Many types of all-ceramic crowns require bonding to a rigid core substructure for optimal strength. Scherrer and de Rijk (1993) found a correlation between the fracture resistance of all-ceramic crowns and the modulus of the supporting core material. Based on these data, one of the selection criteria for a core material should be a high elastic modulus. Purpose: The purpose of this study is to assess the flexural modulus of a variety of currently available composite core buildup materials. Materials and Methods: Flexural strength test specimens were produced similar to those in ADA Spec No. 27 (ISO 4049). Composite was packed into 2mm x 2 mm x 25 mm square glass tubes and cured on both sides with overlapping exposures along the length of the specimen with a Demetron 501 QTH curing light at 730 mW/cm2. Five specimens of each material were fabricated. Materials with both self- and light-curing mechanisms were tested in both modes, and all available shades of each material were tested. A total of 41 groups resulted. Specimens were stored in 37oC distilled water for 24 hours and then ejected from the molds. The beams were tested in three-point bend on an Instron universal testing machine at a crosshead speed of 0.75 mm/min until failure. Multiple one-way ANOVAs with post-hoc Scheffe test were performed at the 0.05% significance level. Results: Moduli ranged from a low of 3.2 GPa (Rebilda SC auto-cured) to a high of 16.7 GPa (ClearFil Photocure). When dual curable materials were light cured, most exhibited a significant increase in modulus compared to autocured. Conclusions: When used with all-ceramic crowns, core materials should be selected carefully as they vary widely in flexural modulus.

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