EVALUATION OF MECHANICAL PROPERTIES OF EXPIRED AND NON-EXPIRED RESIN COMPOSITE. A COMPARATIVE STUDY

This in-vitro study evaluated the mechanical properties in terms of microhardness and degree of conversion of expired versus non-expired resin composite. A total of 120 standardized specimens were prepared for this study using Ceram.x one (E2 Enamel shade) resin composite, of which forty specimens were prepared using valid resin composite (E-0), the other forty specimens were prepared using 6 months-expired resin composite (E-6) and the last forty specimens using 12 months-expired resin composite (E-12). They were light cured using LED curing unit. 20 of each group were subjected to measurement of surface microhardness in Vickers hardness tester. The depth of cure was calculated by obtaining the microhardness ratio through dividing VHN of the bottom surface by VHN of the top surface. The other 20 specimens of each group were tested for the degree of conversion using Fourier transform infrared spectroscopy (FTIR). Data was then recorded, tabulated and statistically analyzed. The highest mean microhardness of the specimen’s top was recorded for the group of 12-months expired resin composite (E-12: 83.17 ± 3.14), which was significantly different in relation to the group of 6-months expired resin composite (E-6: 72.17 ± 2.55) and the group of valid resin composite (E-0: 72.06 ± 4.20). Regarding B/T ratio (%), there were no statistical significant difference between the three groups (E-0: 69.3 ± 10.1; E-6: 66.8 ± 3.9; E-12: 67.9 ± 4.9). As for the degree of conversion results there was no statistical significant difference between the three groups (E-0: 1.48 ± 0.14; E-6: 1.68 ± 0.20; E-12: 1.74 ± 0.18). In conclusion, expired resin composite within1 year interval showed optimum and accepted mechanical properties in terms of Degree of conversion and microhardness compared to that of non-expired resin composite.