Clinically relevant evaluation of fracture strength of all-ceramic crowns

Method: 30 core-veneer crowns were produced for an upper central incisor; 10 with alumina cores (Vita In-Ceram AL for inLab), 10 with zirconia cores (Starceram Z-Al-Mes HD) and 10 with lithium disilacte cores (IPS e-max). The crowns were cemented with zinc phosphate cement on epoxy models of the prepared abutment and exposed to soft loading at the incisal edge until fracture. The soft loading induces a lateral expansion in the middle of the abutment model causing tension at the cervical margin of the crown. The fractographic features were evaluated by light microscopy and compared to a reference group of crowns failed during clinical use.

Result: There crowns with zirconia cores fractured at statistically significant higher loads than the other two materials (Kruskall-Wallis<0.001). No statistical significant difference was found between crowns with alumina and lithium disilicate cores (Mann-Whitney U-test) (Table 1). All crowns fractured in a manner similar to the clinical references. Fracture initiation was in the core material, cervically in the approximal areas.

Conclusion: Clinically relevant test methods should be further developed for assessment of all-ceramic crown failures.

Table 1