How would a dentist treat a very minor gravity?

Cavity? Some minor cavities can be taken care of without anesthetic using lasers and air abrasion.
You mean Cavity. A cavity is a carious lesion in a tooth. In simple terms it means that the bacteria have penetrated the outer protective (enamel) layer of a tooth, into the dentin (the inner layer of a tooth). A small cavity can be removed with a drill and restored with a tooth colored restorative material. If it is really superficial and is still in the enamel layer, the cavity can be removed & a sealnant placed.