Objective: To determine the effect of the cement thickness on the fracture strength of all-ceramic CEREC 3D molar crowns. Methods: Standardized prepared epoxy resin molar dies (Viade Inc.) were fabricated. A standard molar crown was designed using a CEREC 3D machine (Sirona Dental Systems). Twenty-four crowns were milled from Vita Mark II blocks (Vita Zahnfabrik), using adhesive gap settings of 30, 60 and 90µm for each group (n=8). All crowns were cemented to their respective dies using Panavia F (Kurary), dual-cure resin cement, according to manufacturer's instructions. After 1 week storage in distilled water at 37 °C, each crown was loaded in compression until complete failure in an Instron machine and fracture strength was recorded. Fractured specimens were sectioned to determine cement thickness. Sections were examined using a traveling light microscope to measure cement thickness. Data were statistically analyzed with one-way ANOVA. Results: The mean fracture loads and standard deviation values in N were 1,267.57 ± 122.82, 1,225.20 ± 179.46 and 1,180.76 ± 161.77 for the crowns with 30, 60 and 90µm, respectively. ANOVA indicated no significant differences among mean fracture strength values (p = .55). All crowns failed in a catastrophic mode and were not repairable. Conclusions: Adhesive cement gap as achieved with three CEREC 3D settings from 30 to 90µm had no significant effect on fracture strength of crowns made from Vita Mark II blocks. Acknowledgement: Support for this work was received from: Faculty of Dentistry Research Committee, Patterson Dental, Vident and Kurary.

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