Is it unusual for a sixteen year old to have 17 cavities and 3 root canals?

No: There is always a cause that is attributable to the negative effects. Typically we would see poor oral hygiene coupled with high level of carbonated beverages daily. The combination of acid from the phosphoric acid soften the teeth enamel and sugars and plaque buildup on the teeth from poor oral hygiene leads to this rampant level of dental decay.

Yes and No: There are many factors that contribute to the presence of oral disease. We see high rates of tooth decay in certain geographic areas, and very low rates in others. Dietary habits, cultural norms, and socio-economic status are also great contributors to the presence or absence of disease.

Yes, uncommon. In today's era of fluoridated water, fluoridated t'paste, 6 month check-ups, oral hygiene emphasis, and knowledge of healthier snacks, it sounds as if this child was subjected to dental neglect. In my State failure to take a child for regular dental care is classified as child abuse.