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Of the materials tested in this study, the spherical filler composite (Estelite Σ) had similar properties as the nano-composite (Filtek Supreme). Thus, Estelite Σ can be used in anterior regions and restricted posterior restorations. All the materials had a similar shrinkage pattern, in that about 99% of the shrinkage occurred prior to 24 hours; thus, for direct resin composite restorations, a strong initial bonding strength with bonding agent would be necessary. Estelite performed similarly to nano-composite and microhybrid composites in mechanical properties and generalized wear resistance, while Estelite and Supreme had the lowest PS among the materials tested. The 2 microhybrid materials had similar properties, while the 2 microfilled composites were different for most properties tested. Overall, the microfilled composites had lower strength than the other composites except

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Color difference (DeltaE(*) (ab)) between nonworn and worn surfaces was in the range of 0.8-1.4 before staining, which increased to 1.1-3.9 after staining. Color change by staining with methylene blue in nonworn surface was 6.8-20.6, and that in worn surface was 5.2-17.8. Therefore, staining in nonworn surface was higher than that in worn surface (p < 0.05). Generalized wear simulation for approximately 3 years of clinical service resulted in acceptable color change before staining (DeltaE(*) (ab) < 3.3). After staining, color difference between nonworn and worn surface increased to not-acceptable value in one composite resin investigated.