Sealants
The chewing surfaces of back teeth have deep grooves that a toothbrush bristle is physically too wide to reach into. A sealant is a thin coating painted into those grooves so food and bacteria cannot settle there. It takes a few minutes per tooth, involves no drilling and no numbing, and is most useful on children’s permanent molars soon after they come through.
Adults with deep grooves and a history of decay can have them too.