Effect of Bonding Agent on Final Shade of Resin Composite: An In Vitro Study

Abstract

Abstract Objective: The aim of the study was to evaluate the effect of different bonding agents on the final shade of the dental composite. Materials and methods: Two adhesive systems were used: a two-step self-etch adhesive (Clearfil Liner Bond 2V, Kuraray, Noritake, Japan) and a universal adhesive (3M Scotchbond Universal Plus Adhesive, St. Paul, MN, USA). A nanofilled composite of EA1 shade (Filtek XT, 3M ESPE, St. Paul, MN, USA) was used to make 117 discs divided into three groups. Group 1 was the control with no bonding agent, Group 2 received Scotchbond Universal (SB), and Group 3 was treated with the self-etch adhesive (CF). Discs were made using an aluminum mold with three circular openings (diameters 10 mm, thicknesses 0.5, 0.75, and 1 mm). Resin composite was placed in the mold, covered with a glass slide, and light-cured for 20 seconds. After curing, specimens were stored in distilled water at 37°C for 24 hours, then dried before applying the adhesive following the manufacturer's instructions. Color measurements were made using a spectrophotometer. Data were analyzed with Stata MP 17, using two-way ANOVA and Tukey’s post hoc test. Results: Samples' colorimetric properties were analyzed using CIELab parameters (L, a, and b) at three thicknesses (0.5, 0.75, and 1 mm) across Control, SB, and CF groups. In Control, brightness rose from 75.32 ± 0.36 at 0.5 mm to 76.24 ± 0.52 at 0.75 mm, then dropped to 74.31 ± 0.42 at 1 mm; SB showed a similar pattern, while CF remained similar at thinner layers but dropped at 1 mm, indicating thicker samples are less bright. All groups showed increased red (a-values) and yellow hue (b-values) with thickness, causing a yellow shift at higher thicknesses. Color differences (ΔE₀₀) and components (ΔL, Δa, Δb) varied significantly between SB and CF versus Control, with trends confirmed by Tukey’s test (p < 0.05). The Scotchbond group had a non-linear ΔL, while Clearfil’s ΔL consistently decreased. Conclusion: The type of bonding agent and composite thickness critically influence the final restoration shade by affecting light transmission and scattering. Small variations in adhesive application can cause shade mismatches, compromising esthetics, highlighting the need for further research.