In the past, cavities could only be treated with unsightly metal fillings that are alloys for silver and mercury. These fillings, especially when close to the front of the mouth, are highly noticeable and unaesthetic. Sometimes, the filling is so large that it causes discoloration of the entire tooth. These fillings (or restorations) often weaken teeth due to the large amount of the original tooth that has to be removed. Also there is a risk of Mercury poisoning that is used in the filling. Modern dentistry has increasingly turned to Tooth colored or composite fillings as a strong, safe and more natural looking alternative. Composite fillings utilize a soft white plastic substance that is hardened with a blue light.