Assessments of polymerization shrinkage by optical coherence tomography-based digital image correlation analysis-Part I: Parameter identification

Wei-Chi Chen; Shu-Fen Chuang; Po-Chun Tseng; Ting-Weng Lai; Terry Yuan-Fang Chen; Yung-Nien Sun

doi:10.1016/j.dental.2024.05.003

Assessments of polymerization shrinkage by optical coherence tomography-based digital image correlation analysis-Part I: Parameter identification

Dent Mater. 2024 May 9:S0109-5641(24)00101-5. doi: 10.1016/j.dental.2024.05.003. Online ahead of print.

Authors

Wei-Chi Chen¹, Shu-Fen Chuang², Po-Chun Tseng³, Ting-Weng Lai⁴, Terry Yuan-Fang Chen⁵, Yung-Nien Sun⁶

Affiliations

¹ School of Dentistry and Institute of Oral Medicine, National Cheng Kung University, Tainan, Taiwan; Department of Dentistry, Sin-Lau Hospital, Tainan, Taiwan.
² School of Dentistry and Institute of Oral Medicine, National Cheng Kung University, Tainan, Taiwan; Department of Stomatology, National Cheng Kung University Hospital, Tainan, Taiwan. Electronic address: sfchuang@mail.ncku.edu.tw.
³ Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Munich, Germany.
⁴ School of Dentistry and Institute of Oral Medicine, National Cheng Kung University, Tainan, Taiwan; Department of Stomatology, National Cheng Kung University Hospital, Tainan, Taiwan.
⁵ Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan.
⁶ Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan.

PMID: 38729780
DOI: 10.1016/j.dental.2024.05.003

Abstract

Objective: To investigate the feasibility of optical coherence tomography (OCT)-based digital image correlation (DIC) analysis and to identify the experimental parameters for measurements of polymerization shrinkage.

Methods: Class I cavities were prepared on bovine incisors and filled with Filtek Z350XT Flowable (Z350F). One OCT image of the polymerized restoration was processed to generate virtually displaced images. In addition, the tooth specimen was physically moved under OCT scanning. A DIC software analyzed these virtual and physical transformation sets and assessed the effects of subset sizes on accuracy. The refractive index of unpolymerized and polymerized Z350F was measured via OCT images. Finally, different particles (70-80 µm glass beads, 150-212 µm glass beads, and 75-150 µm zirconia powder) were added to Z350F to inspect the analyzing quality.

Results: The analyses revealed a high correlation (>99.99%) for virtual movements within 131 pixels (639 µm) and low errors (<5.21%) within a 10-µm physical movement. A subset size of 51 × 51 pixels demonstrated the convergence of correlation coefficients and calculation time. The refractive index of Z350F did not change significantly after polymerization. Adding glass beads or zirconia particles caused light reflection or shielding in OCT images, whereas blank Z350F produced the best DIC analysis results.

Significance: The OCT-based DIC analysis with the experimental conditions is feasible in measuring polymerization shrinkage of RBC restorations. The subset size in the DIC analysis should be identified to optimize the analysis conditions and results. Uses of hyper- or hypo-reflective particles is not recommended in this method.

Keywords: Digital image correlation analysis; Optical coherence tomography; Polymerization shrinkage; Refractive index; Resin composite; Speckle pattern; Subset size.