The term "white filling" can refer to two classes of dental restorative materials, composite resin ("hard plastic")  or bonded ceramic ("porcelain").

 

The least expensive white filling material is composite resin (a combination of resin and glass filler), a dough-like material which sets with the aid of a high intensity light. It has the tremendous advantage of direct placement in a single visit. However, composite resin is a relatively soft material.  An average person chews over 5,000 times per day and 2,000,000 times per year. Composite resin abrades readily; on rear chewing surfaces it must be replaced every 10 years. After repeated fillings so much tooth is lost that a full coverage bonded ceramic restoration (porcelain crown) is required anyway. Why not place a lifetime bonded ceramic restoration right away and break the cycle of repeated fillings in your lifetime? A fully performing dentition is as desirable at age 90 as it is today.

 

Bonded ceramics compromise a range of materials which we will call  "porcelains". Each class of ceramics has different applications in dentistry. A ceramic is created by firing clay-like minerals to very high temperatures, resulting in a crystalline/glass compound. It is then bonded permanently to the tooth with a resin cement. These materials are beautifully  esthetic and extremely wear resistant. They cover the chewing surface of a tooth with a "coat of armour" , resulting in a restoration that can easily last a lifetime.