IPS e.max CAD-on technique: lithium-disilicate meets zirconia

Objectives: A new technique (IPS e.max CAD-on) allows to connect IPS e.max CAD/lithium-disilicate superstructure to IPS e.max ZirCAD/zirconia framework using IPS e.max CAD Crystall./Connect/fusion glass-ceramic. The innovative fusion-process of CAD/CAM produced veneering superstructure and framework yields in highly esthetic and strong dental restorations. The objective of this investigation was to develop a specific fusion-glass-ceramic (FGC), which forms a compact bond between lithium-disilicate and zirconia during an easy fabrication process. Methods: Three series of bilayered biaxial fracture strength samples were prepared with 1.2mm total thickness: 2 series 0.7mm lithium-disilicate/0.5mm zirconia (LiD-Z) and one serie 0.55mm sintering veneering ceramic/0.65mm zirconia (VC-Z). 1.2mm zirconia (Z) was used as reference. The zirconia was milled, densely sintered and fused together with lithium-disilicate during the crystallization at 840°C using the FGC for the LiD-Z groups. The fracture load criteria was first crack-initiation in the load-displacement curve. The LiD-Z-series were tested either with lithium-disilicate or zirconia in the tensile-stress zone (TSZ). The bond quality of the bilayered systems were analyzed by Scanning Electron Microscope (SEM). Results: The fracture load of the LiD-Z series were 761±119N with lithium-disilicate in TSZ and 681±62N with zirconia in TSZ, while the VC-Z serie achieved 93±15N. Z serie showed a fracture load of 1050±50N. The results of the LiD-Z series were significant above the results of the VC-Z series. Fracture analysis showed a complete crack of LiD-Z while VC-Z has first crack-initiation in the sintered veneering ceramic. The SEM evaluations showed the homogeneous bond quality of the FGC to lithium-disilicate and to zirconia. Conclusions: A new developed fusion glass-ceramics strongly bonds lithium-disilicate and zirconia, which could be shown by fracture load tests and SEM-analysis. The technique is applicable for molar bridges of up to 4 units.