Composite Resins were introduced as an replacement to acrylic resins. Its composition includes:

Resin Matrix, inorganic fillers like glass, quartz and colloidal silica and coupling agent. so, composite resins don't have mercury. It is the silver amalgam that contains mercury in it.  Composite fillings are bio-compatible...For more info you can visit the link...http://www.identalhub.com/article_composition-of-composites-41.aspx