title: 3D assessment of void and gap formation in flowable resin composites using optical coherence tomography.
abstract: OBJECTIVE
  To investigate the effect of composite type and cavity size on gap and void formation using optical coherence tomography (OCT).
  
  
  METHODS
  Class I cavities of two depths (2 mm or 4 mm; 4 mm diameter) were prepared, treated with Tri-S Bond (Kuraray Medical), and bulk filled with either Surefil SDR Flow (SF; Dentsply) or Clearfil Majesty LV (MJ; Kuraray Medical) to form four groups. After 24 h, the specimens were 3D scanned using swept-source OCT (Santec) with 1310 nm laser at a 20 kHz sweep rate. In OCT tomograms, the bonding interface and the bulk of the restorations were evaluated. The percentage values of sealed interfaces (SP) and void volume (VP) for all groups were calculated and statistically analyzed using two- and one-way ANOVA and Tukey's post-hoc test. Selected specimens were cross sectioned and observed using a scanning electron microscope (SEM) and a confocal laser scanning microscope to confirm OCT findings.
  
  
  RESULTS
  The following values were obtained for SP and VP, respectively: SF-2mm: 92% and 0.08%; SF-4mm: 66% and 0.13%; MJ-2mm: 86% and 1.79%; MJ-4mm: 33% and 1.96%. Both composites showed a significant increase in gap formation at 4-mm cavity depth (p < 0.001). While SF showed a rather homogeneous bulk compared to MJ, cavity depth did not significantly affect the void volume fraction (p = 0.08).
  
  
  CONCLUSIONS
  The flowable composite with SDR (stress-decreasing resin) technology performed better than the conventional composite; however, bulk filling a 4-mm-deep cavity will compromise the sealing of the bonding interface regardless of the type of composite. OCT is a unique method of characterizing materials and their behaviors nondestructively and precisely.
authors.affiliation: Department of Restorative Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Amir
authors.initials: A
authors.lastname: Nazari
authors.forename: Alireza
authors.initials: A
authors.lastname: Sadr
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Shimada
authors.forename: Junji
authors.initials: J
authors.lastname: Tagami
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Sumi
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003737:Dental Cavity Preparation / Q000379:methods; D003743:Dental Enamel / Q000648:ultrastructure*; D003764:Dental Materials / Q000737:chemistry*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007834:Lasers; D008422:Materials Testing; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D019279:Resin Cements / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D041623:Tomography, Optical Coherence / Q000379:methods*
chemical_list: C515604:Clearfil Tri-S Bond; D003188:Composite Resins; D003764:Dental Materials; D019279:Resin Cements; C553871:Surefil SDR Flow; C541508:clearfil majesty