engleski

New Method For Measuring Linear Polymerization Shrinkage

Objective: One of the most challenging problems regarding composite resins (CR) is their polymerization shrinkage (PS) induced by photo-polymerization. The aim of the study was to develop a new method for a more reliable and accurate measurement of PS of flowable CR (FCR). We implemented the novel sample holder into the interferometry setup, to enable reliable measurements of PS for FCR as well. Method: FCR samples were placed into a Teflon mould glued on 1 mm thick glass slide, weighted with Teflon piston carrying on its top a small object mirror. The piston moves vertically as sample changes its height. The sample is cured by the LED curing unit for 20 s from below. The dimensional changes of the sample height were continuously recorded during PS over 15 minutes. The sample was then cured again for 20 s in order to induce thermal expansion and test the method reliability. Linear PS was measured by digital laser interferometry (DLI) using proprietary developed software. Our DLI method has introduced several improvements in analyzing interferometric data, reducing systematic errors and improving resolution down to 0.3 nm. Actual accuracy depends on the efficiency to suppress mechanical vibrations. Result: PS measurements on FCR were recorded as continuous 15 minutes shrinkage with the final magnitude of 10-15 μm. Additional 20 s curing of polymerized sample generated by heating a thermal expansion of 2-3 μm, followed by contraction during cooling. Parameters obtained from shrinkage and expansion curves were used for confirming the extent of method reliability. Conclusion: The results obtained turned out to be consistent with the expectations based on the model describing the heat energy transfer from the curing unit tip to the sample holder which proved to be the crucial improvement for reliable PS measurements of flowable CR.

Polymerization Shrinkage; Composite Resins

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