ARTICLE IN PRESS ZEMEDI-10815; No. of Pages 7 Effect of Light Irradiation Condition on Gap Formation Under Polymeric Dental Restoration; OCT study T.A. Bakhsh a,b,∗ , J. Tagami c , A. Sadr d , M.N. Luong d , A. Turkistani a , Y. Almhimeed a , E. Alshouibi e a Restorative Dentistry Department, Faculty of Dentistry, King Abdulaziz University, P.O. Box 80209, Jeddah 215-89, Saudi Arabia b School of Dentistry, Alfarabi Private College, Jeddah, Saudi Arabia c Cariology and Operative Dentistry, Department of Restorative Sciences, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8549, Japan d Department of Restorative Dentistry, University of Washington School of Dentistry, Box 357456, 1959 NE Pacific Street, Seattle, WA 98195-7456, USA e Dental Public Health, Faculty of Dentistry, King Abdulaziz University, P.O. Box 80209, Jeddah 215-89, Saudi Arabia Received 20 September 2019; accepted 2 February 2020 Abstract Objective: To investigate the effect of two light-curing systems; quartz tungsten-halogen (QTH) and light-emitting diode (LED), and irradiation time on interfacial gap formation of dental composite resin restorations bonded with an adhesive resin using optical coherence tomography (OCT). Materials and Methods: Forty cavities were prepared in extracted human molar teeth and divided into four groups (n = 10) based on the type of light curing system QTH (LITEX 680A) and LED (Demi Plus) and curing duration (10 s or 40 s). A single-step self-etching dental adhesive (Tetric ® N-Bond; Ivoclar Vivadent AG, Schaan, FL, Liechtenstein) was applied and polymerized with QTH for 10 s (QTH-10), or for 40 s (QTH-40). Similarly, the adhesive in LED-10 and LED-40 groups was polymerized with an LED for 10 s or 40 s, respectively. Then, all specimens were restored with Filtek TM Z350 XT flowable composite (3 M ESPE AG, St. Paul, MN, USA) and immersed in ammoniacal silver-nitrate contrasting solution. Cross-sectional images were recorded at every 250 m using cross-polarization OCT system (CP-OCT; IVS-300, Santec, Komaki, Aichi, Japan). Image analysis to quantify the percentage of gap at resin-dentin interface was performed using a custom plugin for ImageJ software. Results: Data analysis using one-way ANOVA showed a significant difference in mean gap percentage between the four test groups (p < 0.0001). Mean gap percentage values were 75.8%, 53.2%, 9.9% and 5.6%. The highest for LED-10 followed by LED-40 (p < 0.05). QTH-40 revealed a slightly better adaptation compared with QTH-10, but the difference between them was not significant (p < 0.05). Conclusion: CP-OCT with a contrast agent is a useful non-invasive imaging tool for dental composite resin materials. QTH showed better results than LED under the experimental conditions. When using an LED light-curing unit, prolonged irradiation improved interfacial adaptation of dental composite bonded with a self-etching adhesive. Keywords: Optical Coherence Tomography, OCT, Tooth-composite bond, Flowable composite, Self-etch Adhesive, Halogen polymerization light ∗ Corresponding author. Restorative Dentistry Department, Faculty of Dentistry, King Abdulaziz University, P.O. Box 80209, Jeddah 215-89, Saudi Arabia. Tel.: + 966-12-640-1000 Ext: 20326. Fax::::: + 966-12-640-4002 E-mail: taabakhsh@kau.edu.sa (T.A. Bakhsh). Z Med Phys xxx (2020) xxx–xxx https://doi.org/10.1016/j.zemedi.2020.02.001 www.elsevier.com/locate/zemedi