A filling is recommended when your dentist detects a cavity.  There are many filling materials available depending on the size of a cavity, however the most commonly used is a white filing material so that a natural appearance is achieved.  Smaller cavities are can be filled directly inside the mouth in one convenient visit, where as larger cavities may require a different material and be completed in two visits.  If a cavity is not repaired it will continue to grow and will become painful.  This can lead to a root canal or tooth loss.