Complimentary X-ray and neutron imaging of glass ionomer cements

Method: Two water-based glass ionomer cements were investigated, named Poly (Ionofil Molar AC, Voco) and Aqua (Aqua Ionofil, Voco). Samples fabricated from both cements were protected to avoid water loss or uptake. X-ray tomography was acquired immediately after mixture and at 1, 7, and approximately 20 days after sample preparation. Neutron radiography was taken every 20 seconds during the first 5 hours of setting, as well as after 4, 6, and approximately 60 days. Class I cavities in extracted human premolars were restored with each cement and measured using both X-ray and neutron imaging. 

Result: X-ray tomography confirmed shrinkage of the materials during setting, which occurred earlier and stabilized faster for Poly (1d: Poly 1.4%; Aqua 1.7%). In a moist environment, the cements absorbed water, thus compensating for the setting shrinkage (1d: Poly 0.2%; Aqua 0.7%). Neutron radiography demonstrated that the shrinkage during the first hours of setting occurred due to structural changes. The pore structure of the investigated cements is complex and the pore sizes are highly variable. Shrinkage registered by X-ray (20d: Poly 3.1%; Aqua 3.6%) and neutron imaging (60d: Poly 4%; Aqua 6%) as well as changes in pore volume of the investigated cements in dry conditions evolved with time, although some water loss may have occurred. From the images of the dental restorations, the presence of pores was identified using X-rays, whereas neutron imaging allowed a clear identification of their water content, due to the high cross section of hydrogen.

Conclusion: X-rays and neutrons complimented each other nicely as imaging techniques and may be beneficial in future research on dental cements.