title: 3D-marginal adaptation versus setting shrinkage in light-cured microhybrid resin composites.
abstract: OBJECTIVE
  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=2x4) were prepared, filled with a single layer of EsthetX and Premise resin composites, respectively, without any adhesive cavity pre-treatment, and light-cured for 40s 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, %S(R).
  
  
  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 %S(R) 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biomaterials, University of Athens, School of Dentistry, Greece.
authors.forename: Afrodite
authors.initials: A
authors.lastname: Kakaboura
authors.forename: Christos
authors.initials: C
authors.lastname: Rahiotis
authors.forename: David
authors.initials: D
authors.lastname: Watts
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
authors.forename: George
authors.initials: G
authors.lastname: Eliades
mesh_terms: D000704:Analysis of Variance; D003188:Composite Resins / Q000528:radiation effects; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D003804:Dentin; D006801:Humans; D008027:Light; D008422:Materials Testing; D008964:Molar, Third; D044367:Phase Transition; D012044:Regression Analysis
chemical_list: D003188:Composite Resins; C466112:Esthet-X; C507210:premise composite resin