Influence of the Tooth Mobility on the Fracture Strength

Objectives: Testing new materials under simulated oral conditions is essential in dental research. For the simulation of fracture strength, different simulation devices are used. The results of these in-vitro tests differ, because there is no standardization in the simulation set-ups. Therefore, the aim of this work was to show the influence of the tooth mobility and the Young`s-modulus within the test set-ups on the fracture strength by using the Munich Simulation device for tooth mobility. Methods: For these fracture load experiments standardized test models were performed with a CAD-System by using the design data of the Munich simulation device. Based on these CAD data an idealized bridge was constructed and 24 Zirkondioxid Bridges were manufactured by a CAD milling machine. These bridges were then divided into three groups with different Young`s-modulus and tooth mobility: 1) ridge PMMA, 2) ridge Metal, and 3) tooth mobility degree II (material: C-Temp). After cementation of these bridges on the abutment teeth, the fracture loads were determined with a universal testing machine. The fracture load data were analyzed by the statistical software SPSS 17. Results: All experimental groups showed a statistically significant difference in their fracture behaviour (ANOVA, p < 0.05). When using a rigid metal model the fracture load increases by 157% in comparison with the tooth mobility simulation model. The use of a rigid PMMA-Model reduces the fracture load by 19%. Conclusions: The tooth mobility and the Young`s-modulus of the in-vitro test set-ups exert a significant influence on the breaking load. Therefore, only those results are comparable, which were designed with an identical test set-up. The use of rigid test models should be omitted, because they do not sufficiently depict the in-vivo situation.