Real-time in-depth imaging of gap formation in bulk-fill resin composites

Juri Hayashi, Jorge Espigares, Tomohiro Takagaki, Yasushi Shimada, Junji Tagami, Tomoko Numata, Daniel Chan, Alireza Sadr

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)


Objectives: This study visualized in real-time the gap forming of bulk-fill resin composites during polymerization using optical coherence tomography (OCT). Methods: Light-cured bulk-fill resin composites; Tetric N-ceram Bulk Fill (TNB), SonicFill (SNF), Surefil SDR (SDR), dual-cured bulk-fill resin composite Bulk EZ (BEZ), and light-cured core resin composite Clearfil Photo Core (CPC) were investigated. Swept-source OCT real-time cross-sectional monitoring was obtained during resin composite placement and curing procedure. Gap formation was observed in bonded cylindrical resin composite molds (4-mm depth, 3-mm diameter) and free shrinkage volume was observed at the top and bottom of a tube with similar dimensions (n = 10). OCT 3D data were analyzed to calculate sealing floor area percentage (SFA%) and volumetric shrinkage in bonded tube (VS%). Data were analyzed by ANOVA at significance level of 0.05. The bottom-top degree of conversion ratio (DC%-R) through 4-mm depth was measured using the XploRA Plus micro-Raman spectroscopy. Results: BEZ showed no gap formation at the cavity floor in any specimens while SNF showed the highest gap formation; the statistical order in terms of SFA% was BEZ (100 ± 0) > TNB (84.97 ± 2.98) > CPC (52.13 ± 8.23) = SDR (45.97 ± 9.21) > SNF (16.23 ± 6.00) (p < 0.05). On the other hand, total VS% was statistically ordered as BEZ (3.40 ± 0.14) > SDR (3.22 ± 0.09) > TNB (1.82 ± 0.11) > SNF (1.65 ± 0.04) = CPC (1.56 ± 0.04) (p < 0.05). Unlike BEZ, the light-cured resin composites showed larger shrinkage at specimen bottom than top. TNB showed the lowest DC%-R followed by SNF (p < 0.05). Significance: Light-cured bulk-fill resin composites showed various degrees of gap formation and shrinkage at 4-mm deep cavity. The dual-cured bulk-filled resin composite showed no decrease of degree of conversion through the depth and the highest cavity adaptation despite its tendency for higher volumetric shrinkage.

Original languageEnglish
Pages (from-to)585-596
Number of pages12
JournalDental Materials
Issue number4
Publication statusPublished - Apr 2019


  • Bulk-filled
  • Composite resins
  • Degree of conversion
  • Dental restoration failure
  • Optical coherence tomography
  • Polymerization
  • Self-cured
  • Shrinkage

ASJC Scopus subject areas

  • Materials Science(all)
  • Dentistry(all)
  • Mechanics of Materials


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