The impact of aging and storage conditions on the performance of universal adhesives: A systematic review

Objective: This systematic review evaluated how different storage times and conditions affect universal adhesives' bond strength and degree of conversion (DC).Methods: A literature search was conducted in PubMed, Scopus, Web of Science, and Google Scholar databases for articles published from January 1st, 2000, until May 15th, 2022. The researchers comprehensively evaluated the articles using a multi-step process to identify articles relevant to the topic of interest. Quality assessment was performed through the ROBDEMAT tool. Due to the high heterogeneity in the preliminary data, performing a meta-analysis was not feasible.Results: A total of 3169 records were obtained, and after removing duplicates, 2267 remained. Following title and abstract screening, 2253 studies were excluded based on the predetermined exclusion criteria. Of the 14 remaining studies, seven were further excluded due to the use of non-universal adhesives, experimental adhesives, or lack of aging protocols. Ultimately, seven studies were included in this systematic review. All studies focused on bond strength, with only one addressing DC. The Findings showed that aging or different storage conditions generally led to reduced bond strength and DC values in universal adhesives, although exceptions with stable or improved properties were noted.Conclusions: Adhesives with higher pH and those containing methacrylamides, HEMA-free compositions, or hydrolytically stable monomers showed better durability than others. Strict adherence to storage instructions, lower storage temperatures, and immediate recapping of adhesive bottles after use is recommended to maintain adhesive properties. These findings provide insights for optimizing the long-term performance of universal adhesives in clinical settings.