Effect of layering strategy and prolonged water aging on masking ability of composite resins

Statement of problem: Layered composite resins may adequately mask discolored substrates. However, whether color changes that occur over time affect masking ability is unclear.Purpose: The purpose of this in vitro study was to investigate the effect of layering and water aging on the masking ability of 2 composite resins.Material and methods: Disk specimens (1.5 mm-thick and shade A1) from Charisma Diamond (CD) and Filtek Z350XT (Z350) were made according to the composite resin shade combination used in the layering strategies: bilayer for CD (enamel/dentin) and for Z350 (enamel/body and enamel/dentin) and trilayer for Z350 (enamel/body/dentin) (n=5). Color measurements were obtained with a spectrophotometer over an A3.5 ceramic substrate, and the whiteness index for dentistry (WID) was calculated. The specimens were aged in water at 37 degrees C and evaluated at different times: 24 hours, 1 week, 1 month, 2 months, 6 months, 12 months, 18 months, and 24 months. CIEDE2000 color differences (Delta E-00) and WID differences (Delta WID) were calculated and interpreted by 50:50% color and whiteness perceptibility and acceptability thresholds. Changes among strategies and aging times were analyzed using the Kruskal-Wallis test (alpha=.05). Contrasts were made using the Mann-Whitney U test with Bonferroni correction (alpha=.001).Results: Delta E-00 decreased from 24 hours to 2 months of aging. From 2 months onwards, Delta E-00 increased for all layering strategies and times, without significant changes in lightness for CD (P>.004). Overall, for the CD restorative system, an increase in Delta WID was observed after 1 month of aging (P<.001), while for the Z350 restorative system, Delta WID decreased after aging (P<.001), except for the Z350 bilayer strategy (enamel + dentin) at 1 week and 2 months (P>.004). For all layering strategies and aging times, color differences were higher than the 50:50% perceptibility threshold for Delta E-00 and, after 6 months, higher than the 50:50% acceptability threshold for Delta E-00 and the 50:50% whiteness acceptability threshold.Conclusions: The ability of the tested composite resins to mask a discolored substrate was affected by the layering approach applied and by prolonged water aging.

Automated summary

The study aimed to investigate the effect of layering and water aging on the masking ability of two composite resins. The results showed that the masking ability of the composite resins was affected by the layering approach applied and by prolonged water aging.