Objective: To investigate the effect of monomer chemistry and the oxygen inhibition layer (OIL) thickness on stain resistance of resin based composites (RBCs).
Methods: Two methacrylate-based (Z100 and Z250; 3M ESPE, Seefeld, Germany) and one silorane-based RBC (Silorane; 3M ESPE) were tested. 4 and 8mm diameter x 2mm thick specimens (n=5) were irradiated with an LED curing-unit (~1000 mW/cm2) for 30s, for OIL thickness and colour stability measurements, respectively. Each specimen was cured either in air or nitrogen atmosphere and stored wet or dry for 24h (23±1°C) in a lightproof container. The OIL was measured using a depth of focus technique at five locations on the surface of each specimen. Colour change (ΔE) was measured prior to and following immersion in 0.5% methylene blue solution for 1, 3 and 7 days using a colorimeter and CIE L*a*b* colour parameters. Data was analyzed by ANOVA and post-hoc Tukey or Kruskal-Wallis and Mann-Whiney tests (P=0.05)
Results: No OIL was identified for any material cured in a nitrogen atmosphere. In air, the OIL thickness of Silorane (9.0±6.6µm) was significantly decreased compared with Z250 (19.2±6.3µm; P<0.001) and Z100 (13.7±5.4µm; P=0.008). No differences in ΔE were observed for specimens stored wet or dry prior to dye immersion (P>0.05). Two-way ANOVA revealed a significant increase in ΔE of Z250 compared with Z100 specimens cured in nitrogen, although an opposite significant trend occurred for specimens cured in air (P<0.001). Silorane exhibited a significant reduction in ΔE compared with Z250 and Z100 in both nitrogen and air (P<0.001).
RBCs | Z250 | Z100 | Silorane | |||
| N2 | Air | N2 | Air | N2 | Air |
1 day ΔE | 28.2 (0.9) | 32.2 (1.1) | 22.7 (1.7) | 38.0 (0.9) | 4.1 (0.3) | 26.3 (1.5) |
3 days ΔE | 32.5 (1.4) | 32.7 (0.9) | 25.9 (1.2) | 36.3 (0.8) | 6.0 (0.2) | 25.5 (0.9) |
7 days ΔE | 34.7 (1.9) | 33.1 (0.8) | 28.8 (1.1) | 36.2 (0.5) | 8.7 (0.3) | 25.7 (0.8) |
Conclusions: Monomer chemistry plays a significant role in minimizing OIL thickness, which may subsequently reduce the staining susceptibility of RBC surfaces.