Brian,

Do you think the metals and dyes in the jewelry can be a carcinogen,depending on what kind it is..!!
Some remanent of lead or dyes like diazoaminobenzene which breaks down into benzene in human bodies,would do it -I think.
There are many compounds found to cause genetic damage in some animals.
I was just speculating depending on Ph of every person s saliva & other health factors, various chemicals/metals may have different effect in different people. May be thats why we don't see continuous trend of OC in people with jewelry in the mouth. Like you said What we know ten years from now is anyone's guess, So I won't be surprised if it comes down to type of the jewelry.