Is there a link between concussions and dementia?

Yes. There is more and more evidence about the effect of small craneoencephlic injuries or trauma to the brain and developing dementia. Athletes have 6%more changes of developing dementia ( not alzheimers ) comparing with other populations.Some recent epidemiologic studies have shown that head injury is a risk factor for the development of dementia/alzheimer disease, whereas others have not.
Some types, yes. Yes, head injuries including those that cause concussions increase the risk of demenita. Dementia pugilistica is even named for this type of dementia.