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.
One reason why a 10-year lifespan is quoted is because a dentist can usually provide patients with this figure and be confident that a crown that the dental lab makes will last at least this long. Many dental insurance plans in North America will allow for a crown to be replaced after only five years. The most important factor affecting the lifespan of any restorative is the continuing oral hygiene of the patient.