Biomechanical Examination of Inlay Geometries - Is There a Basic Biomechanical Principle?

Purpose: In this in vitro study, all-ceramic inlays were subjected to a static strength test. The material used in this case was Vita Mark II® ceramic (Vita-Zahnfabrik, Bad Säckingen, Germany). The goal of the study was to evaluate two different inlay preparations with differently designed ceramic inlays resulting from it, to determine which offered the greatest possible resistance in static fracture loading tests. Materials and Methods: Tooth 36 on the model, provided with a standard preparation with a level floor, served as the test object. Two inserts were produced: one with classical preparation pattern, the other with a modified shape of the cavity floor. In one inlay design, the cavity floor was designed according to the guidelines valid for all-ceramic inlay restorations; in the second inlay design, a differently shaped cavity floor was selected to exclusively meet the requirements of the ceramic material. Impressions were then taken, and inlays were designed and produced by means of CAD/CAM technology. Results: Lower fracture strength with mean fracture load values of ca 66.6 N was shown for traditional inlay preparations with a cavity floor segment designed as box. The mean fracture strength of the inlay design consisting of the same material with a hemispherical cavity floor segment was 84.9 (N), 27.5% greater. Conclusion: The question arises whether it is possible, independently of the ceramic used, to achieve an increase in strength by modifying the design of the inlay. Keywords: preparation design, FE analysis, inlay design