Adherence to Protocol Registration Among Systematic Reviews on Photobiomodulation: A Meta-Research Study.

AIMS AND OBJECTIVES: This meta-research study mapped systematic reviews on photobiomodulation (PBM), encompassing low-level laser therapy (LLLT) and light-emitting diode (LED) modalities, to evaluate whether protocols were registered, whether published reviews adhered to and updated their PROSPERO records, and whether topic redundancy occurred across reviews. METHODS: Comprehensive searches were conducted in MEDLINE (via PubMed) and Epistemonikos on June 2, 2025. Data were extracted on protocol registration, registry type, update status on PROSPERO, deviations between registered protocols and published reviews, topic redundancy, and the use of certainty of evidence assessment tools. RESULTS: A total of 285 systematic reviews (with and without meta-analysis) published between 1999 and 2025 were included, of which approximately 40% addressed dentistry and orofacial dysfunctions. Among these, 129 reviews (45%) had a registered protocol, with 125 (96.9%) on the PROSPERO platform and four (3.1%) on other registries, including INPLASY and the Open Science Framework. Despite publication, 72% (90/125) of PROSPERO records remained classified as "ongoing," reflecting limited updates to the registry status. Deviations between registered and published protocols occurred in 22.4% (29/129) of reviews, mainly involving unplanned outcomes, modifications in search strategies, or changes in analytical methods. Redundancy was frequent, with multiple reviews addressing identical or highly similar clinical questions, such as 20 reviews on orthodontic treatment and 18 on temporomandibular dysfunction. Assessment of the certainty of the evidence was also limited, with only 18.5% (53/285) of reviews applying the GRADE approach, which was reported exclusively in reviews with meta-analysis. CONCLUSION: These findings highlight low adherence to protocol registration recommendations, limited status updating, and high levels of duplication, combined with infrequent assessment of evidence certainty. Strengthening prospective registration and transparent reporting is essential to ensure that systematic reviews on PBM provide trustworthy, reproducible evidence to guide clinical decision-making and inform healthcare policy. The study protocol is available at https://osf.io/9vknf/.