Cavities are small holes in teeth caused by tooth decay (also known as dental caries). Commonly, tooth decay is caused by poor oral hygiene, or the over-consumption of sugar.
Depending on the tooth decay and extensive nature, there are different methods for restoration or in some cases the tooth may not be able to be repaired and will need to be extracted. At this point in dentistry, a complete regeneration of an original tooth cannot be done.
The tooth may need a root canal to save it.
One of the reasons for tooth decay is due to reduced saliva that cleans the mouth of acids from certain foods. The lack of saliva can be the result of extensive medications or certain diseases like diabetes.