Fracture Strength of All-Ceramic Bridges Dependent on Die Material Used

Objectives: The purpose of this study was to show the correlation of the fracture strength of 4-unit Zirconia bridges constructed with the Lava-system (3M ESPE) in dependence of the die material used for the in vitro model. For each die material the initial strength of the restoration and the strength after thermocycling were determined.

Methods: The die materials used were fibreglass-enforced resins (DC-Tell, DCS), Zirconia-ceramics and brass. Two dies of each material were embedded in Paladur Clear (Heraeus Kulzer). A defined mobility of the dies was reached by a heat shrink tubing which was wrapped around the dental roots. A silicon matrix thereby enables an almost identical position for all bridges. 20 bridges for each group of die material were cemented with zinc-oxide phosphate (Harvard, Berlin) on the respective models and were stored in water for 21 days. 10 of these bridges were subsequently aged artificially by thermocycling (20 000 cycles, 5°/55°). The fracture strength experiments were carried out with the Zwick-machine (Roell, 0,5 mm/min) and the results were analyzed statistically with the 2 sample t-test.

Results: The results show significantly higher fracture strength values for all-ceramic bridges cemented on ceramic or brass compared to fibreglass-enforced resins dies.  The artificial aging procedure by thermocycling has no significant influence in the case of ceramic or brass die materials. However, it did lead to a significant strength reduction when all-ceramic bridges were cemented on fibre-enforced resin die material.

Conclusion: The results of this study show that all-ceramic bridges made by the Lava-system can reach equivalent fracture strength values compared to conventional metal based bridges. The results also show that if fibre-enforced resins are used as die material, lower fracture strength values are reached.