Effect of light irradiation condition on gap formation under polymeric dental restoration; OCT study.

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). 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™ Z350 XT flowable composite (3M ESPE AG, St. Paul, MN, USA) and immersed in ammoniacal silver-nitrate contrasting solution. Cross-sectional images were recorded at every 250μm 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. 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). 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.

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