A scale and clean (otherwise known as a "scale and polish") is done to remove the plaque and calculus (see Gum Disease Treatment) from the teeth and around the gums. Good oral health requires this be done regularly - every six months in normal cases, or every three months if a person's gums need greater care. Some people only require a scale and clean every twelve months, but these individuals are rare!
Why do I need a scale and clean?
Whilst plaque is easily removed by proper brushing and flossing, remaining plaque hardens into "calculus", which cannot be removed by the average person. Additionally, it is practically impossible to clean properly below the gums and between the teeth by oneself, since these areas are hard to reach with toothbrushes and dental floss. Even dentists need to go regularly to their dentist!
Existing calculus on the teeth and gums is problematic because it is a perfect place for more plaque to develop. Plaque contains bacteria that create acid, which causes tooth decay. See what our sister practice, Dental at Joondalup, has written about this topic ("Why is getting a scale and clean important?") for more information about this process. Additionally, the video below provides more information on the scaling and cleaning process.