Fracture resistance of all-ceramic crowns based on different preparation designs for restoring endodontically treated molars

Objectives To evaluate endodontically treated molar fracture resistance restored with CAD/CAM lithium disilicate (LDS) crowns with different amalgam core preparation design. Materials and Methods Eighty-four recently extracted mandibular third molars were divided into seven groups (n = 12) and embedded in autopolymerizing resin. Coronal tooth structure was removed, pulp chamber exposed, and pulpal remnants removed. One group received LDS endocrowns, while three groups received amalgam cores with 2, 1, and 0 dentin axial wall heights (AWH). Three additional groups were likewise restored using an amalgam adhesive. Scanned preparations were restored with LDS crowns luted with a self-adhesive luting cement. After 24 hours, specimens were loaded to failure with results analyzed with Welch's Test/REGW Range Test at a 95% level of confidence (alpha = 0.05). Results The 1 mm-AWH amalgam core group had the highest failure load and was similar to the 2 mm-AWH amalgam, 2 mm-AWH bonded amalgam, and the 1 mm-AWH bonded amalgam core groups. The endocrowns had lower failure load than the 1 mm and 2 mm AWH amalgam groups but was similar to other groups. Conclusions Adhesively luted LDS crowns with amalgam core preparations overall displayed similar failure load, as endocrown restorations. However, crowns based on amalgam cores demonstrated favorable failure modes.