Complex sentence: Although the mercury in cured amalgam is not available as free mercury, concern of its toxicity has existed since the invention of amalgam as a dental material; it is banned or restricted in Norway, Sweden and Finland.
Split into simpler sentences: Although the mercury in cured amalgam is not available as free mercury, concern of its toxicity has existed since the invention of amalgam as a dental material. It is banned or restricted in Norway, Sweden and Finland.