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Degree of conversion and polymerization shrinkage of experimental amorphous calcium phosphate based composites

Introduction and aim of the study: Amorphous calcium phosphate (ACP) based. composites (ACP) are photo-crosslinkable resins prepared from the various resins (mass fraction 60 %) and ACP fillers (mass fraction 40 %). ACP may act as a precursor in the formation of biological hydroxylapatite. The aim of the study was to determine the degree of conversion and polymerization shrinkage of ACP based composites. Materials and Methods: For three different ACP based composite materials, degree of conversion measurements and polymerization shrinkage measurements were done. Degree of conversion was measured using Fourier transform infrared spectroscopy. Polymerization shrinkage was determined by digital holographic interferometry. Digital interferometry device is described for measuring the thickness variations of the resin composite samples during blue light polymerization. All the samples were illuminated with LED light source Bluephase ( SOF mode) (Ivoclar Vivadent, Liechtenstein) for 40 seconds. Results: Degree of conversion result varied from 74.92&plusmn ; ; ; 1.58 to 82.23&plusmn ; ; ; 0.84. Polymerization shrinkage values varied from 4.12&plusmn ; ; ; 0.25 to 5.72&plusmn ; ; ; 0.08. The highest degree of conversion was obtained for experimental composite containing Bis-GMA and HEMA. Unfortunately, higher degree of conversion values led to higher contraction values, as well. Conclusions and clinical significance of the results: Results obtained revealed higher conversion of experimental ACP based composites as well as higher polymerization contraction compared to hybrid dental composites used in every day clinical practice. However, for wider clinical use, reduction of polymerization contraction, by modification of filler content could lead to optimal bioactive composite.

ACP based composite; polymerization; shrinkage; degree of conversion

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