Post-Irradiation Polymerization of a Silorane-Based Composite

Objectives: The purpose of this study was to evaluate the post-irradiation polymerization of a new silorane-based composite (Filtek LS, 3M/ESPE).  Methods:  Specimens were made by applying uncured composite to the attenuated total reflectance (ATR) attachment of an FTIR (Spotlight 400 FTIR, PerkinElmer) in a thin 0.5mm-thick layer. A curing unit (Elipar S10, 3M ESPE) was positioned with the light guide in contact with the specimen. An uncured spectrum was obtained for each specimen before light-curing for 20 seconds.  Post-irradiation spectra were recorded immediately; 10, 20 and 30 minutes; 1, 2, 4, and 8 hours; and then every 24 hours for one week.  To determine degree of conversion, the FTIR spectra were analyzed between 650 and 950 cm-1, which corresponds with the oxirane ring-opening regions.  Specifically, the stretching vibrations for the epoxy ring, C-O-C (884 cm-1) and Si-CH3 bonds (695 cm-1) were chosen as the analytical and internal-reference absorption bands respectively.   DC was calculated from the ratio of the peak heights of the analytical and reference absorption bands normalized by the ratio of the uncured monomers. Results: The DC of the silorane-based composite had an immediate (baseline) DC of 54.4%, with a DC of 66.1% at 1 hour, 76.0% at one day and 84.4% at 6 days.  Conclusions:  The rate of increase in DC was most rapid during the first hour, with a 21.5% increase from baseline.  The rate of increase slowed significantly at one day with a 0.65% increase per hour from one hour.  The DC reached a plateau at 6 days with a 0.09% increase per hour from one day.  The overall post-irradiation polymerization reaction or percent change in DC from baseline for Filtek LS was 55.1%.