In this in vitro investigation, we studied the static strength of three-unit all-ceramic bridge frameworks with rigid positioning of the abutments. The materials used were Vita InCeramŪ Alumina, Vita InCeramŪ Zirkonia, and zirconium oxide (Vita InCeram (X YZ Cubes for CerecŪ). A finite element calculation was performed for numerical comparison of the load-bearing capacity of two main normal tensions. The purpose of the investigation was to design a framework made from hard core material, that offers the greatest possible resistance in static fracture loading tests. In a model, the 2nd maxillary right premolar and 2nd maxillary right molar served as bridge abutments and were provided with a chamfer preparation. On this base, two different bridge frameworks were constructed using CAD/CAM technology after an impression had been taken. One bridge connector was designed heart-shaped, with contact to the gingiva, while the other was designed as a free-connector at a distance of 1.2 mm from the gingiva. In this framework design, the radius in the cervical connector area is larger. We were uncertain as to whether it would be possible to further increase the strength of the ceramic material by the use of the differently designed pontic, independent of the hard core ceramic used. The least fracture strength was registered for the heartshaped connector constructed from InCeramŪ Alumina, with a mean fracture load of about 1089 Newton (N). The connector designed as a free connector, made from the same material, was stronger by 10%. With the materials InCeramŪ Zirkonia and zirconium dioxide as well, the free-connector design achieved a 10% higher breakage limit than the heart-shaped design. InCeramŪ Zirkonia was 25% more stable in the static load tests than In- CeramŪ Alumina. Zirconium dioxide demonstrated a 2.3-fold greater strength than InCeramŪ Alumina, while the free-connector design showed the greatest mean static loading capacity of 2808 N.
Keywords: CAD/CAM technology, strength behavior, framework design, hard core materials, static load test, all-ceramic bridge framework