Unfortunate as it may be, things are not as simple as that.
Amalgam is an alloy. It is not released from the dental fillings into the mouth or into the body. If it would be, the dental filling would quickly wear away – which it obviously doesn’t.
The very tiny fraction of the amalgam that does get released will remain an amalgam. That is, there is no loose mercury floating around: the mercury remains tightly bound to the other contents of the amalgam.
Mercury poisoning does exist, but the cause is always either working in some dirty industry that uses lots of mercury in an unsafe working environment, or eating large amounts of seafood, especially fish at the top of the food chain. Alarmists like to mix up this real mercury poisoning and the non-existent danger of amalgams or even vaccinations, but there is no real reason to treat such different things as if they would be comparable.
Finally, no organism is known to benefit from mercury. This includes candida. So even if one would have been exposed to mercury (in a dirty gold mine, or by eating lots of seafood), one would experience neural problems, not candida growth.