The Sheldon Patent

Posted Sunday, March 04, 2012.

My grandfather was named Harry Sheldon. He was a Professor of Dentistry at the Georgetown University Dental School. Having graduated from Georgetown, then serving in the Army and having a private dentistry practice, he returned to the school where he was Chair of the Department of Operative Dentistry. He taught at the school along with his good friend, Dr. Everett Cobb. Harry and Everett were neighbors, living down the street from one another, and our families were close when I was growing up.

Harry and Everett collaborated on an invention for which they received a patent in 1968. The patent, U.S. Patent No. 3,367,788, is titled “Substantially Radiopaque Tooth Lining Composition.”

The patent discloses a material that can be used when filling a cavity, and the material is subsequently detectible by X-ray. When filling a cavity, it was known to precede the filling with a compound like calcium hydroxide. The calcium hydroxide rested upon the pulp and promoted healing of the damaged pulp. After the cavity was lined with calcium hydroxide, dental amalgam was applied to complete the filling of the cavity.

The problem was that when the patient returned for a subsequent checkup and X-rays, the calcium hydroxide gave an appearance on the X-ray identical to tooth decay. Evidently, in such a situation, a dentist unaware of the previous work to fill the cavity might needlessly remove the filling, believing decay existed where there was actually only the calcium hydroxide compound. So Harry and Everett set about finding a way to change the appearance on the X-ray of the calcium hydroxide hidden beneath the dental amalgam comprising the remainder of the filling.

Their solution was to mix very small silver particles with the calcium hydroxide prior to lining the cavity with the compound. The silver caused the appearance of the calcium hydroxide layer to be visibly apparent during subsequent X-rays. The patent claims recite different proportions of calcium hydroxide to silver, but the broadest claim discloses a compound made of 40 to 50% of calcium hydroxide and 10 to 25% silver metal particles, with the remainder being thickening agent and water.

The patent was granted February 6, 1968 and would have expired in 1985, around the time I was a junior in high school. Harry and Everett assigned the patent to their employer, Georgetown University. While I was aware my grandfather had received numerous awards and honors related to his work, I don’t remember ever hearing about the patent. It would have been fun to have compared notes with him when I received my own patent, in 1999. Sadly, Harry Sheldon passed away in 1990 at the age of 70, so I never had the chance. Everett Cobb continued to teach and practice for years afterwards, but passed away in 2008. Their friends and families miss both of them.

You can view the Sheldon / Cobb patent here.

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