Objectives:
The physikochemical-mechanical properties of dental restoration materials should be similar to natural enamel and dentin. Therefore, it is essential to know which of these material properties are most important for dental materials development.
Methods:
Extracted human molars were stored in artificial saliva and wrapped during embedding in Parafilm® M (Brand & Co KG) to avoid epoxy resin infiltration (EpoThin, Buehler). The molars were sliced, sectioned to pins and finally into cubes (edge length 1.2 mm, Medim Histosaw). Afterwards, the specimens were divided into enamel and dentin as well as sorted beginning from coronal to apical.
Mechanical parameters were determined using a material testing machine (BZ2.5/TN1S, Zwick GmbH & Co. KG, Ulm, Germany) under free uniaxial compression load (load cell 2500N, force velocity 1 mm min-1). Structure modulus is used instead of Young's modulus since enamel and dentin show an anisotropic viscoelastic material behavior. Statistics: Kruskal Wallis H test (p < 0.05) and Spearman's rank correlation (p < 0.05).
Results:
No differences were found between both structure modulus of enamel and dentin as well as in vertical direction. By contrast, compression strength values of dentin were up to 60 % higher compared to enamel. Otherwise, elongation at break of dentin was approximately twice higher as enamel. From coronal to apical, compression strength as well as elongation at break decreased. Spearman's rank correlation test showed that the structure modulus of enamel decreased with the elongation at break. In contrast, the structure modulus of dentin correlates positively with the compression strength. Therefore, dentin has to be more resistant to compression forces than enamel because the dentin tubules act as buffers to mechanical load which was confirmed by the results as wells as microscopic studies.
Conclusion:
Compression strength and the elongation at break are the most important parameters in restoration material design.