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.
However, it's never too late to get treatment for problems with crooked teeth or misaligned jaws. Braces for adults are similar to braces for children. However, it often takes longer for adults to correct tooth and jaw problems than it does for children. Adults can expect to wear braces for three or four years, while children usually have them for two years.