Application of close-packed structures in dental resin composites

•Maximum loading calculation for idealized packing of uniform-sized spheres.•Maximum loading of uniform-sized spheres = 74.05 vol%, regardless of their sizes.•Fitting secondary particles of size compatible with voids in packed primary particles can increase loading by 7.36%.

ObjectiveThe inorganic filler particles in dental resin composites serve to improve their mechanical properties and reduce polymerization shrinkage during their use. Efforts have been made in academia and industry to increase the filler particle content, but, few studies examine the theoretical basis for the maximum particle loading.MethodsThis work evaluates the packing of spherical particles in a close-packed state for highly loaded composites.ResultsCalculations show that for low dispersity particles, the maximum amount of particles is 74.05 vol%, regardless of the particle size. This can be further improved by using a mix of large and small particles or by the use of non-spherical particles. For representative spherical particles with a diameter of 1000 nm, two types of secondary particles with respective sizes of 414 nm (dI) and 225 nm (dII) are selected. The results show that after embedding secondary particles I & II into primary spherical particles, the packing factor is increased to 81.19% for the close-packed structures, which shows an improvement of 9.64%, compared to the 74.05% obtained only with primary spherical particles. This packing factor is also higher than either structure with the embedded secondary particles I or II.SignificanceExamples of these mixtures with different spherical particle sizes are shown as a theoretical estimation, serving as a guideline for the design and formulation of new dental resin composites with better properties and improved performance.

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