The evolution of dental adhesives: A critical review of the evidence from 4th to 8th generation systems

Abstract

Introduction: Adhesive systems determine the longevity of restorations and the costs of retreatment; their selection and technique influence microleakage and sensitivity. Objective: To analyze recent literature on 4th, 5th, 6th, 7th, and 8th generation bonding agents, describing their composition, representative brands, mechanism of action, and clinical evidence. Methodology: Articles were searched in databases such as PubMed, Scopus, Google Scholar, using keywords: Dental Bonding, Etching, Composite Resins, Photopolymerization, dental adhesive, universal adhesive, 4th-8th generation, bond strength; clinical trial. Results: 4th (total-etch, 3 steps): high adhesion and control, technique-sensitive. 5th (total-etch, 1 bottle): faster, but more hydrophilic; requires rigorous evaporation. 6th (self-etch 2 steps, 10-MDP): MDP-Ca chemical bond and consistent seal in dentin; selective etching improves enamel. 7th (all-in-one): maximum simplicity, but greater permeability; useful with active rubbing, multiple layers, and good aeration. 8th (universal multimode): favorable performance in NCCLs; possible need for activator with dual/self-curing materials; optimal with selective enamel etching and active application. Conclusion: Universal adhesives (8th) offer the best versatility when applied with active rubbing, solvent evaporation, and selective etching; 2-step self-etch adhesives (6th) are highly predictable on dentin; 3-step adhesives (4th) remain the benchmark when durability is prioritized. The choice must be individualized according to the substrate, isolation, and light-curing parameters indicated by the manufacturer.