Effect of High-radiant Emittance and Short Curing Time on Polymerization Shrinkage Vectors of Bulk Fill Composites
To evaluate the effect of short curing time using a high-radiant emittance light on polymerization shrinkage vectors in different consistency bulk-fill composites (BFRCs) using micro-computed tomography. Radiopaque zirconia fillers were homogeneously incorporated and functioned as radiopaque tracers into two regular-paste: TBFill (Tetric EvoCeram Bulk Fill) and TPFill (Tetric PowerFill), and two flowable (n=6): TBFlow (Tetric EvoFlow Bulk Fill) and TPFlow (Tetric PowerFlow) resin composites. Class I cavities (4 mm depth × 4 mm length × 4 mm width) were 3D-printed and filled in a single increment: TBFill and TBFlow were light-activated using a Bluephase Style 20i (10 seconds in high-mode); TPFill and TPFlow were light-activated using a Bluephase PowerCure (three seconds). The same adhesive system (Adhese Universal) was used for all groups. Microcomputed tomography scans were obtained before and after light-activation. Filler particle movement was identified by polymerization shrinkage vectors at five depths (from 0–4 mm): top, top-middle, middle, middle-bottom and bottom. TPFlow showed the lowest total vector displacement, followed by TBFlow, TBFill and TPFill, significantly different among each other (p<0.05). Generally, BFRCs showed decreased vector displacement with increased depth, and higher displacement at the top-surface (p<0.05). Qualitative analysis showed a similar pattern of vector magnitude and displacement for groups TBFill and TPFill, with displacement vectors on occlusal (top) surfaces toward the center of the restoration from the top to middle areas, and relatively limited displacement at the bottom. TBFlow and TPFlow showed more displacement on the occlusal (top). Short curing time with high-radiant emittance on fast-curing BFRCs was shown to be a feasible option in terms of vector displacement. Flowable BFRCs presented lower vector displacement than their regular-viscosity versions.SUMMARY
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Characterization of: (a) Bluephase Style 20i light curing unit (Ivoclar Vivadent) using high power mode. A peak at 460 nm can be observed; and (b) Bluephase PowerCure light curing unit (Ivoclar Vivadent). A peak at 460 nm can be observed.
Representative filler particle displacement vectors seen in sample of: (a) Group TBFill. Vector displacement could be seen on occlusal surface (top) until middle area, as well as on bottom of cavity until top bottom; (b) Group TBFlow. More vector displacement seen on occlusal surface due to deformation after polymerization. Few movements on bottom of cavity; (c) Group TPFill. Vector displacement could be seen on occlusal surface (top) until middle area, as well on bottom of cavity until top bottom; (d) Group TPFlow. Almost no movement could be seen on bottom on cavity. On top displacement related to deformation of material after curing.
Column graph showing displacement vector (mm) mean on the three axes, determined according to depth locations for each group.
Scheme of filler particle displacement vectors for all 4 groups. (a) Group TBFill; (b) Group TBFlow; (c) Group TPFill; and (d) Group TPFlow. The red circles correspond to the mass center of the restoration.
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