Although you should take good care of your teeth on a daily basis by brushing and flossing regularly, there are some things that can be missed that a dentist can help you with.  Semi-annual check-ups and cleanings are very important to your oral health.  Your visit to see your dentist every six months serves several different purposes.  The most important reason is to give your teeth a deep and thorough cleansing.  Other important aspects of a check-up are having an evaluation to check for any problems and getting x-rays.

Professional Cleanings: Assuming you have no other issues with your teeth or mouth, you should always plan to visit your dentist twice a year for a cleaning.  Aside from brushing and flossing, this serves as a foundation for preventing gum disease and tooth decay.  Your professional cleaning or dental prophylaxis is normally performed by a certified dental hygienist who will:
    Remove plaque from the teeth which is the sticky substance that collects on your teeth.  Plaque harbors bacteria that produces acid which, if not removed, can gradually wear down your teeth and irritate your gums.  Plaque must be removed in order to prevent tooth decay and gum disease.
    Remove tartar or calculus from above the gum line.  Tartar is plaque that has hardened on the tooth surface and can be difficult to remove.  A hygienist knows what to look for and has the materials to remove any existing calculus.
    Polish and remove stains from teeth if you choose.  This is not necessarily a regular procedure but one that you can elect to have a hygienist perform.

Dental Examinations: Receiving a dental examination is an important part of a good check-up.  Performing an examination can help to diagnose a disease before it becomes a serious problem which can lead to health issues, irreparable damage and large medical bills.  A dental examination generally will include:
    Oral cancer screening
    Gum disease evaluation
    Visual examination of tooth decay
    Examination of diagnostic x-rays to see cysts, tumors, invisible decay and other problems that can't be seen by the naked eye
    Evaluation of status of current restorations (fillings and others)

X-rays: X-rays are used to find conditions that are not visible in a visual examination.  The information that an x-ray provides is essential for making and confirming a diagnosis.  If you are able to find a potential problem before it actually becomes a problem, you can avoid a lot of pain, health problems and further damage.  Using an x-ray, your dentist will be able to see:
developing permanent teeth and note any abnormalities or missing teeth.
    any extra teeth that might cause damage to the developing permanent teeth.
    decay that might be developing between the teeth so that it can be treated at an early stage before more serious damage is done.
    decay that might be occurring under old fillings so that it can be treated before damage to the dental pulp occurs.
    an abscesses that may have formed at the end of the root of a tooth.  Treating this condition can save the tooth.
    bone loss around the teeth.  This is a sign of periodontal disease and x-rays are an important part of diagnosis and treatment.
    the shape of the roots which is important to know for some treatments.
    broken and retained root fragments that can lead to infections.
    benign and malignant tumors.
    impacted teeth, particularly third molars.  Seeing these will help them make a decision to remove them or not.

There are many advantages to having semi-annual dental cleanings done.  An ounce of prevention goes a long way, so don't wait until you have a disease to treat.  Make sure to make those appointments.