Over time, several sealants have been tried to protect deep fissures and pits on occlusal surfaces. In 1895, Wilson placed dental cement in the grooves and fissures to prevent cavities. In 1929, Bodecker suggested that deep fissures could be enlarged with a large round burr to make the occlusal areas more accessible to self-cleaning, a procedure now known as enameloplasty. In 1923, Hyatt advocated the early introduction of small restorations in grooves and fossae before carious lesions had a chance to develop. He called this procedure prophylactic odontotomy. Again, this procedure is more of a treatment than a preventive approach. Several methods have been used unsuccessfully to seal, or to make fissures more resistant to decay. These attempts have included the use of topically applied zinc chloride, potassium ferrocyanide, and the use of ammonium silver nitrate. Fluorides that protect smooth tooth surfaces are less effective in protecting occlusal surfaces. The use of fluorides led to a large reduction in the incidence of surface caries, but also to a smaller reduction in occlusal caries in grooves and fossae.