Material characteristics of a novel shrinkage-free ZrSiO(4) ceramic for the fabrication of posterior crowns.
OBJECTIVE
To confirm the clinical applicability of a novel ZrSiO(4) (zircon) based shrinkage-free ceramic material, the flexural strength, fracture toughness and chemical solubility were tested. In addition, the fracture load of full crowns made from this material was tested after cyclic thermomechanical loading.


METHODS
Flexural strength of 12 specimens was measured using a biaxial bending test. Fracture toughness was measured using 10 slotted box shaped specimens. The specimens were fractured using a universal testing machine; fracture loads were recorded. A chemical solubility test was performed in accordance with ISO norm 6872. Additionally, 32 ZrSiO(4) all-ceramic crowns were fabricated on extracted caries-free human molars. Sixteen Empress 2 and 16 PFM crowns served as a reference control. After artificial aging of 1.2 million cycles in the chewing simulator, the survival rate of the crowns was determined. The fracture load of all surviving specimens was obtained by loading the crowns until fracture in a universal testing machine.


RESULTS
A flexural strength of 328MPa was found. The fracture toughness of the ZrSiO(4) ceramic was 5.16MPam(0.5). The chemical solubility amounted to 7.2microg/cm(2). All specimens survived the chewing simulation (survival rate: 100%); no crowns had to be re-cemented. A mean fracture strength of 1790N was found for Everest HPC for Empress 2 crowns, 1715N for Empress 2 crowns and 2416N for PFM crowns. Fracture loads of PFM crowns were significantly higher than for Empress 2 crowns (P=0.032) as well as ZrSiO(4)-crowns (P=0.007). There was no significant difference between ZrSiO(4)-crowns and Empress 2 crowns (P=0.743).


CONCLUSIONS
At the present stage, Everest HPC can be recommended for the fabrication of single crowns as an alternative to conventional PFM and other all-ceramic crowns, because its fracture strength exceeds average masticatory forces in the posterior region.
Heydecke
G
G
Department of Prosthodontics, University Hospital, Freiburg, Germany. guido.heydecke@uniklinik-freiburg.de
Butz
F
F
Binder
J R
JR
Strub
J R
JR
D001732:Bite Force; D003442:Crowns; D003776:Dental Porcelain; D003799:Dental Stress Analysis; D004548:Elasticity; D006244:Hardness; D006801:Humans; D018020:Lithium Compounds; D008422:Materials Testing; D016876:Metal Ceramic Alloys; D008963:Molar; D018583:Pliability; D017640:Silicates; D012995:Solubility; D018709:Statistics, Nonparametric; D015040:Zirconium
C118557:Empress 2; D018020:Lithium Compounds; D016876:Metal Ceramic Alloys; D017640:Silicates; D003776:Dental Porcelain; C003784:zircon; D015040:Zirconium