I just noticed black spots along the front of my lower gum line, as well as some erosion. i've been dipping for close to 20 years now. tooth loss?

Get it checked out: Given your prolonged history of dipping and new onset lesions along the gum line, it would be important to have your mouth examined by a physician in order to determine if further workup and/or biopsy is required.

Examination: Given your medical Hx (tobacco), important that you be examined. Would recommend Oral and Maxillofacial Surgeon. Biopsy may be in order.