This review article elucidates sol-gel thin films as an engineering tool for the targeted tuning of restorative interphases within the structure-process-property-performance framework. The primary focus is placed on how low-temperature solution routes, through precursor selection, adjustment of deposition parameters, and control of condensation schedules, can lead to network organization, pore distribution, and the formation of surface functionalities; the components that play a decisive role in interfacial adhesion, light transmission, and initial microbial adhesion. In the adhesion domain, siliceous interphases generated via surface infiltration or overlapping thin coatings create silanol-rich surfaces on yttria-stabilized tetragonal zirconia, thereby enabling durable bonding with methacrylate-based systems. Concurrently, the design of zirconia-silica mixed oxides mitigates local incompatibilities and facilitates uniform primer spreading. In the optical domain, refractive index engineering is pursued through the incorporation of porous silica or nanoscale organic-inorganic networks, strategies that target antireflective behavior, preservation of surface gloss, and increased tolerance to layer thickness variations via gradient structures. In biofilm control, visible-light-responsive titania coatings exhibit effective performance under clinical illumination conditions. In contrast, the siliceous matrices or ion-doped organic-inorganic systems provide localized release of silver or zinc ions and light-independent antibacterial effects. Key challenges reported for these approaches include balancing refractive index reduction and hardness retention, improving hydrolytic stability to mitigate the risk of embrittlement, and preventing undesirable photocatalytic effects on surface color and gloss. From a clinical translation perspective, reproducibility remains dependent on defining narrow processing windows, precise monitoring of layer thickness and surface roughness, alignment with common airborne-particle abrasion and silanization workflows, and judicious adjustment of light dose. Overall, sol-gel nanolayers provide a modular engineering toolbox for selective interphase reinforcement, optical tuning, and surface bioactivation, provided that layer structure and quality control are considered as central design variables.
