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

Abstract

Aim: 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. Materials and Methods: 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. Results: 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. Conclusion: CMD indirect composite showed improved colour stability compared to CM indirect composite. Clinical Significance: 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.