Toward a Functional and Conceptual Framework for Adhesive Materials: The Role of Etching Technique

Background/Objectives: The classification of adhesive systems has historically relied on the type of etching agent and the sequence of application steps, distinguishing etch-and-rinse and self-etch categories. However, these models do not encompass the versatility introduced by universal adhesives or other emerging polymeric materials. This review aimed to integrate etching technique as a defining parameter within adhesive classification, linking material composition, bonding strategy, and clinical execution into a coherent functional framework. Methods: A structured narrative review of experimental, translational, and clinical studies published between 2010 and 2025 was conducted using PubMed and Scopus. Literature addressing adhesive categories, etching strategies, etching techniques, and smear layer characteristics was critically synthesized to identify functional relationships relevant to bonding performance and clinical decision-making. Results: The proposed taxonomy classifies materials as conventional, universal, touch-cure primers, self-adhesive/universal, and glass ionomer cements. Bonding strategies are organized as etch-and-rinse, self-etch, pre-etched, and unassisted, while etching techniques are defined as selective or nonselective families encompassing five clinically defined techniques. Incorporating etching technique clarifies the role of smear layer density, the acidity of adhesive materials, and functional monomer reactivity in demineralization and bonding. This structure enhances the understanding and teaching of adhesive concepts and supports evidence-based clinical selection of materials and techniques. Conclusions: Integrating etching technique into adhesive classification provides a functional and dynamic framework that unifies material, strategy, and technique. This taxonomy facilitates clinical decision-making and can evolve with future adhesive formulations. Further independent, long-term studies are warranted to validate the proposed combinations of materials and etching procedures.