No. Sealants are a preventive treatment applied to intact, healthy tooth surfaces. A tooth with an existing cavity requires restorative treatment — a filling or crown — not a sealant. If there is any question about whether early decay is present in the grooves before sealant placement, your dentist will evaluate the tooth carefully — including with X-rays if indicated — before proceeding. Placing a sealant over decay would seal bacteria in and allow the decay to progress undetected beneath the surface.