Old, unsightly mercury fillings are removed and replaced with porcelain ones. The porcelain holds the tooth structure together, strengthening the teeth. Mercury fillings often crack and break teeth because they are not bonded to them. Porcelain fillings are also used in lieu of destructive crowns because they keep the natural shape and form of the tooth. Patients are often not given the option of having porcelain fillings instead of crowns, and unlike the fillings, crowns require the tooth structure to be drilled down to a stub. Porcelain fillings offer patients metal-free dentistry, which allows light to flow through and reflect off the teeth, leaving a more natural smile.