In composite resin, decreasing the size of filler particles primarily achieves:

Correct answer: A. Smoother surface polish

• A. Correct. Decreasing filler particle size (as in microfill composites) allows for a smoother, higher-luster polish because there are no large particle remnants after polishing. This is why microfill composites are used for anterior esthetic restorations.
• B. Radiopacity is achieved by adding heavy metals (barium, strontium) to filler particles, not by changing their size.
• C. Curing time is primarily affected by the photoinitiator concentration and light intensity, not filler particle size.
• D. Larger macrofiller particles provide greater wear resistance; decreasing particle size does NOT improve abrasion resistance.