Do CAD/CAM-Lithium-Disilicate Shade and Translucency Affect Material’s Fracture Resistance?

Objectives: This study assessed whether the fracture resistance of adhesively bonded CAD/CAM lithium disilicate full-crowns vary as function of material shade/translucency. As shade and translucency of indirect restoratives are thought to interfere with resin-based cements polymerization, we hypothesized that dark shade/low translucency CAD/CAM-lithium-disilicate restorations would exhibit lower fracture resistance in comparison to restorations made of light shade/high translucency CAD/CAM-lithium-disilicate.
Methods: Four shade/translucency combinations of CAD/CAM lithium-disilicate blocks (E.max, Ivoclar/Vivadent) were compared: shade-A1/high-translucency (A1/HT); shade-A1/low-translucency (A1/LT); shade-A3.5/high-translucency (A3.5/HT); shade-A3.5/low-translucency (A3.5/LT). Twelve full-crowns of each shade/translucency combination (n=12/group) were fabricated using standardized 3D-printed resin-based abutments (V2, Formlabs), which mimic a full-crown preparation of tooth #30. Samples were cemented onto abutments using a dual-cure resin-based luting agent (Variolink, - Ivoclar/Vivadent). Each crown surface was light-cured for 20 seconds. Specimens were stored in distilled water at 37 °C for 1-week. By using a stainless-steel bar with a 1mm-diameter-ball end-mounted to a universal testing machine (EZ-XL; 5000N load cell; Shimadzu) static compressive load was applied at crowns central pit until failure. The fracture resistance (expressed in N) were recorded and analyzed by ANOVA and Tukey tests (α=0.05).
Results: Maximum stress ranged from 1117.8 to 2113.4N, respectively for A3.5/LT and A3.5/HT. Mean (±SD) fracture resistance for each experimental group was: A1/HT= 1687.0N (±122); A1/LT= 1582.8N (±180); A3.5/HT= 1920.3N (±153) and A3.5/LT = 1685.92N (±220). Within the same ceramic shade, fracture resistance of HT samples were higher than LT counterpart, but such a difference was only significant for shade A3.5 [A3.5/HT>A3.5/LT] (p=0.01). Unpredictably, light-shade A1 specimens exhibited lower fracture resistance than A3.5 ones, for both translucencies. Accordingly, our initial hypothesis should be partially rejected.
Conclusions: Within the limitations of this study, it can be concluded that lithium disilicate translucency appears to play a more critical role in fracture resistance than material shade.