When a tooth needs a filling there are several alternatives. Today, most people prefer to have a tooth filled or restored with a material that is not only strong and long lasting, but that also looks so natural that one can not tell the tooth has a filling in it.
Depending on the size of the restoration, this is done with either composite or porcelain.
Composite fillings are generally used for small to medium sized restorations. They are the modern replacement for silver amalgam fillings. They are long lasting, relatively inexpensive, are quick to place and come in a wide variety of tooth shades for a natural looking result. The material, a composite resin, is placed directly into the tooth after any pre-existing filling or decay has been removed. Composite fillings have very little post-operative problems and are completed in a single visit.
Once a filling gets so big that there is an inadequate amount of remaining tooth structure to support or hold it without the risk of the tooth or the filling breaking, it becomes time to consider putting a porcelain restoration in it. The advantage of this is that porcelain does not need to be completely contained by tooth structure like a composite filling. If done appropriately, a porcelain onlay, as it is called, can prevent a tooth from cracking. Porcelain also tends to be more resistant to having decay develop around it than composite. Porcelain is generally longer lasting, better wearing, and more protective of the underlying tooth than composite.