My husband's dentist noticed a leukoplakia (white patch with no obvious cause) on his tongue that had emerged since his previous visit several months before. A biopsy by an oral surgeon showed moderate dysplasia -- not cancer -- so an excisional biopsy to remove the whole thing wasn't done for a month. By then it had become very early stage cancer. (Note: Many leukoplakias do not turn all the way to the dark side.)

Perhaps wilckdds or DrMike, both dentists who post here frequently, can offer explanations for what you are seeing.

But if my dentist said something "didn't look good," I'd be on the phone for a second opinion. I see you are in Maryland -- Johns Hopkins is #1 for ENT and #3 for cancer in the latest US News rankings, and has dentists on staff at its head and neck cancer clinic.
All the best,
Leslie