Atomic force microscopy nanoindentation of a dental restorative midifill composite

We investigated the elastic properties of one dental restoration resin composite of common use, Venus Diamond, at submicrometer spatial resolution.

We performed both nanoindentation experiments with atomic force microscopy, and microindentation experiments with a traditional indenter setup. We also used scanning electron microscopy and energy dispersive X-rays spectroscopy to better understand the correlation between properties and microscopic structure and composition.

With atomic force microscopy we obtained quantitative evaluation of the elastic modulus (10.8 ± 4.3 GPa), in agreement with the microindentation value (reduced modulus of 12.7 ± 2.0 GPa), and by microindentation we also obtained an hardness value (460 ± 109 MPa) compatible in turn with the nominal value provided by the material manufacturer (H ∼ 578 MPa). The nanoindentation also revealed that no relevant difference in elasticity appears between the 5 and 10 μm diameter filler particles and the surrounding areas, showing an excellent uniformity of the composite. In support of this finding, compositional uniformity of the material was also observed by X-rays spectroscopy. We conclude that the composite contains prepolymerized particles.

We demonstrate that, in addition to reliable quantitative analysis, the high resolution and two-dimensional mapping capability of atomic force microscopy allows for advanced insights into the microstructure of the composite that are not accessible via traditional microindentation.