Effectiveness of Silica Coatings in Enhancing Resin Cement Adhesion to Zirconia: A Systematic Review

Background: The use of zirconia-based restorations has increased in dentistry due to their aesthetics, high strength, and biocompatibility. However, achieving durable adhesion between resin cements and zirconia remains a challenge in restorative dentistry. Adhesive failures can lead to complications ranging from dentin hypersensitivity to the loss of the restored tooth. This review evaluates the impact of surface treatments based on silica coatings as a strategy to improve the adhesion of resin cements to zirconia. Methods: A systematic review was conducted following PRISMA guidelines. Searches were performed in Scopus, Web of Science, PubMed, EBSCO, and ScienceDirect. In vitro studies were included if they (1) evaluated silica-based coatings on zirconia surfaces; (2) measured bond strength at the zirconia-cement interface through shear tests (MPa) and reported failure type (adhesive, cohesive, mixed); (3) used ≥8 specimens per group; and (4) included an untreated zirconia control group. Data were extracted and compared for conditions before and after thermocycling in the studies that reported this procedure. Results: The average bond strength for silica-coated zirconia was 15 MPa without thermocycling and 11.97 MPa after thermocycling, regardless of the coating technique. These values were significantly higher than those of untreated zirconia (8.45 MPa and 6.41 MPa, respectively). Cohesive and mixed failures predominated in silica-treated groups, suggesting more effective adhesion compared to controls, which presented mainly adhesive failures. Conclusions: Silica coatings, especially when combined with adhesion promoters, MDP-based primers, significantly enhance the bond strength of resin cements to zirconia. This reduces the risk of secondary caries, sensitivity, restoration debonding, and potential tooth fractures. However, the effectiveness of these coatings varies depending on the technique used, suggesting the need to standardize protocols to optimize clinical outcomes.