It's not a competent answer without X-Rays and seeing a patient, but generally speaking if it's a caries lesion, it needs to be removed and filled. Sometimes there's a stain in the grooves on occlusal surfaces of teeth, which I usually put on "WATCH" meaning every 6 months patient comes for exam and cleaning we take a closer look at that particular tooth making sure there's no caries. Otherwise it's better and cheaper for the patient to have caries removed and get a filling rather than going through more extensive treatment later when tooth becomes symptomatic. Hope that helped

Aleksandr Dadashyan