Tooth loss associated with increased cognitive impairment, dementia (nursing.nyu.edu)

> In addition, tooth loss may reflect life-long socioeconomic disadvantages that are also risk factors for cognitive decline.

This is not "in addition." This is another "poverty found to be associated with poverty" study.

This is correlation, but it is very unlikely to be causation.

Having a bad health will certainly cause a person to have all kinds of problems. For example, if your food does not contain enough vitamin C, you are likely to get some form of scurvy[0], which might lead to loss of your teeth, but it will also lead to a lot of other problems.

[0] https://en.wikipedia.org/wiki/Scurvy