasing SOR.