Improved materials for stronger teeth: CERIC study gives new hints for the development of stronger dental cements

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Have you ever had your teeth repaired? If the answer is yes, you may be aware of how much important the material used to fix cavities is, to ensure a long-term health of your teeth.

Introduced in the 1880s, zinc phosphate cements (ZPC) are some of the oldest dental cements. Although the introduction of modern bioactive composite restorative materials reduced their use significantly, ZPCs still belong to the most prominent luting agents in dentistry. ZPC must possess a considerable compressive strength to absorb the physical stress that occurs in the mouth. Such strength is strictly dependent upon the cement microstructure, and, since it is a defect-limited material, the size, distribution and nature of the pores, exert a control on the performance. ZPC is supplied as a solution of phosphoric acid and a zinc oxide powder. After combining the powder with the acid, the mixture becomes a solid cement. This process is called setting of the cement and is analogue to the way cement is prepared in construction works.

Detail from an axial XmCT slice showing a pore containing features (dark gray) with irregular pseudo-dendritic shape in the volume. (Photo source: Elsevier)

The porosity which develops during setting, affects not only the strength but also other important properties, such as the dissolution of the cement in time, the take up or release of fluoride (added to improve the resistance to caries). Therefore, the characterization of the material porosity and the mechanism through which the cement microstructure develops, allows one to gain insights into the parameters affecting the cement performance, enabling a more effective product design.

The research team around the CERIC user Alberto Viani from the Institute of Theoretical and Applied Mechanics in Telč, Czech Republic, investigated two different formulation of commercial dental ZPC. They recently published a study in which the compressive strength is related to the cement formulation and the nature and distribution of pores. To characterise the pores they used microfocus X-ray computed tomography (XmCT) at the CERIC Italian Partner Facility Elettra in Trieste. They observed that detected pores were spherical to sub-spherical and appear to be filled with liquid plus a denser material considered an intermediate product of the setting reaction. Excess liquid in the cement formulation was observed to decrease the mechanical properties, providing criteria for effective cement formulation.

The material within the pores suggests that the porosity evolves, perhaps very slowly after some time, with important consequences for the life of the restorations, and also for other dental cements, opening the door to further studies with new important results.

Original article:

A. Viani, K. Sotiriadis, I. Kumpová, L. Mancini, M.-S. Appavou, Microstructural characterization of dental zincphosphate cements using combined small angleneutron scattering and microfocus X-ray computedtomography, in Dental Materials 33 (2017), pp. 402-417, doi:10.1016/j.dental.2017.01.008