New discoveries have found exceptions to Mendel's basic laws, but none of Mendel's things have been proven to be flat-out wrong. Hail to the Father of Genetics ! The name is ma-ma-ma-ma-ma-Mendel.
Dental crowns should last on average from 10 to 20 years. Crowns are still subject to fracture and cavities, so it is important to take extra care in brushing and flossing around crowned teeth to prevent them from needing replacement too often.
Your dentist may fit you with a temporary crown to protect a damaged tooth while the permanent crown is being made. Depending on the material used to make them, the wear they get and the care they receive, permanent crowns last about 5 to 15 years.