There can be a variety of reasons why a dental crown might need to be replaced. Some of them are:
1-The Formation Of Tooth Decay
While a dental crown cannot decay the tooth on which the crown is cemented on can. If dental plaque is allowed to accumulate on a tooth in the region where the crown and tooth meet, a cavity can start. The worst-case scenario for your dental crown is that in order for your dentist to be able to get at the decay, and subsequently restore your tooth properly, the crown will need to be removed and replaced with a new one.
2-The Dental Crown Becomes Excessively Worn
Dental restorations are not necessarily more wear resistant than your own natural teeth, nor is it in your best interest that they should be. The ideal dental crown would be one made out of a material that has the same wear characteristics as your own teeth. This way neither the dental crown nor your teeth would wear each other excessively. The most wear-resistant dental crowns are those made of metal, particularly gold alloy dental crowns. For people who clench and grind their teeth excessively (bruxism), dental crowns are at a higher risk of wearing out. A dentist will sometimes detect a small hole on the chewing surface of a dental crown in that area where it makes contact with an opposing tooth (meaning a tooth which touches on the crown when you bite). In these cases, since the crown no longer seals over your tooth your dentist will probably recommend that a new crown be made, before that point in time when dental plaque has seeped under the crown and has been able to start a cavity.
3-The Dental Crown Has Broken
Dental crowns can break, or more precisely the porcelain component of a dental crown can fracture, for those with porcelain dental crowns, or porcelain fused on metal dental crowns. Some dental crowns are made in a fashion where their full thickness is porcelain. In these cases if the crown breaks it will most likely break through and through. Even if the broken piece of the crown doesn’t come off, the aesthetics, function, or the seal of the crown will most likely have been compromised and the crown will need to be replaced. For porcelain fused to metal dental crowns, the dental technician first makes a thin metal shell that fully covers over the affected tooth. A layer of porcelain is then fused to this metal so to give the crown a tooth-like color. In cases where this type of crown has broken it is the layer of porcelain that has fractured off, usually revealing the metal tooth covering underneath. While the function and aesthetics of the crown may have been compromised, the crown’s seal over the tooth may not have been affected. Since the seriousness of a dental crown fracture can vary greatly. Your dentist should evaluate any crown that has broken immediately. Some minor damage might not be of much concern, and possibly ameliorated by a little smoothing with a dental drill, but only your dentist should determine this and only after they have had an opportunity to examine your precise situation.