Color stability of composite resins with different photoinitiator systems when subjected to water aging: an in vitro...

The objective of this study was to evaluate the color stability of composite resins with different photoinitiator systems when subjected to water aging for 28 days. A total of 48 disc-shaped specimens (1.5 mm in diameter × 2.0 mm thick) of 3 commercially available composite resins (n = 16 per group) were fabricated in custom acrylic molds. Each of the composite resins is formulated with a distinct photoinitiator system: diphenyl (2,4,6-trimethylbenzoyl) phosphineoxide (TPO), bis(4-methoxybenzoyl) diethylgermanium (Ivocerin), or camphorquinone (CQ). The specimens were polymerized with an LED curing unit and stored in a dark room for 24 hours. Baseline color measurements based on International Commission on Illumination (CIE) L*a*b* parameters were recorded with a spectrophotometer. To evaluate the effects of water aging, specimens were immersed in a thermostatic water bath at 37°C for 28 days; water was replaced every 7 days. Following immersion, specimens were remeasured spectrophotometrically to assess color change. Color differences between baseline values and values obtained after the aging procedures were calculated for each specimen and statistically analyzed using analysis of variance and post hoc Tukey tests. After 28 days of water aging, all specimens exhibited statistically significant (P < 0.001) overall color changes (ΔE*), underscoring a pronounced decline in color stability. A statistically significant difference (P < 0.001) in ΔE* was observed between the TPO and Ivocerin groups, with TPO presenting maximum preservation of color stability. No statistically significant difference (P > 0.05) was found between the TPO and CQ groups or the Ivocerin and CQ groups, suggesting somewhat comparable color stability in these groups. Despite color alterations across all materials, the TPO-based composite resin exhibited superior color stability when compared with the Ivocerin- and CQ-based resins in the study, suggesting that TPO may offer enhanced long-term esthetic durability in clinical applications.