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

## TL;DR

This study shows that saliva contamination during the early stages of curing dental composites reduces their polymerization quality, though extended curing can help recover some performance.

## Contribution

The study introduces a systematic analysis of how timing and duration of salivary contamination during light curing affect composite resin properties.

## Key findings

- Early salivary contamination significantly reduces the degree of conversion in both tested composite resins.
- Extended curing and post-cure incubation partially restore polymerization efficiency, especially in N-Ceram.
- Color stability remains within perceptibility thresholds and is not significantly affected by contamination.

## Abstract

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.

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).

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).

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).

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.

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