Effectiveness of universal adhesives on primary tooth enamel: a literature review

Over recent years, minimally invasive techniques have been increasingly adopted in pediatric dentistry, leading to recommendations for materials that optimize clinical time and minimize handling errors. Consequently, the concept of a single-step adhesive— also known as a universal adhesive—has been widely described in permanent teeth and even in primary dentin as a reliable alternative capable of achieving predictable adhesive results, even without the application of phosphoric acid. However, there is no consensus regarding its use on the enamel of primary teeth. Therefore, the objective of the present literature review was to compile the available evidence to evaluate the effectiveness of universal adhesives. The literature search was conducted in PubMed, Scopus, ScienceDirect, LILACS, Wiley, and SciELO, including only articles published within the last ten years, in English and Spanish, that evaluated or compared at least one universal (single-bottle) adhesive. Both in vitro and clinical studies were considered. Thirteen studies met the eligibility criteria: 10 in vitro studies, 2 clinical trials, and 1 study with a mixed design that simultaneously conducted a clinical trial and an in vitro investigation. Most in vitro studies were performed on sound enamel, with the micro-shear bond strength (µSBS) test being the most frequently used. Overall, the findings suggested that selective enamel etching improved the bond strength of universal adhesives. In contrast, clinical trials evaluated only carious enamel and applied the United States Public Health Service (USPHS) criteria. The maximum follow-up period was 18 months, after which the results were heterogeneous. Although in vitro studies demonstrated increased effectiveness of universal adhesives with selective phosphoric acid etching, current clinical evidence remains insufficient to establish their efficacy in practice. Therefore, further well-designed, controlled clinical trials are warranted to clarify the clinical performance of these adhesives.