Abstract: Abstract: Objective To explore the application of different margin designs (edge to edge margin/concave shoulder margin) to chairside computeraided design/computeraided manufacturing (CAD/CAM).Methods 144 teeth with root canal therapy were randomized into group A that used CAD/CAM with an edge to edge margin design or group B that used CAD/CAM with a concave shoulder margin design.The marginal adaptation,and the fracture and falling off rates of teeth and allceramic onlay restorations were evaluated.Results With no statistical significance (P >0.05),the vertical marginal gap of group A was (80.90±15.99) μm,and that of group B was (82.21±15.39) μm.Followed up within 6 to 12 months,the fracture rate of restorations in group A and B was 0% and 4.17%,respectively.The falling off rate in both groups was 0%.Meanwhile,no teeth fell off or fractured in either group.Conclusions s Both the edge to edge margin and the concave shoulder margin are acceptable for CAD/CAM generated allceramic onlays,and the former is good for teeth and more convenient in clinic.

Key words: CAD/CAM, margin design, edge to edge margin, concave shoulder margin, all-ceramic onlay