Evaluation of the effect of expiration date on composite bond strength and color stability

To comparatively evaluate the dentin bond strength and color stability of expired and non-expired resin composites (RC).

48 caries-free teeth were randomly divided into four groups. The specimens were ground to expose the dentin, and an adhesive (GC Premio Bond) was applied and light-cured. RC (GC G-ænial) in shade A2 was applied to each group (according to its expiration date) using a transparent mold (4 mm x 2 mm) and polymerized. Group 1: expired for 2 years; Group 2: expired for 1 year; Group 3: 1 year remaining until expiration; Group 4: 2 years remaining until expiration. The specimens were immersed in distilled water for 24 hours and then placed in a tea solution, with color measurements taken using a spectrophotometer (EasyShade V) on the 1st, 7th, and 28th days. (CIEDE 2000 formula: L* = 94.48, a* = 0.16, and b* = -0.21). After the color measurements, the specimens underwent a shear bond strength test applied to the bonding interface between the tooth and the composite using a universal testing machine and the values were recorded.

The E1 measurements exhibited the lowest mean color change (5.88 ± 1.02), whereas the E3 measurements had the highest mean color change value (10.13 ± 3.35). The lowest bond strength was observed in Group 1 (97.25 ± 20.33), while the highest value was found in Group 4 (149.45 ± 32.75). The differences between Group 1 and Groups 3 and 4 were statistically significant.

In clinical practice, adherence to proper storage conditions and expiration dates is essential to ensure the success and quality of resin composite materials, which are frequently used in routine dentistry. Within the limitations of this study, the color stability and bond strength of resin composites decreased after expiration dates. Therefore, to achieve optimal clinical results, it is crucial to ensure that restorations are performed using non-expired resin composites.