The influence of salivary contamination during light curing on degree of conversion and color stability of two composite resins.

BACKGROUND

Adequate polymerization of composite resin restorations is critical for their mechanical performance and long-term clinical success. Salivary contamination during light curing can interfere with polymerization and may influence color stability.

OBJECTIVE

This in vitro study examined how artificial saliva contamination at specific intervals during light curing affects the DC (degree of conversion) and short-term color change or ΔE (Delta E) of two composite resins-Gradia Direct (microhybrid) and N-Ceram Bulk Fill (nanohybrid).

METHODS

One hundred eighty disk specimens (n = 90 per composite) were allocated into nine experimental groups differing in contamination timing and curing duration. DC was determined by FTIR-ATR (Fourier-Transform Infrared- Attenuated Total Reflectance) spectroscopy immediately after curing and following 24-h incubation at 37 °C. Color change (ΔE) was measured with a spectrophotometer using the CIE (International Commission on Illumination) Lab∗ system. Statistical analysis employed one- and two-way ANOVA (Analysis of Variance) with Tukey's post hoc test (α = 0.05).

RESULTS

Early contamination (within the first 5-10 s) produced a significant reduction in DC for both materials (p < 0.001), with N-Ceram showing the greatest loss. Gradia achieved higher DC across most conditions. Post-cure incubation improved DC in all groups, most notably in N-Ceram. All ΔE values remained below the perceptibility threshold of 3.3, with no significant differences among groups (p > 0.05).

CONCLUSION

Saliva exposure early in light curing markedly reduces polymerization efficiency, although extended curing and post-cure polymerization can partially restore DC. Short-term color stability appears unaffected. Strict field isolation and optimized curing protocols are essential to maximize clinical performance.