Accelerated fatigue resistance of endodontically treated incisors without ferrule restored with CAD/CAM endocrowns

Purpose: The present study aimed to investigate the resistance and failure mode of broken-down endodonticalty treated incisors without ferrule restored with CAD/CAM endocrowns. Materials and methods: Endodonticalty treated bovine incisors (N = 30) without ferrule were divided into two groups and restored with two types of CAD/CAM endocrowns lithium disilicate (Etd) or resin nanoceramics (Erc). The preparations included a 4-mmdeep 'internal ferrule' and immediate dentin sealing. The samples were subjected to accelerated fatigue testing. Cyclic isometric loading was applied to the incisal edge at a 30-degree angle at a frequency of 5 Hz, beginning with a load of 100 N (5,000 cycles). A 100 N load increase was applied every 15.000 cycles. Specimens were loaded until failure or to a maximum of 140,000 cycles. Previously published data from the same authors regarding lithium disilicate crowns over post-and-core buildups without ferrule (NfPf), core buildups without post without ferrule (NfNpFR), and with a 2-mm ferrule (FNp) using the same experimental setup were included for comparison. Groups were compared using the Kaplan Meier survival analysis for cycles (log rank pairwise post hoc test comparisons at P = 0.05) and Life Table survival analysis for load at failure, followed by the Wilcoxon pairwise comparison at P = 0.05. Results: All specimens failed before 140,000 load cycles. There was no statistically significant difference between the endocrown materials (Eld: 53,448 mean endured cycles. Erc 52,397 mean endured cycles: P = 0.844). Endocrowns outperformed the group with lithium disilicate crowns on incisors without ferrule and post-and-core buildup (NfPf with mean endured 35.025 cycles), showed no statistical difference compared with the group with no-post fiber-reinforced composite resin core buildup (NfNpFR with 45, 5 5 7 mean endured cycles), and had a lower survival rate compared with the group with ferrule (FNp with mean endured 73,244 cycles). Endocrowns generated a majority of non-catastrophic failures (with an advantage for Erc), white 100% of catastrophic failures were found in the group with a post. Conclusions: CAD/CAM endocrowns of nonvital in-cisors without ferrule improved the resistance and optimized the failure mode when compared with traditional bonded crowns with adhesive post-and-core and no-post buildups.