With crowns, we have to fill the middle and drill away the entire outside of the tooth, removing almost the entire tooth from the outside. Then the crown goes on the filling material in the middle. Crowns have to be replaced every 10 to 15 years, and each time it is replaced we have to put it further under the gum line because of inflammation caused by bacteria that gets trapped at the junction where the crown meets the gum line With an onlay, the outside of the tooth stays intact—we are just replacing what was decayed. This eliminates all the gum problems. Nothing is better than your own tooth.