Fatigue survival rate of different core and veneer designs for anterior all-ceramic crowns

Despite significant advances in ceramic dental materials, the rehabilitation of anterior teeth remains challenging due to the complexity of optical and biomechanical properties. Although various esthetic approaches have been proposed, there is still a gap regarding to the mechanical behavior of bilayer crowns used in anterior restorations. OBJECTIVES: To evaluate the biomechanical behavior of bilayer crowns with traditional and modified core designs using fatigue survival testing and finite element analysis (FEA), aiming a suitable rehabilitation for the anterior teeth area. MATERIALS AND METHODS: Forty-five crowns were manufactured, according to the following groups: CC (conventional core), MCS (modified core/stratified veneer) and MCM (modified core/machined veneer). Cores were machined (lithium disilicate); veneers of CC and MCS groups were made through stratification (fluorapatite), and veneers of MCM group were also machined (leucite). Next, the crowns were cemented using resin cement (Variolink Esthetic LC) over full crown preparations made of epoxy resin and then subjected to cyclic fatigue test. After mechanical testing two events were considered: the presence of crack and/or chipping (event 1) and catastrophic failure of the crown (event 2). The average load to failure and number of cycles to failure in which events 1 and 2 occurred were used to perform the survival analysis according to Kaplan-Meier and Log-Rank (Mantel-Cox; 95%). Fracture marks and failure mode of the crowns were evaluated and classified by optical stereomicroscope and scanning electron microscope. Finally, FEA was performed to evaluate the stress distribution on the crowns. RESULTS: Fatigue test results showed that considering event 1 the groups with modified cores (MCS: 1020 N and MCM: 913 N) presented higher average loads and number of cycles to failure than the group CC (773 N). Considering event 2 all groups showed similar fatigue performance (∼1028 N). FEA results evidenced higher stress concentration at the load application area, with a slight stress at the cervical margin of the crowns regardless the group. CONCLUSIONS: Modified core designs improved resistance to initial veneer damage without compromising catastrophic failure performance. Stress distribution patterns supported the mechanical findings, indicating favorable biomechanical behavior.