The aim of this study is to evaluate the effects of different shoulder finishing line depth (0.5 mm, 1.0 mm and 1.5 mm) on fracture strength of CAD/CAM lithium disilicate restorations. Lithium disilicate (IPS e-max CAD; Ivoclar Viva dent) design was done according to the finishing line depth (FLD), with Cerec inLab software program (Version, 4.2.0.57192) with 120 μ cement film thicknesses. A total of 36 specimens of coping design were prepared as monolithic crown on novel nickel chrome dies. Each with a diameter of 8 mm and height of 6 mm as they were used to support the restoration. 12 specimens of coping design for each material and finishing line depth where prepared, to be in three groups according to FLD. Panavia V5 resin cement system where used as a luting agent for fixation of each coping restorations. For the measurement of fracture resistance value, each sample where subjected to fracture test with a universal test machine. Kruskal –Wallis and Mann-Whitney tests as well as Anova test were performed to compare all groups with different p values.

It was found that lithium disilicate crowns with 1.5 mm thickness of marginal design showed the maximum mean value of fracture strength of about 2721 ± 967 N among all the groups.
It was concluded that lithium disilicate crown material seems to be increased their strength to fracture as the finishing line depth where increased.

Keywords: Finishing line, Fracture resistance, Lithium Disilicate
*This research was supported by the Scientific Research Projects Division of Van Yuzuncu Yil University with the project number TDK-2017-5915.