A common question that I get from patients is how long it will take for the color of a new composite filling to change. The answer to this has changed over time as our materials have evolved. Modern composites are at less risk of yellowing or darkening over time than some of the original materials, but there are still some factors that cause color instability. Studies have shown that composite resin materials due undergo a yellowing process as they age, and this is true despite the chemical composition.
A common photoinitiator in composite resin is camphoroquinone, which has a yellowish hue to it. During the process of polymerization, the composite is photobleached or the compound loses this yellowish color. Any residual camphoroquinone can contribute to a yellowing of the composite resin. In addition as a composite ages we can see degradation of the amine structure produced during polymerization and this creates color instability. Another chemical factor affecting color instability is formation of broken carbon double bonds int he matrix of the composite resin. From a technique perspective one of the things we can do to decrease color instability is make sure our composite resins are fully cured. I always try to remember that under curing is a problem, over curing isn’t.
Most of these issues are a process of the composite aging, so we can tell our patients that they can expect the material to yellow over time. Now one of the things we can also remember is that our teeth yellow and age over time, so the composite becoming esthetically unpleasing only occurs when the color difference between it and the natural teeth becomes visible. One factor that will accelerate this is the use of bleaching agents. Studies have shown that carbamide peroxide has little to no effect on the color of composite resin, therefore consistent tooth bleaching will accelerate the rate at which the composite appears yellow compared to the surrounding tooth.