Many diseases of the mouth and oral cavity – including the teeth and surrounding tissues and bone – cannot be seen properly or at all, when a dentist examines your mouth just using his eyesight.
An x-ray machine/exam will help the dentist to see and sometimes diagnose;
small areas of decay between the teeth or below fillings
bone damage from a tooth infection (such as an abscess) or a cyst
bone loss due to periodontal/gum disease
some types of tumours
the effects of oral trauma
the position of un-erupted teeth in children and adults
Finding and dealing with dental problems early in, in their development is vital, and can not only save time and money, but also unnecessary discomfort or larger problems, and help to prevent more serious health problems. Using an X-ray machine and assessing X-ray images may be able to help the dentist detect any oral/dental issues early on, or those needing immediate attention and treatment. As already stated often theses things cannot be seen during a regular dental check up.
If you happen to change your dentist, you can usually arrange to have copies of your x-ray images sent from your previous dentists to your new dentist.