An in vitro analysis of fracture resistance and marginal fit of strength-gradient multilayered implant crowns

Although zirconia materials have advanced, there remains a lack of experimental studies comparing the properties of multilayered zirconia implant-supported dental crowns. This study evaluated the fracture resistance and marginal fit of two multilayered strength-gradient ceramic materials for posterior implant crowns. Forty tissue level implants with regular neck were embedded in acrylic resin blocks and connected with prefabricated straight titanium abutments. The specimens were allocated into two groups ( n = 20), featuring distinct multilayered ceramic materials: a high-strength ceramic (IPS e.max ZirCAD Prime) and a high-translucency ceramic (IPS e.max ZirCAD MT Multi). Crowns were milled using a 5-axis milling device and were cemented to abutment using a polymer-based universal self-adhesive resin cement. The prepared samples were subjected to thermocyclic aging to simulate the oral conditions. The fracture load and marginal fit was assessed via universal testing machine and digital microscopy, respectively. The specimens were further examined to determine the predominant failure pattern. All statistical analysis was conducted using SPSS software. The comparison between the group were performed using Mann–Whitney U tests and independent t-tests. Statistical significance was defined as p < 0.05. The ZirCAD Prime exhibited a non-significantly, higher mean fracture load of 1511.8 N compared to 1326.9 N for ZirCAD MT group ( p > 0.05). Marginal fit analysis revealed that the Prime zirconia group achieved a tighter and more consistent fit (1.27 ± 0.01 μm) compared to the ZirCAD MT zirconia group (2.34 ± 0.3 μm), with a statistically significant difference ( p < 0.05). The fracture mode analysis revealed that all specimens in both groups demonstrated fractured crown without abutment or implant-abutment fracture. The predominant failure pattern in both groups followed a single longitudinal fracture from the central fossa, bifurcating the crown into two fragments. The zirconia materials evaluated exhibited excellent fracture resistance and precise marginal adaptation under static-loading conditions, remaining well within established acceptable thresholds. While both materials are structurally viable, ZirCAD Prime offers a better advantage in scenarios where maximum loading and marginal adaptation are prioritized.