Thermocycling Stain Challenge and Colour Stability of two Current Zirconium Silicate-filled Indirect Composite Restorative Materials

This study compares the colour stability of two zirconium silicate-filled indirect composite materials CM and its improved formulation CMD using an in vitro thermocycling stain challenge model with 2 immersion solutions. The rationale of the thermocycling stain challenge model is to replicate the intraoral conditions that the indirect composite materials may be exposed to during a clinical service, water or saliva absorption and cyclical exposure to staining food colourant at varying temperature extremes.

Ten discs each from shade A1 subtypes of CM and CMD indirect composites (Dentine Body A1B, Incisal 58, and Translucent HVT) were subjected to a thermocycling stain challenge following final polishing, which consisted of static immersion in 37°C of distilled water, followed by 500 thermocycles in 5°C of tea and 55°C of soy sauce and finally a 10-minute cleaning using an ultrasonic device. L*, a* and b* colour coordinates were measured, and the mean colour difference expressed as Delta E (ΔE) at different time points of the experiment were calculated and compared.

CM and CMD indirect composites had a significant color difference at all experimental time points (F=37.818, p<0.001). ΔE for CM subtypes and CMD subtypes in descending order, respectively, were Translucent HVT>Incisal 58>Dentin Body A1B and Incisal 58>Translucent HVT>Dentin Body A1B.

CMD indirect composite showed improved colour stability compared to CM indirect composite.

Limiting the usage of translucent shades and polishing according to the manufacturer’s recommendation may improve the overall colour of prostheses made using indirect zirconium silicate-filled composite materials.