Artificial aging effect on color stability and bond strength of one-shaded versus multi-shaded composite resins

Abstract Aim To investigate the effect of thermocycling on color stability and shear bond strength of one single-shaded versus (Omnichroma) multi-shaded composite resins (Filtek Z350 XT). Materials and methods A total of 40 discs from both tested resin materials (Omnichroma and Filtek Z350) were prepared using a Teflon mold (8 mm diameter and 1 mm thickness) for color stability testing. Specimens of each tested resin composite material ( n = 20) were randomly divided into two equal groups I and II ( n = 10), according to the cycles of thermocycling 500 and 1000, respectively. Sixty extracted human maxillary central incisors were used for shear bond strength testing. Their crowns were secured to self-cure acrylic resin blocks with the labial surfaces facing upwards. The labial enamel surfaces were flattened with a wet 600 grit silicon carbide paper. After total etching and bonding procedures, tested composite resin materials were applied to the flat enamel surfaces by the aid of Teflon molds (4 mm diameter and 2 mm thickness) then light cured. The specimens of each tested material ( n = 30) were randomly divided into three equal groups (10 specimens each) according to thermocycling mode as follows; control group (without thermocycling), group I (thermocycling for 500 cycles) and group II (thermocycling for 1000 cycles). After aging, all the specimens were subjected to measurement of color stability (ΔE) using spectrophotometer and shear bond strength test using Instron testing machine. The data will be collected, tabulated, and statistically analyzed. Results ΔE values for Omnichroma did not differ significantly when aged for 500 (group I) or 1000 cycle (group II) recording ( P = 0.052). While ΔE values for Filtek Z350 after 1000 cycle differed significantly ( P = 0.01). Shear bond strength values for omnichroma did not differ significantly from Filtek Z350 at baseline ( P = 0.304). While, when aged for 500 or 1000 cycle, shear bond strength values differed significantly between groups I and II ( P = 0.000 and 0.011, respectively). Conclusions Artificial aging by thermocycling (500 and 1000 cycles) decreased the color stability and shear bond strength of both tested composites. Single-shaded composite resin (Omnichroma) exhibited better performance regarding the maintenance of the baseline condition, being the material with less color change and more color stability.