Although people in the United States are known for sparkling smiles, we don’t always have less cavities than other areas of the world. In fact, the prevalence of cavities in many African countries are among the lowest in the world (at least for now).
This low prevalence of tooth decay is due to the relative scarcity of processed sugars in the typical diet across Africa. Without sugars, cavity causing bacteria are less prevalent in these populations. There is less vertical transmission of cariogenic bacteria from mother to child and little possibility of a shift the oral environment towards an unhealthy balance due to frequent sugar exposure.
Here is a quote straight from the 2003 WHO oral health report:
Currently, the disease level is high in the Americas but relatively low in Africa. In light of changing living conditions, however, it is expected that the incidence of dental caries will increase in many developing countries in Africa, particularly as a result of a growing consumption of sugars and inadequate exposure to fluorides.
What we should take away from all this is the important role of dietary and environmental pressures in determining our risk for tooth decay. Even in the absence of modern dentistry, smart choices with our diet can produce significant improvements in our oral health.