As others have said, many dentists will send you on to somebody more specialized in detection of cancer. In my case my dentist referred me to an oral surgeon, who performed a biopsy and discovered the cancer that way.
I have a radiology oncologist and a medical oncologist, but my 'primary' doc is an ENT who specializes in H/N cancers. The oral surgeon who confirmed my cancerous diagnosis referred me to him. Other's routes are different (in terms of what types of docs or specialists they see and in what order), that's just how mine went down.