It seems that some people have a way higher propensity to cavities than others. Is this because they have some bacterial overgrowth? Maybe the wrong bacteria? Has there been any research into this and how to bring your mouth bacteria back to normal levels?

I'd love to not have my dentist tell me my gums are receding despite flossing and brushing the recommended amount and not usually eating sweets or carbs.

Bad dental health kills, cancer, heart disease etc. everyone knows this.

Not much more to say other than look after you teeth.

> but not to establish a direct cause-and-effect link

This is quite important, certain bacteria can cause more severe tooth decay and there will be ways to manage these (Electric toothbrush with a app to teach you how to brush).

It seems highly likely to me it'll be as expected the damage to teeth causes the HNSCC.

Either way it's good research as long as they don't mislead without proper evidence.