The Effect of Curing Light Intensity on Free Volume Size in Some Dental Composites

BACKGROUND: Dental composite resins - reinforced polymers - are types of synthetic resins that are used in dentistry as restorative material or adhesives. The effect of curing-light intensity on free volume sizes of 4 commercial dental composites has been studied by means of the well-known positron annihilation lifetime spectroscopy technique. OBJECTIVES: The aim of the study was to compare the photosensitivity of 4 commercial dimethacrylate-based dental composites. MATERIAL AND METHODS: Positron lifetime spectra were collected using a slow-fast coincidence lifetime spectrometer with a time resolution of 365 ps. The positron source was a ~20 μCi 22Na beta emitter between two 7 μm thick stainless steel foils. The positron source was sandwiched between two identical samples under investigation. The 1st group of samples was polymerized by a 20-second photo-exposure, and the 2nd group of samples was irradiated by the blue curing light for 40 s. The positron annihilation lifetime spectrums were separated into components using the PAScual Positron Annihilation Spectroscopy data analysis program. RESULTS: The results showed that the lifetime component associated with free volumes differed in the different composites and depended on the irradiation time. The results indicated that the Coltene composite has higher photosensitivity than the other samples; the Denfil composite exhibited the lowest photosensitivity of the 4. CONCLUSIONS: The appropriate light-curing intensity depends on the thickness of the composite, which in turn is proportional to the depth of the hole in the tooth undergoing repair.