"Enamel layering" using double-layered enamel-shade resin composites: The strategy to simulate the optical characteristics of human enamel.

Objective: To evaluate the optical match between enamel and resin composites fabricated using mono-layered and double-layered techniques.

Materials And Methods: Enamel slabs were prepared from human upper incisors and canines. Mono-layered composite replicas were prepared from seven Filtek Z350XT and Estelite Sigma shades using silicone molds prepared from the respective enamel surfaces. Translucent and enamel shades (A2 or A3) of the two materials were produced from incisor molds for double-layered replicas, and the groups with the best results underwent accelerated aging. Spectrophotometric evaluation was performed using CIE color system. The differences in translucency (ΔTP) and color (ΔE ) between the enamel and paired composite replicas were calculated and analyzed using parametric statistics (α = 0.05).

Results: For the mono-layered composites, white enamel and translucent shades of Filtek yielded the lowest ΔTP for canines (4.6) and incisors (8.9), respectively. The ΔE of mono-layered replicas ranged from 5.1 to 11.8. Double-layered Filtek replicas displayed a better 1-day optical match with the lowest ΔTP (3.4-4.0) and ΔE (4.2-4.6), irrespective of each layer's thickness.

Conclusions: For canines, the lowest ΔTP of Filtek white enamel was close to the acceptable threshold (4.43). For incisors, the thicker translucent double-layered Filtek composites demonstrated the greatest optical match before and after aging.

Clinical Significance: Upper incisors and canines have distinct enamel optical properties. Enamel layering using specific double-layered resin composites could achieve a better optical match with upper incisor enamel.