Restorative dentstry is the branch of dentistry responsible for the reconstruction of teeth that have been affected by cavities, traumatism, abrasions, etc. The restorations used can be plastic (they are prepared in the mouth), or rigid (they are prepared in the lab). The most used materials for plastic restorations are compound resins (composites of the same color as teeth) and amalgam. On the other hand, pure porcelain fillings are used for rigid restorations. 

Amalgam vs. Composites

There is no material “better” than the other, but there is one more  appropriate for  a specific case. Despite there being no doubt that compound resins have nicer aesthetics than amalgams (the former  have the same color as teeth, while the latter have  a metallic color), amalgams have  greater  durability than composites, which must be changed more frequently because of filtrations. This means that composites require longer treatments, with higher costs, and a loss of dental tissue. Notwithstanding how good the professional is, there is always a minimum amount of loss when changing the restoration.
Each situation must  be evaluated  , taking  into consideration the needs and  desires of the patient.