Nanoindentation derived stress-strain properties of dental materials

The aim of the study is to investigate the stress-strain response of different dental materials, especially dental brittle materials, and compare them with enamel.

A nano-based indentation system (Ultra Micro-Indentation System, UMIS-2000, CSIRO, Australia) was used to determine the indentation stress-strain response of two kinds of dental ceramics (Cerec 2 Mark II and Vita VM9), one kind of dental alloy (Wiron 99) and healthy enamel. A spherical indenter was used to test the materials with nanometer and micro-Newton displacement and force resolution. Assuming the elastic modulus remained constant, a plot of contact pressure versus contact strain, H-a/R, of each material was obtained.

By comparing the H-a/R curve of the different materials with enamel, it can be concluded that only the metallic alloy, has similar stress-strain response as enamel. Dental ceramics showed much higher yield stress response than enamel. VM9, a porcelain veneer component of crown/bridge structure, is slightly softer than its core, Mark II. The yield point for Mark II and VM9 are nearly 10 and 7GPa, respectively, and approximately 2GPa for Wiron alloy and enamel.

H-a/R curves provide a new method to compare the mechanical properties of different dental materials. From the standpoint of structural reliability, strong and tough materials with primarily elastic response, such as toughened ceramics are required to enable dental crown/bridges to have long term reliability. On the other hand, materials with too high hardness or yield response may damage opposing teeth during occlusal contact. Future studies may establish a relationship between stress and strain property and abrasive wear of dental material.