Failure responses of a dental porcelain having three surface treatments under three stressing conditions

Surface conditions are of interest in all-ceramic restorations since they can control both bonding and strength. Tensile testing methods are commonly used to evaluate surface conditions of ceramics. This work evaluated tensile properties of a feldspathic ceramic as-finished, sandblasted and etched under three stressing conditions: (1) biaxial flexure; (2) monotonic mastication loading, dry; and, (3) cyclic mastication loading, wet.

Feldspathic CAD/CAM blocks were sliced into Tabs 1mm thick, n=135 specimens were divided into 3 groups assigned to as-finished (600 grit SiC; control), sandblasted, and etched. Of the 45 specimens per group, 35 specimens were used for bonded tests and 10 specimens for biaxial flexure testing. Pin-on-three ball biaxial testing was performed per ISO 6872. 35 specimens were bonded to dentin-analog bases and loaded to radial crack pop-in beneath a 3mm diameter piston. 20 specimens were tested dry with failure determined by acoustic emission methods. 15 specimens, bonded to bases having micro-channels for water transport, were cyclically loaded beneath the 3mm piston under water at 15Hz for 500,000 cycles.

Biaxial flexure distinguished among all three surface conditions (p<0.05, ANOVA). Monotonic testing could not distinguish among groups. Cyclic testing could not distinguish between sandblasted and etched groups but both were weaker than as-finished.

Mastication loading of bonded specimens creates a different stress state than simple flexure due to contributions of the cement-ceramic interface. Water adds a damage accumulation effect. Tensile stress conditions need to be chosen with the desired outcomes considered.