Local deformation fields and marginal integrity of sculptable bulk-fill, low-shrinkage and conventional composites

- Shrinkage of bulk-fill and low-shrinkage composites was comparable to conventional composites.
- Strain distribution across depth differed in 4-mm and 2-mm layered composites.
- Marginal integrity was more often compromised along the gingival than axial dentin wall.

ObjectiveTo compare strain and displacement of sculptable bulk-fill, low-shrinkage and conventional composites as well as dye penetration along the dentin-restoration interface.MethodsModified Class II cavities (N = 5/group) were filled with sculptable bulk-fill (Filtek Bulk Fill Posterior, 3M ESPE; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent; fiber-reinforced EverX Posterior, GC; giomer Beautifil Bulk, Schofu), low-shrinkage (Kalore, GC), nanohybrid (Tetric EvoCeram, Ivoclar Vivadent) or microhybrid (Filtek Z250, 3M ESPE) composites. Strain and displacement were determined using the 3D digital image correlation method based on two cameras with 1 μm displacement sensitivity and 1600 × 1200 pixel resolution (Aramis, GOM). Microleakage along dentin axial and gingival cavity walls was measured under a stereomicroscope using a different set of teeth (N = 8/group). Data were analyzed using analyses of variance with Tukey's post-test, Pearson correlation and paired t-test (α = 0.05).ResultsStrain of TEC Bulk, Filtek Bulk, Beautifil Bulk and Kalore was in the range of 1-1.5%. EverX and control composites showed 1.5-2% strain. Axial displacements were between 5 μm and 30 μm. The least strain was identified at 2 mm below the occlusal surface in 4-mm but not in 2-mm layered composites. Greater microleakage occurred along the gingival than axial wall (p < 0.05). No correlation was found between strain/displacements and microleakage axially (r2 = 0.082, p = 0.821; r2 = −0.2, p = 0.605, respectively) or gingivally (r2 = −0.126, p = 0.729, r2 = −0.278, p = 0.469, respectively).SignificanceStrain i.e. volumetric shrinkage of sculptable bulk-fill and low-shrinkage composites was comparable to control composites but strain distribution across restoration depth differed. Marginal integrity was more compromised along the gingival than axial dentin wall.