Comparison of the static loading capacity of all-ceramic bridge frameworks in posterior teeth using three hard core materials.

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 InCeram Alumina, Vita InCeram Zirkonia, and zirconium oxide (Vita InCeram (X YZ Cubes for Cerec). 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 "heart-shaped connector" constructed from InCeram 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 InCeram Zirkonia and zirconium dioxide as well, the "free-connector" design achieved a 10% higher breakage limit than the heart-shaped design. InCeram Zirkonia was 25% more stable in the static load tests than InCeram Alumina. Zirconium dioxide demonstrated a 2.3-fold greater strength than InCeram Alumina, while the free-connector design showed the greatest mean static loading capacity of 2808 N.

PREPassistant: a system for evaluating tooth preparations.

Learning the widely differing forms of tooth preparation, especially in restorative dentistry, places high demands on both trainees and instructors with regard to precision, reproducibility, assessment, evaluation and three-dimensional conceptualization. In the past, evaluation of such preparations has been against subjective parameters and their interpretation by the assessor (usually the instructor). The use of CAD systems in teaching seminars and courses allows an objective assessment of tooth preparations and offers the trainee the possibility of measuring him/herself against a standard, of detecting errors, and of achieving perfection in the required tasks. The PREPassistant system described in this article is one such CAD-assisted learning system. It is recommended both for students in dental schools and for the continuing education of established dentists. Its strengths are that it produces a design for a tooth preparation, enables exact comparison with an ideal preparation, detects errors, and promotes improvements and perfection.