3D-marginal adaptation versus setting shrinkage in light-cured microhybrid resin composites

Purpose: To comparatively evaluate the 3D-marginal adaptation to dentine versus shrinkage strain of two light-cured microhybrid resin composites. Methods: Dentine cavities (Ø: 2 mm; h: 1 mm; n = 2 × 4) were prepared, filled with a single layer of EsthetX and Premise resin composites, respectively, without any adhesive cavity pre-treatment, and light-cured for 40 s at 750 mW/cm2. All the specimens were imaged by computerized X-ray microtomography. Sequential sections (n = 11) at 8.09 pixel size were taken at top, middle and bottom sites of each restoration relative to the axial wall and the interfacial micro-void volume fraction (%VF) was calculated. Shrinkage strain (%S) and strain rate (%SR) of the composites were measured by the bonded-disc method (n = 4). The results of %VF per material and restoration site were subjected to statistical analysis by 2-way ANOVA and Tukey's test, whereas the results of %S and %SR were analysed by t-test (p = 0.05). Regression analysis was performed to determine correlations between %PF and %S, %SR. Results: The results of %VF at top (t), middle (m) and bottom (b) restoration sites were (%, mean ± S.D.): EsthetX 0.84 ± 0.11 (t), 0.80 ± 0.32 (m), 6.74 ± 5.12 (b), Premise 0.99 ± 0.24 (t), 0.92 ± 0.38 (m), 1.72 ± 0.97 (b). The results of %S were (%, mean ± S.D.): EsthetX 2.60 ± 0.29, Premise 1.91 ± 0.10 and of %SR were (%, mean ± S.D.): EsthetX 1.47 ± 0.04, Premise 1.18 ± 0.02. %VF(b) of EsthetX showed the highest values within and between the testing groups (p <0.05). %S and %SR values of EsthetX were significantly higher from Premise (p <0.05). Strong positive correlations were documented between %VF(b)-%S (r = 0.843) and %VF(b)-%SR (r = 0.943). Clinical significance: The results confirmed a positive correlation between setting shrinkage and interfacial gap volume at bottom sites of light-cured microhybrid composite restoration due to differential shrinkage. Shrinkage strain rate seems to be a more sensitive factor in determining percentage volume of interfacial porosity at bottom restoration sites. © 2006 Academy of Dental Materials.