Tooth decay and cavities are caused by a bacterial infection known as caries.
An acidic oral environment drives this infection.
Brushing and flossing alone does not stop this infection.
The good news is that this infection is treatable and preventable.

Cavities are the demineralized areas, or the holes, that form in teeth and are the result of a bacterial infection known as caries. This infection takes place when the normal healthy bacteria are replaced by acid-producing bacteria. This shift in bacteria is primarily caused by two things:
Prolonged acidic (low pH) oral environment: contributing factors include a lack of saliva, and or a sugary acidic diet that encourages acid-producing bacteria.
Transmission: this infection is contagious! You can be infected by someone through exchange of saliva.

Drilling and filling has been the traditional method of treating cavities, but it doesn't treat the underlying cause, the bacterial infection. Brushing and flossing has been the traditional method of prevention, but it does not change the pH (acidity) of the oral environment or treat the infection once it exists.

Dental Facts
New dental decay affects up to 5 million Australians each year.
Caries is the single most chronic disease among children.
Hospitalization for dental extractions and restorations are the most common reason for hospital separations for children aged
1-4 years, 5-9 years and 10-14 years than any other reason.

Teenagers

• Teenage children have been identified as being at increased risk of dental disease.
• Between 40% and 57% of 12–15 year old teenagers had some history of decay in their permanent teeth.
• On average 12 year old children had slightly more than one decayed, missing and filled permanent tooth per child, while 15 year old children had two decayed, missing and filled permanent teeth on average.
• The 10% of teenagers with the most extensive history of permanent tooth decay had between five and eight permanent teeth affected, which was about 4.5 times the national average.

Pre-Teen Children

• Nearly half (48.9%) of 6 year old children had a history of decay in the deciduous ‘baby’ teeth.
• The 10% of 4–6 year old children with the most extensive history of deciduous tooth decay had more than nine deciduous teeth affected, which was about 4.5 times the national average.
  Source: Dental health of Australia’s teenagers and pre-teen children. The Child Dental Health Survey, Australia 2003–04 (Published 2009)
  Australia’s Health 2006, Australia Institue of Health and Welfare

Expert Advice
Visit a dentist who provides "caries risk assessment and bacterial screening", where they evaluate risk factors that can contribute to you getting cavities and offers treatment beyond "drilling and filling".