Universal Adhesives: Evaluation of the Relationship between Bond Strength and Application Strategies—A Systematic Review and Meta-Analyses

Adhesive resins with guided application protocols have been developed with the main goal of reducing the number of clinical steps. Universal Adhesives (UA) can be applied with both Self-Etch (SE) or Etch-and-Rinse (ER) adhesion strategies. This review aims to evaluate the bond strength of UA, applied to dental tissues, by a systematic bibliometric review of in vitro studies. The research question, through the PICO model, aimed to assess the current knowledge of the immediate and long-term bond strength of UA, applied with a direct restorative technique. PubMed and ScienceDirect database searches focused on the bond resistance of UA applied with the ER and SE strategies. Studies assessing shear bond strength and microtensile bond strength, in both enamel and dentin, were included. From 1109 screened articles, 12 fulfilled the inclusion criteria. The bond strength of UA to enamel showed better results with the ER approach, while the adhesion strategy did not significantly affect the bond strength of UA to dentin. Evidence from in vitro studies has tended to suggest that the use of the SE adhesion approach seems to be a better choice to improve the bond strength to the dentin. The selective enamel etching is advisable when applied with the SE adhesion approach to optimize the UA bond strength to the enamel.