Using Oxygen Radical Scavengers to Reduce the Oxygen-Inhibited Layer on Resins

Objectives: The oxygen-inhibited layer (OIL) found on the surface of polymerised dental resins compromises its surface hardness, wear resistance, marginal adaptation, can elicit adverse mucosal reactions when free monomer is eluted into saliva, and is a known inhibitor of PVS polymerisation. This study assesses the viability of oxygen radical scavengers as a treatment to eliminate the OIL.
Methods: High Performance Liquid Chromatography (HPLC) was used to detect traces of free monomers Bisphenol A Diglycidyl Ether Dimethacrylate (Bis-GMA) and Triethylene Glycol Dimethacrylate (TEGDMA) eluted from the OIL formed on three polymerised resin composite materials (Filtek Z250, Filtek Supreme Ultra Flowable, Helioseal F). Eight treatment groups were allocated. 1) No treatment, 2) 70% isopropyl alcohol, 3) Glycerin, 4) α-Tocopherol (Vitamin E), 5) Butylated Hydroxytoluene (BHT), 6) Ascorbate (Vitamin C), 7) Sodium Metabisulphite (Na₂S₂O₅), 8) Glutathione (C₁₀H₁₇N₃O₆S). All eluted monomer measurements were performed three times for each of the extracts. The concentrations of the leaching monomers Bis-GMA and TEGDMA from the OIL were calculated by using coefficients obtained by a linear regression analysis of the results from an established standard. Statistical analysis was performed using the Kruskal-Wallis Analysis of Variance (ANOVA) and Kruskal-Wallis range test to assess significant differences in monomer concentrations recorded (p<0.05).
Results: 70% isopropyl alcohol treatment was ineffective in reducing the concentration of eluted Bis-GMA and TEGDMA. Glycerin treatment presented with a significant reduction of both monomers tested based on two pair comparison tests (p<0.01). All oxygen radical scavengers tested (Vitamin E, BHT, Vitamin C, Sodium Metabisulphite, Glutathione) were more effective in reducing eluted monomers when compared to glycerin (p<0.0001). No treatment method tested was capable of achieving 0µg/mL, or complete elimination of residual monomer from the OIL.
Conclusions: The use of biocompatible peroxyl radical scavengers is a more effective method at removing the OIL than conventional techniques using glycerin.