Polymerization shrinkage by volume was overcome by adding:
Advantages of adding fillers:

Reduces the coefficient of thermal expansion
Reduces polymerization shrinkage
Increases abrasion resistance
Decreases water sorption
Increases tensile and compressive strengths
Increases fracture toughness
Increases flexure modulus
Provides radiopacity
Improves handling properties
Increases translucency

Ref: Textbook of Operative Dentistry, Nisha and Amit Garg, 3rd edition, Pg no:253
Fillers
Coupling agents
TEGDMA
All of the above