Influence of bond quality on failure load of leucite- and lithia disilicate-based ceramics

The long-term survival of bonded ceramic restorations for posterior teeth is a clinical concern. The durability of the bond between the ceramic and dentin during clinical service is a factor in the load-bearing capacity of the restoration.

This study aimed to evaluate the effect of interfacial bonding quality on the interface failure initiation loads of 2 all-ceramic systems.

One leucite-reinforced ceramic, IPS Empress (E1), and 1 lithia disilicate glass-ceramic, IPS Empress 2 (E2), were used to form disks 8.5 mm in diameter, with an approximate 1.35-mm total thickness (n=45). The ceramic specimens were fabricated in a manner that simulated their clinical application. The E1 specimens were fabricated using the staining technique, and the E2 specimens were made using a layering technique. Completed disks of each ceramic system were divided into 3 subgroups (n=15) that were subsequently cemented using 1 of 3 bonding conditions (Control, Cer, Sub). The control group followed ideal bonding protocol, whereas groups Cer and Sub had bonds that were compromised between the cement and the ceramic (Cer) or the substrate and the cement (Sub). All luted specimens were loaded at the center with a 10-mm-diameter ball indenter at a crosshead speed of 0.01 mm/min in a universal testing machine. Intermittent loads were applied in increasing increments of 50 N until a fracture could be observed in the ceramic substrate by transillumination with x2.6 optical magnification. The maximum load applied prior to crack observation was recorded as the failure initiation load. Survival analytical methods were used to determine differences between groups.

The characteristic fracture initiation loads ranged from 223.5 to 760.6 N. Group E2 had the greatest mean observed load to failure (715.6 N), which was significantly greater than group E1 (P<.001). For both the E1 and E2 ceramic systems, the control groups had significantly greater mean fracture initiation loads than either of the interface-inhibited Cer and Sub groups.

Poor bond quality at either the ceramic-cement or dentin-cement interface can significantly reduce the fracture initiation load-bearing capacity of ceramic disks bonded to compliant dentin-like substrates. For the E2 ceramic material, disruption of the ceramic-cement interface had a more detrimental effect on the load-bearing capacity of the simulated restoration than the disruption of the cement-dentin interface.