Oxygen inhibition layer: A dilemma to be solved

OBJECTIVE: This study aimed to evaluate the thickness of oxygen inhibition layer (OIL), produced on various composite materials, and to compare their interlayer shear bond strength (SBS), by treating the OIL with various agents. MATERIALS AND METHODS: The thickness of OIL of three different composite materials (120 specimens divided into three groups) Group 1 – Ivoclar Tetric N-Ceram (nanohybrid composite), Group 2 – Ivoclar Te Econom Plus (microhybrid composite), and Group 3 – GC EverX Posterior (a short glass fiber-reinforced composite) was evaluated. Each group was divided into four subgroups (A, B, C, and D) depending on the surface treatment given – no surface treatment (control group), ethanol, water spray, and grinding with SiC paper. This was followed by interlayer SBS testing. STATISTICAL ANALYSIS: The data were statistically analyzed using ANOVA at a significance level of P < 0.05. Tukey’s post hoc analysis was performed following ANOVA to determine differences among the groups. RESULTS: The control group showed higher SBS irrespective of the type of composite material. The group treated with SiC paper resulted in the lowest interlayer SBS among all groups. Glass fiber composite showed higher interlayer SBS compared to both nanohybrid and microhybrid composites, irrespective of the surface treatment given. CONCLUSION: The OIL, which acts as an intermediate layer, is retained on the surface of the composite even after treatment with ethanol and water spray. The presence of an OIL improved the interlayer SBS of two adjacent composite layers and led to more durable adhesion. Rather, the absence of an OIL adversely affected the bond strength and led to adhesive interfacial failures.