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.
Very few procedures in dentistry will last a lifetime. The average crown or bridge should last about 5-7 years. A well done crown or bridge can last longer than 10 years provided that the person has good oral hygiene and comes to the dentist at least twice a year for examinations, cleaning, and follow-up care.