Effect of Lithium-Disilicate Liners on Bond Strength and Fracture Resistance of Bilayered Zirconia Systems: A Systematic Review of In Vitro Evidence

<b>Background</b>/<b>Objectives:</b> Chipping of the veneering part of the crown at the zirconia-porcelain interface remains a major complication of bilayered zirconia systems. This systematic review evaluated whether incorporating a lithium-disilicate (LD) liner or press-on or CAD-on interlayer between zirconia and veneer improves bond strength and fracture performance in vitro. <b>Methods:</b> Following PRISMA 2020, we searched PubMed, Scopus, and Web of Science up to 7 September 2025 for open-access English in vitro studies using LD-based interlayers at zirconia-veneer interfaces and reporting quantitative bond and/or fracture outcomes. Data included extracted materials, processing parameters, and mechanical results; due to heterogeneity, findings were synthesized descriptively and as the ratio-of-means (ROM). <b>Results:</b> Five in vitro studies from Korea, Thailand, and India met the criteria. LD interlayers increased microtensile bond strength from 18.83 to 44.20 MPa and from 19.6 to 47.7 MPa, and shear bond strength from 41.3 to 59.7 MPa, 11.40 ± 1.29 to 18.81 ± 1.76 MPa, and 21.5 to 60.2 MPa. Corresponding ROMs ranged from 1.46 to 2.80 (median 2.35), with thermocycled LD groups maintaining strengths >25 MPa. LD liners also raised crown fracture loads from ~2.18 to ~3.45 kN and characteristic strength from 3.42 to 5.64 kN, while chipping loads in implant crowns increased from ~0.34 to ~0.84 kN and global fracture from ~1.71 to ~1.93 kN. <b>Conclusions:</b> Across diverse zirconia-veneer configurations, LD interlayers consistently enhanced bond metrics and fracture/chipping resistance, supporting their use as a targeted interfacial strategy; however, clinical confirmation is still needed.