Objectives: Depth-of-Cure (DoC) is a key parameter of bulk-fill composites: potentially a function of: (i) composite formulation; (ii) cavity mold material /dimensions; (iii) irradiation source & protocol – irradiance x time; (iv) the selected cure-dependent property. As part of a comprehensive investigation, we focus here on DoCs from hardness-depth profiles for bulk-fill composites, in relation to their light absorption coefficients, with a single light-cure-unit (LCU).
Methods: Six bulk-fill composites were examined and assigned the codes: SDR-BF, TEC-BF, V-BF, XB-BF, F-BF, SF-BF. Two standard composites were studied for comparison: TEC and CX. Six specimens of each material were prepared in circular cavities (diameter 5 mm) in a series of white Acetal molds of increasing cavity depth (d), from 1-6 mm. Materials were directly irradiated with an Elipar S10 LCU, of irradiance 1200 mW/cm2 (MARC-RC, BlueLight Analytics, Inc), for manufacturer-recommended time-periods. After light-cure, the specimens were allowed to dark post-cure for 24 h at 37 oC. Vickers hardness (Hv) of each specimen was then measured 10 x on both top and bottom surfaces, (300 g load, 15 s). Light transmission through specimens was subsequently measured via MARC-RC.
Results: Maximum Hv varied within the range 40-80, depending on filler loading. Top-surface Hv was approximately invariant with mold depth (d). Bottom-surface Hv decreased gradually with increasing d, for BF materials, and DoC could be assigned - corresponding to 80 % of maximal Hv - which ranged from 3.3 to 5.5 mm. When light absorption coefficients (a) were derived (Watts: J Dent 1994, 22: 112-7) from the BF transmission data, excluding XB-BF, a negative linear regression was found (r = - 0.900) of DoC on a.
Conclusion: Measurement of 24 h bottom-hardness versus (Acetal) mold depth is a viable method of deriving Depth-of-Cure data, which for five BF composites varied approximately according to the light-absorption coefficient.
Keywords: Composites, Dental materials, Hardness, Light-Curing and Polymerization
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Signed on 10/07/2013 by D.C. WATTS
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