Real-Time Imaging of Gap Progress during and after Composite Polymerization

Abstract

The aims of this study were to observe the behavior of composite and formation of gaps during and immediately after light polymerization using swept source optical coherence tomography (OCT) and to compare the interfacial integrity of adhesives in cavities through 3-dimensional (3D) image analysis. Forty tapered cylindrical cavities (4-mm diameter, 2-mm depth) were prepared in bovine incisors and restored using Bond Force (BF), Scotchbond Universal Adhesive (SBU), OptiBond XTR (XTR), or Clearfil SE Bond 2 (SE2), followed by Estelite Flow Quick flowable composite. Real-time imaging was performed at the center of restoration by the OCT system (laser center wavelength: 1,330 nm; frequency: 30 KHz) during and up to 10 min after light curing. The 3D scanning was performed 0, 1, 3, 5, and 10 min after light curing. The percentages of sealed enamel and dentin interface area (E%, D%) were calculated using Amira software. In real-time videos, the initial gaps appeared as a bright scattered area mainly on dentin floor and rapidly progressed along the cavity floor. The timing, rate, and extent of gap formation were different among the specimens. From 3D visualization, gap progress could be seen on both enamel and dentin even after irradiation; furthermore, typical toroidal gap patterns appeared at the dentin floor of BF and SBU. XTR and SE2 showed nearly perfect sealing performance on the dentin floor up to the 10 min that images were recorded. From quantitative analysis, SE2 and XTR showed significantly higher E% and D% than other groups. SBU showed the smallest E% and BF showed a significantly smaller D% than other groups ( P < 0.05). In conclusion, real-time observation of composite placement and 3D quantification of interfacial gaps were implemented within the experimental limitations. Interfacial gap formation during polymerization of the composite depended on the adhesive system used. The formed gaps continued to propagate after composite light curing finished.

Effect of light-curing time on light-cure/post-cure volumetric polymerization shrinkage and regional ultimate tensile strength at different depths of bulk-fill resin composites

“…Recently, SS-OCT has been used for the detection of caries, tooth fractures, and secondary caries at the restoration-tooth interface in vivo and in vitro 6,28) . Additionally, some studies have demonstrated that SS-OCT can be used for the quantitative measurement of gaps between resin composite and cavity walls 32) and observation of real-time gap progression 26) . A recent study using SS-OCT observation, reported that internal gap formations in resin composite restorations were correlated with the shrinkage parameters of resin composites 3) .…”

“…Collected backscattered light from the sample is returned to the system, digitized in time scale, and analyzed in the Fourier domain to form a depth-resolving scan (A-scan) at each point. A serial set of A-scans along a certain section creates a row data file of back-scattered signal intensity (B-scan) and a 2-dimensional cross-sectional (2D) image 26) .…”

“…Additionally, it has been reported that composite specimens with a low level of polymerization after the primary light-curing phase generated greater post-cure polymerization 14,24) . Recently, non-contact 2D and 3D imaging methods such as micro-computed tomography 10,25) and optical coherence tomography 26,27) have been employed to investigate the sealing performance of resin composite in cavities. Swept-source optical coherence tomography (SS-OCT) can obtain 2D and 3D cross-sectional images of teeth and periodontal tissues in a non-invasive and nondestructive way, and analyze the behavior of restorative materials inside the cavity in real time 26,28) .…”

“…Recently, non-contact 2D and 3D imaging methods such as micro-computed tomography 10,25) and optical coherence tomography 26,27) have been employed to investigate the sealing performance of resin composite in cavities. Swept-source optical coherence tomography (SS-OCT) can obtain 2D and 3D cross-sectional images of teeth and periodontal tissues in a non-invasive and nondestructive way, and analyze the behavior of restorative materials inside the cavity in real time 26,28) . Therefore, this method would enable the VS of resin composite in cavities to be investigated during light-irradiation, and 24 h later or more.…”

Hard X-ray phase-contrast-enhanced micro-CT for quantifying interfaces within brittle dense root-filling-restored human teeth

“…Current treatment protocols advocate bonded sealing for a variety of reasons. These include increased mechanical stability of the restoration due to an improved distribution and resistance to stresses, as well as prevention of bacterial percolation at the interface (Hayashi et al, 2017).…”